Linux in a Nutshell

Ellen Siever

Stephen Figgins

Robert Love

Arnold Robbins

Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo

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Preface

This is a book about Linux, a freely available clone of the Unix operating system whose uses range from embedded systems and personal data assistants (PDAs) to corporate servers, web servers, and massive clusters that perform some of the world’s most difficult computations.

Whether you are using Linux for personal software projects, for a small office or home office (the so-called SOHO environment), to provide services to a small group of colleagues, or to administer a site responsible for millions of email and web connections each day, you need quick access to information on a wide range of tools. This book covers all aspects of administering and making effective use of Linux systems. Among its topics are booting, package management, and revision control. But foremost in Linux in a Nutshell are the immeasurable utilities and commands that make Linux one of the most powerful and flexible systems available.

In addition to the tools and features written specifically for it, Linux has inherited many from the Free Software Foundation’s GNU project, the Berkeley Software Distribution (BSD), the X Window System, and contributions from major corporations as well as the companies that created the major Linux distributions. More recent projects extend Linux in exciting ways, some through changes to the kernel and some through libraries and applications that radically change the user’s experience.

This book is a quick reference for the basic commands and features of the Linux operating system. As with other books in O’Reilly’s “In a Nutshell” series, this book is geared toward users who know what they want to do and have some idea how to do it, but can’t always remember the correct command or option. The sixth edition has been examined from start to end and checked against the most common Linux distributions (Debian, Ubuntu, Fedora, and SUSE) so that it reflects the most useful and popular commands.

Organization of This Book

This book is a reference to the most important commands and utilities available on Linux systems.

Chapter 1, explains Linux’s strengths and the key aspects of working with Linux, and lays out the scope of this book.

Chapter 2, introduces TCP/IP networking and the Linux commands used for system administration and network management.

Chapter 3, is the core of the book, a reference listing of hundreds of the most important shell commands available on Linux.

Chapter 4, covers the commands used to control booting on Linux, particularly LILO and GRUB.

Chapter 5, explains the apt series of commands that manage updating and installation on Debian, and the RPM system and yum used by Red Hat/Fedora, Novell/SUSE, and several other distributions of Linux.

Chapter 6, documents Bash, the default command-line interpreter on Linux.

Chapter 7, introduces regular expressions and explains how different tools interpret these powerful tools for searching and text processing.

Chapter 8, provides reference information on Emacs, a text editor and full-featured development environment.

Chapter 9, describes the classic vi editor that is the most popular text-manipulation tool on Linux.

Chapter 10, describes this “stream editor” that is useful for processing files in standardized ways.

Chapter 11, documents another valuable tool for processing text files, the GNU version of awk that is the default on Linux systems.

Chapter 12, provides the background for understanding Subversion and Git, which are valuable tools for tracking changes to files and projects, and are discussed in the following two chapters.

Chapter 13, provides a description of a popular source code management and version-control tool.

Chapter 14, describes a distributed version control system with many advanced features including the ability to access project history even when not connected to a central server.

Chapter 15, describes virtualization on Linux, which allows multiple virtual servers to run on a single physical server. Tools covered include Xen, KVM, the libvirt API, and the VMware command-line interface.

Other Resources

This book doesn’t tell you how to install and get up to speed on a Linux system. For that, you’ll probably want O’Reilly’s Running Linux, by Matthias Kalle Dahlheimer and Matt Welsh, an in-depth guide suitable for all major distributions. For networking information, check out Linux Network Administrator’s Guide by Tony Bautts et al. (O’Reilly). If you’re new to Linux/Unix concepts, O’Reilly’s Learning the Unix Operating System, by Jerry Peek et al., provides introductory information. In addition to these and other Linux titles, O’Reilly’s wide range of Unix, X, web-related, and scripting and programming language titles may also be of interest.

Online Documentation

The Internet is full of information about Linux. One of the best resources is the Linux Documentation Project at http://www.tldp.org (or one of the dozens of mirror sites around the world), which has numerous short guides called HOWTOs, along with some full manuals. For online information about the GNU utilities covered in this book, consult http://www.gnu.org (also widely mirrored). The Free Software Foundation, which is in charge of the GNU project, publishes its documentation in a number of hardcopy and online books about various tools.

Each distribution maintains its own website, and contains documentation for the software it provides as well as guides to maintaining your system under that distribution.

Websites

As befits a hot phenomenon, Linux is the central subject of several websites and a frequent topic of discussion on others. Some sites offer original content; others just have links to articles posted elsewhere and threaded discussions (which can be a useful service). Among the sites frequented by Linux users are:

http://lwn.net

Linux Weekly News, a site with weekly in-depth articles and frequent news updates

http://www.linuxgazette.net

Linux Gazette, a site published monthly with articles and tips in many languages

http://www.linuxquestions.org

A very popular source for technical guidance, including a growing wiki (site maintained by user contributions) at http://wiki.linuxquestions.org

http://linuxsecurity.com

Linux Security, a collection of security-related news

http://linuxinsider.com

Linux Insider, a news feed

http://linuxtoday.com

Linux Today, another news feed

http://slashdot.org

Slashdot, a famous discussion list

Linux Journal and Linux Magazine

Linux Journal and Linux Magazine are monthly magazines for the Linux community, written and published by a number of Linux activists. These magazines are two of the oldest among many monthly print and online magazines devoted to Linux. With both print editions and websites, they offer articles ranging from questions and answers for novices to kernel programming internals. Linux Journal, at http://www.linuxjournal.com, is the older magazine. Linux Magazine is at http://www.linux-mag.com.

Usenet Newsgroups

Most people can receive Usenet news at work or through their ISPs. While this communications technology has lost ground in the past several years to web-based threaded discussions, it is still a valuable source of help and community connections on many topics. The following Linux-related newsgroups are popular:

comp.os.linux.announce

A moderated newsgroup containing announcements of new software, distributions, bug reports, and goings-on in the Linux community. All Linux users should read this group. Submissions may be mailed to cola@stump.algebra.com.

comp.os.linux.development.apps

Guidance for using features of Linux for application development, and for understanding the effects of the operating system on user-space programs.

comp.os.linux.development.system

Discussions about developing the Linux kernel and the system itself.

comp.os.linux.networking

Discussions relating to networking with Linux.

comp.os.linux.x

Help on getting the X graphical window system to work. This list used to see some of the highest traffic of any Linux group back when distributions had more trouble setting up graphics automatically. This is no longer the case, thanks to the increasing sophistication of autodetection and configuration software.

There are also several newsgroups devoted to Linux in languages other than English, as well as newsgroups and online forums for the different distributions.

Online Linux Support

There are many ways of obtaining help online, where volunteers from around the world offer expertise and services to assist users with questions and problems.

The freenode IRC service is an Internet relay chat network devoted to so-called “peer-directed” projects, particularly those involving free software. Some of its channels are designed to provide online Linux support services.

Internet relay chat is a network service that allows you to talk interactively on the Internet to other users. IRC networks support multiple channels where different groups of people type their thoughts. Whatever you type in a channel is seen by all other users of that channel.

There are a number of active channels on the freenode IRC network, where you will find users 24 hours a day, 7 days a week who are willing and able to help you solve any Linux problems you may have, or just chat. You can use this service by installing an IRC client (some distributions install them by default), connecting to server name irc.freenode.org:6667, and joining a channel focusing on Linux, such as:

#linpeople

General help and discussion

#debian

Help for Debian distribution

#gentoo

Help for Gentoo distribution

#redhat

Help for Red Hat distribution

#suse

Help for SUSE distribution

And so on. Please be sure to read up on the rules of chat etiquette before chatting. In particular, the participants in these groups tend to expect people to read documentation and do some experimentation before asking for help with a problem. Some IRC clients include Xchat, Konqueror, and KVirc. Note that these are all graphical programs and as such are not described in this book.

Linux User Groups

Many Linux User Groups around the world offer direct support to users. Typically, Linux User Groups engage in such activities as installation days, talks and seminars, demonstration nights, and purely social events. Linux User Groups are a great way of meeting other Linux users in your area. There are a number of published lists of Linux User Groups. Linux Online (http://www.linux.org) has a list of Linux user groups organized by country at http://www.linux.org/groups.

Using Code Examples

This book is here to help you get your job done. In general, you may use the code in this book in your programs and documentation. You do not need to contact O’Reilly for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: "Linux in a Nutshell, Sixth Edition, by Ellen Siever, Stephen Figgins, Robert Love, and Arnold Robbins. Copyright 2009 Ellen Siever, Stephen Figgins, and Robert Love, 978-0-596-15448-6.”

If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact the publisher at permissions@oreilly.com.

Conventions

This desktop quick reference follows certain typographic conventions:

Bold

Used for commands, programs, and options. All terms shown in bold are typed literally.

Italic

Used to show arguments and variables that should be replaced with user-supplied values. Italic is also used to introduce new terms, indicate filenames and directories, and to highlight comments in examples.

Constant width

Used to show the contents of files or the output from commands.

Constant width bold

Used in examples to show commands or other text that should be typed literally by the user.

Constant width italic

Used in examples to show text that should be replaced with user-supplied values.

$

Used in some examples as the bash shell prompt ($).

[ ]

Surround optional elements in a description of syntax. (The brackets themselves should never be typed.) Note that many commands show the argument [files]. If a filename is omitted, standard input (e.g., the keyboard) is assumed. End with an end-of-file character.

EOF

Indicates the end-of-file character (normally Ctrl-D).

|

Used in syntax descriptions to separate items for which only one alternative may be chosen at a time.

Tip

This icon indicates a note, which is an important aside to its nearby text.

Warning

This icon indicates a warning.

A final word about syntax. In many cases, the space between an option and its argument can be omitted. In other cases, the spacing (or lack of spacing) must be followed strictly. For example, -wn (no intervening space) might be interpreted differently from -w n. It’s important to notice the spacing used in option syntax.

How to Contact Us

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Acknowledgments

This sixth edition of Linux in a Nutshell is the result of the cooperative efforts of many people. Many thanks to Avery Pennarun for writing the Git chapter. Thanks also to Simon St.Laurent and Andy Oram for their editorial skills. For technical review, thanks go to Greg Goddard, Leam Hall, Forrest Humphrey, Josh More, and Dave Pawson.

Chapter 1. Introduction

It is hard to chart the rise of Linux without risking the appearance of exaggeration and hyperbole. During the past few years alone, Linux has grown from a student/hacker playground to an upstart challenger in the server market to a well-respected system taking its rightful place in educational and corporate networks. Many serious analysts claim that its trajectory has just begun, and that it will eventually become the world’s most widespread operating system.

Linux was first developed by Linus Torvalds at the University of Helsinki in Finland. From his current location in Silicon Valley, Linus continues to centrally coordinate improvements. The Linux kernel continues to develop under the dedicated cultivation of a host of other programmers and hackers all over the world, joined by members of programming teams at major computer companies, all connected through the Internet.

By “kernel,” we mean the core of the operating system itself, not the applications (such as the compiler, shells, and so forth) that run on it. Today, the term “Linux” is often used to mean a software environment with a Linux kernel, along with a large set of applications and other software components. In this larger meaning, many people prefer the term GNU/Linux, which acknowledges the central role played by tools from the Free Software Foundation’s GNU project as complements to the development of the Linux kernel.

Linux systems cannot be technically referred to as a “version of Unix,” as they have not undergone the required tests and licensing.[1] However, Linux offers all the common programming interfaces of standard Unix systems, and, as you can see from this book, all the common Unix utilities have been reimplemented on Linux. It is a powerful, robust, fully usable system.

The historical impact of Linux goes beyond its role as a challenge to all versions of Unix as well as Microsoft Windows, particularly on servers. Linux’s success has also inspired countless other free software or open source (defined at http://opensource.org) projects, including Samba, GNOME, and a mind-boggling collection of innovative projects that you can browse at numerous sites like SourceForge (http://sourceforge.net) and Freshmeat (http://freshmeat.net). As both a platform for other developers and a development model, Linux gave a tremendous boost to the GNU project and has also become a popular platform for Java development. In short, Linux is a focal point in the most exciting and productive free-software movement ever seen.

If you haven’t obtained Linux yet, or have it but don’t know exactly how to get started using it, see Other Resources in Other Resources.

[1] Before an operating system can be called “Unix,” it must be branded by The Open Group.

The Excitement of Linux

Linux is, first of all, free software: anyone can download the source from the Internet or buy it on a low-cost CD-ROM. But Linux is becoming well known because it’s more than just free software — it’s unusually good software. You can get more from your hardware with Linux and be assured of fewer crashes; even its security is better than many commercial alternatives.

Linux first appeared in organizations as ad hoc installations by hackers running modest web servers or development systems at universities and research institutions, but it now extends deeply into corporations around the world. People deploying Linux for mission-critical systems tend to talk about its ample practical advantages, such as the ability to deliver a lot of bang for the buck and the ease of deploying other powerful tools on Linux, such as Apache, Samba, and Java environments. They also cite Linux’s ability to grow and sprout new features of interest to large numbers of users. But these advantages can be traced back to the concept of software freedom, which is the root of the broad wave of innovation driving Linux.

As free software, Linux revives the grand creativity and the community of sharing that Unix was long known for. The unprecedented flexibility and openness of Unix — which newcomers usually found confusing and frustrating, but eventually found they couldn’t live without — continually inspired extensions, new tools, and experiments in computer science that sometimes ended up in mainstream commercial computer systems.

Many programmers fondly remember the days when AT&T provided universities with Unix source code at no charge and the University of Berkeley started distributing its version in any manner that allowed people to get it. For these older hackers, Linux brings back the spirit of working together — all the more so because the Internet is now so widespread. And for the many who are too young to remember the first round of open systems or whose prior experience has been constricted by trying to explore and adapt proprietary operating systems, now is the time to discover the wonders of freely distributable source code and infinitely adaptable interfaces.

The economic power behind Linux’s popularity is its support for an enormous range of hardware. People who are accustomed to Microsoft Windows are often amazed at how much faster their hardware appears to work with Linux — it makes efficient use of its resources.

For the first several years after its appearance, users were attracted to Linux for a variety of financial and political reasons, but soon they discovered an unexpected benefit: Linux works better than many commercial systems. With the Samba file and print server, for instance, Linux provides stable Windows-based networking to a large number of end-user PCs. With the Apache web server, it provides more of the useful features web administrators want than competing products do. Embedded versions of the Linux kernel are growing in use because, although they are larger than the most stripped-down operating systems, they deliver a range of powerful features within a remarkably small footprint.

Opinions still differ on how suitable Linux is as a general-purpose desktop system. But the tremendous advances in usability and stability of the desktop software and its applications are undisputed. Soon (if not today), one will find Linux in many offices and other end-user environments. Meanwhile, the strides made by Linux in everyday computing tasks are reflected in the many new commands found in this edition.

Distribution and Support

Because of the vast number and variety of tools beyond the kernel required for a functional computing environment, building a Linux installation from scratch is quite complex. Over the years, therefore, commercial and noncommercial packages called distributions have emerged. The first distribution consisted of approximately 50 diskettes, at least one of which would usually turn out to be bad and have to be replaced. Since then, CD and DVD drives, as well as high-speed Internet connections, have become widespread and sharing Linux has become much easier.

After getting Linux, the average user is concerned next with support. While online newsgroups and forums offer quick responses and meet the needs of many intrepid users, you can also buy support from the vendors of the major distributions and a number of independent experts. Linux is supported at least as well as commercial software. When you buy a distribution from a vendor, you typically are entitled to a period of free support as well.

Intel’s x86 family and other compatible chips are still by far the most common hardware running Linux, but Linux is also now commercially available on a number of other hardware systems, notably the PowerPC, the Intel Itanium processor, and Sun Microsystems’ SPARC.

Commands on Linux

Linux commands are not the same as standard Unix ones. Most of the commands are provided by the GNU project run by the Free Software Foundation (FSF). GNU means “GNU’s Not Unix” — the first word of the phrase is expanded with infinite recursion.

Benefiting from years of experience with standard Unix utilities and advances in computer science, programmers on the GNU project have managed to create versions of standard tools that have more features, run faster and more efficiently, and lack the bugs and inconsistencies that persist in the original standard versions.

While GNU provided the programming utilities and standard commands such as grep, many of the system and network administration tools on Linux came from the Berkeley Software Distribution (BSD). In addition, some people wrote tools that specifically allow Linux to deal with special issues such as filesystems. This book documents the standard Unix commands that are commonly available on most Linux distributions.

The third type of software most commonly run on Linux is the X Window System, ported by the XFree86 and X.org projects to standard Intel chips. This book does not discuss the X Window System; see the O’Reilly book Running Linux, by Matthias Kalle Dalheimer and Matt Welsh, for an introduction to X.

What This Book Offers

Originally based on the classic O’Reilly quick reference, Unix in a Nutshell, this book has been expanded to include much information that is specific to Linux. These enhancements include chapters on:

- Package managers (which make it easy to install, update, and remove related software files)

- Boot methods

- The Subversion and Git version control systems

- Virtualization

The book also contains dozens of Linux-specific commands, along with tried-and-true Unix commands that have been supporting users for decades (though they continue to sprout new options).

This book does not cover the graphical tools contained in most distributions of Linux. Many of these, to be sure, are quite useful and can form the basis of everyday work. Examples of these tools include OpenOffice (Sun Microsystems’ free, open source version of the StarOffice suite), Evolution (a mail, calendar, and office productivity tool from Novell), Firefox and Thunderbird (a browser and mail program from Mozilla), and the GIMP (a graphic image-manipulation program and provider of a powerful library used by the GNOME project). But they are not Linux-specific, and their graphical models do not fit well into the format of this book.

While you probably log in to one of the graphical desktop environments such as GNOME or KDE and do much of your work with the graphical applications, the core of Linux use is the text manipulation and administration done from the command line, within scripts, or using text editors such as vi and Emacs. Linux remains largely a command-driven system, and this book continues to focus on this level of usage; for many tasks, the command line is the most efficient and flexible tool. In your day-to-day work, you’ll likely find yourself moving back and forth between graphical programs and the commands listed in this book.

Every distribution of Linux is slightly different. There are variations in directory structure, choice of standard utilities, and software versions, but you’ll find that the commands we document are the ones you use most of the time, and that they work the same on all distributions. Note, though, that some commands are only available with certain devices or configurations, or have alternatives that may be preferred in your environment. Basic commands, programming utilities, system administration, and network administration are all covered. However, some areas were so big that we had to leave them out. The many applications that depend on the X Window System didn’t make the cut. Nor did the many useful programming languages — such as Java, Perl, and Python — with which users can vastly expand the capabilities of their systems. XML isn’t covered here, either. These subjects would stretch the book out of its binding.

Linux in a Nutshell doesn’t teach you Linux — it is, after all, a quick reference — but novices as well as highly experienced users will find it of great value. When you have some idea of what command you want but aren’t sure just how it works or what combinations of options give you the exact output required, this book is the place to turn. It can also be an eye-opener, making you aware of options that you never knew about before.

Once you’ve installed Linux, the first thing you need to do is get to know the common utilities run from the shell prompt. If you know absolutely nothing about Unix, we recommend you read a basic guide (introductory chapters in the O’Reilly books Learning Red Hat Enterprise Linux and Fedora, by Bill McCarty, and Running Linux, mentioned previously, can get you started). This chapter and Chapter 2 offer a context for understanding different kinds of commands (including commands for programming, system administration, and network administration). Chapter 3 is the central focus of the book, containing about one half its bulk.

The shorter chapters immediately following Chapter 3 help you get your system set up. Since most users do not want to completely abandon other operating systems (whether a Microsoft Windows system or some Unix flavor), many users opt for a dual-boot system, with Linux residing on the same computer as other operating systems. Users can then boot to the system they need for a particular job. Chapter 4 describes the commonly used booting options on Intel systems, including LILO (Linux Loader) and GRUB (the GRand Unified Bootloader). Chapter 5 covers the Red Hat package manager (rpm) — which is supported by many distributions, including Red Hat Enterprise Linux, Fedora, SUSE, and Mandriva — and the Debian package-management system, which is used by such distributions as Ubuntu, Knoppix, and Gnoppix. It also describes some of the frontend package-management tools that simplify package management and automatically resolve dependencies. These tools include yum for rpm-based systems and aptitude and synaptic for Debian-based systems. Package managers are useful for installing and updating software; they make sure you have all the files you need in the proper versions.

All commands are interpreted by the shell. The shell is simply a program that accepts commands from the user and executes them. Different shells sometimes use slightly different syntax to mean the same thing. Under Linux, the standard shell is bash. Others, such as the ksh Korn shell, the tcsh enhanced C shell, and zsh, are available. Chapter 6 provides thorough coverage of bash; you may decide to read this chapter after you’ve used Linux for a while, because it mostly covers powerful, advanced features that you’ll want when you’re a steady user. Chapter 7 covers pattern matching, which is used by the Linux text-editing utilities for searching based on a pattern rather than an explicit string.

To get any real work done, you’ll have to learn some big, comprehensive utilities, notably an editor and some scripting tools. Two major editors are used on Linux: vi and Emacs. Emacs is covered in Chapter 8, and vi is discussed in Chapter 9. Chapter 9 also describes vim, an extended version of vi, commonly found on Linux systems. Chapter 10 and Chapter 11 cover two classic Unix tools for manipulating text files on a line-by-line basis: sed and gawk (the GNU version of the traditional awk). O’Reilly offers separate books about these topics that you may find valuable, as they are not known for being intuitive upon first use. (Emacs does have an excellent built-in tutorial, though; to invoke it, press Ctrl-h followed by t for “tutorial.”)

The Subversion and Git version control systems manage files so you can retrieve old versions and maintain different versions simultaneously. Originally used by programmers, who have complicated requirements for building and maintaining applications, these tools have turned out to be valuable for anyone who maintains files of any type, particularly when coordinating a team of people. Version control systems have become a distribution channel for thousands of free software projects. Chapter 12 offers a brief overview of version control, including basic terms and concepts. Chapter 13 presents Subversion commands, and Chapter 14 presents Git commands.

Chapter 15 covers virtualization and examines several virtualization systems such as Xen and VMWare and their command-line tools.

Our goal in producing this book is to provide convenience, and that means keeping the book (relatively) small. It certainly doesn’t have everything the manual pages have, but you’ll find that it has what you need 95 percent of the time. See the man command in Chapter 3 for information on reading the manpages. They can also be read with the info command, the GNU hypertext documentation reader, also documented in Chapter 3.

Sources and Licenses

Some distributions contain the source code for Linux; it is also easily available for download at http://www.kernel.org and elsewhere. Source code is similarly available for all the utilities on Linux (unless your vendor offers a commercial application or library as a special enhancement). You may never bother looking at the source code, but it’s key to Linux’s strength. Under the Linux license, the source code has to be provided or made available by the vendor, and it permits those who are competent at such things to fix bugs, provide advice about the system’s functioning, and submit improvements that benefit everyone. The license is the GNU project’s well-known General Public License, also known as the GPL or “copyleft,” invented and popularized by the Free Software Foundation (FSF).

The FSF, founded by Richard Stallman, is a phenomenon that many people might believe to be impossible if it did not exist. (The same goes for Linux, in fact — 20 years ago, who would have imagined a robust operating system developed by collaborators over the Internet and made freely redistributable?) One of the most popular editors on Unix, GNU Emacs, comes from the FSF. So do gcc and g++ (C and C++ compilers), which for a while set the standard in the industry for optimization and the creation of fast code. One of the most ambitious projects within GNU is the GNOME desktop, which encompasses several useful general-purpose libraries and applications that use these libraries to provide consistent behavior and interoperability.

Dedicated to the sharing of software, the FSF provides all its code and documentation on the Internet and allows anyone with a whim for enhancements to alter the source code. One of its projects is the Debian distribution of Linux.

To prevent hoarding, the FSF requires that the source code for all enhancements be distributed under the same GPL that it uses. This encourages individuals or companies to make improvements and share them with others. The only thing someone cannot do is add enhancements, withhold the source code, and then sell the product as proprietary software. Doing so would be taking advantage of the FSF and users of the GPL. You can find the text of the GPL in any software covered by that license, or online at http://www.gnu.org/copyleft/gpl.html.

As we said earlier, many Linux tools come from BSD instead of GNU. BSD is also free software. The license is significantly different, but that probably doesn’t concern you as a user. The effect of the difference is that companies are permitted to incorporate the software into their proprietary products, a practice that is severely limited by the GNU license.

Beginner’s Guide

If you’re just beginning to work on a Linux system, the abundance of commands might prove daunting. To help orient you, the following lists present a sampling of commands on various topics.

Communication

Command

Action

dig

Query DNS server.

ftp

File Transfer Protocol.

login

Sign on.

rsync

Transfer files, particularly across a network.

scp

Securely copy files to remote system.

sftp

Secure file transfer program.

ssh

Run shell or single command on remote system (secure).

Comparisons

Command

Action

cmp

Compare two files, byte by byte.

comm

Compare items in two sorted files.

diff

Compare two files, line by line.

diff3

Compare three files.

sdiff

Compare and interactively merge two files.

File Management

Command

Action

cat

Concatenate files or display them.

chattr

Change attributes on an ext2 file.

chgrp

Change group of files.

chmod

Change access modes on files.

chown

Change ownership of files.

chsh

Change login shell.

cp

Copy files.

csplit

Split a file into pieces with a specific size or at specific locations.

dd

Copy files in raw disk form.

file

Determine a file’s type.

head

Show the first few lines of a file.

hexdump

Display files in hexadecimal format.

less

Display files by screenful, forward and backward.

ln

Create filename aliases.

ls

List files and directories.

md5sum

Compute MD5 checksum.

merge

Merge changes from different files.

mkdir

Create a directory.

more

Display files by screenful, forward only.

mv

Move or rename files or directories.

newgrp

Change current group.

od

Display files in octal format.

pwd

Print working directory.

rm

Remove files.

rmdir

Remove directories.

sha1sum

Compute SHA1 checksum

shred

Securely delete files.

split

Split files evenly.

tac

Print lines of a file in reverse order.

tail

Show the last few lines of a file.

tailf

Follow the growth of a logfile.

touch

Update file timestamps and create the file if it doesn’t exist.

wc

Count lines, words, and characters.

Media

Command

Action

cdparanoia

Rip a CD while providing extra features.

cdrdao

Copy a CD.

eject

Eject a removable disk or tape.

genisoimage

Generate a binary image from a directory tree.

icedax

Rip a CD or DVD to create a computer-friendly WAV format.

readom

Read or write a data CD or DVD.

volname

Provide the volume name of a CD-ROM.

wodim

Record to a CD or DVD.

Printing

Command

Action

lpq

Show status of print jobs.

lpr

Send to the printer.

lprm

Remove print job.

lpstat

Get printer status.

pr

Format and paginate for printing.

Programming

Command

Action

ar

Create and update library files.

as

Generate object file.

bison

Generate parsing tables.

cpp

Preprocess C code.

flex

Lexical analyzer.

g++

GNU C++ compiler.

gcc

GNU C compiler.

ld

Link editor.

ldd

Print shared library dependencies.

m4

Macro processor.

make

Create programs.

ranlib

Regenerate archive symbol table.

rpcgen

Translate RPC to C code.

yacc

Generate parsing tables.

Program Maintenance

Command

Action

ctags

Generate symbol list for use with the vi editor.

etags

Generate symbol list for use with the Emacs editor.

gdb

GNU debugger.

git

Scalable, distributed revision control system.

gprof

Display object file’s profile data.

make

Maintain, update, and regenerate related programs and files.

nm

Display object file’s symbol table.

objcopy

Copy and translate object files.

objdump

Display information about object files.

patch

Apply patches to source code.

pmap

Print the memory map of a process.

size

Print the size of an object file in bytes.

strace

Trace system calls and signals.

strip

Strip symbols from an object file.

svn

Subversion revision control system.

Searching

Command

Action

apropos

Search manpages for topic.

egrep

Extended version of grep.

fgrep

Search files for literal words.

find

Search the system for files by name and take a range of possible actions.

grep

Search files for text patterns.

locate

Search a preexisting database to show where files are on the system.

look

Search file for string at the beginning of lines.

strings

Search binary files for text patterns.

updatedb

Update the locate database.

whereis

Find command.

which

Print pathname of a command.

Shell Programming

Command

Action

basename

Remove leading directory components from a path.

echo

Repeat command-line arguments on the output.

envsubst

Substitute the value of environment variables into strings.

expr

Perform arithmetic and comparisons.

mktemp

Generate temporary filename and create the file.

printf

Format and print command-line arguments.

sleep

Pause during processing.

test

Test a condition.

Storage

Command

Action

bunzip2

Expand compressed .bz2 files.

bzip2

Compress files to free up space.

cpio

Create and unpack file archives.

gunzip

Expand compressed (.gz and .Z) files.

gzip

Compress files to free up space.

tar

Copy files to or restore files from an archive medium.

zcat

Display contents of compressed files.

zforce

Force gzip files to have .gz extension.

System Status

Command

Action

at

Execute commands later.

atq

Show jobs queued by at.

atrm

Remove job queued by at.

crontab

Automate commands.

date

Display or set date.

df

Show free disk space.

du

Show disk usage.

env

Show environment variables.

finger

Display information about users.

free

Show free and used memory.

hostname

Display the system’s hostname.

kill

Terminate a running command.

printenv

Show environment variables.

ps

Show processes.

quota

Display disk usage and limits.

stat

Display file or filesystem status.

stty

Set or display terminal settings.

top

Display tasks currently running.

tty

Display filename of the terminal connected to standard input.

uname

Display system information.

uptime

Show how long the system has been running.

vmstat

Show virtual memory statistics.

who

Show who is logged in.

Text Processing

Command

Action

col

Process control characters.

cut

Select columns for display.

emacs

Work environment with powerful text-editing capabilities.

ex

Line editor underlying vi.

expand

Convert tabs to spaces.

fmt

Produce roughly uniform line lengths.

fold

Break lines.

gawk

Process lines or records one by one.

groff

Format troff input.

gs

Display PostScript or PDF file.

ispell

Interactively check spelling.

join

Merge different columns into a database.

paste

Merge columns or switch order.

rev

Print lines in reverse.

sed

Noninteractive text editor.

sort

Sort or merge files.

tr

Translate (redefine) characters.

unexpand

Convert spaces to tabs.

uniq

Find repeated or unique lines in a file.

vi

Visual text editor.

vim

Enhanced version of vi.

Miscellaneous

Command

Action

bc

Arbitrary precision calculator.

cal

Display calendar.

clear

Clear the screen.

info

Get command information from the GNU hypertext reader.

man

Get information on a command.

nice

Reduce a job’s priority.

nohup

Launch a command that will continue to run after logging out.

openvt

Run a program on the next available virtual terminal.

passwd

Set your login password.

script

Produce a transcript of your login session.

su

Become a different user, often the superuser.

sudo

Execute an authorized command as root or another user.

tee

Simultaneously store output in file and send to screen.

time

Time the execution of a command.

wall

Send a message to all terminals.

whoami

Print the current user id.

xargs

Process many arguments in manageable portions.

Chapter 2. System and Network Administration Overview

Common Commands

Following are lists of commonly used system administration commands.

Clocks

Command

Action

hwclock

Manage hardware clock.

rdate

Get time from network time server.

Daemons

Command

Action

apmd

Advanced Power Management daemon.

atd

Queue commands for later execution.

bootpd

Internet Boot Protocol daemon.

cupsd

Printer daemon.

ftpd

File Transfer Protocol daemon.

imapd

IMAP mailbox server daemon.

klogd

Manage syslogd.

mountd

NFS mount request server.

named

Internet domain nameserver.

nfsd

NFS daemon.

pppd

Maintain Point-to-Point Protocol (PPP) network connections.

rdistd

Remote file distribution server.

rexecd

Remote execution server.

rlogind

rlogin server.

routed

Routing daemon.

rpc.rusersd

Remote users server.

rpc.statd

NFS status daemon.

rshd

Remote shell server.

rsyslogd

Alternate system logging daemon.

rwhod

Remote who server.

sshd

Secure shell daemon.

syslogd

System logging daemon.

xinetd

Extended Internet services daemon. Starts other services as needed.

ypbind

NIS binder process.

yppasswdd

NIS password modification server.

ypserv

NIS server process.

Hardware

Command

Action

agetty

Start user session at terminal.

arp

Manage the ARP cache.

fdisk

Maintain disk partitions.

hdparm

Get and set hard drive parameters.

kbdrate

Manage the keyboard’s repeat rate.

ramsize

Print information about RAM disk.

setkeycodes

Change keyboard scancode-to-keycode mappings.

slattach

Attach serial lines as network interfaces.

Host Information

Command

Action

arch

Print machine architecture.

dig

Query Internet domain nameservers.

domainname

Print NIS domain name.

free

Print memory usage.

host

Print host and zone information.

hostname

Print or set hostname.

uname

Print host information.

Installation

Command

Action

cpio

Copy files to and from archives.

install

Copy files into locations providing user access and set permissions.

rdist

Distribute files to remote systems.

tar

Copy files to or restore files from an archive medium.

Mail

Command

Action

formail

Convert input to mail format.

mailq

Print a summary of the mail queue.

makemap

Update sendmail’s database maps.

newaliases

Rebuild sendmail’s alias database.

rmail

Handle uucp mail.

sendmail

Send and receive mail.

Managing Filesystems

To Unix systems, a filesystem is a device (such as a partition) that is formatted to store files. Filesystems can be found on hard drives, floppies, CD-ROMs, USB drives, or other storage media that permit random access.

The exact format and means by which the files are stored are not important; the system provides a common interface for all filesystem types that it recognizes. By default, almost all modern distributions of Linux use a journaling filesystem. When the kernel interacts with a journalling filesystem, writes to disk are first written to a log or journal before they are written to disk. This slows down writes to the filesystem, but reduces the risk of data corruption in the event of a power outage. It also speeds up reboots after a system unexpectedly loses power.

Most current Linux distributions default to the Third Extended (ext3) Filesystem. The ext3 filesystem was developed primarily for Linux and supports 256-character filenames and 4-terabyte maximum filesystem size. This ext3 filesystem is essentially a Second Extended (ext2) filesystem with an added journal. Since it is in all other ways identical to the ext2 system, it is both forward- and backward-compatible with ext2 — all ext2 utilities work with ext3 filesystems.

Although not covered in this edition of Linux in a Nutshell, Linux supports other open source journaling filesystems including: IBM’s Journaled Filesystem (JFS), SGI’s Extensible Filesystem (XFS), and the Naming System Venture’s Reiser Filesystem (ReiserFS). In some situations these can be faster than ext3. Some Linux distributions use these alternative filesystems by default. Other common filesystems include the FAT and VFAT filesystems, which allow files on partitions and floppies of Microsoft Windows systems to be accessed under Linux, and the ISO 9660 filesystem used by CD-ROMs.

Command

Action

debugfs

Debug ext2 filesystem.

dosfsck

Check and repair a DOS or VFAT filesystem.

dump

Back up data from a filesystem.

dumpe2fs

Print information about superblock and blocks group.

e2fsck

Check and repair an ext2 filesystem.

e2image

Store disaster-recovery data for an ext2 filesystem.

e2label

Label an ext2 filesystem.

edquota

Edit filesystem quotas with vim.

fdformat

Format floppy disk.

fsck

Another name for e2fsck.

fsck.ext2

Check and repair an ext2 filesystem.

mke2fs

Make a new ext2 filesystem.

mkfs

Make a new filesystem.

mkfs.ext2

Another name for mke2fs.

mkfs.ext3

Yet another name for mke2fs.

mklost+found

Make lost+found directory.

mkraid

Set up a RAID device.

mkswap

Designate swapspace.

mount

Mount a filesystem.

quotacheck

Audit stored quota information.

quotaon

Enforce quotas.

quotaoff

Do not enforce quotas.

quotastats

Display kernel quota statistics.

rdev

Describe or change values for root filesystem.

repquota

Display quota summary.

resize2fs

Enlarge or shrink an ext2 filesystem.

restore

Restore data from a dump to a filesystem.

rootflags

List or set flags to use in mounting root filesystem.

setquota

Edit filesystem quotas.

showmount

List exported directories on a remote host.

swapoff

Cease using device for swapping.

swapon

Begin using device for swapping.

sync

Write filesystem buffers to disk.

tune2fs

Manage an ext2 filesystem.

umount

Unmount a filesystem.

warnquota

Mail disk usage warnings to users.

Managing the Kernel

Command

Action

depmod

Create module dependency listing.

lsmod

List kernel modules.

modinfo

Print kernel module information.

modprobe

Load and remove a module and its dependent modules.

sysctl

Examine or modify kernel parameters at runtime.

Networking

Command

Action

ifconfig

Manage network interfaces.

iptables

Administer firewall facilities (2.4 kernel).

named

Translate between domain names and IP addresses.

nameif

Assign names to network devices.

netstat

Print network status.

nfsstat

Print statistics for NFS and RPC.

nsupdate

Submit dynamic DNS update requests.

portmap

Map daemons to ports (renamed rpcbind).

rarp

Manage RARP table.

rndc

Send commands to a BIND nameserver.

route

Manage routing tables.

routed

Dynamically keep routing tables up to date.

rpcbind

Map daemons to ports (replaces portmap).

rpcinfo

Report RPC information.

traceroute

Trace network route to remote host.

Printing

Command

Action

accept

Tell printer daemon to accept jobs.

lpadmin

Configure printer and class queues.

lpinfo

Show available printers and drivers.

lpmove

Move a print job to a different queue.

reject

Tell printer daemon to reject jobs.

tunelp

Tune the printer parameters.

Security and System Integrity

Command

Action

badblocks

Search for bad blocks.

chroot

Change root directory.

Starting and Stopping the System

The job of booting and rebooting a machine falls to a special program called init. Init is responsible for finishing the boot process once the kernel is done loading, launching the services necessary to run the computer. Init is also responsible for stopping services when needed and for shutting down or rebooting the computer when instructed.

For decades, the software handling these duties was called SysVinit, or System V init. Modern Linux distributions have begun switching to a replacement called Upstart (a less common replacement, init-ng, we will not discuss). The traditional model, facilitated by SysVinit, divides potential system states into multiple runlevels, each with a distinct purpose. Runlevel 3, for example, indicates a standard booted system; runlevel 6 indicates a reboot. When entering a runlevel N, SysVinit runs all of the commands in the directory /etc/rcN.d. In this manner, the scripts in /etc/rc3.d handle a system’s booting while those in /etc/rc6.d handle a reboot. Various commands (see accompanying table) allow a system administrator to force the system into a given runlevel. The file /etc/inittab specifies what runlevel is entered on boot, as well as configuration for the system’s tty’s.

Upstart replaces this functionality with a more general mechanism for the stopping, starting, and monitoring of services. Upstart operates asynchronously and is a much more powerful system than SysVinit. Thankfully, however, it is backward compatible with SysVinit and most distributions use it in a way in which much of the preceding paragraph remains accurate. Indeed, most modern Linux distributions have moved to Upstart but still manage runlevels via SysVinit-style scripts in /etc/rcN.d.

The biggest change with Upstart is with configuration. Instead of an inittab, Upstart maintains a directory of configuration scripts, /etc/event.d. Files within this directory describe how Upstart should handle tty’s and SysVinit-style runlevels: /etc/event.d/ttyN configures ttyN while /etc/event.d/rcN configures runlevel N.

Command

Action

chkconfig

Manage which services run in a runlevel.

ctrlaltdel

Shut down and then soft reboot system.

halt

Stop or shut down system.

initctl

Manage the Upstart init daemon.

reboot

Shut down and then hard reboot system.

runlevel

Print system runlevel.

shutdown

Shut down system.

telinit

Change the current runlevel.

uptime

Display uptimes of local machines.

System Activity and Process Management

A number of additional commands in Chapter 3 are particularly useful in controlling processes, including kill, killall, pidof, ps, and who.

Command

Action

fuser

Identify processes using file or filesystem.

renice

Change the priority of running processes.

top

Show most CPU-intensive processes.

vmstat

Print virtual-memory statistics and process statistics.

Users

Command

Action

chpasswd

Change multiple passwords.

groupadd

Add a new group.

groupdel

Delete a group.

groupmod

Modify groups.

grpck

Check the integrity of group system files.

grpconv

Convert group file to shadow group file.

lastlog

Generate report of last user login times.

newusers

Add new users in a batch.

pwck

Check the integrity of password system files.

pwconv

Convert password file to shadow passwords.

rusers

Print who-style information on remote machines.

rwall

Print a message to remote users.

useradd

Add a new user.

userdel

Delete a user and that user’s home directory.

usermod

Modify a user’s information.

w

List logged-in users.

wall

Write to all users.

whoami

Show how you are currently logged in.

Miscellaneous

Command

Action

anacron

Schedule commands for periodic execution.

atrun

Schedule commands for later execution.

cron

Schedule commands for specific times.

dmesg

Print bootup messages after the system is up.

ldconfig

Update library links and do caching.

logger

Send messages to the system logger.

logrotate

Compress and rotate system logs.

run-parts

Run all scripts in a directory.

Overview of Networking

Networks connect computers so that the different systems can share information. For users and system administrators, Unix systems have traditionally provided a set of simple but valuable network services that let you check whether systems are running, refer to files residing on remote systems, communicate via electronic mail, and so on.

For most commands to work over a network, one system must be continuously running a server process in the background, silently waiting to handle the user’s request. This kind of process is called a daemon. Common examples, on which you rely for the most basic functions of your Linux system, are named (which translates between numeric IP addresses and more human-readable alphanumeric names), cupsd (which sends documents to a printer, possibly over a network).

Most Unix networking commands are based on Internet protocols, standardized ways of communicating across a network on hierarchical layers. The protocols range from addressing and packet routing at a relatively low layer to finding users and executing user commands at a higher layer.

The basic user commands that most systems support over Internet protocols are generally called TCP/IP commands, named after the two most common protocols. You can use all of these commands to communicate with other Unix systems in addition to Linux systems. Many can also be used to communicate with non-Unix systems, almost all systems support TCP/IP.

This section also covers NFS and NIS — which allow for transparent file and information sharing across networks — and sendmail.

TCP/IP Administration

Command

Action

arp

Manipulate address resolution protocol tables.

dig

Query domain nameservers.

ftpd

Server for file transfers.

host

Print host and zone information.

ip

Network configuration tool with Cisco IOS-like syntax. Replaces ifconfig, route, and arp on some systems.

ifconfig

Configure network interface parameters.

named

Translate between domain names and IP addresses.

netstat

Print network status.

ping

Check that a remote host is online and responding.

pppd

Create PPP serial connection.

quagga

Routing daemon.

rdate

Notify time server that date has changed.

route

Manage routing tables.

routed

Dynamically keep routing tables up to date.

slattach

Attach serial lines as network interfaces.

sshd

Server for secure shell connections.

tcpdump

Write network packet information to screen or file.

telnetd

Server for Telnet sessions from remote hosts.

tftpd

Server for restricted set of file transfers.

zebra

Routing daemon.

NFS and NIS Administration

Command

Action

domainname

Set or display name of current NIS domain.

makedbm

Rebuild NIS databases.

rpcbind

DARPA port to RPC program number mapper.

portmap

The old name for rpcbind.

rpcinfo

Report RPC information.

ypbind

Connect to NIS server.

ypcat

Print values in NIS database.

ypinit

Build new NIS databases.

ypmatch

Print value of one or more NIS keys.

yppasswd

Change user password in NIS database.

yppasswdd

Update NIS database in response to yppasswd.

yppoll

Determine version of NIS map at NIS server.

yppush

Propagate NIS map.

ypserv

NIS server daemon.

ypset

Point ypbind at a specific server.

yptest

Check NIS configuration.

ypwhich

Display name of NIS server or map master.

ypxfr

Transfer NIS database from server to local host.

Overview of TCP/IP

TCP/IP is a suite of communications protocols that define how different types of computers talk to one another. It’s named for its foundational protocols, the Transmission Control Protocol and the Internet Protocol. The Internet Protocol provides logical addressing as data moves between hosts: it splits data into packets, which are then forwarded to machines via the network. The Transmission Control Protocol ensures that the packets in a message are reassembled in the correct order at their final destination and that any missing datagrams are re-sent until they are correctly received. Other protocols provided as part of TCP/IP include:

Address Resolution Protocol (ARP)

Translates between Internet and local hardware addresses (Ethernet, etc.).

Internet Control Message Protocol (ICMP)

Error-message and control protocol.

Point-to-Point Protocol (PPP)

Enables TCP/IP (and other protocols) to be carried across both synchronous and asynchronous point-to-point serial links.

Reverse Address Resolution Protocol (RARP)

Translates between local hardware and Internet addresses (opposite of ARP).

Simple Mail Transport Protocol (SMTP)

Used by sendmail to send mail via TCP/IP.

Simple Network Management Protocol (SNMP)

Performs distributed network management functions via TCP/IP.

User Datagram Protocol (UDP)

Transfers data without first making a persistent connection between two systems the way TCP does. Sometimes called unreliable transport.

TCP/IP is covered in depth in the three-volume set Internetworking with TCP/IP (Prentice Hall). The commands in this chapter and the next are described in more detail in TCP/IP Network Administration and Linux Network Administrator’s Guide, both published by O’Reilly.

In the architecture of TCP/IP protocols, data is passed down the stack (toward the Network Access Layer) when it is sent to the network, and up the stack when it is received from the network (see Figure 2-1).

Figure 2-1. Layers in the TCP/IP protocol architecture

IP Addresses

The IP (Internet protocol) address is a binary number that differentiates your machine from all others on the network. Each machine on the Internet must have a unique IP address. The most common form of IP address used currently (IPv4) uses a 32-bit binary address. An IPv4 address contains two parts: a network part and a host part. The number of address bits used to identify the network and host differ according to the class of the address. There are three main address classes: A, B, and C (see Figure 2-2). The leftmost bits indicate what class each address is.

Figure 2-2. IP address structure

A standard called Classless Inter-Domain Routing (CIDR, or supernetting) extends the class system’s idea of using initial bits to identify where packets should be routed. Under CIDR, a new domain can be created with any number of fixed leftmost bits (not just a multiple of eight). A CIDR address looks like a regular IPv4 address followed by a slash and a number indicating the number of network bits. For example: 192.168.32.1/24 or 128.66.128.1/17. Virtually all Internet gateway hosts now use CIDR.

IPv6, a newer standard, changes the method of addressing and increases the number of fields. An IPv6 address is 128 bits. Part of an IPv6 address is based on the Media Access Control (MAC) address of the network interface. The MAC address is unique for each network interface. When written, it is usually divided into eight 16-bit hexadecimal blocks separated by colons. For example:

FE80:0000:0000:0000:0202:B3FF:FE1E:8329

To shorten this, leading zeros may be skipped, and any one set of consecutive zeros can be replaced with double colons. For example, the above address can be reduced to:

FE80::202:B3FF:FE1E:8329

When IPv4 and IPv6 networks are mixed, the IPv4 address can be packed into the lower four bytes, yielding an address like 0:0:0:0:0:0:192.168.1.2, or ::192.168.1.2, or even ::C0A8:102.

Because improvements in IPv4, including CIDR, have relieved much of the pressure to migrate to IPv6, organizations have been slow to adopt IPv6. Some use it experimentally, but communication between organizations using IPv6 internally is still usually encapsulated inside IPv4 datagrams, and it will be a while before IPv6 becomes common.

If you wish to connect to the Internet, contact an Internet Service Provider (ISP). For most users, an ISP dynamically assigns an IP address to their systems. If you wish to always have the same address, have them assign you a static network address or range of addresses. If you are not connecting to an outside network, you can choose your own network address as long as it conforms to the IP address syntax. You should use the special reserved addresses provided in RFC 1597, which lists IP network numbers for private networks that don’t have to be registered with the IANA (Internet Assigned Numbers Authority). An IP address is different from an Ethernet address, which is assigned by the manufacturer of the physical Ethernet card.

Gateways and Routing

Gateways are hosts responsible for exchanging routing information and forwarding data from one network to another. Each portion of a network that is under a separate local administration is called an autonomous system (AS). Autonomous systems connect to each other via exterior gateways. An AS also may contain its own system of networks, linked via interior gateways.

Gateway protocols

Gateway protocols include:

EGP (Exterior Gateway Protocol)
BGP (Border Gateway Protocol)

Protocols for exterior gateways to exchange information

RIP (Routing Information Protocol)

Interior gateway protocol; most popular for LANs

Hello Protocol
OSPF (Open Shortest Path First)

Interior gateway protocols

Routing daemons

While most networks will use a dedicated router as a gateway, routing daemons like quagga and GNU Zebra, can be run on a host to make it function as a gateway. Thes replace the older gated daemon. Only one of them can run on a host at any given time. They allow a host to function as both an exterior and interior gateway and simplify routing configuration by combining the protocols RIP, Hello, BGP, EGP, and OSPF into a single package. We do not cover quagga or GNU Zebra in this book.

routed, a network routing daemon that uses RIP, allows a host to function only as an interior gateway, and manages the Internet routing tables. For more details on routed, see Chapter 3.

Routing tables

Routing tables provide information needed to route packets to their destinations. This information includes destination network, gateway to use, route status, and number of packets transmitted. Routing tables can be displayed with the netstat command.

Name Service

Each host on a network has a name that points to information about that host. Hostnames can be assigned to any device that has an IP address. A name service translates the hostnames (which are easy for people to remember) to IP addresses (the numbers the computer deals with).

DNS and BIND

The Domain Name System (DNS) is a distributed database of information about hosts on a network. Its structure is similar to that of the Unix filesystem — an inverted tree, with the root at the top. The branches of the tree are called domains (or subdomains) and correspond to IP addresses. The most popular implementation of DNS is the BIND (Berkeley Internet Name Domain) software.

DNS works as a client/server application. The resolver is the client, the software that asks questions about host information. The nameserver is the process that answers the questions. The server side of BIND is the named daemon. You can interactively query nameservers for host information with the dig and host commands. See Chapter 3 for more details on named, dig, and host.

The nameserver of a domain is responsible for keeping (and providing on request) the names of the machines in its domain. Other nameservers on the network forward requests for these machines to this nameserver.

Domain names

The full domain name is the sequence of names from the current domain back to the root, with a period separating the names. For instance, oreilly.com indicates the domain oreilly (for O’Reilly Media, Inc.), which is under the domain com (for commercial). One machine under this domain is www.oreilly.com. Top-level domains include:

aero

Air-transport industry

biz

Commercial organizations

com

Commercial organizations

coop

Cooperatives

edu

United States educational organizations

gov

United States government organizations

info

Informative sites

int

International organizations

mil

United States military departments

museum

Museums

name

Names of individuals

net

Commercial Internet organizations, usually Internet service providers

org

Miscellaneous organizations

pro

Professionals, including accountants, lawyers, and physicians

Countries also have their own two-letter top-level domains based on two-letter country codes. For example, the web server for the British Broadcasting System (BBC) in the United Kingdom has the following domain name: www.bbc.co.uk. Some domains (e.g., edu, gov, and mil) are sponsored by organizations that restrict their use; others (e.g., com, info, net, and org) are unrestricted. One special domain, arpa, is used for technical infrastructure purposes. The Internet Corporation for Assigned Names and Numbers (ICANN) oversees top-level domains and provides contact information for sponsored domains.

Configuring TCP/IP

Certain commands are normally run in the system’s startup files to enable a system to connect to a network. These commands can also be run interactively.

Network interfaces

The network interface represents the way that the networking software uses the hardware: the driver, the IP address, and so forth. To configure a network interface, use the ip command. This command replaces the older ifconfig command. It has a Cisco IOS-like command syntax that will be familiar to many network administrators. With ip, you can assign an address to a network interface, setting the netmask, broadcast address, and IP address at boot time. You can also set network interface parameters, including the use of ARP, the use of driver-dependent debugging code, the use of one-packet mode, and the address of the correspondent on the other end of a point-to-point link. For more information on ip, see Chapter 3.

Serial-line communication

There are two protocols for serial-line communication: Serial Line IP (SLIP) and Point-to-Point Protocol (PPP). These protocols let computers transfer information using the serial port instead of a network card, and a serial cable instead of an Ethernet cable. SLIP is rarely used anymore, having been replaced by PPP.

PPP was intended to remedy some of SLIP’s failings; it can hold packets from -non-Internet protocols, it implements client authorization and error detection/correction, and it dynamically configures each network protocol that passes through it. Under Linux, PPP exists as a driver in the kernel and as the daemon pppd. For more information on pppd, see Chapter 3.

Troubleshooting TCP/IP

The following commands can be used to troubleshoot TCP/IP. For more details on these commands, see Chapter 3:

dig

Query the DNS name service.

ifconfig

Provide information about the basic configuration of the network interface.

ifup and ifdown

On many systems used to start or stop a network interface.

iwconfig, iwlist, and wlancfg

Tools commonly used to configure a wireless network interface.

nc

Read and write data across a network connection.

netstat

Display network status.

ping

Indicate whether a remote host can be reached.

route

Allows you to read and set default gateway information, as well as static routes.

tcpdump

Dump network packet information to the screen or to file.

traceroute

Trace route taken by packets to reach network host.

Overview of Firewalls and Masquerading

A firewall is a secure computer that sits between an internal network and an external network (i.e., the Internet). It is configured with a set of rules that it uses to determine what traffic is allowed to pass and what traffic is barred. While a firewall is generally intended to protect the network from malicious or even accidentally harmful traffic from the outside, it can also be configured to monitor traffic leaving the network. As the sole entry point into the system, the firewall makes it easier to construct defenses and monitor activity.

The firewall can also be set up to present a single IP address to the outside world, even though multiple IP addresses may be used internally. This is known as masquerading. Masquerading can act as additional protection, hiding the very existence of a network. It also saves the trouble and expense of obtaining multiple IP addresses.

IP firewalling and masquerading are implemented with netfilter, also known as iptables. Tthe facilities provided by netfilter are designed to be extensible; if there is some function missing from the implementation, you can add it.

The packet filtering facilities provide built-in rule sets. Each network packet is checked against each rule in the rule set until the packet either matches a rule or is not matched by any rule. These sets of rules are called chains. These chains are organized into tables that separate filtering functions from masquerading and packet mangling functions. If a match is found, the counters on that rule are incremented and any target for that rule is applied. A target might accept, reject, or masquerade a packet, or even pass it along to another chain for processing. Details on the chains provided in iptables can be found in Chapter 3.

In addition to these chains, you can create your own user-defined chains. You might want a special chain for your PPP interfaces or for packets from a particular site. To call a user-defined chain, you just make it the target for a match.

It is possible to make it through a chain without matching any rules that have a target. If no rule matches the packet in a user-defined chain, control returns to the chain from which it was called, and the next rule in that chain is checked. If no rule matches the packet in a built-in chain, a default policy for that chain is used. The default policy can be any of the special targets that determine what is done with a packet. The valid targets are detailed in Chapter 3.

You use the iptables command to define the rules. Once you have the rules defined you can use iptables-save to create a file with all the rule definitions, and iptables-restore to restore those definitions when you reboot.

For more information on the kinds of decisions you need to make and the considerations that go into defining the rules, see a general book on firewalls such as Building Internet Firewalls (O’Reilly) by Elizabeth D. Zwicky et al. For more details on iptables, consult the Linux Network Administrator’s Guide (O’Reilly) by Tony Bautts et al., Linux iptables Pocket Reference (O’Reilly) by Gregor N. Purdy, or one of the relevant HOWTOs, such as the “Packet Filtering HOWTO.” These HOWTOs and a number of tutorials are available on the Netfilter website at http://www.netfilter.org/.

Overview of NFS

The Network File System (NFS) is a distributed filesystem that allows users to mount remote filesystems as if they were local. NFS uses a client/server model in which a server exports directories to be shared and clients mount the directories to access the files in them. NFS eliminates the need to keep copies of files on several machines by letting the clients all share a single copy of a file on the server. NFS is an RPC-based application-level protocol. For more information on the architecture of network protocols, see Overview of TCP/IP in Overview of TCP/IP.

Administering NFS

To set up NFS clients and servers, you must start the NFS daemons on the servers, export filesystems from the NFS servers, and mount the filesystems on the clients. The /etc/exports file is the NFS server configuration file; it controls which files and directories are exported and which kinds of access are allowed. Names and addresses for clients that should be allowed or denied access to NFS are kept in the /etc/hosts.allow and /etc/hosts.deny files.

Daemons

NFS server daemons, called nfsd daemons, run on the server and accept RPC calls from clients. NFS servers also run the mountd daemon to handle mount requests. On the client, caching and buffering are handled by biod, the block I/O daemon. The rpcbind daemon maps RPC program numbers to the appropriate TCP/IP port numbers. If the rpcbind daemon is not running properly, NFS will not work either. On older systems rpcbind is named portmap.

Exporting Filesystems

To set up an NFS server, first check that all the hosts that will mount your filesystem can reach your host. Next, edit the /etc/exports file on the server. Each entry in this file indicates the name of a directory to be exported, domain names of machines that will have access to that particular mount point, and any options specific to that machine. A typical entry looks like:

/projects hostname1(rw) hostname2(ro)

If you are running mountd, the files will be exported as allowed by the permissions in /etc/exports. See the exports manpage for all available export options.

Mounting Filesystems

To enable an NFS client, mount a remote filesystem after NFS is started, either by using the mount command or by specifying default remote filesystems in /etc/fstab. For example:

#mount servername:/projects /mnt/nfs/projects

A mount request calls the server’s mountd daemon, which checks the access permissions of the client and returns a pointer to a filesystem. Once a directory is mounted, it remains attached to the local filesystem until it is unmounted with the umount command or until the local system is rebooted.

Usually, only a privileged user can mount filesystems with NFS. However, you can enable users to mount and unmount selected filesystems using the mount and unmount commands if the user option is set in /etc/fstab. This can reduce traffic by having filesystems mounted only when needed. To enable user mounting, create an entry in /etc/fstab for each filesystem to be mounted. You can verify filesystems that have been mounted by using the mount or showmount commands. Or, you can read the contents of the /etc/mtab file.

Overview of NIS

The Network Information System (NIS) refers to the service formerly known as Sun Yellow Pages (YP). It is used to make configuration information consistent on all machines in a network. It does this by designating a single host as the master of all the system administration files and databases and distributing this information to all other hosts on the network. The information is compiled into databases called maps. NIS is built on the RPC protocol.

Another version of NIS, NIS+, adds encryption and strong authentication to NIS. NIS+ is a proprietary standard created by Sun Microsystems. This chapter discusses standard NIS, which is supported by most Linux systems. There are currently two NIS servers freely available for Linux, yps and ypserv. We describe ypserv in this book.

Servers

In NIS, there are two types of servers: master servers and slave servers. Master servers are responsible for maintaining the maps and distributing them to the slave servers. The files are then available locally to requesting processes.

Domains

An NIS domain is a group of hosts that use the same set of maps. The maps are contained in a subdirectory of /var/yp having the same name as the domain. The machines in a domain share password, host, and group file information. NIS domain names are set with the domainname command.

NIS Maps

NIS stores information in database files called maps. Each map consists of a pair of dbm database files, one containing a directory of keys (a bitmap of indices) and the other containing data values. The non-ASCII structure of dbm files necessitates using NIS tools such as yppush to move maps between machines.

The file /var/yp/YP_MAP_X_LATE contains a complete listing of active NIS maps, as well as NIS aliases for NIS maps. All maps must be listed in this file in order for NIS to serve them.

Map Manipulation Utilities

The following utilities are used to administer NIS maps:

makedbm

Make dbm files. Modify only ypserv’s map and any nondefault maps.

ypinit

Build and install NIS databases. Manipulate maps when NIS is being initialized. Should not be used when NIS is already running.

yppush

Transfer updated maps from the master server.

Administering NIS

NIS is enabled by setting up NIS servers and NIS clients. The descriptions given here describe NIS setup using ypserv, which does not support a master/slave server configuration. All NIS commands depend on the RPC rpcbind program, so make sure it is installed and running before setting up NIS.

Setting Up an NIS Server

Setting up an NIS server involves the following steps:

1. Set a domain name for NIS using domainname.

2. Edit the ypMakefile, which identifies which databases to build and what sources to use in building them.

3. Copy the ypMakefile to /var/yp/Makefile.

4. Run make from the /var/yp directory, which builds the databases and initializes the server.

5. Start ypserv, the NIS server daemon.

Setting Up an NIS Client

Setting up an NIS client involves only the following steps:

1. Set the domain name for NIS using domainname, which should be the same name used by the NIS server.

2. Run ypbind.

NIS User Accounts

NIS networks have two kinds of user accounts: distributed and local. Distributed accounts must be administered from the master machine; they provide information that is uniform on each machine in an NIS domain. Changes made to distributed accounts are distributed via NIS maps. Local accounts are administered from the local computer; they provide account information unique to a specific machine. They are not affected by NIS maps, and changes made to local accounts do not affect NIS. When NIS is installed, preexisting accounts default to local accounts.

RPC and XDR

RPC (remote procedure call) is the session protocol used by both NFS and NIS. It allows a host to make a procedure call that appears to be local but is really executed remotely on another machine on the network. RPC is implemented as a library of procedures, plus a network standard for ordering bytes and data structures called XDR (eXternal Data Representation).

Chapter 3. Linux Commands

This chapter presents the Linux user, programmer, and system administration commands. These are entered into a shell at the console or on a virtual terminal on a graphical desktop.

Each entry is labeled with the command name on the outer edge of the page. The syntax line is followed by a brief description and a list of available options. Many commands come with examples at the end of the entry. If you need only a quick reminder or suggestion about a command, you can skip directly to the examples.

Typographic conventions for describing command syntax are listed in the preface. For help in locating commands, see the index at the back of this book.

We’ve tried to be as thorough as possible in listing options. The basic command information and most options should be correct; however, there are many Linux distributions and many versions of commands. New options are added, and occasionally old options are dropped. You may, therefore, find some differences between the options you find described here and the ones on your system. When there seems to be a discrepancy, check the manpage. For most commands, you can also use the option --help to get a brief usage message. (Even when it isn’t a valid option, it will usually result in an “invalid option” error along with the usage message.)

Traditionally, commands take single-letter options preceded by a single hyphen, such as -d. A more recent convention allows long options preceded by two hyphens, such as --debug. Often, a feature can be invoked through either the old style or the new style of options.

Alphabetical Summary of Commands

Name

accept

Synopsis

accept [option] queue

System administration command. Instruct printing system to accept jobs for the specified print queue or queues. Depending on queue settings, the system may prompt for a password.

Option

-E

Force encrypted connection.

-h host [port]

Connect to specified server.

-U username

Use alternate username when connecting to server.

Name

access

Synopsis

access [mode] [filename]

Check whether a file is available for the action specified with the mode argument: r for read, w for write, x for execute. Used mostly in scripting, access works better than test because it uses a direct system call rather than looking at the file permissions, which can be misleading when a filesystem is mounted read-only.

Options

--help

Display help message, then quit.

--version

Display version, then quit.

Name

aclocal

Synopsis

aclocal [options]

GNU autoconf tool. Place m4 macro definitions needed by autoconf into a single file. The aclocal command first scans for macro definitions in m4 files in its default directory (/usr/share/aclocal on some systems) and in the file acinclude.m4. It next scans for macros used in the configure.in file. It generates an aclocal.m4 file that contains definitions of all m4 macros required by autoconf.

Options

--acdir=dir

Look for macro files in directory dir instead of the default directory.

--help

Print help message, then exit.

-I dir

Additionally, search directory dir for m4 macro definitions.

--output=file

Save output to file instead of aclocal.m4.

--print-ac-dir

Print the name of the directory to be searched for m4 files, then exit.

--verbose

Print names of files being processed.

--version

Print version number, then exit.

Name

aconnect

Synopsis

aconnect [options] [sender] [receiver]
aconnect [options]

Like its GUI relative alsa-patch-bay, aconnect connects ports in MIDI hardware and software to route events, similar to running patch cables between different mixers and synthesizers in an all-hardware audio system. aconnect is part of the ALSA (Advanced Linux Sound Architecture) system.

Options

-d, --disconnect

Undo the connection described.

-e, --exclusive

The connection being created must be exclusive: the sender and receiver ports may not connect to any other port.

-i, --input

List all input (sender) ports. This flag is used without any other arguments or flags.

-o, --output

List all output (receiver) ports. This flag is used without any other arguments or flags.

-r, --real queue-name

All events processed through this connection get new timestamps from the named real-time queue. The receiving port must have access to, and use, the real-time queue.

-t, --tick queue-name

All events processed through this connection get new timestamps from the specified tick queue.

-x, --remove-all

Cancel all connections. This flag is used without any other arguments or flags.

Name

acpi

Synopsis

acpi [options]

Displays information about the ACPI (Advanced Configuration and Power Interface) system, based on the /proc/acpi file. Most kernels after 2.4 support ACPI hardware, and in both hardware and software, ACPI is gradually replacing the older APM (Advanced Power Management) system. Some operating systems, including SUSE, ship a combined ACPI/APM power interface called powersaved. Most, however, require either ACPI or APM software.

Note that some ACPI systems have special events that are not available on others. For example, some laptops have events related to their docking stations and keyboard lights that are not used on nondocking or unlighted laptops. On all systems, the /proc/acpi directory must be present for acpi commands to work.

Options

--a, --ac-adapter

Show whether the AC adapter is connected.

-A, --without-ac-adapter

Do not show information about the AC adapter.

b, --battery

Display battery information.

-B, --without-battery

Do not display battery information.

-c, --celcius

Use degrees Celsius as the temperature unit. This is the default unit.

-d, --directory path

Use the specified path to ACPI information. The default is /proc/acpi.

-f, --fahrenheit

Use degrees Fahrenheit as the temperature unit.

-h, --help

Display help information.

-k, --kelvin

Use degrees Kelvin as the temperature unit.

-s, --show-empty

Display information even on devices that are not available or not installed, such as empty slots for extra batteries.

-S, --hide-empty

Do not display information on devices that are not operational or not installed.

-t, --thermal

Display temperature information.

-T, --without-thermal

Do not display temperature information.

-v, --version

Display version information.

-V, --everything

Show all information on every device.

Name

acpid

Synopsis

acpid [options]

Daemon that informs user-space programs about ACPI (Advanced Configuration and Power Interface) events, such as battery warnings, power-supply changes, and laptop lid closings. As ACPI hardware replaces older APM (Advanced Power Management) hardware, acpid replaces apmd. Like other daemons, this application is controlled primarily through a configuration file that determines which events merit action, and what those actions are.

Options

-c directory, --confdir=directory

Set the directory used for configuration files. The default directory is /etc/acpi/events. All files in this directory, except those beginning with a period (.), are parsed as configuration files. Typically, a single file is used for each ACPI event to be acted upon.

In the configuration files, blank lines and those beginning with # are ignored. Other lines are expected to consist of a regular expression and a command to be executed when an ACPI event matches the expression.

-d, --debug

Debug mode: run the daemon in the foreground and send all log output to stderr and stdout, rather than a logfile.

-e filename, --eventfile=filename

Set the file used to find events. Normally this is /proc/acpi/event.

-g group, --socketgroup=group

Set the group ownership of the socket to which acpid publishes events. This allows you to restrict which users on the system can access ACPI event information.

-l filename, --logfile=filename

Set the logfile location. Normally, it is /var/log/acpid.

-m mode, --socketmode=mode

Set the permission mode of the socket. Normally, it is 666, with the sticky bit off.

-s filename, --socketfile=filename

Set the file used to define the socket. Normally, this is /var/run/acpid.socket.

-S, --nosocket

Tells acpid not to open a socket at all. Overrides all other socket options.

-v, --version

Print version information and quit.

-h, --help

Print help message and quit.

Name

addr2line

Synopsis

addr2line [options] [addresses]

Translate hexadecimal program addresses into filenames and line numbers for the executable given with the -e option, or a.out if -e is not specified. If addresses are given on the command line, display the filename and line number for each address. Otherwise, read the addresses from standard input and display the results on standard output (useful for use in a pipe). addr2line prints two question marks (??) if it cannot determine a filename, and 0 if it cannot determine the line number. addr2line is used for debugging.

Options

-b bfdname, --target=bfdname

Set the binary file format using its binary file descriptor name, bfdname. Use the -h option for a list of supported formats for your system.

-C, --demangle[=style]

Decode (demangle) low-level symbol names into usernames. See the -h help output for a list of styles supported by your compiler.

-e file, --exe=file

Specify the filename of the executable to use. The default filename is a.out.

-f, --functions

Display function names in addition to filenames and line numbers.

-h, --help

Display help information and exit.

-s, --basenames

Strip directories off filenames and show only the basenames.

Name

agetty

Synopsis

agetty [options] port baudrate [term]

System administration command. agetty opens a tty port, prompts for login, and invokes the login command with the user’s name as an argument. While reading the name, agetty attempts to adapt the system to the speed and type of device being used. agetty is usually invoked by init using parameters specified in the /etc/inittab file, or in newer distributions of linux by an upstart event using parameters given in /etc/event.d/tty[1–6] files. On some systems this command may also be invoked as getty or replaced by an alternative command like mingetty. (See discussion of upstart in Chapter 2.)

You must specify a port, which agetty will search for in the /dev directory. You may use -, in which case agetty reads from standard input. You must also specify baudrate, which may be a comma-separated list of rates through which agetty will step. Optionally, you may specify the term, which is used to override the TERM environment variable.

Options

−8

Disable parity detection and assume tty is 8-bit clean.

-f file

Specify the use of file instead of /etc/issue upon connection to terminal. It is overridden by -i.

-h

Specify hardware, not software, flow control.

-H hostname

Write login hostname into the utmp file. By default, no login host is specified.

-I string

Specify string to be sent to the tty or modem.

-i

Suppress printing of /etc/issue before printing the login prompt.

-l program

Specify the use of program instead of /bin/login.

-L

Do not require carrier detect; operate locally only. Use this when connecting terminals.

-m

Attempt to guess the appropriate baud rate.

-n

Don’t prompt for a login name.

-t timeout

Specify that agetty should exit if the open on the line succeeds and there is no response to the login prompt in timeout seconds.

-U

Enable uppercase-only terminal detection. This will turn on some upper- to lowercase conversions if the login name is given in all capitals.

-w

Wait for carriage return or linefeed before sending login prompt. Use when sending an initialization string.

Name

alsactl

Synopsis

alsactl [options] [command] [card]

Control advanced configuration settings for sound cards using the ALSA (Advanced Linux Sound Architecture) system. Driver settings are written to and loaded from configuration files. The card can be specified as a card number, id, or device. If no card is specified, the configuration for all cards is saved or loaded. The default configuration file is /etc/asound.state.

Commands

init

Attempt to initialize all sound cards to a default state.

restore

Load the driver information from the configuration file.

store

Save the current driver information to the configuration file.

Options

-d, --debug

Debug mode: increased information output to the console.

-E var=value, --env var=value

Set an environment variable. Useful for init or to override ALSA_CONFIG_PATH.

-f file, --file=file

Specify the use of file instead of /etc/asound.state as a configuration file.

-F, --force

Force the restoration of settings; used with restore. This is the default.

-g, --ignore

With store and restore, do not display errors and do not set error exit codes.

-h, --help

Display help message and quit.

-i file, --initfile=file

Specify the configuration file for init. The default is /usr/share/alsa/init/00main.

-p, --pedantic

Ignore mismatched control settings; used with restore.

-r file, --runstate=file

Save restore and init errors to the specified file, appending new errors to the end of the file (unless -R is specified).

-R, --remove

Remove the runstate file first, before running the restore or init.

-v, --version

Display version information and quit.

Name

alsamixer

Synopsis

alsamixer [options]

An ALSA mixer with an ncurses interface, for use with ALSA soundcard drivers. alsamixer supports multiple sound cards with multiple drivers. Use ESC or Alt-Q to exit.

Options

-c cardnum

Specify the number or id of the soundcard to use, if there are multiple cards. Card numbers start from 0 (the default).

-D deviceid

Specify the id of the mixer device to control.

-g

Toggle use of color or monochrome in the alsamixer window.

-h, --help

Display brief usage message and exit.

-s

Minimize the mixer window.

-V mode

Select the starting view mode. The possible modes are playback, capture, or all.

Name

amidi

Synopsis

amidi [options]

Read and write raw MIDI files (.syx format, without timing information) to ALSA ports. For standard MIDI (.mid) files, use aplaymidi and arecordmidi.

Options

-a, --active-sensing

Record and send active-sensing (FEh) bytes in MIDI commands. By default, these bytes are ignored.

-d, --dump

Output received data directly to the screen as hexadecimal bytes.

-h, --help

Display help information and quit.

-l, --list-devices

List all hardware MIDI ports.

-L, --list-rawmidis

List all RawMIDI definitions. Useful for debugging configuration files.

-p, --port=name

Use the specified port. This overrides the port set in the configuration file. If neither this flag nor the configuration file sets a port, the default is port 0 on device 0, which may or may not exist.

-r, --receive=filename

Write data from the port specified with the -p or --port flag to the file named here, which is a raw file, and should end in .syx. Unless you use the -a option, the data does not include Active Sensing (FEh) bytes.

-s, --send=filename

Send the file to the port specified with the -p or --port flag. Use raw (.syx) MIDI files only.

-S, --send-hex=”hex-numbers..."

Send a string of hexadecimal numbers to the port specified with the -p or --port flag.

-t, --timeout=n

Stop listening after n seconds of receiving no data.

-V, --version

Display version information and quit.

Name

amixer

Synopsis

amixer [options] [command]

Command-line ALSA mixer. For an ncurses interface, use alsamixer. amixer displays or changes the current mixer settings for the current sound card and sound device. To display all mixer settings, use with no flags or commands.

Commands

contents

List card controls and their contents.

controls

Display a complete list of card controls. These controls can be set with the cset command, in contrast to simple mixer controls, which use set or sset.

cget [control]

Display the contents of the specified card control.

cset [control] [parameter]

Set the card control to the value specified in the parameter. Card controls may be identified by iface, name, index, device, subdevice, or numid. The parameter is normally a number or percentage value. For example, the command amixer -c 1 cset numid=16 50% sets the 16th element of the first sound card to 50%.

get, sget [control]

Display the current values for the specified simple mixer control.

help

Display help message and quit.

info

Display information about the current card or the card specified with the -c flag.

scontents

Display a complete list of simple mixer controls and their contents.

scontrols

Display a list of simple mixer controls. Simple mixer controls can be set with the set or sset commands, in contrast to card controls, which use the cset command.

set, sset [control] [parameter]

Set one of the controls listed by scontrols. You can specify the volume with a percentage from 0% to 100%, or a specific hardware value. Append + or − to the number to increase or decrease the volume by that amount. To set recording and muting values, use the parameters cap (meaning capture, or record), nocap, mute, unmute, or toggle. To specify individual channels, use the parameters front, rear, center, or woofer. For example, the command amixer -c 1 sset Line,0 100% unmute sets Line 0 on the first sound card to 100% and unmutes it.

Options

-c n

The number of the card to adjust.

-D devicename

Specify the name of the device. By default, the name is default.

-h

Display help information and quit.

-q

Quiet mode: do not show the results of changes made.

-s, --stdin

Read command lines from standard input and execute sequentially.

Name

anacron

Synopsis

anacron [options] [job]

System administration command. Normally started in a system startup file. Execute commands periodically. By default, anacron reads a list of jobs from a configuration file, /etc/anacrontab. The file consists of shell variables to use when running commands, followed by a list of tasks to run. Each task specifies how often in days it should be run, a delay in minutes to wait before running the task, a unique job identifier used to store a timestamp, and the shell command to execute. Timestamps for the last run of each task are stored in the /var/spool/anacron file. For each task, anacron compares the stored timestamp against the current time. If the command has not been executed within the specified frequency, the command is run. Upon completion, anacron records the new date in the timestamp file. Limit anacron to a specified task by providing the task’s unique job identifier on the command line.

The anacron command is often used to support the cron daemon on systems that do not run continuously.

Options

-d

Run in foreground rather than as a background process. Send messages to standard error.

-f

Run tasks ignoring timestamps.

-h

Print help message, then exit.

-n

Run tasks now, ignoring delay specifications.

-q

Suppress messages to standard error when using the -d option.

-s

Execute tasks serially. Do not start new task until previous task is completed.

-S directory

Store timestamps in directory instead of /var/spool/anacron.

-t file

Read tasks from file instead of from /etc/anacrontab.

-T

Test validity of configuration file. Can be used with -t.

-u

Update timestamps for tasks, but don’t run them.

-V

Print version number, then exit.

Name

aplay

Synopsis

aplay [options] [file]

Play sound files using the ALSA sound system. The related arecord records sound files.

Options

-c, --channels=n

Use n channels: 1 for mono, 2 for stereo.

-d, --duration=n

Set an interrupt for n seconds after playback begins.

-D, --device=devicename

Select a PCM device by name.

-f, --format=format

Specify the sample format. The sample formats available will depend on hardware. For CD and DAT output, use the cd and dat shortcuts, which set the sample rate, format, and channel numbers all at once.

-h, --help

Print help message, then exit.

-l, --list-devices

List available sound cards and digital audio devices.

-L, --list-pcms

List all PCM (pulse-coded modulation, or digital audio) devices that have been defined. PCMs may be defined in the .asoundrc file.

-q, --quiet

Run quietly. Do not display messages.

-r, --rate=n

Set the sample rate in Hertz. The default is 8000 Hertz.

-s, --sleep-min=n

Set the minimum number of ticks to sleep. The default is not to sleep.

-t, --file-type=type

Name the file type used. Files may be voc, wav, raw, or au.

--version

Print version and quit.

Name

aplaymidi

Synopsis

aplaymidi [options] [file]

Play MIDI files using the ALSA sound system; output is to ALSA sequencer ports.

Options

-d, --delay=n

Delay n seconds at the end of a file to allow for reverberation of the final notes.

-h, --help

Print help message, then exit.

-V, --version

Print version and quit.

-l, --list

List output ports available.

-p, --port=client:port

Specify the port to which the MIDI file will be sent. If no port is specified, the file will be sent to port 0.

Name

apmd

Synopsis

apmd [options]

System administration command. apmd handles events reported by the Advanced Power Management BIOS driver. The driver reports on battery level and requests to enter sleep or suspend mode. apmd will log any reports it gets via syslogd and take steps to make sure that basic sleep and suspend requests are handled gracefully. You can fine-tune the behavior of apmd by editing the apmd_proxy script, which apmd runs when it receives an event. Note that the APM hardware standard has been replaced by the ACPI (Advanced Configuration and Power Interface) standard, and apmd by acpid.

Options

-c n, --check n

Set the number of seconds to wait for an event before rechecking the power level. Default is to wait indefinitely. Setting this causes the battery levels to be checked more frequently.

-p n, --percentage n

Log information whenever the power changes by n percent. The default is 5. Values greater than 100 will disable logging of power changes.

-P command, --proxy command

Specify the apmd_proxy command to run when APM driver events are reported. This is generally a shell script. The command will be invoked with parameters indicating what kind of event was received. The parameters are listed in the next section.

-T [n], --proxy-timeout [n]

Set time-out for proxy to n seconds. Without this option apmd will wait indefinitely for the proxy to finish. Default value of n is 30 seconds.

-v, --verbose

Verbose mode; all events are logged.

-V, --version

Print version and exit.

-w n, --warn n

Log a warning at ALERT level when the battery charge drops below n percent. The default is 10. Negative values disable low-battery-level warnings.

-W, --wall

Use wall to alert all users of a low battery status.

-q, --quiet

Disable low-battery-level warnings.

-?, --help

Print help summary and exit.

Parameters

The apmd proxy script is invoked with the following parameters:

start

Invoked when the daemon starts.

stop

Invoked when the daemon stops.

standby [ system | user ]

Invoked when the daemon receives a standby request. The second parameter indicates whether the request was made by the system or by the user. Standby mode powers off the monitor and disks, but the system continues to run and use power.

suspend [ system | user ]

Invoked when the daemon receives a suspend request. The second parameter indicates whether the request was made by the system or by the user. Suspend, also known as “hibernate,” effectively powers the system down but has a quicker recovery than a normal boot process.

resume [ suspend | standby | critical ]

Invoked when the system resumes normal operation. The second parameter indicates the mode the system was in before resuming. critical suspends indicate an emergency shutdown. After a critical suspend, the system may be unstable, and you can use the resume command to help you recover from the suspension.

change power

Invoked when system power is changed from AC to battery or from battery to AC.

change battery

Invoked when the APM BIOS driver reports that the battery is low.

change capability

Invoked when the APM BIOS driver reports that some hardware that affects its capability has been added or removed.

Name

apropos

Synopsis

apropos string ...

Search the short manual page descriptions in the whatis database for occurrences of each string and display the result on standard output. Similar to whatis, except that it searches for strings instead of words. Equivalent to man -k.

Name

apt

Synopsis

apt

The Advanced Package Tool, the Debian package management system. A freely available packaging system for software distribution and installation. For detailed information on apt and its commands, see Chapter 5.

Name

ar

Synopsis

ar key [args] [posname] [count] archive [files]

Maintain a group of files that are combined into a file archive. Used most commonly to create and update static library files, as used by the link editor (ld). Compiler frontends often call ar automatically. Only one key letter may be used, but each can be combined with additional args (with no separations between). posname is the name of a file in archive. When moving or replacing files, you can specify that they be placed before or after posname. ar has largely been superseded by tar and bzip2.

Keys

d

Delete files from archive.

m

Move files to end of archive.

p

Print files in archive.

q

Append files to archive.

r

Replace files in archive.

t

List the contents of archive or list the named files.

x

Extract contents from archive or only the named files.

Arguments

a

Use with r or m key to place files in the archive after posname.

b

Same as a, but before posname.

c

Create archive silently.

f

Truncate long filenames.

i

Same as b.

l

For backward compatibility; meaningless in Linux.

N

Use count parameter. Where multiple entries with the same name are found, use the count instance.

o

Preserve original timestamps.

P

Use full pathname. Useful for non-POSIX-compliant archives.

s

Force regeneration of archive symbol table (useful after running strip).

S

Do not regenerate symbol table.

u

Use with r to replace only files that have changed since being put in archive.

v

Verbose; print a description of actions taken.

V

Print version number.

Example

Replace mylib.a with object files from the current directory:

ar r mylib.a `ls *.o`

Name

arch

Synopsis

arch

Print machine architecture type to standard output. Equivalent to uname -m.

Name

arecord

Synopsis

arecord [options] [filename]

Records sound using ALSA. Accepts the same arguments and options as aplay.

Name

arecordmidi

Synopsis

arecord [options] [filename]

Records midi files using ALSA. You must specify the port using the -p flag.

Options

-b, --bmp=n

Set the tempo value to n beats per minute. The default is 120.

-f, --fps=n

Set timing (SMPTE resolution) to n frames per second. The value is normally 24, 25, 29.97 (NTSC dropframe), or 30.

-h, --help

Display help message.

-i, --timesig=numerator:denominator

Set the time signature for the file and the metronome, specified as the numerator and the denominator separated by a colon. The denominator must be a power of 2. Defaults to 4:4.

-l, --list

List available ports.

-m, --metronome=client:port

Play a metronome signal on the specified sequencer port.

-p, --port=host:port

Set the sequencer host and port used. The default host is the local host, and the default port is port 0.

-s, --split-channels

For each channel of input, create a separate track in the MIDI output file.

-t, --ticks=n

Set the frequency with which timestamps, or ticks, are used in the file. For MIDI files using musical tempo, timestamps are set in ticks per beat (default 384), while those with SMPTE timing use ticks per frame (default 40).

-v, --version

Display version number.

Name

arp

Synopsis

arp [options]

TCP/IP command. Clear, add to, or dump the kernel’s Address Resolution Protocol (ARP) cache (/proc/net/arp). ARP is used to translate protocol addresses to hardware interface addresses. Modifying your ARP cache can change which interfaces handle specific requests. ARP cache entries may be marked with the following flags: C (complete), M (permanent), and P (publish). While arp can create a proxy for a single system, subnet proxies are now handled by the arp kernel module, arp(7). See the “Linux Advanced Routing & Traffic Control HOWTO” for details.

Options

host option arguments may be given as either a hostname or an IP address. With the -D option, they may also be given as a hardware interface address (e.g., eth0, eth1).

-a [hosts], --all [hosts]

Display entries in alternate (BSD) style for hosts or, if none are specified, all entries.

-d host [pub], --delete host [pub]

Remove the specified host’s entry. To delete a proxy entry, add the pub argument and specify the interface associated with the proxy using -i.

-D, --use-device

Use the hardware address associated with the specified interface. This may be used with -s when creating a proxy entry.

-e

Display entries in default (Linux) style.

-f file, --file file

Read entries from file and add them.

-H type, --hw-type type, -t type

Search for type entries when examining the ARP cache. type is usually ether (Ethernet), which is the default, but may be ax25 (AX.25 packet radio), arcnet (ARCnet), pronet (PROnet), or netrom (NET/ROM).

-i interface, --device interface

Select an interface. If you are dumping the ARP cache, this option will cause the command to display only the entries using that interface. When setting entries, this will cause the interface to be associated with that entry. If you do not use this option when setting an entry, the kernel will guess.

-n, --numeric

Display host IP addresses instead of their domain names.

-s host hardware-address [netmask mask] [pub], --set host hardware-address [netmask mask] [pub]

Add a permanent entry for host at hardware-address. A -hardware-address for type ether hardware is 6 hexadecimal bytes, colon-separated. The pub argument can be used to set the publish flag, creating a proxy entry.

-v, --verbose

Verbose mode.

Examples

Display entry for host eris:

arp -a eris

Set a permanent cache entry for host illuminati, whose hardware address you know:

arp -s illuminati 00:05:23:73:e6:cf

Set an ARP proxy for host fnord using the eth0 interface’s hardware address:

arp -Ds fnord eth0 pub

Remove the fnord ARP proxy:

arp -i eth0 -d fnord pub

Name

as

Synopsis

as [options] files

Generate an object file from each specified assembly-language source file. Object files have the same root name as source files but replace the .s suffix with .o. There may be some additional system-specific options.

Options

-- [ | files]

Read input files from standard input, or from files if the pipe is used.

-a[cdhlmns][=file]

With only the -a option, list source code, assembler listing, and symbol table. The other options specify additional things to list or omit:

-ac

Omit false conditionals.

-ad

Omit debugging directives.

-ah

Include the high-level source code, if available.

-al

Include an assembly listing.

-am

Include macro expansions.

-an

Suppress forms processing.

-as

Include a symbol listing.

=file

Set the listing filename to file.

--defsym symbol=value

Define the symbol to have the value value, which must be an integer.

-f

Skip whitespace and comment preprocessing.

--fatal-warnings

Treat warnings as errors.

--gstabs

Generate debugging information in stabs format.

--gdwarf2

Generate DWARF2 debugging information.

-o objfile

Place output in object file objfile (default is file.o).

--statistics

Print information on how much time and space assembler uses.

-v

Display the version number of the assembler.

-I path

Include path when searching for .include directives.

-J

Don’t warn about signed overflow.

-R

Combine both data and text in text section.

-W

Don’t show warnings.

-Z

Generate object file even if there are errors.

Name

at

Synopsis

at [options] time [date]

Execute commands at a specified time and optional date. The commands are read from standard input or from a file. (See also batch.) End input with EOF. time can be formed either as a numeric hour (with optional minutes and modifiers) or as a keyword. It can contain an optional date, formed as a month and date, a day of the week, or a special keyword (today or tomorrow). An increment can also be specified.

The at command can always be issued by a privileged user. Other users must be listed in the file /etc/at.allow if it exists; otherwise, they must not be listed in /etc/at.deny. If neither file exists, only a privileged user can issue the command.

Options

-c job [job...]

Display the specified jobs on the standard output. This option does not take a time specification.

-d job [job...]

Delete the specified jobs. Same as atrm.

-f file

Read job from file, not from standard input.

-l

Report all jobs that are scheduled for the invoking user. Same as atq.

-m

Mail user when job has completed, regardless of whether output was created.

-q letter

Place job in queue denoted by letter, where letter is any single letter from a-z or A-Z. Default queue is a. (The batch queue defaults to b.) Higher-lettered queues run at a lower priority.

-V

Display the version number.

Time

hh:[mm] [modifiers]

Hours can have one digit or two (a 24-hour clock is assumed by default); optional minutes can be given as one or two digits; the colon can be omitted if the format is h, hh, or hhmm (e.g., valid times are 5, 5:30, 0530, 19:45). If modifier am or pm is added, time is based on a 12-hour clock.

midnight | noon | teatime | now

Use any one of these keywords in place of a numeric time. teatime translates to 4:00 p.m.; now must be followed by an increment (described in a moment).

Date

month num[, year]

month is one of the 12 months, spelled out or abbreviated to its first three letters; num is the calendar date of the month; year is the four-digit year. If the given month occurs before the current month, at schedules that month next year.

day

One of the seven days of the week, spelled out or abbreviated to its first three letters.

today | tomorrow

Indicate the current day or the next day. If date is omitted, at schedules today when the specified time occurs later than the current time; otherwise, at schedules tomorrow.

Increment

Supply a numeric increment if you want to specify an execution time or day relative to the current time. The number should precede any of the keywords minute, hour, day, week, month, or year (or their plural forms). The keyword next can be used as a synonym of + 1.

Examples

In typical usage, you run at and input commands that you want executed at a particular time, followed by EOF.

$ at 1:00 am tomorrow
at> ./total_up > output
at> mail joe < output
at> <EOT>
Entered by pressing Ctrl-D
job 1 at 2003-03-19 01:00

The two commands could also be placed in a file and submitted as follows:

$ at 1:00 am tomorrow < scriptfile

More examples of syntax follow. Note that the first two commands here are equivalent:

$ at 1945 December 9
$ at 7:45pm Dec 9
$ at 3 am Saturday
$ at now + 5 hours
$ at noon next day

Name

atd

Synopsis

atd options

System administration command. Normally started in a system startup file. Execute jobs queued by the at command.

Options

-b n

Wait at least n seconds after beginning one job before beginning the next job. Default is 60.

-d

Print error messages to standard error instead of using syslog.

-l average

When system load average is higher than average, wait to begin a new job. Default is 0.8.

-n

Don’t fork. Run in foreground.

-s

Process queue once, then exit.

Name

atq

Synopsis

atq [options]

List the user’s pending jobs, unless the user is a privileged user; in that case, list everybody’s jobs. Same as at -l, and related to batch and atrm.

Options

-q queue

Query only the specified queue and ignore all other queues.

-V

Print the version number.

Name

atrm

Synopsis

atrm [option] job [job...]

Delete jobs that have been queued for future execution. Same as at -d.

Option

-V

Print the version number and then exit.

Name

autoconf

Synopsis

autoconf [options] [template_file]

Generate a configuration script from m4 macros defined in template_file, if given, or in a configure.ac or configure.in file in the current working directory. The generated script is almost invariably called configure.

Options

-d, --debug

Don’t remove temporary files.

-f, --force

Replace files generated previously by autoconf.

-h, --help

Print help message, then exit.

-i, --initialization

When tracing calls with the -t option, report calls made during initialization.

-o file, --output=file

Save output to file.

-t macro, --trace=macro

Report the list of calls to macro.

-v, --verbose

Verbosely print information about the progress of autoconf.

-B dir, --prepend-include=dir

Prepend directory dir to the search path.

-I dir, --include=dir

Append directory dir to the search path.

-V, --version

Print version number, then exit.

-W category, --warnings=category

Print any warnings related to category. Accepted categories are:

cross

Cross compilation.

obsolete

Obsolete constructs.

syntax

Questionable syntax.

all

All warnings.

no-category

Turn off warnings for category.

none

Turn off all warnings.

error

Treat warnings as errors.

Name

autoheader

Synopsis

autoheader [options] [template_file]

GNU autoheader tool. Generate a template file of C #define statements from m4 macros defined in template_file, if given, or in a configure.ac or configure.in file in the current working directory. The generated template file is almost invariably called config.h.in.

Options

-d, --debug

Don’t remove temporary files.

-f, --force

Replace files generated previously by autoheader.

-h, --help

Print help message, then exit.

-o file, --output=file

Save output to file.

-v, --verbose

Verbosely print information about the progress of autoheader.

-B dir, --prepend-include=dir

Prepend directory dir to the search path.

-I dir, --include=dir

Append directory dir to the search path.

-V, --version

Print version number, then exit.

-W category, --warnings=category

Print any warnings related to category. Accepted categories are:

obsolete

Obsolete constructs.

all

All warnings.

no-category

Turn off warnings for category.

none

Turn off all warnings.

error

Treat warnings as errors.

Name

automake

Synopsis

automake [options] [template_file]

GNU automake tool. Create GNU standards-compliant Makefile.in files from Makefile.am template files and can be used to ensure that projects contain all the files and install options required to be standards-compliant. Note that versions 1.4 and 1.6 differ enough that many distributions include an automake14 package for backward compatibility.

Options

-a, --add-missing

Add any missing files that automake requires to the directory by creating symbolic links to automake’s default versions.

-c, --copy

Used with the -a option. Copy missing files instead of creating symbolic links.

--cygnus

Specifies project has a Cygnus-style source tree.

-f, --force-missing

Used with the -a option. Replace required files even if a local copy already exists.

--foreign

Treat project as a non-GNU project. Check only for elements required for proper operation.

--gnu

Treat project as a GNU project with the GNU project structure.

--gnits

A stricter version of --gnu, performing more checks to comply with GNU project structure rules.

--help

Print help message, then exit.

-i, --ignore-deps

Disable automatic dependency tracking.

--libdir=dir

Used with the -a option. Search in directory dir for default files.

--no-force

Update only Makefile.in files that have updated dependents.

-v, --verbose

List files being read or created by automake.

--version

Print version number, then exit.

-Werror

Treat warnings as errors.

Name

autoreconf

Synopsis

autoreconf [options]

GNU autoreconf tool. Update configure scripts by running autoconf, autoheader, aclocal, automake, and libtoolize in specified directories and subdirectories. This command is seldom invoked manually. It is usually called automatically from other autoconf tools.

Options

-d, --debug

Don’t remove temporary files.

-f, --force

Remake all configure scripts, even when newer than their template files.

-h, --help

Print help message, then exit.

-i, --install

Add any default files missing from package by copying versions included with autoconf and automake.

-s, --symlink

Used with the -i option. Create symbolic links to default files instead of copying them.

-v, --verbose

Verbosely print information about the progress of autoreconf.

-I dir, --include=dir

Search in directory dir for input files.

-V, --version

Print version number, then exit.

-W category, --warnings=category

Print any warnings related to category. Accepted categories are:

cross

Cross compilation.

obsolete

Obsolete constructs.

syntax

Questionable syntax.

all

All warnings.

no-category

Turn off warnings for category.

none

Turn off all warnings.

error

Treat warnings as errors.

Name

autoscan

Synopsis

autoscan [options] [directory]

GNU autoscan tool. Create or maintain a preliminary configure.ac file named configure.scan based on source files in specified directory, or current directory if none given. If a configure.ac file already exists, autoconf will check it for completeness and print suggestions for correcting any problems it finds.

Options

-d, --debug

Don’t remove temporary files.

-h, --help

Print help message, then exit.

-v, --verbose

Verbosely print information about the progress of autoscan.

-I dir, --include=dir

Search in directory dir for input files. Use multiple times to add multiple directories.

-B dir, --prepend-include=dir

Search dir for input files before searching in other directories. Use multiple times to add multiple directories.

-V, --version

Print version number, then exit.

Name

autoupdate

Synopsis

autoupdate [options] [file]

GNU autoupdate tool. Update the configure template file file, or configure.ac if no file is specified. This command is seldom invoked manually. It is usually called automatically from other autoconf tools.

Options

-d, --debug

Don’t remove temporary files.

-f, --force

Remake all configure scripts, even when newer than their template files.

-h, --help

Print help message, then exit.

-v, --verbose

Verbosely print information about the progress of autoupdate.

-I dir, --include=dir

Search in directory dir for input files.

-V, --version

Print version number, then exit.

Name

badblocks

Synopsis

badblocks [options] deviceblock-count

System administration command. Search device for bad blocks. You must specify the number of blocks on the device (block-count). e2fsck and mke2fs will invoke badblocks automatically when given the -c option.

Options

-b blocksize

Expect blocksize-byte blocks.

-c blocksize

Test blocksize-byte blocks at a time. Default is 16.

-e number

Abort test after finding specified number of blocks.

-f

Force a read/write or nondestructive write test on a mounted device. Use only when /etc/mtab incorrectly reports a device as mounted.

-i file

Skip test of known bad blocks listed in file.

-n

Perform a nondestructive test by writing to each block and then reading back from it while preserving data.

-o file

Direct output to file.

-p number

Repeat search of device until no new bad blocks have been found in number passes. Default is 0.

-s

Show block numbers as they are checked.

-t pattern

Test blocks by reading and writing the specified pattern. You may specify pattern as a positive integer or as the word random. If you specify multiple patterns, badblocks tests all blocks with one pattern, and then tests all blocks again with the next pattern. Read-only mode accepts only one pattern. It does not accept random.

-v

Verbose mode.

-w

Test by writing to each block and then reading back from it. This option will destroy data. Don’t use it on devices that contain filesystems.

Name

base64

Synopsis

base64 [option] [file]

Use base64 encoding to encode or decode the specified file and print the results to standard output. With no file or with a dash (-), read the data from standard input.

Options

-d, --decode

Decode the data.

--help

Print help message and exit.

-i, --ignore-garbage

When decoding, ignore nonalphabetic characters except newline.

--version

Print version information and exit.

-w cols, --wrap=cols

When encoding, wrap lines after cols characters. The default is 76, while 0 disables line wrap.

Name

basename

Synopsis

basename name [suffix]
basename option

Remove leading directory components from a path. If suffix is given, remove that also. The result is printed to standard output. This is useful mostly in a script when you need to work with a filename but can’t predict its full path in every instance.

Options

--help

Print help message and then exit.

--version

Print the version number and then exit.

Examples

$ basename /usr/lib/libm.a
libm.a

$ basename /usr/lib/libm.a .a
libm

Name

bash

Synopsis

bash [options] [file [arguments]]
sh [options] [file [arguments]]

Standard Linux shell, a command interpreter into which all other commands are entered. For more information, see Chapter 6.

Name

batch

Synopsis

batch

Execute commands entered on standard input. Commands are run when the system load permits (when the load average falls below 0.8). Very similar to at, but takes no parameters on the command line. See at for details.

Name

bc

Synopsis

bc [options] [files]

bc is a language (and compiler) whose syntax resembles that of C, but with unlimited-precision arithmetic. bc consists of identifiers, keywords, and symbols, which are briefly described in the following entries. Examples are given at the end.

Interactively perform arbitrary-precision arithmetic or convert numbers from one base to another. Input can be taken from files or read from the standard input. To exit, type quit or EOF.

Options

-h, --help

Print help message and exit.

-i, --interactive

Interactive mode.

-l, --mathlib

Make functions from the math library available.

-s, --standard

Ignore all extensions, and process exactly as in POSIX.

-w, --warn

When extensions to POSIX bc are used, print a warning.

-q, --quiet

Do not display welcome message.

-v, --version

Print version number.

Identifiers

An identifier is a series of one or more characters. It must begin with a lowercase letter but may also contain digits and underscores. No uppercase letters are allowed. Identifiers are used as names for variables, arrays, and functions. Variables normally store arbitrary-precision numbers. Within the same program you may name a variable, an array, and a function using the same letter. The following identifiers would not conflict:

x

Variable x.

x[i]

Element i of array x. i can range from 0 to 2047 and can also be an expression.

x(y,z)

Call function x with parameters y and z.

Input-output keywords

ibase, obase, scale, and last store a value. Typing them on a line by themselves displays their current value. You can also change their values through assignment. The letters A-F are treated as digits whose values are 10-15.

ibase = n

Numbers that are input (e.g., typed) are read as base n (default is 10).

obase = n

Numbers that are displayed are in base n (default is 10). Note: once ibase has been changed from 10, use A to restore ibase or obase to decimal.

scale = n

Display computations using n decimal places (default is 0, meaning that results are truncated to integers). scale is normally used only for base-10 computations.

last

Value of last printed number.

Statement keywords

A semicolon or a newline separates one statement from another. Curly braces are needed when grouping multiple statements:

if (rel-expr) {statements} [else {statements}]

Do one or more statements if relational expression rel-expr is true. Otherwise, do nothing, or if else (an extension) is specified, do alternative statements. For example:

if (x=  =y) {i = i + 1} else {i = i − 1}

while (rel-expr) {statements}

Repeat one or more statements while rel-expr is true. For example:

while (i>0) {p = p*n; q = a/b; i = i-1}

for (expr1; rel-expr; expr2) {statements}

Similar to while. For example, to print the first 10 multiples of 5, you could type:

for (i=1; i<=10; i++) i*5

GNU bc does not require three arguments to for. A missing argument 1 or 3 means that those expressions will never be evaluated. A missing argument 2 evaluates to the value 1.

break

Terminate a while or for statement.

print list

GNU extension. It provides an alternate means of output. list consists of a series of comma-separated strings and expressions; print displays these entities in the order of the list. It does not print a newline when it terminates. Expressions are evaluated, printed, and assigned to the special variable last. Strings (which may contain special characters--i.e., characters beginning with \) are simply printed. Special characters can be:

a

Alert or bell

b

Backspace

f

Form feed

n

Newline

r

Carriage return

q

Double quote

t

Tab

\

Backslash

continue

GNU extension. When within a for statement, jump to the next iteration.

halt

GNU extension. Cause the bc processor to quit when executed.

quit

GNU extension. Cause the bc processor to quit whether line is executed or not.

limits

GNU extension. Print the limits enforced by the local version of bc.

Function keywords

define f(args) {

Begin the definition of function f having the arguments args. The arguments are separated by commas. Statements follow on successive lines. End with }.

auto x, y

Set up x and y as variables local to a function definition, initialized to 0 and meaningless outside the function. Must appear first.

return(expr)

Pass the value of expression expr back to the program. Return 0 if (expr) is left off. Used in function definitions.

sqrt(expr)

Compute the square root of expression expr.

length(expr)

Compute how many significant digits are in expr.

scale(expr)

Same as length, but count only digits to the right of the decimal point.

read( )

GNU extension. Read a number from standard input. Return value is the number read, converted via the value of ibase.

Math library functions

These are available when bc is invoked with -l. Library functions set scale to 20:

s(angle)

Compute the sine of angle, a constant or expression in radians.

c(angle)

Compute the cosine of angle, a constant or expression in radians.

a(n)

Compute the arctangent of n, returning an angle in radians.

e(expr)

Compute e to the power of expr.

l(expr)

Compute the natural log of expr.

j(n, x)

Compute the Bessel function of integer order n.

Operators

These consist of operators and other symbols. Operators can be arithmetic, unary, assignment, or relational:

arithmetic

+ - * / % ^

unary

- ++ --

assignment

=+ =- =* =/ =% =^ =

relational

< <= > >= = = !=

Other symbols

/* */

Enclose comments.

( )

Control the evaluation of expressions (change precedence). Can also be used around assignment statements to force the result to print.

{ }

Use to group statements.

[ ]

Indicate array index.

"text"

Use as a statement to print text.

Examples

Note in these examples that when you type some quantity (a number or expression), it is evaluated and printed, but assignment statements produce no display.

ibase = 8       Octal input
20              Evaluate this octal number
16              Terminal displays decimal value
obase = 2       Display output in base 2 instead of base 10
20              Octal input
10000           Terminal now displays binary value
ibase = A       Restore base-10 input
scale = 3       Truncate results to 3 decimal places
8/7             Evaluate a division
1.001001000     Oops!  Forgot to reset output base to 10
obase = 10      Input is decimal now, so A isn't needed
8/71.142           Terminal displays result (truncated)

The following lines show the use of functions:

define p(r,n){  Function p uses two arguments
auto v          v is a local variable
v = r^n         r raised to the n power
return(v)}      Value returned
scale = 5
x = p(2.5,2)    x = 2.5 ^ 2
x               Print value of x
6.25
length(x)       Number of digits
3
scale(x)        Number of places right of decimal point
2

Name

bison

Synopsis

bison [options] file

Given a file containing context-free grammar, convert into tables for subsequent parsing while sending output to file.c. To a large extent, this utility is compatible with yacc, and is in fact named for it. All input files should use the suffix .y; output files will use the original prefix. All long options (those preceded by --) may instead be preceded by +.

Options

-b prefix, --file-prefix=prefix

Use prefix for all output files.

-d, --defines

Generate file.h, producing #define statements that relate bison’s token codes to the token names declared by the user.

-r, --raw

Use bison token numbers, not yacc-compatible translations, in file.h.

-k, --token-table

Include token names and values of YYNTOKENS, YYNNTS, YYNRULES, and YYNSTATES in file.c.

-l, --no-lines

Exclude #line constructs from code produced in file.c. (Use after debugging is complete.)

-n, --no-parser

Suppress parser code in output, allowing only declarations. Assemble all translations into a switch statement body and print it to file.act.

-o file, --output-file=file

Output to file.

-p prefix, --name-prefix=prefix

Substitute prefix for yy in all external symbols.

-t, --debug

Compile runtime debugging code.

-v, --verbose

Verbose mode. Print diagnostics and notes about parsing tables to file.output.

-V, --version

Display version number.

-y, --yacc, --fixed-output-files

Duplicate yacc’s conventions for naming output files.

Name

bzcmp

Synopsis

bzcmp [options] file1 file2

Apply cmp to the data from files in the bzip2 format without requiring on-disk decompression. See bzip2 and cmp for usage.

Name

bzdiff

Synopsis

bzdiff [options] file1 file2

Apply diff to data from files in the bzip2 format without requiring on-disk decompression. See bzip2 and diff for usage.

Name

bzgrep

Synopsis

bzgrep [options] pattern [file...]

Apply grep to data from files in the bzip2 format without requiring on-disk decompression. See bzip2 and grep for usage.

Name

bzip2

Synopsis

bzip2 [options] filenames
bunzip2 [options] filenames
bzcat [option] filenames
bzip2recover filename

File compression and decompression utility similar to gzip, but uses a different algorithm and encoding method to get better compression. bzip2 replaces each file in filenames with a compressed version of the file and with a .bz2 extension appended. bunzip2 decompresses each file compressed by bzip2 (ignoring other files, except to print a warning). bzcat decompresses all specified files to standard output, and bzip2recover is used to try to recover data from damaged files.

Additional related commands include bzcmp, which compares the contents of bzipped files; bzdiff, which creates diff (difference) files from a pair of bzip files; bzgrep, to search them; and the bzless and bzmore commands, which apply the more and less commands to bzip output, as bzcat does with the cat command. See cat, cmp, diff, and grep for information on how to use those commands.

Options

--

End of options; treat all subsequent arguments as filenames.

-dig

Set block size to dig × 100 KB when compressing, where dig is a single digit from 1 to 9. For gzip compatibility, you can use --fast as an alias for −1 and --best for −9, but they have little effect on the compression speed.

-c, --stdout

Compress or decompress to standard output.

-d, --decompress

Force decompression even if invoked by bzip2 or bzcat.

-f, --force

Force overwrite of output files. Default is not to overwrite. Also forces breaking of hard links to files.

-k, --keep

Keep input files; don’t delete them.

-L, --license, -V, --version

Print license and version information, and exit.

-q, --quiet

Print only critical messages.

-s, --small

Use less memory, at the expense of speed.

-t, --test

Check the integrity of the files, but don’t actually compress them.

-v, --verbose

Verbose mode. Show the compression ratio for each file processed. Add more -vs to increase the verbosity.

-z, --compress

Force compression, even if invoked as bunzip2 or bzcat.

Examples

To produce two files: fileone.txt.bz2 and filetwo.ppt.bz2, while deleting the two original files:

bzip2 fileone.tzt filetwo.ppt

To produce a single compressed file, output.bz2, which can be decompressed to reconstitute the original fileone.txt and filetwo.txt:

bzip2 -c fileone.txt filetwo.txt > output.bz2

The tar command, combined with the -j or --bzip2 option, creates the output file nutshell.tar.bz2:

tar -cjf nutshell.tar.bz2 /home/username/nutshell

Name

bzless

Synopsis

bzless [options] file

Applies less to datafiles in the bzip2 format without requiring on-disk decompression. See bzip2 and less for usage.

Name

bzmore

Synopsis

bzmore [options] file

Applies more to datafiles in the bzip2 format without requiring on-disk decompression. See bzip2 and more for usage.

Name

c++

Synopsis

c++ [options] files

See g++.

Name

c++filt

Synopsis

c++filt [options] [symbol]

Decode the specified C++ or Java function name symbol, or read and decode symbols from standard input if no symbol is given. This command reverses the name mangling used by C++ and Java compilers to support function overloading, multiple functions that share the same name.

Options

-_, --strip-underscores

Remove initial underscores from symbol names.

--help

Print usage information, then exit.

-j, --java

Print names using Java syntax.

-n, --no-strip-underscores

Preserve initial underscores on symbol names.

-s format, --format=format

Expect symbols to have been coded in the specified format. Format may be one of the following:

arm

C++ Annotated Reference Manual.

edg

EDG (Intel) compiler.

gnu

Gnu compiler (the default).

gnu-new-abi

Gnu compiler with the new application binary interface (for gcc 3.x.)

hp

HP compiler.

lucid

Lucid compiler.

--version

Print version number, then exit.

Name

cal

Synopsis

cal [options] [[[day] month] year]

Print a 12-month calendar (beginning with January) for the given year, or a one-month calendar of the given month and year. With a day specified as well, print the calendar for that month and year, with the day highlighted. month ranges from 1 to 12. year ranges from 1 to 9999. With no arguments, print a calendar for the current month.

Options

−3

Display the previous, current and next month.

-j

Display Julian dates (days numbered 1 to 365, starting from January 1).

-m

Display Monday as the first day of the week (the default is Sunday).

-y

Display entire year.

Examples

cal 12 2006
cal 2006 > year_file

Name

cat

Synopsis

cat [options] [files]

Read (concatenate) one or more files and print them on standard output. Read standard input if no files are specified or if - is specified as one of the files; input ends with EOF. You can use the > operator to combine several files into a new file, or >> to append files to an existing file. When appending to an existing file, use Ctrl-D, the end-of-file symbol, to end the session.

Options

-A, --show-all

Same as -vET.

-b, --number-nonblank

Number all nonblank output lines, starting with 1.

-e

Same as -vE.

-E, --show-ends

Print $ at the end of each line.

-n, --number

Number all output lines, starting with 1.

-s, --squeeze-blank

Squeeze down multiple blank lines to one blank line.

-t

Same as -vT.

-T, --show-tabs

Print TAB characters as ^I.

-u

Ignored; kept for Unix compatibility.

-v, --show-nonprinting

Display control and nonprinting characters, with the exception of LINEFEED and TAB.

Examples

cat ch1                Display a file
cat ch1 ch2 ch3 > all  Combine files
cat note5 >> notes     Append to a file
cat > temp1            Create file at terminal. To exit, enter EOF
Ctrl-D).
cat > temp2 << STOP    Create file at terminal. To exit, enter STOP.

Name

cc

Synopsis

cc [options] files

See gcc.

Name

cdda2wav

Synopsis

cdda2wav [options] [files]

Convert Compact Disc Digital Audio (CDDA) to the WAV format. This process is often called “ripping” a CD-ROM and is generally performed before using an encoder to convert the file to a compressed music format, such as OGG or MP3.

cdda2wav is now generally a symbolic link to icedax.

Name

cdparanoia

Synopsis

cdparanoia [options] span [outfile]

cdparanoia records Compact Disc audio files as WAV, AIFF, AIFF-C, or raw format files. It uses additional data-verification and sound-improvement algorithms to make the process more reliable and is used by a number of graphical recording programs as a backend. The output is written to outfile if specified; otherwise it is written to one of cdda.wav, cdda.aifc, or cdda.raw depending on the output-format option given.

The command takes one argument, span, which describes how much of the CD to record. It uses numbers followed by bracketed times to designate track numbers and time within them. For example, the string 1[2:23]-2[5] indicates a recording from the two-minute and twenty-three-second mark of the first track up to the fifth second of the second track. The time format is demarcated by colons, hours:minutes:seconds:.sectors, with the last item, sectors, preceded by a decimal point (a sector is 1/75 of a second). It’s best to put this argument within quotes.

If you use the -B option, the span argument is not required.

Options

-a, --output-aifc

Output in AIFF-C format.

-A, --analyze-drive

Analyze and log drive caching, timing and reading. Implies -vQL.

-B, --batch

Split output into multiple files, one per track. Each file begins with the track number. This is the most commonly used flag for this command.

-C, --force-cdrom-big-endian

Force cdparanoia to treat the drive as a big-endian device.

-c, --force-cdrom-little-endian

Force cdparanoia to treat the drive as a little-endian device.

-d, --force-cdrom-device devicename

Specify a device name to use instead of the first readable CD-ROM available.

-e, --stderr-progress

Send all progress messages to standard error instead of standard output; used by wrapper scripts.

-f, --output-aiff

Output in AIFF format. The default format is WAV.

-h, --help

Display options and syntax.

-l, --log-summary [file]

Write results to file if specified, otherwise to cdparanoia.log.

-L, --log-debug [file]

Write device autosensing and debugging output to file if specified, otherwise to cdparanoia.log.

-p, --output-raw

Output headerless raw data.

-R, --output-raw-big-endian

Output raw data in big-endian byte order.

-r, --output-raw-little-endian

Output raw data in little-endian byte order.

-Q, --query

Display CD-ROM table of contents and quit.

-q, --quiet

Quiet mode.

-S, --force-read-speed n

Set the read speed to n on drives that support it. This is useful if you have a slow hard disk or not much RAM.

-s, --search-for-drive

Search for a drive, even if /dev/cdrom exists.

-V, --version

Print version information and quit.

-v, --verbose

Verbose mode.

-w, --output-wav

Output in WAV format. This is the default.

-X, --abort-on-skip

If a read fails and must be skipped, skip the entire track and delete any partially completed output file.

-z, --never-skip[=retries]

If a read fails (for example, due to a scratch in the disc), keep trying. If you specify a number, cdparanoia will try that number of times. If you do not, cdparanoia will retry until it succeeds. The default number of attempts is 20.

Progress symbols

The output during operation of cdparanoia includes both smiley faces and more standard progress symbols. They are:

:-)

Operation proceeding normally.

:-|

Operation proceeding normally, but with jitter during reads.

:-/

Read drift.

8-|

Repeated read problems in the same place.

:-O

SCSI/ATAPI transport error (hardware problem not related to the disc itself).

:-(

Scratch detected.

;-(

Unable to correct a problem.

8-X

Aborted read due to uncorrectable error.

:^D

Finished.

Blank space in the progress indicator means that no corrections were necessary.

-

Jitter correction was required.

+

Read errors.

!

Errors even after correction; repeated read errors.

e

Corrected transport errors.

V

An uncorrected error or a skipped read.

Name

cdrdao

Synopsis

cdrdao command [options] toc-file

Write all content specified in description file toc-file to a CD-R disk drive in one step. This is called disk-at-once (DAO) mode, as opposed to the more commonly used track-at-once (TAO) mode. DAO mode allows you to change the length of gaps between tracks and define data to be written in these gaps (like hidden bonus tracks or track intros). The toc file can be created by hand or generated from an existing CD using cdrdao’s read-toc command. A cue file, as generated by other audio programs, can be used instead of a toc file. The file format for toc files is discussed at length in the cdrdao manpage.

Commands

The first argument must be a command. Note that not all options are available for all commands. Run cdrdao command -h to see the options that apply to a particular command.

blank

Blank a CD-RW. The default is to do minimal blanking; use --blank-mode to change to full blanking.

copy

Copy the CD. If you use a single drive, you will be prompted to insert a CD-R after reading. An image file is created unless you use the --on-the-fly flag and two CD drives.

discid

Display CDDB information.

disk-info

Display information about the CD-R currently in the drive.

drive-info

Display information about the drive.

msinfo

Display multisession information. Useful mostly for wrapper scripts.

read-cd

Read from a CD and create a disk image and toc file that will allow creation of duplicates. Use --datafile to specify a filename.

read-cddb

Check a CDDB server for data about the CD represented by a given toc file; then write that data to the toc file as CD-TEXT data.

read-test

Check the validity of the audio files described in the toc file.

read-toc

Create a toc file from an audio CD.

scanbus

Scan the system bus for devices.

show-data

Print out the data that will be written to the CD-R. Useful for checking byte order.

show-toc

Print a summary of the CD to be created.

simulate

A dry run: do everything except write the CD. Equivalent to write --simulate.

toc-info

Display a summary of the toc file.

toc-size

Display the total toc blocksize.

unlock

Unlock the recorder after a failure. Run this command if you cannot eject the CD after using cdrdao.

write

Write the CD.

Options

--blank-mode mode

Set the blanking mode to full or minimal. The default is minimal.

--buffers n

Set the number of buffers. Since each buffer holds 1 second of data, this is equivalent to setting the number of seconds of data to be buffered. The default is 32; set to a higher number if your read source is unreliable or is slower than the CD-R. The minumum is 10.

--cddb-servers server,server

Enter hosts for servers. Servers may include ports, paths, and proxies; you can list multiple servers separated by spaces or commas.

--cddb-timeout s

Set the timeout for CDDB server connections to s seconds.

--cddb-directory localpath

CDDB data that is fetched will be saved in the directory localpath.

--datafile filename

When used with the read-toc command, this option specifies the datafile placed in the toc file. When used with read-cd and copy, it specifies the name of the image file created.

--device bus,id,logicalunit

Set the SCSI address of the CD-R using the bus number, ID number, and logical-unit number.

--driver driver-id:option-flags

Force cdrdao to use the driver you choose with the driver options named, instead of the driver it autodetects.

--eject

Eject the disc when done.

--force

Override warnings and perform the action anyway.

--keep

On exit, keep any temporary WAV files created.

--keepimage

Keep the image file created during the copy process. Used only with the copy command.

--multi

Record as a multisession disc.

-n

Do not wait 10 seconds before writing the disc.

--on-the-fly

Do not create an image file: pipe data directly from source to CD-R.

--overburn

If you are using a disc with more storage space than cdrdao detects, use this option to keep writing even when cdrdao thinks you’re out of space.

--paranoia-mode n

Specify the amount of error correction in the CD read, where n is a value from 0 to 3. 0 is none; 3 is full. Set error correction to a lower number to increase read speed. The default is 3.

--read-raw

Used only with the read-cd command. Write raw data to the image file.

--reload

Allow the drive to be opened before writing, without interrupting the process. Used with simulation runs.

--save

Save current options to the settings file $HOME/.cdrdao.

--session n

Used only with the read-toc and read-cd commands when working with multisession CDs. Specify the number of the session to be processed.

--source-device bus,id,logicalunit

Used only with the copy command and two drives. Set the SCSI address of the source device.

--source-driver driver-id:option-flags

Used only with the copy command. Set the source device driver and flags.

--speed value

Set the write speed to value. The default is the highest available speed; use a lower value if higher values give poor results.

--swap

Swap byte order for all samples.

-v verbose-level

Set the amount of information printed to the screen. 0, 1, and 2 are fine for most users; greater numbers are useful for debugging.

--with-cddb

Use CDDB to fetch information about the disc and save it as CD-TEXT data. Used with the copy, read-toc, and read-cd commands.

Examples

To find devices on the system:

cdrdao scanbus

To copy from a CD device (at 1,1,0) to a CD-R device (at 1,0,0):

cdrdao copy --source 1,1,0 --device 1,0,0 --buffers 64

Name

cdrecord

Synopsis

cdrecord [options] track1,track2...

Record data or audio compact discs. This program normally requires root access. cdrecord is now generally a symbolic link to wodim.

Name

cfdisk

Synopsis

cfdisk [options] [device]

System administration command. Partition a hard disk using a full-screen display. Normally, device will be /dev/hda, /dev/hdb, /dev/sda, /dev/sdb, /dev/hdc, /dev/hdd, and so on; the default is the first device on the system. See also fdisk.

Options

-a

Use an arrow on the left side to highlight the currently selected partition, instead of reverse video.

-c cylinders

Specify the number of cylinders to use to format the specified device.

-g

Ignore driver-provided geometry; guess one instead.

-h heads

Specify the number of heads to use to format the specified device.

-s sectors

Specify the number of sectors per track to use to format the specified device.

-v

Print version number and exit.

-z

Do not read the partition table; partition from scratch.

-P format

Display the partition table in format, which must be r (raw data), s (sector order), or t (table format). See the manpage for the meaning of the fields in the raw format, which shows what will be written by cfdisk for each partition. The sector format shows information about the sectors used by each partition. The table format shows the starting and ending head, sector, and cylinder for each partition.

Commands

up arrow, down arrow

Move among partitions.

left arrow, right arrow

Move among commands at the bottom of the screen.

Enter key

Select currently highlighted command or value.

b

Toggle flag indicating whether selected partition is bootable.

d

Delete partition (allow other partitions to use its space).

g

Alter the disk’s geometry. Prompt for what to change: cylinders, heads, or sectors (c, h, or s, respectively).

h

Help.

m

Attempt to ensure maximum usage of disk space in the partition.

n

Create a new partition. Prompt for more information.

p

Print the partition table to the screen or a file. Possible formats are the same as for the -P option.

q

Quit without saving information.

t

Prompt for a new filesystem type, and change to that type.

u

Change the partition-size units. The choice of units rotates from megabytes to sectors to cylinders and back.

W

Save information. Must be uppercase, to prevent accidental writing.

Name

chage

Synopsis

chage [options] user

Change information about user password expirations. If run with no option flags, chage prompts for values to be entered; you may also use option flags to change or view information. Requires a shadow password file. An unprivileged user can only run chage with the -l option.

Options

-d lastday, --lastday=lastday

Date of last password change. This may be expressed as a date in YYYY-MM-DD format, or as the number of days between January 1, 1970 and the last password change.

-E expiredate, --expiredate=expiredate

Set the date when the account will be locked. This is not a date for password expiration, but for account expiration. It may be expressed in YYYY-MM-DD format or as a number of days since January 1, 1970.

-I inactivedays, --inactive=inactivedays

If a password expires and the user does not log in for this number of days, the account will be locked and the user must contact a system administrator before logging in. Set to 0 to disable the feature.

-l, --list

This flag is used without any others and causes chage to display the current password expiration attributes for the user.

-m mindays, --mindays=mindays

Specify the minimum number of days between password changes. Default is zero, meaning that the user may change the password at any time.

-M maxdays, --maxdays=maxdays

Maximum number of days between password changes.

-W warndays, --warndays=warndays

The number of days before password expiration that a user will be warned to change passwords.

Name

chattr

Synopsis

chattr [options] mode files

Modify file attributes. Specific to Linux Second and Third Extended Filesystems (ext2 and ext3). Like symbolic chmod, chattr specifies attributes with +, -, and = but it operates on extended file attributes (see the upcoming section Attributes). mode is in the form opcode attribute. See also lsattr.

Options

-R

Modify directories and their contents recursively.

-f

Suppress most error messages.

-V

Verbose; print modes of attributes after changing them.

-v version

Set the file’s version.

Opcodes

+

Add attribute.

-

Remove attribute.

=

Assign attributes (removing unspecified attributes).

Attributes

A

Don’t update access time on modify.

a

Append only for writing. Can be set or cleared only by a privileged user.

c

Compressed.

D

Write changes synchronously to disk.

d

No dump.

H

The file’s blocks are stored in units of the filesystem blocksize, not of sectors. The file is or was at one time larger than 2 TB.

I

A directory is indexed using hashed trees.

i

Immutable. Can be set or cleared only by a privileged user. A file marked as immutable cannot be deleted, renamed, modified, or linked to until the setting has been cleared.

j

Journalled file. This is useful only in cases where you are using an ext3 filesystem mounted with the data="ordered” or data="writeback” attributes. The data="journal” option for the filesystem causes this operation to be performed for all files in the system and makes this option irrelevant.

S

Synchronous updates.

s

Secure deletion. The contents are zeroed on deletion, and the file cannot be undeleted or recovered in any way.

u

Undeletable. This causes a file to be saved even after it has been deleted, so that a user can undelete it later.

Example

chattr +a myfile    As superuser

Name

chfn

Synopsis

chfn [options] [username]

Change the information that is stored in /etc/passwd and displayed to the finger query. With no options, chfn enters interactive mode and prompts for changes. To blank a field, enter the keyword none. Only a privileged user can change information for another user. For regular users, chfn prompts for the user’s password before making the change.

Options

-f name, --full-name name

Specify new full name.

-h homephone, --home-phone homephone

Specify new home phone number.

-o office, --office office

Specify new office number.

-p officephone, --office-phone officephone

Specify new office phone number.

-u, --help

Print help message and then exit.

-v, --version

Print version information and then exit.

Example

chfn -f "Ellen Siever" ellen

Name

chgrp

Synopsis

chgrp [options] newgroup files

Change the group of one or more files to newgroup. newgroup is either a group ID number or a group name located in /etc/group. Only the owner of a file or a privileged user may change the group.

Options

-c, --changes

Print information about files that are changed.

--dereference

Change the group of the file pointed to by a symbolic link, not the group of the symbolic link. This is the default behavior.

-f, --silent, --quiet

Do not print error messages about files that cannot be changed.

-h, --no-dereference

Change the group of the symbolic link.

-H

Used with -R. If a command-line argument is a symbolic link to a directory, traverse the directory.

--help

Print help message and then exit.

-L

Used with -R. Traverse every symbolic link that points to a directory.

--no-preserve-root

Do not treat / as special. This is the default behavior.

-P

Used with -R. Do not traverse any symbolic links. This is the default behavior.

--preserve-root

Do not operate recursively on /.

-R, --recursive

Traverse subdirectories recursively, applying changes.

--reference=filename

Change the group to that associated with filename. In this case, newgroup is not specified.

-v, --verbose

Verbosely describe ownership changes.

--version

Print version information and then exit.

Name

chkconfig

Synopsis

chkconfig [options] [service [flag]]

System administration command. Manipulate symbolic links in the /etc/rc.d/rc[0–6].d directories. chkconfig manages which services will run in a specified runlevel. Valid flags are on, off, reset or resetpriorities to reset the service to default on/off or priorities given in its initialization script in /etc/rc.d/init.d. This command is available in Fedora and RedHat-style distributions, including SUSE and SUSE-based distributions. To specify defaults in a standard initialization script, add a comment line to the script beginning with chkconfig: followed by the runlevels in which the service should run, and the start and kill priority numbers to assign--e.g., chkconfig: 2345 85 15. To override defaults specified in init files, you can create a file with the same service name in /etc/chkconfig.d. Place a chkconfig line in this override file. This allows you to safely customize package maintained services.

Options

--add service

Create a start or kill symbolic link in every runlevel for the specified service according to default behavior specified in the service’s initialization script.

--del service

Remove entries for specified service from all runlevels.

--level numbers

Specify by number the runlevels to change. Provide numbers as a numeric string: e.g., 016 for levels 0, 1, and 6. Use this to override specified defaults.

--list [service]

Print whether the specified service is on or off in each level. If no service is specified, print runlevel information for all services managed by chkconfig.

--override service

If service is configured according to defaults in /etc/rc.d/init.d and an override file exists in /etc/chkconfig.d, reconfigure service to match the override settings.

Name

chmod

Synopsis

chmod [options] mode files
chmod [options] --reference=filename files

Change the access mode (permissions) of one or more files. Only the owner of a file or a privileged user may change the mode. mode can be numeric or an expression in the form of who opcode permission. who is optional (if omitted, the default is a); choose only one opcode. Separate multiple modes by commas.

Options

-c, --changes

Print information about files that are changed.

-f, --silent, --quiet

Do not notify user of files that chmod cannot change.

--help

Print help message and then exit.

--no-preserve-root

Do not treat / as special. This is the default behavior.

--preserve-root

Do not operate recursively on /.

-R, --recursive

Traverse subdirectories recursively, applying changes.

--reference=filename

Change permissions to match those associated with filename.

-v, --verbose

Print information about each file, whether changed or not.

--version

Print version information and then exit.

Who

u

User.

g

Group.

o

Other.

a

All (default).

Opcode

+

Add permission.

-

Remove permission.

=

Assign permission (and remove permission of the unspecified fields).

Permissions

r

Read.

w

Write.

x

Execute.

X

Execute if file is a directory or already has execute permission for some user.

s

Set user (or group) ID.

t

Sticky bit; used on directories to prevent removal of files by nonowners.

u

User’s present permission.

g

Group’s present permission.

o

Other’s present permission.

Alternatively, specify permissions by a three-digit octal number. The first digit designates owner permission; the second, group permission; and the third, other’s permission. Permissions are calculated by adding the following octal values:

4

Read.

2

Write.

1

Execute.

Note that a fourth digit may precede this sequence. This digit assigns the following modes:

4

Set user ID on execution to grant permissions to process based on the file’s owner, not on permissions of the user who created the process.

2

Set group ID on execution to grant permissions to process based on the file’s group, not on permissions of the user who created the process.

1

Set sticky bit.

Examples

Add execute-by-user permission to file:

chmod u+x file

Either of the following assigns read/write/execute permission by owner (7), read/execute permission by group (5), and execute-only permission by others (1) to file:

chmod 751 file
chmod u=rwx,g=rx,o=x file

Any one of the following assigns read-only permission to file for everyone:

chmod =r file
chmod 444 file
chmod a-wx,a+r file

The following makes the executable setuid, assigns read/write/execute permission by owner, and assigns read/execute permission by group and others:

chmod 4755 file

Name

chown

Synopsis

chown [options] newowner files
chown [options] --reference=filename files

Change the ownership of one or more files to newowner. newowner is either a user ID number or a login name located in /etc/passwd. chown also accepts users in the form newowner:newgroup or newowner.newgroup. The last two forms change the group ownership as well. If no owner is specified, the owner is unchanged. With a period or colon but no group, the group is changed to that of the new owner. Only the current owner of a file or a privileged user may change the owner.

Options

-c, --changes

Print information about files that are changed.

--dereference

Follow symbolic links.

-f, --silent, --quiet

Do not print error messages about files that cannot be changed.

--from=currown:currgroup

Only change owner and/or group if the current owner and group match those specified in --from. If currown or currgroup is omitted, a match is not required for that attribute.

-h, --no-dereference

Change the ownership of each symbolic link (on systems that allow it), rather than the referenced file.

-v, --verbose

Print information about all files that chown attempts to change, whether or not they are actually changed.

-R, --recursive

Traverse subdirectories recursively, applying changes.

-H

With -R, traverse symbolic link to a directory.

-L

With -R, traverse every symbolic link that leads to a directory.

-P

With -R, do not traverse any symbolic links. This is the default.

--reference=filename

Change owner to the owner of filename instead of specifying a new owner explicitly.

--help

Print help message and then exit.

--version

Print version information and then exit.

Name

chpasswd

Synopsis

chpasswd [options]

System administration command. Change user passwords in a batch. chpasswd accepts input in the form of one username:password pair per line. Unless the -e option is specified, password is encrypted before being stored. This command doesn’t use PAM. It updates the /etc/passwd and /etc/shadow files.

Option

-e, --encrypted

Passwords given are already encrypted.

-m, --md5

Use MD5 Encryption

Name

chroot

Synopsis

chroot newroot [command]

System administration command. Change root directory for command or, if none is specified, for a new copy of the user’s shell. This command or shell is executed relative to the new root. The meaning of any initial / in pathnames is changed to newroot for a command and any of its children. In addition, the initial working directory is newroot. This command is restricted to privileged users.

Name

chrt

Synopsis

chrt [options] [prio] [pid | command ...]

Set or retrieve the real-time scheduling properties of a given process, or run a new process with the given real-time scheduling properties.

Options

-b, --batch

Use the batch scheduling policy.

-f, --fifo

Use the FIFO (first-in, first-out) scheduling policy.

-h, --help

Display usage information and then exit.

-m, --max

Show the minimum and maximum valid scheduling priorities.

-o, --other

Use the normal (called “other”) scheduling policy.

-p, --pid

Operate on the given, existing PID and do not execute a new command.

-r, --rr

Use the round-robin scheduling policy.

-v, --version

Display version information and then exit.

Name

chsh

Synopsis

chsh [options] [username]

Change your login shell, either interactively or on the command line. Warn if shell does not exist in the file /etc/shells. Specify the full path to the shell. chsh prompts for your password. Only a privileged user can change another user’s shell.

Options

-l, --list-shells

Print valid shells, as listed in /etc/shells, and then exit.

-s shell, --shell shell

Specify new login shell.

-u, --help

Print help message and then exit.

-v, --version

Print version information and then exit.

Example

chsh -s /bin/tcsh

Name

chvt

Synopsis

chvt N

Switch to virtual terminal N (that is, switch to /dev/ttyN). If you have not created /dev/ttyN, it is created when you run this command. There are keyboard shortcuts for this functionality as well. From a graphical desktop, you can press Ctrl-Alt-F1 through F12 to switch to different virtual terminals. In text mode, you can skip the Ctrl key and just use Alt-F1 through F12. To switch back to graphical mode, use Alt-F7.

Name

cksum

Synopsis

cksum [files]

Compute a cyclic redundancy check (CRC) checksum for all files; this is used to ensure that a file was not corrupted during transfer. Read from standard input if the character - is given or no files are given. Display the resulting checksum, the number of bytes in the file, and (unless reading from standard input) the filename. Also see md5sum and sha1sum.

Name

clear

Synopsis

clear

Clear the terminal display. Equivalent to pressing Ctrl-L.

Name

cmp

Synopsis

cmp [options] file1 file2 [skip1 [skip2]]

Compare file1 with file2. Use standard input if file1 is - or missing. This command is normally used for comparing binary files, although files can be of any type. (See also diff.) skip1 and skip2 are optional offsets in the files at which the comparison is to start.

Options

-i num, --ignore-initial=num

Ignore the first num bytes of input. num can be given as num1:num2 to skip a different number of bytes in file1 and file2.

-l, --verbose

Print offsets and codes of all differing bytes.

-s, --quiet, --silent

Work silently; print nothing, return an exit code:

0

Files are identical.

1

Files are different.

2

Files are inaccessible.

Example

Print a message if two files are the same (exit code is 0):

cmp -s old new && echo 'no changes'

Name

col

Synopsis

col [options]

A postprocessing filter that handles reverse linefeeds and escape characters, allowing output from tbl or nroff to appear in reasonable form on a terminal.

Options

-b

Ignore backspace characters; helpful when printing manpages.

-f

Process half-line vertical motions, but not reverse line motion. (Normally, half-line input motion is displayed on the next full line.)

-l n

Buffer at least n lines in memory. The default buffer size is 128 lines.

-p

Do not filter out unrecognized control sequences, but pass them through.

-x

Normally, col saves printing time by converting sequences of spaces to tabs. Use -x to suppress this conversion.

Examples

Run myfile through tbl and nroff, then capture output on screen by filtering through col and more:

tbl myfile | nroff | col | more

Save manpage output for the ls command in out.print, stripping out backspaces (which would otherwise appear as ^H):

man ls | col -b > out.print

Name

colcrt

Synopsis

colcrt [options] [files]

A postprocessing filter that handles reverse linefeeds and escape characters, allowing output from tbl or nroff to appear in reasonable form on a terminal. Put half-line characters (e.g., subscripts or superscripts) and underlining (changed to dashes) on a new line between output lines.

Options

-

Do not underline.

−2

Double space by printing all half-lines to make subscripts and superscripts visible.

Name

colrm

Synopsis

colrm [start [stop]]

Remove specified columns from a file, where a column is a single character in a line. Read from standard input and write to standard output. Columns are numbered starting with 1. Begin deleting columns at (including) the start column, and stop at (including) the stop column; if stop is not given, delete all columns to the end. Entering a tab increments the column count to the next multiple of either the start or stop column; entering a backspace decrements it by 1.

Example

colrm 3 5 < test1 > test2

Name

column

Synopsis

column [options] [files]

Format input from one or more files into columns, filling rows first. Read from standard input if no files are specified.

Options

-c num

Format output into num columns.

-s char

Delimit table columns with char. Meaningful only with -t.

-t

Format input into a table. Delimit with whitespace, unless an alternate delimiter has been provided with -s.

-x

Fill columns before filling rows.

Name

comm

Synopsis

comm [options] file1 file2

Compare lines common to the sorted files file1 and file2. Output is in three columns, from left to right: lines unique to file1, lines unique to file2, and lines common to both files. comm is similar to diff in that both commands compare two files. But comm can also be used like uniq; comm selects duplicate or unique lines between two sorted files, whereas uniq selects duplicate or unique lines within the same sorted file.

Options

-num

Suppress printing of column num. Multiple columns may be specified and should not be space-separated.

--help

Print help message and exit.

--version

Print version information and exit.

Example

Compare two lists of top-10 movies, and display items that appear in both lists:

comm −12 siskel_top10 ebert_top10

Name

cp

Synopsis

cp [options] file1 file2
cp [options] files directory

Copy file1 to file2, or copy one or more files to the same names under directory. If the destination is an existing file, the file is overwritten; if the destination is an existing directory, the file is copied into the directory (the directory is not overwritten).

Options

-a, --archive

Preserve attributes of original files where possible. The same as -dpr.

-b, --backup[=control]

Back up files to be overwritten. As -b, takes no argument. For --backup, control specifies the type of backup and can also be set with the environment variable VERSION-CONTROL. The default is existing. Valid arguments are:

t, numbered

Always make numbered backups.

nil, existing

Make numbered backups of files that already have them; otherwise, make simple backups.

never, simple

Always make simple backups.

none, off

Never make backups, even if --backup is specified.

-c

The same as --preserve=context.

--copy-contents

Copy contents of special files when recursive.

-d

The same as --no-dereference --preserve=links.

-f, --force

Remove an existing file in the destination if it can’t be opened. See also --remove-destination.

-H

Follow command-line symbolic links in the source.

-i, --interactive

Prompt before overwriting destination files. On most systems, this flag is turned off by default except for the root user, who is normally prompted before overwriting files.

-l, --link

Make hard links, not copies, of nondirectories.

-L, --dereference

Always follow symbolic links.

--no-preserve[=attribs]

Do not preserve the specified attributes. See --preserve for the list of possible attributes.

-p

The same as --preserve=mode,ownership,timestamps.

--preserve[=attribs]

Preserve the specified attributes. By default, preserve ownership, permissions, and timestamps. Other possible attributes include context, links, all.

-P, --no-dereference

Never follow symbolic links.

--parents

Preserve intermediate directories in source. The last argument must be the name of an existing directory. For example, the command:

cp --parents jphekman/book/ch1 newdir

copies the file jphekman/book/ch1 to the file newdir/jphekman/book/ch1, creating intermediate directories as necessary.

-r, -R, --recursive

Copy directories recursively.

--remove-destination

Remove existing destination files without attempting to open them. See also --force.

-s, --symbolic-link

Make symbolic links instead of copying. Source filenames must be absolute.

-S backup-suffix, --suffix=backup-suffix

Set suffix to be appended to backup files. This may also be set with the SIMPLE_BACKUP_SUFFIX environment variable. The default is ˜. You need to explicitly include a period if you want one before the suffix (for example, specify .bak, not bak).

--sparse=[always|auto|never]

Handle files that have “holes” (are defined as a certain size but have less data). always creates a sparse file, auto creates one if the input file is sparse (the default), and never creates a non-sparse file without holes.

--strip-trailing-slashes

Remove trailing slashes from each source file argument.

-u, --update

Do not copy a file to an existing destination with the same or newer modification time.

-v, --verbose

Before copying, print the name of each file.

-x, --one-file-system

Stay on the current filesystem.

Example

Copy the contents of the guest directory recursively into the /archives/guest/ directory, and display a message for each file copied:

cd /archives && cp -av /home/guest guest

Name

cpio

Synopsis

cpio mode [options]

Copy file archives from or to tape or disk, or to another location on the local machine. Each of the three modes -i, -o, or -p accepts different options.

Mode

-i, --extract [options] [patterns]

Copy in (extract) from an archive files whose names match selected patterns. Each pattern can include Bourne shell filename metacharacters. (Patterns should be quoted or escaped so that they are interpreted by cpio, not by the shell.) If pattern is omitted, all files are copied in. Existing files are not overwritten by older versions from the archive unless -u is specified.

-o, --create [options]

Copy out to an archive a list of files whose names are given on the standard input.

-p, --pass-through [options] directory

Copy (pass) files to another directory on the same system. Destination pathnames are interpreted relative to the named directory.

Comparison of valid options

Single-character options available to the -i, -o, and -p modes are shown here (the - is omitted for clarity):

i:   bcdf mnrtsuv B SVCEHMR IF
o: 0a c         vABL VC HM O F
p: 0a  d lm    uv  L V    R

Options

−0, --null

Expect list of filenames to be terminated with null, not newline. This allows files with a newline in their names to be included.

-a, --reset-access-time

Reset access times of input files after reading them.

-A, --append

Append files to an existing archive, which must be a disk file. Specify this archive with -O or -F.

-b, --swap

Swap bytes and half-words to convert between big-endian and little-endian 32-bit integers.

-B

Block input or output using 5120 bytes per record (default is 512 bytes per record).

--block-size=size

Set input or output size to size × 512 bytes.

-c

Read or write header information as ASCII characters, which is useful when source and destination machines are different types.

-C n, --io-size=n

Like -B, but block size can be any positive integer n.

-d, --make-directories

Create directories as needed.

-E file, --pattern-file=file

Extract from the archives filenames that match patterns in file.

-f, --nonmatching

Reverse the sense of copying; copy all files except those that match patterns.

-F file, --file=file

Use file as the archive, not stdin or stdout. file can reside on another machine, if given in the form [user@]hostname:file (where user@ is optional).

--force-local

Assume that file (provided by -F, -I, or -O) is a local file, even if it contains a colon (:) indicating a remote file.

-H type, --format=type

Use type format. Default for copy-out is bin; default for copy-in is autodetection of the format. Valid formats (all caps also accepted) are:

bin

Binary.

odc

Old (POSIX.1) portable format.

newc

New (SVR4) portable format.

crc

New (SVR4) portable format with checksum added.

tar

Tar.

ustar

POSIX.1 tar (also recognizes GNU tar archives).

hpodc

HP-UX portable format.

-I file

Read file as an input archive. May be on a remote machine (see -F).

-k

Ignored. For compatibility with other versions of cpio.

-l, --link

Link files instead of copying.

-L, --dereference

Follow symbolic links.

-m, --preserve-modification-time

Retain previous file modification time.

-M msg, --message=msg

Print msg when switching media, as a prompt before switching to new media. Use variable %d in the message as a numeric ID for the next medium. -M is valid only with -I or -O.

-n, --numeric-uid-gid

When verbosely listing contents, show user ID and group ID numerically.

--no-absolute-filenames

Create all copied-in files relative to the current directory.

--no-preserve-owner

Make all copied files owned by yourself, instead of the owner of the original. Can be used only if you are a privileged user. Valid in copy-in and pass-through modes.

-O file

Archive the output to file, which may be a file on another machine (see -F).

--only-verify-crc

For a CRC-format archive, verify the CRC of each file; don’t actually copy the files in.

--quiet

Don’t print the number of blocks copied.

-r, --rename

Rename files interactively.

-R [user][:group], --owner [user][:group]

Reassign file ownership and group information to the user’s login ID (privileged users only).

--rsh-command=cmd

Use the specified command to communicate with remote systems.

-s, --swap-bytes

Swap bytes of each two-byte half-word.

-S, --swap-half-words

Swap half-words of each four-byte word.

--sparse

For copy-out and copy-pass, write files that have large blocks of zeros as sparse files.

-t, --list

Print a table of contents of the input (create no files). When used with the -v option, resembles output of ls -l.

--to-stdout

In copy-in mode, extract files to standard output.

-u, --unconditional

Unconditional copy; old files can overwrite new ones.

-v, --verbose

Print a list of filenames processed.

-V, --dot

Print a dot for each file read or written (this shows cpio at work without cluttering the screen).

--version

Print version number and then exit.

Examples

Generate a list of files whose names end in .old using find; use the list as input to cpio:

find . -name "*.old" | cpio -ocBv > /dev/rst8

Restore from a tape drive all files whose names contain save (subdirectories are created if needed):

cpio -icdv "*save*" < /dev/rst8

Move a directory tree:

find . -depth | cpio -padm /mydir

Name

cpp

Synopsis

cpp [options] [ifile [ofile]]

GNU C language preprocessor. cpp is normally invoked as the first pass of any C compilation by the gcc command. The output of cpp is a form acceptable as input to the next pass of the C compiler. The ifile and ofile options are, respectively, the input and output for the preprocessor; they default to standard input and standard output.

Options

-$

Do not allow $ in identifiers.

-ansi

Use 1990 ISO C standard. This is equivalent to -std=c89.

-dD

Similar to -dM, but exclude predefined macros and include results of preprocessing.

-dM

Suppress normal output. Print series of #defines that create the macros used in the source file.

-dN

Similar to -dD, but don’t print macro expansions.

-dI

Print #include directives in addition to other output.

-fpreprocessed

Treat file as already preprocessed. Skip most processing directives, remove all comments, and tokenize file.

-ftabstop=width

Set distance between tabstops so columns will be reported correctly in warnings and errors. Default is 8.

-fno-show-column

Omit column numbers in warnings and errors.

-gcc

Define _ _GNUC_ _, _ _GNUC_MINOR_ _, and _ _GNUC_PATCHLEVEL_ _ macros.

--help

Print usage message and exit.

-idirafter dir

Search dir for header files when a header file is not found in any of the included directories.

-imacros file

Process macros in file before processing main files.

-include file

Process file before main file.

-iprefix prefix

When adding directories with -iwithprefix, prepend prefix to the directory’s name.

-isystem dir

Search dir for header files after searching directories specified with -I but before searching standard system directories.

-iwithprefix dir

Append dir to the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory’s name.

-iwithprefixbefore dir

Insert dir at the beginning of the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory’s name.

-lang-c, -lang-c++, -lang-objc, -lang-objc++

Expect the source to be in C, C++, Objective C, or Objective C++, respectively.

-lint

Display all lint commands in comments as #pragma lint command.

-nostdinc

Search only specified, not standard, directories for header files.

-nostdinc++

Suppress searching of directories believed to contain C++-specific header files.

-o file

Write output to file. (Same as specifying a second filename in the command line.)

-pedantic

Warn verbosely.

-pedantic-errors

Produce a fatal error in every case in which -pedantic would have produced a warning.

-std=standard

Specify C standard of input file. Accepted values are:

iso9899:1990, c89

1990 ISO C standard.

iso9899:199409

1994 amendment to the 1990 ISO C standard.

iso9899:1999, c99, iso9899:199x, c9x

1999 revised ISO C standard.

gnu89

1990 C Standard with gnu extensions. The default value.

gnu99, gnu9x

1999 revised ISO C standard with gnu extensions.

-traditional

Behave like traditional C, not ANSI.

-trigraphs

Convert special three-letter sequences, meant to represent missing characters on some terminals, into the single character they represent.

-undef

Suppress definition of all nonstandard macros.

-v

Verbose mode.

-version

Print version number, then process file.

--version

Print version number, then exit.

-w

Don’t print warnings.

-x language

Specify the language of the input file. language may be c, c++, objective-c, or assembler-with-cpp. By default, language is deduced from the filename extension. If the extension is unrecognized, the default is c.

-A name[=def]

Assert name with value def as if defined by #assert. To turn off standard assertions, use -A-.

-A -name[=def]

Cancel assertion name with value def.

-C

Retain all comments except those found on cpp directive lines. By default, cpp strips C-style comments.

-Dname[=def]

Define name with value def as if by a #define. If no =def is given, name is defined with value 1. -D has lower precedence than -U.

-E

Preprocess the source files, but do not compile. Print result to standard output. This option is usually passed from gcc.

-H

Print pathnames of included files, one per line, on standard error.

-Idir

Search in directory dir for #include files whose names do not begin with / before looking in directories on standard list. #include files whose names are enclosed in double quotes and do not begin with / will be searched for first in the current directory, then in directories named on -I options, and last in directories on the standard list.

-I-

Split includes. Search directories specified by -I options preceding this one for header files included with quotes (#include “file.h”) but not for header files included with angle brackets (#include <file.h>). Search directories specified by -I options following this one for all header files.

-M [-MG]

Suppress normal output. Print a rule for make that describes the main source file’s dependencies. If -MG is specified, assume that missing header files are actually generated files, and look for them in the source file’s directory.

-MF file

Print rules generated by -M or -MM to file.

-MD file

Similar to -M, but output to file; also compile the source.

-MM

Similar to -M, but describe only those files included as a result of #include "file".

-MMD file

Similar to -MD, but describe only the user’s header files.

-MQ target

Similar to -MT, but quote any characters that are special to make.

-MT target

Specify the target to use when generating a rule for make. By default, the target is based on the name of the main input file.

-P

Preprocess input without producing line-control information used by next pass of the C compiler.

-Uname

Remove any initial definition of name, where name is a reserved symbol predefined by the preprocessor, or a name defined on a -D option. Names predefined by cpp are unix and i386 (for Intel systems).

-Wall

Warn both on nested comments and trigraphs.

-Wcomment, -Wcomments

Warn when encountering the beginning of a nested comment.

-Wtraditional

Warn when encountering constructs that are interpreted differently in ANSI than in traditional C.

-Wtrigraphs

Warn when encountering trigraphs, which are three-letter sequences meant to represent missing characters on some terminals.

Special names

cpp understands various special names, some of which are:

_ _DATE_ _

Current date (e.g., Jan 10 2003).

_ _FILE_ _

Current filename (as a C string).

_ _LINE_ _

Current source line number (as a decimal integer).

_ _TIME_ _

Current time (e.g., 12:00:00).

These special names can be used anywhere, including in macros, just like any other defined names. cpp’s understanding of the line number and filename may be changed using a #line directive.

Directives

All cpp directive lines start with # in column 1. Any number of blanks and tabs is allowed between the # and the directive. The directives are:

#assert name (string)

Define a question called name, with an answer of string. Assertions can be tested with #if directives. The predefined assertions for #system, #cpu, and #machine can be used for architecture-dependent changes.

#unassert name

Remove assertion for question name.

#define name token-string

Define a macro called name, with a value of token-string. Subsequent instances of name are replaced with token-string.

#define name( arg, ... , arg ) token-string

This allows substitution of a macro with arguments. token-string will be substituted for name in the input file. Each call to name in the source file includes arguments that are plugged into the corresponding args in token-string.

#undef name

Remove definition of the macro name. No additional tokens are permitted on the directive line after name.

#ident string

Put string into the comment section of an object file.

#include "filename", #include<filename>

Include contents of filename at this point in the program. No additional tokens are permitted on the directive line after the final " or >.

#line integer-constant "filename"

Cause cpp to generate line-control information for the next pass of the C compiler. The compiler behaves as if integer-constant is the line number of the next line of source code and filename (if present) is the name of the input file. No additional tokens are permitted on the directive line after the optional filename.

#endif

End a section of lines begun by a test directive (#if, #ifdef, or #ifndef). No additional tokens are permitted on the directive line.

#ifdef name

Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if name is currently defined. No additional tokens are permitted on the directive line after name.

#ifndef name

Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if name is not currently defined. No additional tokens are permitted on the directive line after name.

#if constant-expression

Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if constant-expression evaluates to nonzero.

#elif constant-expression

An arbitrary number of #elif directives are allowed between an #if, #ifdef, or #ifndef directive and an #else or #endif directive. The lines following the #elif and up to the next #else, #elif, or #endif directive will appear in the output if the preceding test directive and all intervening #elif directives evaluate to zero, and the constant-expression evaluates to nonzero. If constant-expression evaluates to nonzero, all succeeding #elif and #else directives will be ignored.

#else

Lines following this directive and up to the matching #endif will appear in the output if the preceding test directive evaluates to zero, and all intervening #elif directives evaluate to zero. No additional tokens are permitted on the directive line.

#error

Report fatal errors.

#warning

Report warnings, but then continue processing.

Name

crond

Synopsis

crond [options]

System administration command. Normally started in a system startup file. Execute commands at scheduled times, as specified in users’ files in /var/spool/cron. Each file shares its name with the user who owns it. The files are controlled via the command crontab. The crond command will also read commands from the /etc/crontab file and from the /etc/cron.d/ directory. See anacron for scheduling events on systems that are frequently rebooted or powered off, such as notebook computers.

Options

-m command

User command to send mail instead of sendmail.

-n

Run the command in the foreground.

-p

Remove security restrictions on crontab file permissions.

Name

crontab

Synopsis

crontab [options] [file]

View, install, or uninstall your current crontab file. A privileged user can run crontab for another user by supplying -u user. A crontab file is a list of commands, one per line, that will execute automatically at a given time. Numbers are supplied before each command to specify the execution time. The numbers appear in five fields, as follows:

Minute        0-59
Hour          0-23
Day of month   1-31
Month        1-12
Jan, Feb, Mar, ...
Day of week     0-6, with 0 = Sunday
Sun, Mon, Tue, ...

Use a comma between multiple values, a hyphen to indicate a range, an asterisk to indicate all possible values, and a slash (/) to indicate a repeating range. For example, assuming these crontab entries:

59 3 * * 5         find / -print | backup_program
0 0 1,15 * *       echo "Timesheets due" | mail user

the first command backs up the system files every Friday at 3:59 a.m., and the second command mails a reminder on the 1st and 15th of each month.

The superuser can always issue the crontab command. Other users must be listed in the file /etc/cron.allow if it exists; otherwise, they must not be listed in /etc/cron.deny. If neither file exists, only the superuser can issue the command.

Options

The -e, -l, and -r options are not valid if any files are specified.

-e

Edit the user’s current crontab file (or create one).

-l

Display the user’s crontab file on standard output.

-r

Delete the user’s crontab file.

-u user

Indicate which user’s crontab file will be acted upon.

Name

csplit

Synopsis

csplit [options] file arguments

Separate file into context-based sections and place sections in files named xx00 through xxn (n < 100), breaking file at each pattern specified in arguments. The byte count for each section is written to standard output. See also split.

Options

-

Read from standard input.

-b format, --suffix-format=format

Use sprintf format instead of %02d for the suffix.

-f prefix, --prefix=prefix

Name new files prefix00 through prefixn (default is xx00 through xxn).

-k, --keep-files

Keep newly created files even when an error occurs (which would normally remove these files). This is useful when you need to specify an arbitrarily large repeat argument, {n}, and you don’t want an out-of-range error to cause removal of the new files.

-n num, --digits=num

Use output filenames with numbers num digits long. The default is 2.

-s, -q, --silent, --quiet

Suppress display of character counts.

-z, --elide-empty-files

Do not create empty output files. However, number as if those files had been created.

Arguments

Any one or a combination of the following expressions may be specified as arguments. Arguments containing blanks or other special characters should be surrounded by single quotes.

/expr/[offset]

Create file from the current line up to the line containing the regular expression expr. offset should be of the form +n or -n, where n is the number of lines below or above expr.

%expr%[offset]

Same as /expr/, except no file is created for lines before a line containing expr.

num

Create file from current line up to (but not including) line number num. When followed by a repeat count (number inside { }), put the next num lines of input into another output file.

{n}

Repeat argument n times. May follow any of the preceding arguments. Files are split at instances of expr or in blocks of num lines. If * is given instead of n, repeat argument until input is exhausted.

Examples

Create up to 20 chapter files from the file novel:

csplit -k -f chap. novel '/CHAPTER/' '{20}'

Create up to 100 address files (xx00 through xx99), each four lines long, from a database named address_list:

csplit -k address_list 4 {99}

Name

ctags

Synopsis

ctags [options] files

Create a list of function and macro names defined in a programming source file. More than one file may be specified. ctags understands many programming languages, including C, C++, FORTRAN, Java, Perl, Python, flex, yacc, and bison. The output list (named tags by default) contains lines of the form:

name     file     context

where name is the function or macro name, file is the source file in which name is defined, and context is a search pattern that shows the line of code containing name. After the list of tags is created, you can invoke vi on any file and type:

:set tags=tagsfile
:tag name

This switches the vi editor to the source file associated with the name listed in tagsfile (which you specify with -t).

etags produces an equivalent file for tags to be used with Emacs.

Options

-a

Append tag output to existing list of tags.

-e

Create tag files for use with emacs.

-h extensionlist

Interpret files with filename extensions specified in extensionlist as header files. The default list is “.h.H.hh.hpp.hxx.h++.inc.def”. To indicate that files without extensions should be treated as header files, insert an additional period in the list before another period or at the end of the list, or use just a period by itself. To use this option multiple times and have the specified lists ANDed together, use a plus sign as the first character in the list. To restore the default, use the word “default”.

-n

Use numeric ex commands to locate tags. Same as --excmd= number.

-o file, -f file, --output=file

Write to file.

--packages-only

Include tag entries for members of structure-like constructs.

-R

Recursively read files in subdirectories of the directory given on the command line.

-u

Don’t sort tag entries.

-x

Produce a tabular listing of each function, and its line number, source file, and context.

-B

Search for tags backward through files.

-I tokenlist

Specify a list of tokens to be specially handled. If tokenlist is given as a file, use ex pattern commands to locate tags. Same as --excmd=pattern.

-N

Use ex pattern commands to locate tags. Same as --excmd= pattern.

-S, --ignore-indentation

Normally ctags uses indentation to parse the tag file; this option tells ctags to rely on indentation less.

-T, --typedefs-and-c++

Include tag entries for typedefs, structs, enums, unions, and C++ member functions.

-V, --version

Print the version number and exit.

Name

cupsd

Synopsis

cupsd options

System administration command. Start the print scheduler for the Common UNIX Printing System.

Options

-c file

Use specified configuration file instead of /etc/cups/cupsd.conf.

-f

Run scheduler in foreground.

-F

Run scheduler in foreground but detach it from the controlling terminal and current directory. Sometimes used when running cupsd from init.

Name

cut

Synopsis

cut options [files]

Cut out selected columns or fields from one or more files. With no file, or if file is -, read from standard input. In the following options, list is a sequence of integers. Use a comma between values, and a hyphen to specify a range (e.g., 1-10,15,20 or 50-). See also paste and join.

Options

-b list, --bytes list

Specify list of positions; only bytes in these positions will be printed.

-c list, --characters list

Cut the column positions identified in list. Column numbers start with 1.

-d c, --delimiter c

Use with -f to specify field delimiter as character c (default is tab); special characters (e.g., a space) must be quoted.

-f list, --fields list

Cut the fields identified in list.

-n

Don’t split multibyte characters. Use with -b.

-s, --only-delimited

Use with -f to suppress lines without delimiters.

--output-delimiter=string

Use string as the output delimiter. By default, the output delimiter is the same as the input delimiter.

--help

Print help message and exit.

--version

Print version information and exit.

Examples

Extract usernames and real names from /etc/passwd:

cut -d: -f1,5 /etc/passwd

Find out who is logged on, but list only login names:

who | cut -d" " -f1

Cut characters in the fourth column of file, and paste them back as the first column in the same file:

cut -c4 file | paste - file

Name

date

Synopsis

date [options] [+format] [date]

Print the current date and time. You may specify a display format, which can consist of literal text strings (blanks must be quoted) as well as field descriptors, whose values are described in the following entries (the listing shows some logical groupings). A privileged user can change the system’s date and time.

Options

+format

Display current date in a nonstandard format. For example:

$ date +"%A %j %n%k %p"
Friday 051
23 PM

The default is %a %b %e %T %Z %Y (e.g., Fri Feb 20 22:59:43 EST 2009).

-d date, --date date

Display date, which should be in quotes and may be in the format d days or m months d days, to print a date in the future. Specify ago to print a date in the past. You may include formatting (see the following section).

-f datefile, --file=datefile

Like -d, but printed once for each line of datefile.

-r file, --reference=file

Display the time file was last modified.

-R, --rfc-2822

Display the date and time in RFC 2822 format.

--rfc-3339=timespec

Display the date and time in RFC 3339 format. The value of timespec can be one of date, seconds, or ns (nanoseconds) to get the desired degree of precision.

--help

Print help message and exit.

--version

Print version information and exit.

-s date, --set=date

Set the date.

-u, --utc, --universal

Set the date to Coordinated Universal Time, not local time.

Format

The exact result of many of these codes is locale-specific and depends upon your language setting, particularly the LANG environment variable. See locale.

%%

Literal %.

- (hyphen)

Do not pad fields (default: pad fields with zeros).

_ (underscore)

Pad fields with space (default: zeros).

^

Use uppercase if possible.

#

Use the opposite case if possible.

%a

Abbreviated weekday.

%A

Full weekday.

%b

Abbreviated month name.

%B

Full month name.

%c

Country-specific date and time format.

%C

Century; like %Y but show only the two-digit century (e.g., show 20, not 2009).

%d

Day of month (01–31).

%D

Date in %m/%d/%y format.

%e

Day of month padded with spaces.

%h

Same as %b.

%H

Hour in 24-hour format (00–23).

%I

Hour in 12-hour format (01–12).

%j

Julian day of year (001–366).

%k

Hour in 24-hour format, without leading zeros (0–23).

%l

Hour in 12-hour format, without leading zeros (1–12).

%m

Month of year (01–12).

%M

Minutes (00–59).

%n

Insert a new line.

%N

Nanoseconds (000000000-999999999).

%p

String to indicate a.m. or p.m.

%P

Like %p but lowercase.

%r

Time in %I:%M:%S %p (12-hour) format.

%R

Time in %H:%M (24-hour) format.

%s

Seconds since “the Epoch,” which is 1970-01-01 00:00:00 UTC (a nonstandard extension).

%S

Seconds (00–59).

%t

Insert a tab.

%T

Time in %H:%M:%S format.

%u

Day of the week (1-7, Monday = 1).

%U

Week number in year (00–53); start week on Sunday.

%V

Week number in year (01–52); start week on Monday.

%w

Day of week (0–6, Sunday = 0).

%W

Week number in year (00–53); start week on Monday.

%x

Country-specific date format.

%X

Country-specific time format.

%Y

Four-digit year (e.g., 2006).

%y

Last two digits of year (00-99).

%z

RFC 822-style numeric time zone.

%Z

Time-zone name.

Strings for setting date

Strings for setting the date may be numeric or nonnumeric. Numeric strings consist of time, day, and year in the format MMDDhhmm[[CC]YY][.ss]. Nonnumeric strings may include month strings, time zones, a.m., and p.m.

time

A two-digit hour and two-digit minute (hhmm); hh uses 24-hour format.

day

A two-digit month and two-digit day of month (MMDD); default is current day and month.

year

The year specified as either the full four-digit century and year or just the two-digit year; the default is the current year.

Examples

Set the date to July 1 (0701), 4 a.m. (0400), 2009 (09):

date 0701040009

The command:

date +"Hello%t Date is %D %n%t Time is %T"

produces a formatted date as follows:

Hello     Date is 02/20/09
Time is 17:53:39

Name

dd

Synopsis

dd options

Make a copy of an input file (if) using the specified conditions, and send the results to the output file (or standard output if of is not specified). Any number of options can be supplied, although if and of are the most common and are usually specified first. Because dd can handle arbitrary block sizes, it is useful when converting between raw physical devices.

Options

bs=n

Set input (ibs) and output (obs) block size to n bytes; this option overrides ibs and obs set separately.

cbs=n

Set the size of the conversion buffer (logical record length) to n bytes. Use only if the conversion format is ascii, ebcdic, ibm, block, or unblock.

conv=format

Convert the input according to one or more (comma--separated) formats listed next. The first five formats are mutually exclusive.

ascii

EBCDIC to ASCII.

ebcdic

ASCII to EBCDIC.

ibm

ASCII to EBCDIC with IBM conventions.

block

Variable-length records (i.e., those terminated by a newline) to fixed-length records.

unblock

Fixed-length records to variable-length records.

excl

Fail if the output file already exists.

fdatasync

Physically write the output file before finishing.

fsync

Physically write both the output file and the metadata before finishing.

lcase

Uppercase to lowercase.

nocreate

Do not create an output file.

noerror

Continue processing after read errors.

notrunc

Don’t truncate output file.

swab

Swap each pair of input bytes.

sync

Pad input blocks to ibs with trailing zeros.

ucase

Lowercase to uppercase.

count=n

Copy only n input blocks.

ibs=n

Set input block size to n bytes (default is 512).

if=file

Read input from file (default is standard input).

obs=n

Set output block size to n bytes (default is 512).

of=file

Write output to file (default is standard output).

seek=n

Skip n output-sized blocks from start of output file.

skip=n

Skip n input-sized blocks from start of input file.

--help

Print help message and then exit.

--version

Print the version number and then exit.

You can multiply size values (n) by a factor of 1024, 512, or 2 by appending the letter k, b, or w, respectively. You can use the letter x as a multiplication operator between two numbers.

Examples

Convert an input file to all lowercase:

dd if=caps_file of=small_file conv=lcase

Retrieve variable-length data and write it as fixed-length to out:

[data_retrieval_cmd]| dd of=out conv=sync,block

Name

deallocvt

Synopsis

deallocvt N

Deallocate and destroy the unused virtual console /dev/ttyN. Multiple consoles may be named with additional spaces and integers: deallocvt 1 4 deallocates the /dev/tty1 and /dev/tty4 consoles. Consoles are considered unused if they are not in the foreground, have no open processes, and have no selected text. The command does not destroy consoles that are still active.

Name

debugfs

Synopsis

debugfs [[option] device]

System administration command. Provide direct access to data structure of an ext2 or ext3 filesystem in order to debug problems with the device. device is the special file corresponding to the device containing the filesystem (e.g., /dev/hda3). debugfs may be used on a mounted filesystem device.

Option

-b blocksize

Use the specified blocksize for the filesystem.

-c

Catastrophic mode. Open the filesystem in read-only mode; do not read the inode and group bitmaps initially.

-f file

Read commands from file. Exit when done executing commands.

-i

Specify filesystem device is an ext2 image file created by e2image.

-s block

Read the superblock from the specified block.

-w

Open the filesystem in read-write mode.

-R request

Execute the given request (see list below), then exit.

-V

Print version number, then exit.

Requests

bmap file logicalblock

Given the logicalblock of inode file, print the corresponding physical block.

cat file

Dump the contents of an inode to standard output.

cd directory

Change the current working directory to directory.

chroot directory

Change the root directory to be the specified inode.

close

Close the currently open filesystem.

clri file

Clear the contents of the inode corresponding to file.

dump [-p] file out_file

Dump the contents of inode file to out_file. Change ownership and permissions of out_file to match file if -p is specified.

expand_dir directory

Expand directory.

feature [[-]feature]

Set filesystem feature listed on the command line, then print current feature settings. Use - to clear a feature.

find_free_block [[n] goal]

Find and allocate first n free blocks starting from goal (if specified).

find_free_inode [dir [mode]]

Find a free inode and allocate it.

freeb block [n]

Free n blocks beginning from block. Default is 1 block.

freei file

Free the inode corresponding to file.

help

Print a list of commands understood by debugfs.

icheck block

Do block-to-inode translation.

imap file

Print the location of the inode data structure for file.

init_filesys device blocksize

Create an ext2 filesystem on device.

kill_file file

Remove file and deallocate its blocks.

lcd directory

Change current working directory on native filesystem.

ln source_file dest_file

Create a link.

logdump [-acs] [-bblock] [-iinode] [-fjournal_file] [out_file]

Print the ext3 journal contents to screen or to the specified out_file. Prints the superblock journal by default. Specify other journal information by block or inode. You can also specify a journal_file containing journal data. Use -a to print the contents of descriptor blocks. Use -b to print records referring to a specified block. Use -c to print the hexadecimal and ASCII contents of blocks referenced by the logdump.

ls [-l] [-d] [-p] [pathname]

Emulate the ls command. Use -l for verbose format and -d to list deleted entries. Use -p for output that can be more easily parsed by scripts.

modify_inode file

Modify the contents of the inode corresponding to file.

mkdir directory

Make directory.

mknod file [p|[[c|b] major minor]]

Create a special device file.

ncheck inode

Do inode-to-name translation.

open [-b blocksize] [-c] [-e] [-f] [-i] [-w] [-s block] device

Open a filesystem. The -f option forces the filesystem to open disregarding any unknown or incompatible features that would otherwise prevent it from opening. The -e option causes the filesystem to be opened in exclusive mode. The remaining options are identical to the command-line options for debugfs.

pwd

Print the current working directory.

quit

Quit debugfs.

rdump directory dest_directory

Recursively dump directory and its contents to dest_directory on the native filesystem.

rm file

Remove file.

rmdir directory

Remove directory.

setb block [n]

Mark n blocks as allocated, beginning from block. Default is 1 block.

set_block_group number field value

Set descripter field to value for the block group specified by number.

seti file

Mark in use the inode corresponding to file.

set_super_value [-l] field value

Set superblock field to value. Use -l to print a list of valid fields.

show_super_stats [-h]

List the contents of the superblock and block group descriptors. Use -h to list only the superblock contents.

stat file

Dump the contents of the inode corresponding to file.

testb block [n]

Print whether each of n blocks is in use, beginning with block. By default, just check the specified block.

testi file

Test whether the inode corresponding to file is marked as allocated.

undel <inode> [pathname]

Undelete (mark as used) the specified inode. You must include the angle brackets. Optionally link the recovered inode with pathname. If undeleting multiple inodes, linking may not be safe. Use a separate pass to link the pathname after all inodes have been undeleted. Always run e2fsck after undeleting inodes.

unlink file

Remove a link.

write source_file file

Create a file in the filesystem named file, and copy the contents of source_file into the destination file.

Name

depmod

Synopsis

depmod [options] modules

System administration command. Create a dependency file for the modules given on the command line. This dependency file can be used by modprobe to automatically load the relevant modules. The normal use of depmod is to include the line /sbin/depmod -a in one of the files in /etc/rc.d so that the correct module dependencies will be available after booting the system.

Options

-a, --all

Create dependencies for all modules listed in /etc/modules.conf.

-A, --quick

Check timestamps and only update the dependency file if anything has changed.

-b dir, --basedir dir

Specify a base directory to use instead of /lib/modules.

-C file, --config file

Use the specified configuration file instead of /etc/modules.dep. May also be set using the MODULECONF environment variable.

-e, --errsyms

Print a list of all unresolved symbols.

-F file, --kernelsyms file

Use the specified kernel symbol file to build dependencies. Usually this is either a copy of a system’s System.map file or the output of /proc/ksyms.

-h, --help

Print help message, then exit.

-n, --dry-run, --show

Write dependency file to standard output instead of writing to module directory.

-q, --quiet

Don’t display error messages about missing symbols.

-r, --root

Allow root to load modules not owned by root.

-s, --syslog

Write error messages to the syslog daemon instead of to standard error.

-v

Print a list of all processed modules.

-V, --version

Print version number.

Files

/etc/modules.dep, /etc/depmod.d

Information about modules: which ones depend on others, and which directories correspond to particular types of modules.

/sbin/insmod, /sbin/rmmod

Programs that depmod relies on.

Name

devdump

Synopsis

devdump isoimage

Interactively display the contents of the device or filesystem image isoimage. devdump displays the first 256 bytes of the first 2048-byte sector and waits for commands. The prompt shows the extent number (zone) and offset within the extent, and the contents display at the top of the screen.

Commands

+

Search forward for the next instance of the search string.

a

Search backward within the image.

b

Search forward within the image.

f

Prompt for a new search string.

g

Prompt for a new starting block and go there.

q

Exit.

Name

df

Synopsis

df [options] [name]

Report the amount of free disk space available on all mounted filesystems or on the given name. (df cannot report on unmounted filesystems.) Disk space is shown in 1 KB blocks (default) or 512-byte blocks if the environment variable POSIXLY_CORRECT is set. name can be a device name (e.g., /dev/hd*), the directory name of a mounting point (e.g., /usr), or a directory name (in which case df reports on the entire filesystem in which that directory is mounted).

Options

-a, --all

Include empty filesystems (those with 0 blocks).

-B n, --block-size=n

Show space as n-byte blocks.

-h, --human-readable

Print sizes in a format friendly to human readers (e.g., 1.9 MB instead of 1967156).

-H, --si

Like -h, but show as power of 1000 rather than 1024.

-i, --inodes

Report free, used, and percent-used inodes.

-k

Print sizes in kilobytes.

-l, --local

Show local filesystems only.

-m, --megabytes

Print sizes in megabytes.

--no-sync

Show results without invoking sync first (i.e., without flushing the buffers). This is the default.

-P, --portability

Use POSIX output format (i.e., print information about each filesystem on exactly one line).

--sync

Invoke sync (flush buffers) before getting and showing sizes.

-t type, --type=type

Show only filesystems of the specified type.

-T, --print-type

Print the type of each filesystem in addition to the sizes.

-x type, --exclude-type=type

Show only filesystems that are not of type type.

--help

Print help message and then exit.

--version

Print the version and then exit.

Name

diff

Synopsis

diff [options] file1 file2

Compare two text files. diff reports lines that differ between file1 and file2. Output consists of lines of context from each file, with file1 text flagged by a < symbol and file2 text by a > symbol. Context lines are preceded by the ed command (a, c, or d) that would be used to convert file1 to file2. If one of the files is -, standard input is read. If one of the files is a directory, diff locates the filename in that directory corresponding to the other argument (e.g., diff my_dir junk is the same as diff my_dir/junk junk). If both arguments are directories, diff reports lines that differ between all pairs of files having equivalent names (e.g., olddir/program and newdir/program); in addition, diff lists filenames unique to one directory, as well as subdirectories common to both. See also cmp.

Options

-n

For context and unified diff, print n lines of context. Same as specifying a number with -C or -U.

-a, --text

Treat all files as text files. Useful for checking to see if binary files are identical.

-b, --ignore-space-change

Ignore repeating blanks and end-of-line blanks; treat successive blanks as one.

-B, --ignore-blank-lines

Ignore blank lines in files.

-c

Context diff: print three lines surrounding each changed line.

-C n, --context[=n]

Context diff: print n lines surrounding each changed line. The default context is three lines.

-d, --minimal

Ignore segments of numerous changes and output a smaller set of changes.

-D symbol, --ifdef=symbol

When handling C files, create an output file that contains all the contents of both input files, including #ifdef and #ifndef directives that reflect the directives in both files.

-e, --ed

Produce a script of commands (a, c, d) to recreate file2 from file1 using the ed editor.

-F regexp, --show-function-line[=regexp]

For context and unified diff, show the most recent line containing regexp before each block of changed lines.

-H, --speed-large-files

Speed output of large files by scanning for scattered small changes; long stretches with many changes may not show up.

--help

Print brief usage message.

--horizon-lines=n

In an attempt to find a more compact listing, keep n lines on both sides of the changed lines when performing the comparison.

-i, --ignore-case

Ignore case in text comparison. Uppercase and lowercase are considered the same.

-I regexp, --ignore-matching-lines=regexp

Ignore lines in files that match the regular expression regexp.

-l, --paginate

Paginate output by passing it to pr.

-L label, --label=label

For context and unified diff, print label in place of the filename being compared. The first such option applies to the first filename and the second option to the second filename.

--left-column

For two-column output (-y), show only left column of common lines.

-n, --rcs

Produce output in RCS diff format.

-N, --new-file

Treat nonexistent files as empty.

-p, --show-c-function

When handling files in C or C-like languages such as Java, show the function containing each block of changed lines. Assumes -c, but can also be used with a unified diff.

-P, --unidirectional-new-file

If two directories are being compared and the first lacks a file that is in the second, pretend that an empty file of that name exists in the first directory.

-q, --brief

Output only whether files differ.

-r, --recursive

Compare subdirectories recursively.

-s, --report-identical-files

Indicate when files do not differ.

-S filename, --starting-file=filename

For directory comparisons, begin with the file filename, skipping files that come earlier in the standard list order.

--suppress-common-lines

For two-column output (-y), do not show common lines.

-t, --expand-tabs

Produce output with tabs expanded to spaces.

-T, --initial-tab

Insert initial tabs into output to line up tabs properly.

-u

Unified diff: print old and new versions of lines in a single block, with 3 lines surrounding each block of changed lines.

-U n, --unified[=n]

Unified diff: print old and new versions of lines in a single block, with n lines surrounding each block of changed lines. The default context is 3 lines. With the -U form, n must be given.

-v, --version

Print version number of this version of diff.

-w, --ignore-all-space

Ignore all whitespace in files for comparisons.

-W n, --width=n

For two-column output (-y), produce columns with a maximum width of n characters. Default is 130.

-x regexp, --exclude=regexp

Do not compare files in a directory whose basenames match regexp.

-X filename, --exclude-from=filename

Do not compare files in a directory whose basenames match patterns described in the file filename.

-y, --side-by-side

Produce two-column output.

Name

diff3

Synopsis

diff3 [options] file1 file2 file3

Compare three files and report the differences. No more than one of the files may be given as - (indicating that it is to be read from standard input). The output is displayed with the following codes:

= = = =

All three files differ.

= = = =1

file1 is different.

= = = =2

file2 is different.

= = = =3

file3 is different.

diff3 is also designed to merge changes in two differing files based on a common ancestor file (i.e., when two people have made their own set of changes to the same file). diff3 can find changes between the ancestor and one of the newer files and generate output that adds those differences to the other new file. Unmerged changes occur where both of the newer files differ from each other and at least one of them differs from the ancestor. Changes from the ancestor that are the same in both of the newer files are called merged changes. If all three files differ in the same place, it is called an overlapping change.

This scheme is used on the command line, with the ancestor being file2, the second filename. Comparison is made between file2 and file3, with those differences then applied to file1.

Options

−3, --easy-only

Create an ed script to incorporate into file1 unmerged, nonoverlapping differences between file1 and file3.

-a, --text

Treat files as text.

-A, --show-all

Create an ed script to incorporate all changes, showing conflicts in bracketed format.

-e, --ed

Create an ed script to incorporate into file1 all unmerged differences between file2 and file3.

-E, --show-overlap

Create an ed script to incorporate unmerged changes, showing conflicts in bracketed format.

--help

Print usage information and exit.

-i

Append the w (save) and q (quit) commands to ed script output.

-L label, --label=label

Use label to replace filename in output.

-m, --merge

Create file with changes merged (not an ed script).

-T, --initial-tab

To line tabs up properly in output, begin lines with a tab instead of two spaces.

-v, --version

Print version information and then exit.

-x, --overlap-only

Create an ed script to incorporate into file1 all differences where all three files differ (overlapping changes).

-X

Same as -x, but show only overlapping changes in bracketed format as with -E.

Name

dig

Synopsis

dig [@server] [options] [name] [type] [class] [query-options]
dig @server name type
dig -h

TCP/IP command. The dig command is used to query DNS servers; it is more flexible than the deprecated nslookup command. When invoked with just the -h option, it displays a list of options for the command. If you use it without any options or arguments, it will search for the root server. The standard arguments are:

server

The server to query. If no server is supplied, dig will check the nameservers listed in /etc/resolv.conf. The address may be an IPv4 dotted address or an IPv6 colon-delimited address. It may also be a hostname, which dig will resolve (through the nameservers in /etc/resolv.conf).

name

The domain name to look up.

type

The type of query to perform, such as A, ANY, MX, SIG, and so forth. The default is A, but you may use any valid BIND9 query type.

Options

You may use the following option flags with dig:

-b address

Set the source IP address for the query.

-c class

Set the class of query. The default value is IN (internet), but you can choose HS for Hesiod or CH for CHAOSNET.

-f filename

Operate in batch mode, performing the queries in the file you specify.

-k filename

Specify a TSIG keyfile; used for signed transactions. You can also use the -y key, although this is less secure.

-p portnumber

Choose the port number for the query. The default value is the standard DNS port, 53.

-q name

Specify domain name to query. Sometimes this is needed to distinguish the domain name from other options.

-t type

Set the type of query, as with the query argument. The default value is A, but you may use any valid BIND9 query.

-x addr

Use the -x flag for reverse lookups, specifying an IPv4 or IPv6 address. You do not need the name, class, or type arguments if you use the -x flag.

-y keyname: keyvalue

Enter the actual key name and value when conducting a signed transaction. Because the key and value can be seen in the output of ps, this is not recommended for use on multiuser systems; use -k instead.

Query options

There are a large number of query options for dig. Each query option is preceded by +, and many have an opposite version beginning with no. For example, the tcp flag is passed as +tcp, and negated with +notcp. Because there are so many options, only a few are discussed here. For greater detail, see the dig manpage.

+tcp, +notcp

Use (or do not use) the TCP protocol instead of the default UDP.

+domain=searchdomain

Perform a search in the domain specified; this is equivalent to using the +search option and having “searchdomain” as the sole entry in the search list or domain directive of /etc/resolv.conf.

+search, +nosearch

Use (or do not use) the search list provided in /etc/resolv.conf. The default is not to use the search list.

+time=t

Timeout for queries, in seconds. The default is 5, and the minimum is 1.

+tries=n

The number of times to retry UDP queries. The default is 3, and the minimum is 1.

Examples

Query the mail exchange record for example.com:

dig mx example.com

Ask a specific nameserver to resolve a domain:

dig @ns.example.com smtp.example.com

Perform a reverse look up on an IP address:

dig -x 208.201.239.37

Name

dir

Synopsis

dir [options] [file]

List directory contents. dir is equivalent to the command ls -C -b (list files in columns, sorted vertically, special characters escaped), and it takes the same arguments as ls. This is an alternate invocation of the ls command and is provided for the convenience of those converting from Microsoft Windows and the DOS shell.

Name

dircolors

Synopsis

dircolors [options] [file]

Set the color options for the ls command. dircolors outputs shell commands which, when evaluated, update the LS_COLORS environment variable. If you specify a file, dircolors reads it to determine which colors to use. Otherwise, it uses a default set of colors. If the shell is not specified, dircolors checks the SHELL environment variable.

Options

The program takes three options in addition to the standard --help and --version flags:

-b, --sh, --bourne-shell

Use the Bourne shell syntax when setting the LS_COLORS variable.

-c, --csh, --c-shell

Use csh (C shell) syntax when setting the LS_COLORS variable.

-p, --print-database

Display the default colors. You can copy this information into a file and change it to suit your preferences, and then run the program with the file as its argument to set the colors to your new values.

Example

Set LS_COLORS using the default color database:

eval `dircolors`

Name

dirname

Synopsis

dirname pathname

Print pathname, excluding the last level. Useful for stripping the actual filename from a pathname. If there are no slashes (no directory levels) in pathname, dirname prints . to indicate the current directory. See also basename.

Name

dmesg

Synopsis

dmesg [options]

System administration command. Display the system control messages from the kernel ring buffer. This buffer stores all messages since the last system boot, or the most recent ones if the buffer has been filled.

Options

-c

Clear buffer after printing messages.

-nlevel

Set the level of system message that will display on console.

-sbuffersize

Specify buffersize of kernel ring buffer. This is useful if you have changed the kernel default.

Name

doexec

Synopsis

doexec /path/to/command [argv[0]] ... [argv[n]]

Execute the specified command with the specified options and arguments. Differs from the normal exec command in that argv[0] may be completely arbitrary, and in that it passes all options to the executable being run.

Name

domainname

Synopsis

domainname [name]

NFS/NIS command. Set or display name of current NIS domain. With no argument, domainname displays the name of the current NIS domain. Only a privileged user can set the domain name by giving an argument; this is usually done in a startup script.

Name

dosfsck

Synopsis

dosfsck [options] device
fsck.msdos [options] device

System administration command. Similar to fsck, but specifically intended for MS-DOS filesystems. When checking an MS-DOS filesystem, fsck calls this command. Normally dosfsck stores all changes in memory, then writes them when checks are complete.

Options

-a

Automatically repair the system; do not prompt the user.

-d file

Drop the named file from the file allocation table. Force checking, even if kernel has already marked the filesystem as valid. dosfsck will normally exit without checking if the system appears to be clean.

-f

Save unused cluster chains to files.

-l

List pathnames of files being processed.

-r

Repair the system, prompting user for advice.

-t

Mark unreadable clusters as bad.

-u file

Attempt to undelete the named file.

-v

Verbose mode.

-w

Write changes to disk immediately.

-y

When queried, answer “yes.”

-A

Filesystem is an Atari version of MS-DOS.

-V

Repeat test to verify all errors have been corrected.

Name

du

Synopsis

du [options] [directories]

Print disk usage (as the number of 1 KB blocks used by each named directory and its subdirectories; default is the current directory).

Options

−0, --null

End output lines with null, not newline.

-a, --all

Print disk usage for all files, not just subdirectories.

--apparent-size

Print the apparent sizes, not disk usage.

-b, --bytes

Print sizes in bytes.

-B bytes, --block-size=bytes

Use the specified number of bytes for the blocksize.

-c, --total

In addition to normal output, print grand total of all arguments.

-D, --dereference-args

Follow symbolic links, but only if they are command-line arguments.

--exclude=pattern

Exclude files that match pattern.

-h, --human-readable

Print sizes in human-readable format.

-H, --si

Like -h, but show as power of 1000 rather than 1024. -H also produces a warning.

--help

Print help message and then exit.

-k, --kilobytes

Print sizes in kilobytes (this is the default).

-l, --count-links

Count the size of all files, whether or not they have already appeared (i.e., via a hard link).

-L, --dereference

Follow symbolic links.

-m

Print sizes in megabytes.

--max-depth=num

Report sizes for directories only down to num levels below the starting point (which is level 0).

-P, --no-dereference

Do not follow symbolic links (the default).

-s, --summarize

Print only the grand total for each named directory.

-S, --separate-dirs

Do not include the sizes of subdirectories when totaling the size of parent directories.

--time[=word]

Print the last-modification time. With word, show the time as one of the following, not as modification time: atime, access, use, ctime, or status.

--time-style=style

Show times using the specified style. Possible values are: full-iso, long-iso, iso, +format (interpreted as in date). Used with --time.

--version

Print the version and then exit.

-x, --one-file-system

Display usage of files in current filesystem only.

-X file, --exclude-from=file

Exclude files that match any pattern in file.

Name

dump

Synopsis

dump [options] files

System administration command. This simple backup utility accesses ext2 and ext3 file devices directly, quickly backing up files without affecting file access times. files may be specified as a mount point or as a list of files and directories to back up. While you can use this on a mounted system, dump may write corrupted information to the backup when the kernel has written only part of its cached information. Dump maintains a record of which files it has saved in /etc/dumpdates, and will perform incremental backups after creating an initial full backup. Use the restore command to restore a dump backup.

Options

-a

Write until end-of-media. Default behavior when writing to tape drives.

-A file

Create a table of contents for the archive in the specified file.

-bblocksize

Block size in kilobytes to use in dumped records. By default, it is 10, or 32 when dumping to a tape with a density greater than 6250 bpi.

-Bblocks

Specify number of blocks to write per volume.

-c

Treat target as a 1700-foot-long cartridge tape drive with 8000 bpi. Override end-of-media detection.

-d density

Specify tape density.

-D file

Write dump information to file instead of /etc/dumpdates.

-E file

Exclude inodes specified in file.

-f files

Write backup volumes to the specified files or devices. Use - to write to standard output. Separate multiple files with a comma. Use host:file or user@host:file to write to a networked host using either the rmt program or the program specified by the RMT environment variable.

-F script

Run script at the end of each volume other than the last. dump will pass the current device and volume number to the script. The script should return 0 to continue, 1 to prompt for a new tape, or any other exit value to abort the dump. The script will run with the processes real user and group ID.

-i inodes

Specify a comma-separated list of inodes to skip.

-I n

Ignore the first n read errors. dump ignores 32 read errors by default. Specify 0 to ignore all errors. You may need to do this when dumping a mounted filesystem.

-j[level]

Compress each block using the bzlib library at the specified compression level. By default dump uses level 2 compression.

-k

Use Kerberos authentication when writing to a remote system.

-L label

Write the specified volume label into the dump header.

-m

Save only metadata when backing up changed but not modified files.

-M

Create a multivolume backup. Treat any filename provided with -f as a prefix.

-n

Use wall to notify members of group operator when prompting for information.

-q

Abort the backup instead of prompting for information when operator input is required.

-Q file

Create Quick Access information in the specified file for use by restore.

-s n

Write only n feet of tape in a single volume. Prompt for a new tape upon reaching this limit.

-S

Calculate and print the amount of space required to perform the backup, then exit.

-T date

Only back up files changed or modified since date. This overrides the time given in /etc/dumpdates.

-u

Update /etc/dumpdates after completing the backup.

-v

Print verbose information about the dump.

-W

Generate a report on the backup status of all filesystems based on information in /etc/dumpdates and /etc/fstab.

-w

Generate a report of filesystems that need to be backed up. Only report on filesystems listed in /etc/fstab and /etc/mtab that need to be backed up.

-y

Compress each block using the lzo library.

-z[level]

Compress each block using the zlib library. If provided, use the specified compression level. The default is 2.

Name

dumpe2fs

Synopsis

dumpe2fs device

System administration command. Print ext2/ext3 information about device’s superblock and blocks group.

Options

-b

List blocks marked as bad.

-f

Force display of filesystems with unknown feature flags.

-h

Display superblock information only.

-i

Specify device is an image file created by e2image.

-o superblock=superblock

Specify location of the superblock.

-o blocksize=blocksize

Specify blocksize to use when examining filesystem.

-x

Print block numbers in hexadecimal.

-V

Print version number and exit.

Name

dumpiso

Synopsis

dumpiso [options] [file]

Listen on selected channels and dump IEEE 1394 packets received into the specified file, or to standard output if file is not specified. The current number of packets is written to standard error.

Options

-c nums, --channels=nums

Set channels to listen to, as a single number or a range. Channel numbers can be from 0 to 63, and the option can be specified multiple times to add new channels each time. Without this option, dumpiso defaults to all channels.

-h, --help

Print usage information and exit.

-p port, --port=port

Specify the IEEE 1394 port to receive on; only required if there is more than one on your system. The default is 0.

Name

dumpkeys

Synopsis

dumpkeys [options]

Print information about the keyboard driver’s translation tables to standard output. Further information is available in the manual pages under keymaps(5).

Options

−1, --separate-lines

Print one line for each modifier/keycode pair, and prefix plain to each unmodified keycode.

-ccharset, --charset=charset

Specify character set with which to interpret character code values. The default character set is iso-8859-1. Use --help for the list of valid character sets.

--compose-only

Print compose key combinations only. Requires compose key support in the kernel.

-f, --full-table

Output in canonical, not short, form: for each key, print a row with modifier combinations divided into columns.

--funcs-only

Print function-key string definitions only; do not print key bindings or string definitions.

-h, --help

Print help message and the version.

-i, --short-info

Print in short-info format, including information about acceptable keycode keywords in the keytable files; the number of actions that can be bound to a key; a list of the ranges of action codes (the values to the right of a key definition); and the number of function keys that the kernel supports.

--keys-only

Print key bindings only; do not print string definitions.

-l, --long-info

Print the same information as in --short-info, plus a list of the supported action symbols and their numeric values.

-n, --numeric

Print action code values in hexadecimal notation; do not attempt to convert them to symbolic notation.

Name

dvdrecord

Synopsis

dvdrecord [options] track1,track2...

Record data to a DVD recorder. dvdrecord is generally a symbolic link to wodim. See wodim for more information.

Name

e2fsck

Synopsis

e2fsck [options] device
fsck.ext2 [options] device

System administration command. Checks and repairs a disk, as does fsck, but specifically designed for ext2 (Linux Second Extended) and ext3 (Third Extended, a journaling version of ext2) filesystems. fsck actually uses this command when checking ext2 and ext3 filesystems. Most often used after a sudden shutdown, such as from a power outage, or when damage to the disk is suspected.

Options

-b superblock

Use superblock instead of the default superblock.

-B size

Expect to find the superblock at size; if it’s not there, exit.

-c

Find bad blocks using the badblocks command. Specify this option twice to perform the scan with a nondestructive read-write test.

-C filedescriptor

Write completion information to the specified filedescriptor. If 0, print a completion bar.

-d

Debugging mode.

-D

Optimize directories by reindexing, sorting, and compressing them where possible.

-f

Force checking, even if kernel has already marked the filesystem as valid. e2fsck will normally exit without checking if the system appears to be clean.

-F

Flush buffer caches before checking.

-j file

Use the specified external journal file.

-k

Preserve all previously marked bad blocks when using the -c option.

-l file

Consult file for a list of bad blocks, in addition to checking for others.

-L file

Consult file for list of bad blocks instead of checking filesystem for them.

-n

Ensure that no changes are made to the filesystem. When queried, answer “no.”

-p

“Preen.” Repair all bad blocks noninteractively.

-s

Byte-swap the filesystem if necessary to standard (little-endian) byte-order.

-S

Byte-swap the filesystem.

-t

Display timing statistics.

-v

Verbose.

-y

When queried, answer “yes.”

Name

e2image

Synopsis

e2image [option] device file

System administration command. Store disaster recovery data for ext2 filesystem on device to image file file. Weekly filesystem images can be an important part of a disaster recovery plan.

Option

-r

Create a raw image file that can be checked and debugged using filesystem utilities such as e2fsck or debugfs. Raw images are created as sparse files. Either compress the image file before moving it, or use the --sparse=always option when copying it with cp.

-I

Restore filesystem metadata in image to device. Note you will lose any changes to the filesystem since your image was created.

Name

e2label

Synopsis

e2label device [label]

System administration command. Display the filesystem label on an ext2 filesystem device. Change filesystem label to label if specified.

Name

echo

Synopsis

echo [options] [string]

Send (echo) the input string to standard output. This is the /bin/echo command. echo also exists as a command built into bash. You may have to specify the full path to run /bin/echo instead of the shell built-in command. The following character sequences have special meaning:

\a

Alert (bell).

\b

Backspace.

\c

Suppress trailing newline.

\f

Form feed.

\n

Newline.

\r

Carriage return.

\t

Horizontal tab.

\v

Vertical tab.

\\

Literal backslash.

\nnn

The octal character whose ASCII code is nnn.

Options

-e

Enable character sequences with special meaning. (In some versions, this option is not required in order to make the sequences work.)

-E

Disable character sequences with special meaning.

-n

Suppress printing of newline after text.

--help

Print help message and exit.

--version

Print version information and exit.

Examples

/bin/echo "testing printer" | lp
/bin/echo "TITLE" > file ; cat doc1 doc2 >> file
/bin/echo "Warning: ringing bell \a"

Name

edquota

Synopsis

edquota [options] [name]

System administration command. Edit filesystem quotas using a text editor. When edits are complete, edquota writes the new information to the binary quota files. Uses the editor specified in the EDITOR environment variable, or vi by default.

Options

-ffilesystem

Only apply changes to the specified filesystem.

-Fformat

Specify filesystem quota format to use. See quota for a list of accepted values.

-g

Edit group quotas.

-pprototype

Apply the same settings as used for the specified user or group: prototype.

-r

Edit quotas on remote systems.

-t

Edit grace times for block and inode quotas.

-T

Edit grace times for individual user or group name.

-u

Edit user quotas. (This is the default.)

Name

egrep

Synopsis

egrep [options] [regexp] [files]

Search one or more files for lines that match an extended regular expression regexp. egrep doesn’t support the regular expressions \(, \), \n, \<, \>, \{, or \}, but it does support the other expressions, as well as the extended set +, ?, |, and ( ). Remember to enclose these characters in quotes. Regular expressions are described in Chapter 7. Exit status is 0 if any lines match, 1 if none match, and 2 for errors.

See grep for the list of available options. Also see fgrep.

Examples

Search for occurrences of Victor or Victoria in file:

egrep 'Victor(ia)*' file
egrep '(Victor|Victoria)' file

Find and print strings such as old.doc1 or new.doc2 in files, and include their line numbers:

egrep -n '(old|new)\.doc?' files

Name

eject

Synopsis

eject [options] [device]

Eject removable media such as a CD, DVD, floppy, or tape. You may name the device by its /dev or /mnt filename. The /dev and /mnt prefixes are optional for any items in the /dev and /mnt directories. If no device is named, it is assumed that “cdrom” should be ejected.

Options

The eject command takes the following option flags:

-a, --auto on|1|off|0

Set the auto-eject mode to on or off (equivalent to 1 or 0, respectively). If auto-eject mode is on, the device is ejected when closed or unmounted.

-c slotnumber, --changerslot slotnumber

If using a CD-ROM changer, select a CD from one of the slots. Slot numbers start with 0, and the CD-ROM drive must not be playing music or mounted to read data.

-d, --default

List the default device name rather than doing anything.

-f, --floppy

Use floppy commands to eject the drive. Normally, the system tries all methods (CD-ROM, SCSI, floppy, tape) to eject.

-h, --help

Display help information.

-m, --no-unmount

Do not try to unmount the device.

-n, --noop

Do not perform any actions; merely display the actions that would be performed.

-p, --proc

Use the mounted files listed in /proc/mounts rather than in /etc/mtab.

-q, --tape

Use tape commands to eject the drive. Normally, the system tries all methods (CD-ROM, SCSI, floppy, tape) to eject.

-r, --cdrom

Use CD-ROM commands to eject the drive. Normally, the system tries all methods (CD-ROM, SCSI, floppy, tape) to eject.

-s, --scsi

Use SCSI commands to eject the drive. Normally, the system tries all methods (CD-ROM, SCSI, floppy, tape) to eject.

-t, --trayclose

Close the CD-ROM drive. Not all drives respond to this option.

-T, --traytoggle

Close the CD-ROM drive if it’s open and eject the CD if it’s closed. Not all drives respond to this option.

-v, --verbose

Verbose mode: display additional information about actions.

-V, --version

Display version information and exit.

-x speed, --cdspeed speed

Set the speed multiplier for the CD-ROM to an integer, usually a power of 2. Not all devices support this option. Setting the speed to 0 indicates that the drive should operate at its maximum speed.

-X, --listspeed

Detect and list all available speeds that can be specified with -x. Not all devices support this option.

Name

elvtune

Synopsis

elvtune [options] devices

System administration command. Set the latency in the elevator algorithm used to schedule I/O activities for the specified block devices. If no options are given, print the current settings for devices.

Options

-b n

Set the maximum coalescing factor allowed on writes when reads are pending to n.

-h

Print help message, then exit.

-r n

Set the maximum read latency (basically, the number of sectors to read before writes are allowed) to n. The default is 8192.

-v

Print version number, then exit.

-w n

Set the maximum write latency (sectors to write before allowing a read) to n. The default is 16,384.

Name

emacs

Synopsis

emacs [options] [files]

A text editor and all-purpose work environment. For more information, see Chapter 8.

Name

enable

Synopsis

enable -E [destination]

Enable printers or printer classes. Part of the CUPS system. More often invoked as accept.

Name

env

Synopsis

env [option] [variable=
value ... ] [command]

Display the current environment or, if an environment variable is specified, set it to a new value and display the modified environment. If command is specified, execute it under the modified environment.

Options

-, -i, --ignore-environment

Ignore current environment entirely.

-u name, --unset name

Unset the specified variable.

--help

Print help message and then exit.

--version

Print version information and then exit.

Name

envsubst

Synopsis

envsubst [options] [shell-format]

Substitutes environment variables in a shell string or script. When used with no options, copies stdin to stdout, replacing any environment variable string, such as $VARIABLE or ${VARIABLE}, with the appropriate environment variable value. So, “My editor is $EDITOR” would be converted to “My editor is /usr/bin/emacs.” Specifying a shell format limits the substitutions to those variables referenced in the shell format.

Options

-h, --help

Print help message and then exit.

-v, --variables

Display the variables referenced in the shell format, and then exit.

-V, --version

Print version information and then exit.

Name

etags

Synopsis

etags [options] files

Create a list of function and macro names defined in a programming source file. etags generates tags for use by emacs. (ctags produces an equivalent tags file for use with vi.) More than one file may be specified. etags understands many programming languages, including C, C++, FORTRAN, Java, Perl, Python, flex, yacc, and bison. The output list (named TAGS by default) contains lines of the form:

name     file     context

where name is the function or macro name, file is the source file in which name is defined, and context is a search pattern that shows the line of code containing name. After the list of tags is created, you can invoke Emacs on any file and type:

M-x visit-tags-table

You will be prompted for the name of the tag table; the default is TAGS. To switch to the source file associated with the name listed in tagsfile, type:

M-x find-tag

You will be prompted for the tag you would like Emacs to search for.

Options

-a, --append

Append tag output to existing list of tags.

-d, --defines

Include tag entries for C preprocessor definitions.

-i file, --include=file

Add a note to the tags file that file should be consulted in addition to the normal input file.

-l language, --language=language

Consider the files that follow this option to be written in language. Use the -h option for a list of languages and their default filename extensions.

-o file, --output=file

Write to file.

-r regexp, --regex=regexp

Include a tag for each line that matches regexp in the files following this option.

-C, --c++

Expect .c and .h files to contain C++, not C, code.

-D, --no-defines

Do not include tag entries for C preprocessor definitions.

-H, -h, --help

Print usage information.

-R, --noregex

Do not include tags based on regular-expression matching for the files that follow this option.

-S, --ignore-indentation

Normally, etags uses indentation to parse the tag file; this option tells it to rely on it less.

-V, --version

Print the version number.

Name

ex

Synopsis

ex [options] file

An interactive command-based editor. For more information, see Chapter 9.

Name

expand

Synopsis

expand [options] [files]

Convert tabs in given files (or standard input, if the file is given as -) to the appropriate number of spaces; write results to standard output.

Options

--help

Print help message and then exit.

-i, --initial

Convert tabs only at the beginning of lines.

-tabs, -t tabs, --tabs tabs

tabs is a comma-separated list of integers that specify tab stops. With one integer, the tab stops are set to every integer spaces. By default, tab stops are eight spaces apart. With -t and --tabs, the list may be separated by whitespace instead of commas.

--version

Print version information and then exit.

Name

expr

Synopsis

expr arg1 operator arg2 [ operator arg3 ... ]

Evaluate arguments as expressions and print the results to standard output. Arguments and operators must be separated by spaces. In most cases, an argument is an integer, typed literally or represented by a shell variable. There are three types of operators: arithmetic, relational, and logical, as well as keyword expressions. Exit status for expr is 0 (expression is nonzero and nonnull), 1 (expression is 0 or null), 2 (expression is invalid), or 3 (an error occurred).

Arithmetic operators

Use these to produce mathematical expressions whose results are printed:

+

Add arg2 to arg1.

-

Subtract arg2 from arg1.

*

Multiply the arguments.

/

Divide arg1 by arg2.

%

Take the remainder when arg1 is divided by arg2.

Addition and subtraction are evaluated last, unless they are grouped inside parentheses. The symbols *, (, and ) have meaning to the shell, so they must be escaped (preceded by a backslash or enclosed in single quotes).

Relational operators

Use these to compare two arguments. Arguments can also be words, in which case comparisons are defined by the locale. If the comparison statement is true, the result is 1; if false, the result is 0. Symbols > and < must be escaped.

=, ==

Are the arguments equal?

!=

Are the arguments different?

>

Is arg1 greater than arg2?

>=

Is arg1 greater than or equal to arg2?

<

Is arg1 less than arg2?

<=

Is arg1 less than or equal to arg2?

Logical operators

Use these to compare two arguments. Depending on the values, the result can be arg1 (or some portion of it), arg2, or 0. Symbols | and & must be escaped.

|

Logical OR; if arg1 has a nonzero (and nonnull) value, the result is arg1; otherwise, the result is arg2.

&

Logical AND; if both arg1 and arg2 have a nonzero (and nonnull) value, the result is arg1; otherwise, the result is 0.

:

Like grep; arg2 is a pattern to search for in arg1. arg2 must be a regular expression. If part of the arg2 pattern is enclosed in \( \) (escaped parentheses), the result is the portion of arg1 that matches; otherwise, the result is simply the number of characters that match. By default, a pattern match always applies to the beginning of the first argument (the search string implicitly begins with a ^). Start the search string with .* to match other parts of the string.

Keywords

index string character-list

Return the first position in string that matches the first possible character listed in character-list. Continue through character-list until a match is found, or return 0.

length string

Return the length of string.

match string regex

Same as string : regex.

+ token

Treat token as a string, even if it would normally be a keyword or an operator.

substr string start length

Return a section of string, beginning with start, with a maximum length of length characters. Return null when given a negative or nonnumeric start or length.

Examples

Division happens first; result is 10:

expr 5 + 10 / 2

Addition happens first; result is 7 (truncated from 7.5):

expr \( 5 + 10 \) / 2

Add 1 to variable i. This is how variables are incremented in shell scripts:

i=`expr $i + 1`

Print 1 (true) if variable a is the string “hello”:

expr $a = hello

Print 1 (true) if b plus 5 equals 10 or more:

expr $b + 5 \>= 10

Find the 5th, 6th, and 7th letters of the word character:

expr substr character 5 3

In the examples that follow, variable p is the string "version.100". This command prints the number of characters in p:

expr $p : '.*'    Result is 11

Match all characters and print them:

expr $p : '\(.*\)' Result is "version.100"

Print the number of lowercase letters at the beginning of p:

expr $p : '[a-z]*'  Result is 7

Match the lowercase letters at the beginning of p:

expr $p : '\([a-z]*\)' Result is ""version""

Truncate $x if it contains five or more characters; if not, just print $x. (Logical OR uses the second argument when the first one is 0 or null, i.e., when the match fails.)

expr $x : '\(.....\)' \| $x

In a shell script, rename files to their first five letters:

mv $x `expr $x : '\(.....\)' \| $x`

(To avoid overwriting files with similar names, use mv -i.)

Name

factor

Synopsis

factor [options] n

Calculate and display the prime factors of number n, which must be a positive integer. If n is not specified, numbers are read from standard input, separated by commas, spaces, or tabs.

Options

--help

Display help information.

--version

Display version information.

Example:

user@systemname:˜> factor 60
60: 2, 2, 3 5

Name

false

Synopsis

false

A null command that returns an unsuccessful (nonzero) exit status. Normally used in bash scripts. See also true.

Name

fc-cache

Synopsis

fc-cache [options] [dirs]

Create font information caches for fontconfig system, enabling applications that use fontconfig to load fonts more rapidly. If no directory is specified, the current font configuration directories are used. Only fonts readable by FreeType are cached.

Options

-f, --force

Regenerate cache files, even if they seem to be up to date.

-s, --system-only

Scan directories of fonts for the whole system, not the fonts in the user’s home directory.

-v, --verbose

Verbose mode: display status information during operation.

-V, --version

Display version information.

-?, --help

Display help information.

Name

fc-list

Synopsis

fc-list [options] [pattern] [element]

Part of the fontconfig system. Lists available fonts and font styles. The first argument limits listed fonts to those matching the pattern, and the second displays the listed font attribute or element. To set the element argument without setting a pattern, use the : character to match all fonts. For example, fc-list : family displays all available fonts, with their font family information.

Options

-v, --verbose

Verbose mode: display status information during operation.

-?, --help

Display help message

-V, --version

Display version information and quit.

Name

fdisk

Synopsis

fdisk [options] [device]

System administration command. fdisk displays information about disk partitions, creates and deletes disk partitions, and changes the active partition. It is possible to assign a different operating system to each of the four possible primary partitions, though only one partition is active at any given time. You can also divide a physical partition into several logical partitions. The minimum recommended size for a Linux system partition is 40 MB. Normally, each device will be /dev/hda, /dev/hdb, /dev/sda, /dev/sdb, /dev/hdc, /dev/hdd, and so on. An interactive, menu-driven mode is also available. Note that this command can be destructive if used improperly.

Options

-b sectorsize

Set the size of individual disk sectors. May be 512, 1024, or 2048. Most systems now recognize sector sizes, so this is not necessary.

-l

List partition tables and exit.

-u

Report partition sizes in sectors instead of cylinders.

-s partition

Display the size of partition, unless it is a DOS partition.

-v

Print version number, then exit.

-C cylinders

Specify the number of cylinders on the disk.

-H heads

Specify the number of heads per cylinder.

-S sectors

Specify sectors per track for partitioning.

Commands

a

Toggle a bootable flag on current partition.

b

Edit disklabel of a BSD partition.

c

Toggle DOS compatibility flag.

d

Delete current partition.

l

List all partition types.

m

Main menu.

n

Create a new partition; prompt for more information.

o

Create an empty DOS partition table.

p

Print a list of all partitions and information about each.

q

Quit; do not save.

t

Replace the type of the current partition.

u

Modify the display/entry units, which must be cylinders or sectors.

v

Verify: check for errors, and display a summary of the number of unallocated sectors.

w

Save changes and exit.

x

Switch to expert commands.

Name

fgconsole

Synopsis

fgconsole

Print the number of the current virtual console. For example, if you are using /dev/tty1, the command would return 1.

Name

fgrep

Synopsis

fgrep [options] string [files]

Search one or more files for lines that match the specified text string. Exit status is 0 if any lines match, 1 if not, and 2 for errors. fgrep is faster than normal grep searches, but less flexible: it can only find fixed text, not regular expressions.

See grep for the list of available options. Also see egrep.

Examples

Print lines in file that don’t contain any spaces:

fgrep -v ' ' file

Print lines in file that contain the words in the file spell_list:

fgrep -f spell_list file

Name

file

Synopsis

file [options] files

Classify the named files according to the type of data they contain. file checks the magic file (usually /usr/share/magic) to identify some file types. If the file type cannot be determined, it is shown as “data.” file does its best to identify the file type, but it is sometimes incorrect. See also the strings command to search for printable strings in nontext files.

Options

-b, --brief

Brief mode; do not prepend filenames to output lines.

-c, --checking-printout

Check the format of the magic file (the files argument is invalid with -c). Usually used with -m.

-f file, --files-from file

Read the names of files to be checked from file.

-h, --no-dereference

Do not follow symbolic links. The default unless the environment variable POSIXLY_CORRECT is defined.

--help

Print help message and exit.

-i, --mime

Print mime strings rather than the traditional strings.

-L, --dereference

Follow symbolic links. By default, symbolic links are not followed.

-m file, --magic-file file

Search for file types in file instead of /usr/share/magic, where file can be either a single file or a colon-separated list of files.

--mime-type, --mime-encoding

Like -i, but print only the mime type or the mime encoding.

-n, --no-buffer

Flush standard output after checking a file.

-N, --no-pad

Do not pad filenames to align in the output.

-s, --special-files

Check files that are block or character special files in addition to checking ordinary files.

-v, --version

Print the version.

-z, --uncompress

Attempt checking of compressed files.

Many file types are understood. The output lists each filename, followed by a brief classification such as:

ascii text
c program text
c-shell commands
data
empty
iAPX 386 executable
directory
[nt]roff, tbl, or eqn input text
shell commands
symbolic link to path

Examples

List all files that are deemed to be troff/nroff input:

file * | grep roff

Print the file type of the status file:

file status
status: ASCII English text

Print the file type of the status file in mime format:

file status
status: text/plain charset=us-ascii

Name

find

Synopsis

find [pathnames] [conditions]

An extremely useful command for finding particular groups of files (numerous examples follow this description). find descends the directory tree beginning at each pathname and locates files that meet the specified conditions. The default pathname is the current directory. The most useful conditions include -name and -type (for general use), -exec and -size (for advanced use), and -mtime and -user (for administrators).

Conditions may be grouped by enclosing them in \( \) (escaped parentheses), negated with !, given as alternatives by separating them with -o, or repeated (adding restrictions to the match; usually only for -name, -type, or -perm). Note that “modification” refers to editing of a file’s contents, whereas “change” means a modification, or permission or ownership changes. In other words, -ctime is more inclusive than -atime or -mtime.

Conditions and actions

-amin +n| -n| n

Find files last accessed more than n (+n), less than n (-n), or exactly n minutes ago.

-anewer file

Find files that were accessed after file was last modified. Affected by -H or -L when after them on the command line.

-atime +n| -n| n

Find files that were last accessed more than n (+n), less than n (-n), or exactly n days ago. Note that find changes the access time of directories supplied as pathnames.

-cmin +n| -n| n

Find files last changed more than n (+n), less than n (-n), or exactly n minutes ago.

-cnewer file

Find files that were changed after they were last modified. Affected by -H or -L when after them on the command line.

-ctime +n| -n| n

Find files that were changed more than n (+n), less than n (-n), or exactly n days ago. A change is anything that changes the directory entry for the file, such as a chmod.

-daystart

Calculate times from the start of the day today, not 24 hours ago. Only affects tests that come after it on the command line.

-delete

Delete files. Automatically turns on -depth.

-depth

Descend the directory tree, skipping directories and working on actual files first, and then the parent directories. Useful when files reside in unwritable directories (e.g., when using find with cpio).

-empty

Continue if file is empty. Applies to regular files and directories.

-exec command{ } \ ;

Run the Linux command, from the starting directory on each file matched by find (provided command executes successfully on that file--i.e., returns a 0 exit status). When command runs, the argument { } substitutes the current file. Follow the entire sequence with an escaped semicolon (\;). In some shells, the braces may need to be escaped as well.

-false

Return false for each file encountered.

-fstype type

Match files only on type filesystems. Acceptable types include minix, ext, ext2, xia, msdos, umsdos, vfat, proc, nfs, iso9660, hpfs, sysv, smb, and ncpfs.

-gid num

Find files with numeric group ID of num.

-group gname

Find files belonging to group gname. gname can be a group name or a group ID number.

-ilname pattern

A case-insensitive version of -lname.

-iname pattern

A case-insensitive version of -name.

-inum n

Find files whose inode number is n.

-ipath pattern

A case-insensitive version of -path.

-iregex pattern

A case-insensitive version of -regex.

-links n

Find files having n links.

-lname pattern

Search for files that are symbolic links, pointing to files named pattern. pattern can include shell metacharacters and does not treat / or . specially. The match is case-insensitive.

-maxdepth num

Do not descend more than num levels of directories.

-mindepth num

Begin applying tests and actions only at levels deeper than num levels.

-mmin +n| -n| n

Find files last modified more than n (+n), less than n (-n), or exactly n minutes ago.

-mount, -xdev

Search only for files that reside on the same filesystem as pathname. -xdev is for compatibility with other versions of find.

-mtime +n| -n| n

Find files that were last modified more than n (+n), less than n (-n), or exactly n days ago. A modification is a change to a file’s data.

-name pattern

Find files whose names match pattern. Filename metacharacters may be used but should be escaped or quoted.

-newer file

Find files that were modified more recently than file; similar to -mtime. With -H or -L, if file is a symbolic link, use the modification time of the file the link points to.

-nogroup

The file’s group ID does not correspond to any group.

-noleaf

Normally, find assumes that each directory has at least two hard links that should be ignored (a hard link for its name and one for “.” -- i.e., two fewer “real” directories than its hard link count indicates). -noleaf turns off this assumption, a useful practice when find runs on non-Unix-style filesystems. This forces find to examine all entries, assuming that some might prove to be directories into which it must descend (a time-waster on Unix).

-nouser

The file’s user ID does not correspond to any user.

-ok command { }\;

Same as -exec, but prompts user to respond with y or Y before command is executed.

-path pattern

Find files whose names match pattern. Expect full pathnames relative to the starting pathname (i.e., do not treat / or . specially).

-perm nnn

Find files whose permission flags (e.g., rwx) match octal number nnn exactly (e.g., 664 matches -rw-rw-r--). Use a minus sign before nnn to make a “wildcard” match of any unspecified octal digit (e.g., -perm −600 matches -rw-******, where * can be any mode).

-print

Print the matching files and directories, using their full pathnames. Return true. This is the default behavior.

-regex pattern

Like -path, but uses Emacs-style regular expressions instead of the shell-like globbing used in -name and -path.

-regextype pattern

Use an alternative regular expression syntax for -regex and -iregex. The possible types are Emacs (the default), posix-awk, posix-basic, posix-egrep, and posix-extended.

-size n[u]

Find files containing n blocks. If u, is specified, measure size in one of the following units: b (512-byte blocks), c (bytes), k (kilobytes), G (gigabytes), M (megabytes), or w (two-byte words).

-true

Return true for each file encountered.

-type c

Find files whose type is c. c can be b (block special file), c (character special file), d (directory), p (fifo or named pipe), l (symbolic link), s (socket), or f (plain file).

-user user

Find files belonging to user (name or numeric ID).

Examples

List all files (and subdirectories) in your home directory:

find $HOME -print

List all files named chapter1 in the /work directory:

find /work -name chapter1

List all files beginning with memo owned by ann:

find /work -name 'memo*' -user ann -print

Search the filesystem (begin at root) for manpage directories:

find / -type d -name 'man*' -print

Search the current directory, look for filenames that don’t begin with a capital letter, and send them to the printer:

find . \! -name '[A-Z]*' -exec lpr {  }\;

Find and compress files whose names don’t end with .gz:

gzip `find . \! -name '*.gz' -print`

Remove all empty files on the system (prompting first):

find / -size 0 -ok rm {  } \;

Search the system for files that were modified within the last two days (good candidates for backing up):

find / -mtime −2 -print

Recursively grep for a pattern down a directory tree:

find /book -print | xargs grep '[Nn]utshell'

If the files kt1 and kt2 exist in the current directory, their names can be printed with the command:

$ find . -name 'kt[0-9]'
./kt1
./kt2

Since the command prints these names with an initial ./ path, you need to specify the ./ when using the -path option:

$ find . -path './kt[0-9]'
./kt1
./kt2

The -regex option uses a complete pathname, like -path, but treats the following argument as a regular expression rather than a glob pattern (although in this case the result is the same):

$ find . -regex './kt[0-9]'
./kt1
./kt2

Name

flex

Synopsis

flex [options] [file]

flex (Fast Lexical Analyzer Generator) is a faster variant of lex. It generates a lexical analysis program (named lex.yy.c) based on the regular expressions and C statements contained in one or more input files. See also bison, yacc, and the O’Reilly book lex & yacc.

Options

-b

Generate backup information to lex.backup.

-d

Debug mode.

-f

Use a faster scanner. The result is larger but faster.

-h

Help summary.

-i

Scan case-insensitively.

-l

Maximum lex compatibility.

-o file

Write output to file instead of lex.yy.c.

-p

Print performance report.

-s

Exit if the scanner encounters input that does not match any of its rules.

-t

Print to standard output. (By default, flex prints to lex.yy.c.)

-v

Print a summary of statistics.

-w

Suppress warning messages.

-B

Generate batch (noninteractive) scanner.

-F

Use the fast scanner table representation. This option is usually as fast as -f and often generates smaller data (although for some data sets, it generates larger data).

-I

Generate an interactive scanner (default).

-L

Suppress #line directives in lex.yy.c.

-P prefix

Change default yy prefix to prefix for all globally visible variable and function names.

-V

Print version number.

−7

Generate a 7-bit scanner.

−8

Generate an 8-bit scanner (default).

-+

Generate a C++ scanner class.

-C

Compress scanner tables but do not use equivalence classes.

-Ca

Align tables for memory access and computation. This creates larger tables but gives faster performance.

-Ce

Construct equivalence classes. This creates smaller tables and sacrifices little performance (default).

-Cf

Generate full scanner tables, not compressed.

-CF

Generate faster scanner tables, like -F.

-Cm

Construct metaequivalence classes (default).

-Cr

Bypass use of the standard I/O library; use read( ) system calls instead.

Name

fmt

Synopsis

fmt [options] [files]

Convert text to specified width by filling lines and removing newlines. Concatenate files on the command line, or read text from standard input if - (or no file) is specified. By default, preserve blank lines, spacing, and indentation. fmt attempts to break lines at the end of sentences and to avoid breaking lines after a sentence’s first word or before its last.

Options

-c, --crown-margin

Crown margin mode. Do not change indentation of each paragraph’s first two lines. Use the second line’s indentation as the default for subsequent lines.

-p prefix, --prefix=prefix

Format only lines beginning with prefix.

-s, --split-only

Suppress line-joining.

-t, --tagged-paragraph

Tagged paragraph mode. Same as crown mode when the indentations of the first and second lines differ. If the indentation is the same, treat the first line as its own separate paragraph.

-u, --uniform-spacing

Reduce spacing to a maximum of one space between words and two between sentences.

-w width, --width=width

Set output width to width. The default is 75.

--help

Print help message and exit.

--version

Print version information and exit.

Name

fold

Synopsis

fold [option] [files]

Break the lines of the named files so that they are no wider than the specified width. fold breaks lines exactly at the specified width, even in the middle of a word. Reads from standard input when given - as a file. By default, fold cuts at 80 columns; tab counts as multiple columns, and a backspace as negative one.

Options

-b, --bytes

Count bytes instead of columns, making tab, backspace, and return characters count as one byte instead of altering the column count, as in the default behavior.

-c, --characters

Count characters, not columns. Similar to counting by bytes.

-s, --spaces

Break at spaces only, if possible.

-w, --width width, -width

Set the maximum line width to width. The flags -w 6, --width 6, and −6 all set the maximum width to six columns.

Name

formail

Synopsis

formail [options]

Filter standard input into mailbox format. Useful for splitting mail digests or passing the contents of a mail file to another program, such as a spam filter, for additional processing. If no sender is apparent, provide the sender foo@bar. By default, escape bogus From lines with >.

Options

+skip

Do not split first skip messages.

-total

Stop after splitting total messages.

-a headerfield

Append headerfield to header, unless it already exists. If header-field is Message-ID or Resent-Message-ID with no contents, generate a unique message ID.

-A headerfield

Append headerfield whether or not it already exists.

-b

Do not escape bogus From lines.

-B

Assume that input is in BABYL rmail format.

-c

When header fields are more than one line long, concatenate the lines.

-d

Do not assume that input must be in strict mailbox format. This option disables recognition of the Content-Length field so you can split digests or use nonstandard mailbox formats.

-D maxlen idcache

Remember old message IDs (in idcache, which will grow no larger than approximately maxlen). When splitting, refuse to output duplicate messages. Otherwise, return true on discovering a duplicate. With -r, look at the sender’s mail address instead of the message ID.

-e

Allow messages to begin one immediately after the other; do not require empty space between them.

-f

Do not edit non-mailbox-format lines. By default, formail prepends From to such lines.

-i headerfield

Like -A, but rename each existing headerfield to Old-headerfield, unless it is empty.

-I headerfield

Like -i, but also remove existing similar fields. If there is only a field name but no content, delete the field.

-k

For use only with -r. Keep the body as well as the fields specified by -r.

-l folder

Generate a log summary in procmail format. You can then use mailstat to summarize the logs.

-m minfields

Require formail to find at least minfields consecutive headers before recognizing the beginning of a new message. Default is 2.

-n [max]

Allow simultaneous formail processes to run. Specify max to set the number of simultaneous processes allowed.

-p prefix

Set off quoted lines with prefix instead of >.

-q

Do not display write errors, duplicate messages, or mismatched Content-Length fields. This is the default; use -q- to turn it off and display the messages.

-r

Throw away all existing fields, retaining only X-Loop, and generate autoreply header instead. You can preserve particular fields with the -i option.

-R oldfield newfield

Change all fields named oldfield to newfield.

-s [progname]

Must be the last option; everything following -s is assumed to be its arguments. Divide input to separate mail messages, and pipe them to the program specified or concatenate them to standard output (by default).

-t

Assume sender’s return address to be valid. (By default, formail favors machine-generated addresses.)

-u headerfield

Delete all but the first occurrence of headerfield.

-U headerfield

Delete all but the last occurrence of headerfield.

-x headerfield

Display the contents of headerfield; to always display on a single line, use with -c.

-X headerfield

Like -x, but also display the field name.

-Y

Format in traditional Berkeley style (i.e., ignore Content-Length fields).

-z

When necessary, add a space between field names and contents. Remove (“zap”) empty fields.

Name

free

Synopsis

free [options]

Display statistics about memory usage: total free, used, physical, swap, shared, and buffers used by the kernel.

Options

-b

Calculate memory in bytes.

-k

Default. Calculate memory in kilobytes.

-m

Calculate memory in megabytes.

-o

Do not display “buffer adjusted” line. The -o switch disables the display “-/+ buffers” line that shows buffer memory subtracted from the amount of memory used and added to the amount of free memory.

-s time

Check memory usage every time seconds.

-t

Display all totals on one line at the bottom of output.

-V

Display version information.

Name

fsck

Synopsis

fsck [options] [filesystem] ...

System administration command. Call the filesystem checker for the appropriate system type to check and repair unmounted filesystems. If a filesystem is consistent, the number of files, number of blocks used, and number of blocks free are reported. If a filesystem is inconsistent, fsck prompts before each correction is attempted. fsck’s exit code can be interpreted as the sum of all conditions that apply:

0

No errors found.

1

Errors were found and corrected.

2

Reboot suggested.

4

Errors were found but not corrected.

8

fsck encountered an operational error.

16

fsck was called incorrectly.

32

fsck canceled by user request.

128

A shared library error was detected.

Options

--

Pass all subsequent options to filesystem-specific checker. All options that fsck doesn’t recognize will also be passed.

-s

Serial mode. Check one filesystem at a time.

-t fstype

Specify the filesystem type. Do not check filesystems of any other type. Multiple filesystem types to check can be specified in a comma-separated list.

-A

Check all filesystems listed in /etc/fstab. The root filesystem is checked first.

-C [fd]

Display completion (progress) bar. Optionally specify a file-descriptor to receive the progress. (Useful for a GUI frontend.)

-M

Don’t check mounted filesystems. Returns a 0 exit code for mounted system.

-N

Suppress normal execution; just display what would be done.

-P

Meaningful only with -A: check root filesystem in parallel with other systems. This option is potentially dangerous.

-R

Meaningful only with -A: check all filesystems listed in /etc/fstab except the root filesystem.

-T

Suppress printing of title.

-V

Verbose mode.

Name

ftp

Synopsis

ftp [options] [hostname]

Transfer files to and from remote network site hostname. ftp prompts the user for a command. The commands are listed after the options. Some of the commands are toggles, meaning they turn on a feature when it is off and vice versa. Note that some versions may have different options.

Options

-d

Enable debugging.

-g

Disable filename globbing.

-i

Turn off interactive prompting.

-n

No autologin upon initial connection.

-v

Verbose. Show all responses from remote server.

Commands

![command [args]]

Invoke an interactive shell on the local machine. If arguments are given, the first is taken as a command to execute directly, with the rest of the arguments as that command’s arguments.

$macro-name [args]

Execute the macro macro-name that was defined with the macdef command. Arguments are passed to the macro unglobbed.

account [passwd]

Supply a supplemental password that will be required by a remote system for access to resources once a login has been successfully completed. If no argument is given, prompt the user for an account password in a nonechoing mode.

append local-file [remote-file]

Append a local file to a file on the remote machine. If remote-file is not given, the local filename is used after being altered by any ntrans or nmap setting. File transfer uses the current settings for type, format, mode, and structure.

ascii

Set the file transfer type to network ASCII (default).

bell

Sound a bell after each file transfer command is completed.

binary, image

Set file transfer type to support binary image transfer.

bye, quit

Terminate FTP session and then exit ftp.

case

Toggle remote-computer filename case mapping during mget. The default is off. When case is on, files on the remote machine with all-uppercase names are copied to the local machine with all-lowercase names.

cd remote-directory

Change working directory on remote machine to remote-directory.

cdup

Change working directory on remote machine to its parent directory.

chmod [mode] [remote-file]

Change file permissions of remote-file. If options are omitted, the command prompts for them.

close, disconnect

Terminate FTP session and return to command interpreter.

cr

Toggle carriage-return stripping during ASCII-type file retrieval.

delete remote-file

Delete file remote-file on remote machine.

debug [debug-value]

Toggle debugging mode. If debug-value is specified, it is used to set the debugging level.

dir [remote-directory] [local-file]

Print a listing of the contents in the directory remote-directory and, optionally, place the output in local-file. If no directory is specified, the current working directory on the remote machine is used. If no local file is specified or - is given instead of the filename, output comes to the terminal.

form format

Set the file transfer form to format. Default format is file.

get remote-file [local-file], recv remote-file [local-file]

Retrieve remote-file and store it on the local machine. If local-file is not specified, the file is given the same name as on the remote machine, subject to alteration by the current case, ntrans, and nmap settings. If local-file is -, the output comes to the terminal.

glob

Toggle filename expansion for mdelete, mget, and mput. If globbing is turned off, the filename arguments are taken literally and not expanded.

hash

Toggle hash sign (#) printing for each data block transferred.

help [command], ? [command]

Print help information for command. With no argument, ftp prints a list of commands.

idle [seconds]

Get/set idle timer on remote machine. seconds specifies the length of the idle timer; if omitted, the current idle timer is displayed.

lcd [directory]

Change working directory on local machine. If directory is not specified, the user’s home directory is used.

ls [remote-directory] [local-file]

Print listing of contents of directory on remote machine, in a format chosen by the remote machine. If remote-directory is not specified, current working directory is used.

macdef macro-name

Define a macro. Subsequent lines are stored as the macro macro-name; a null line terminates macro input mode. When $i is included in the macro, loop through arguments, substituting the current argument for $i on each pass. Escape $ with \.

mdelete [remote-files]

Delete the remote-files on the remote machine.

mdir remote-files local-file

Like dir, except multiple remote files may be specified.

mget remote-files

Expand the wildcard expression remote-files on the remote machine and do a get for each filename thus produced.

mkdir directory-name

Make a directory on the remote machine.

mls remote-files local-file

Like nlist, except multiple remote files may be specified, and the local file must be specified.

mode [mode-name]

Set file transfer mode to mode-name. Default mode is stream.

modtime file-name

Show last modification time of the file on the remote machine.

mput local-files

Expand wildcards in local-files given as arguments and do a put for each file in the resulting list.

newer remote-file [local-file]

Get the remote file if it is newer than the local file.

nlist [remote-directory] [local-file]

Print list of files in a directory on the remote machine to local-file (or to the screen if local-file is not specified). If remote-directory is unspecified, the current working directory is used.

nmap [inpattern outpattern]

Set or unset the filename mapping mechanism. The mapping follows the pattern set by inpattern, a template for incoming filenames, and outpattern, which determines the resulting mapped filename. The sequences $1 through $9 are treated as variables; for example, the inpattern $1.$2, along with the input file readme.txt, would set $1 to readme and $2 to txt. An outpattern of $1.data would result in an output file of readme.data. $0 corresponds to the complete filename. [string1, string2] is replaced by string1 unless that string is null, in which case it’s replaced by string2.

ntrans [inchars [outchars ]]

Set or unset filename character translation. Characters in a filename matching a character in inchars are replaced with the corresponding character in outchars. If no arguments are specified, the filename mapping mechanism is unset. If arguments are specified:

- Characters in remote filenames are translated during mput and put commands issued without a specified remote target filename.

- Characters in local filenames are translated during mget and get commands issued without a specified local target filename.

open host [port]

Establish a connection to the specified host FTP server. An optional port number may be supplied, in which case ftp attempts to contact an FTP server at that port.

prompt

Toggle interactive prompting.

proxy ftp-command

Execute an FTP command on a secondary control connection (i.e., send commands to two separate remote hosts simultaneously to allow the transfer of files between the two servers).

put local-file [remote-file], send local-file [remote-file]

Store a local file on the remote machine. If remote-file is not specified, the local filename is used after processing according to any ntrans or nmap settings in naming the remote file. File transfer uses the current settings for type, file, structure, and transfer mode.

pwd

Print name of the current working directory on the remote machine.

quote arg1 arg2...

Send the arguments specified, verbatim, to the remote FTP server.

reget remote-file [local-file]

Retrieve a file (like get), but restart at the end of local-file. Useful for restarting a dropped transfer.

remotehelp [command-name]

Request help from the remote FTP server. If command-name is specified, remote help for that command is returned.

remotestatus [filename]

Show status of the remote machine or, if filename is specified, of filename on remote machine.

rename [from] [to]

Rename file from on remote machine to to.

reset

Clear reply queue.

restart marker

Restart the transfer of a file from a particular byte count.

rmdir directory-name

Delete a directory on the remote machine.

runique

Toggle storing of files on the local system with unique filenames. When this option is on, rename files as .1 or .2, and so on, as appropriate, to preserve unique filenames, and report each such action. Default value is off.

sendport

Toggle the use of PORT commands.

site [command]

Run a site-specific command on the remote machine.

size filename

Return size of filename on remote machine.

status

Show current status of ftp.

struct [struct-name]

Set the file transfer structure to struct-name. By default, stream structure is used.

sunique

Toggle storing of files on remote machine under unique filenames.

system

Show type of operating system running on remote machine.

tenex

Set file transfer type to that needed to talk to TENEX machines.

trace

Toggle packet tracing.

type [type-name]

Set file transfer type to type-name. If no type is specified, the current type is printed. The default type is network ASCII.

umask [mask]

Set user file-creation mode mask on the remote site. If mask is omitted, the current value of the mask is printed.

user username [password] [account]

Identify yourself to the remote FTP server. ftp prompts the user for the password (if not specified and the server requires it) and the account field.

verbose

Toggle verbose mode.

Name

ftpd

Synopsis

in.ftpd [options]

TCP/IP command. Internet File Transfer Protocol server. The server uses the TCP protocol and listens at the port specified in the ftp service specification. ftpd is usually started by xinetd and must have an entry in xinetd’s configuration file, /etc/xinetd.conf. It can also be run in standalone mode using the -p option. There are several FTP daemons available. On many Linux distributions, the default is the Kerberos-supporting DARPA version, which we document here.

Options

-a

Require authentication via ftp AUTH. Allow anonymous users as well, if configured to do so.

-A

Require authentication via ftp AUTH, but allow only users who are authorized to connect without a password. Allow anonymous users as well, if configured to do so.

-C

Require local credentials for nonanonymous users. Prompt for a password unless the user forwards credentials during authentication.

-d, -v

Write debugging information to syslogd.

-l

Log each FTP session in syslogd.

-p port

Use port as the FTP control port instead of reading the appropriate port from /etc/services. This option will launch ftpd in standalone mode.

-q

Use PID files to record the process IDs of running daemons. This is the default. These files are needed to determine the current number of users.

-r file

Read Kerberos configuration from file instead of /etc/krb5.conf.

-s file

Read Kerberos V4 authentication information from file instead of /etc/srvtab.

-t n

Set default inactivity timeout period to n seconds. (The default is 15 minutes.)

-T n

Allow ftp clients to request a different timeout period of up to n seconds. (The default is 2 hours.)

-u umask

Set the default umask to umask.

-U file

Read the list of users denied remote access from file instead of /etc/ftpusers.

-w format

Specify the format for the remote hostname passed to login. Use one of the following formats:

ip

Pass the IP address.

n[,[no]striplocal]

Pass hostnames less than n characters in length, and IP addresses for longer hostsnames. Set n to 0 to use the system default. The striplocal portion of the option determines whether or not to strip local domains from hostnames. The default is to strip them.

Name

fuser

Synopsis

fuser [options] [files | filesystems]

Identifies and outputs the process IDs of processes that are using the files or local filesystems. Each process ID is followed by a letter code: c if process is using file as the current directory; e if executable; f if an open file; F if open file for writing; m if a shared library; and r if the root directory. Any user with permission to read /dev/kmem and /dev/mem can use fuser, but only a privileged user can terminate another user’s process. fuser does not work on remote (NFS) files.

If more than one group of files is specified, the options may be respecified for each additional group of files. A lone dash (-) cancels the options currently in force, and the new set of options applies to the next group of files. Like a number of other administrator commands, fuser is usually installed to the /sbin directory. You may need to add that directory to your path or execute the command as /sbin/fuser.

Options

-

Return all options to defaults.

-signal

Send signal instead of SIGKILL.

-a

Display information on all specified files, even if they are not being accessed by any processes.

-i

Request user confirmation to kill a process. Ignored if -k is not also specified.

-k

Send SIGKILL signal to each process.

-l

List signal names.

-m

Expect files to exist on a mounted filesystem; include all files accessing that filesystem.

-n space

Set the namespace checked for usage. Acceptable values are file for files, udp for local UPD ports, and tcp for local TCP ports.

-s

Silent.

-u

User login name, in parentheses, also follows process ID.

-v

Verbose.

-V

Display version information.

Name

g++

Synopsis

g++
[options] files

Invoke gcc with the options necessary to make it recognize C++. g++ recognizes all the file extensions gcc does, in addition to C++ source files (.C, .cc, or .cxx files) and C++ preprocessed files (.ii files). See also gcc.

Name

gawk

Synopsis

gawk [options] 'script' [var=value...] [files]
gawk [options] -f scriptfile [var=value...] [files]

The GNU version of awk, a program that does pattern matching, record processing, and other forms of text manipulation. For more information, see Chapter 11.

Name

gcc

Synopsis

gcc [options] files

GNU Compiler Collection. gcc, formerly known as the GNU C Compiler, compiles multiple languages (C, C++, Objective-C, Ada, FORTRAN, and Java) to machine code. Here we document its use to compile C, C++, or Objective-C code. gcc compiles one or more programming source files; for example, C source files (file.c), assembler source files (file.s), or preprocessed C source files (file.i). If the file suffix is not recognizable, assume that the file is an object file or library. gcc normally invokes the C preprocessor, compiles the process code to assemble language code, assembles it, and then links it with the link editor. This process can be stopped at one of these stages using the -c, -S, or -E option. The steps may also differ depending on the language being compiled. By default, output is placed in a.out. In some cases, gcc generates an object file having a .o suffix and a corresponding root name.

Preprocessor and linker options given on the gcc command line are passed on to these tools when they are run. These options are briefly described here, but some are more fully described under entries for cpp, as, and ld. The options that follow are divided into general, preprocessor, linker, and warning options. gcc accepts many system-specific options not covered here.

Tip

gcc is the GNU form of cc; on most Linux systems, the command cc will invoke gcc. The command g++ will invoke gcc with the appropriate options for interpreting C++.

General options

-a

Provide profile information for basic blocks.

-aux-info file

Print prototyped declarations and information on their origins to file.

-ansi

Enforce full ANSI conformance.

-b machine

Compile for use on machine type.

-c

Create linkable object file for each source file, but do not call linker.

-dumpmachine

Print compiler’s default target machine, then exit.

-dumpspecs

Print built-in specification strings, then exit.

-dumpversion

Print version number, then exit.

-foption

Set the specified compiler option. Many of these control debugging, optimization of code, and special language options. Use the --help -v options for a full listing.

-g

Include debugging information for use with gdb.

-glevel

Provide the given level of debugging information. level must be 1, 2, or 3, with 1 providing the least amount of information. The default is 2.

--help

Print most common basic options, then exit. When used with option -v, print options for all of gcc’s subprocesses. For options specific to a target, use --target-help.

-moption

Set the specified machine specific option. Use the --target-help option for a full listing.

-o file

Specify output file as file. Default is a.out.

-p

Provide profile information for use with prof.

-pass-exit-codes

On error, return highest error code as the exit code, instead of 1.

-pedantic

Warn verbosely.

-pedantic-errors

Generate an error in every case in which -pedantic would have produced a warning.

-pg

Provide profile information for use with gprof.

-print-file-name=file

Print the full path to the library specified by filename file, then exit. This is the library gcc would use for linking.

-print-search-dirs

Print installation directory and the default list of directories gcc will search to find programs and libraries, then exit.

-pipe

Transfer information between stages of compiler by pipes instead of temporary files.

-save-temps

Save temporary files in the current directory when compiling.

-std=standard

Specify C standard of input file. Accepted values are:

iso9899:1990, c89

1990 ISO C standard (C89).

iso9899:199409

1994 amendment to the 1990 ISO C standard.

iso9899:1999, c99, iso9899:199x, c9x

1999 revised ISO C standard (C99).

gnu89

1990 C Standard with GNU extensions (the default value).

gnu99, gnu9x

1999 revised ISO C standard with GNU extensions.

c++98

1998 ISO C++ standard plus amendments.

gnu++98

1998 ISO C++ standard plus amendments and GNU extensions.

-time

Print statistics on the execution of each subprocess.

-v

Verbose mode. Print subprocess commands to standard error as they are executed. Include gcc version number and preprocessor version number. To generate the same output without executing commands, use the option -###.

-w

Suppress warnings.

-x language

Expect input file to be written in language, which may be c, objective-c, c-header, c++, ada, f77, ratfor, assembler, java, cpp-output, c++-cpp-output, objc-cpp-output, f77-cpp-output, assembler-with-cpp, or ada. If none is specified as language, guess the language by filename extension.

-Bpath

Specify the path directory in which the compiler files are located.

-E

Preprocess the source files, but do not compile. Print result to standard output. This option is useful to meaningfully pass some cpp options that would otherwise break gcc, such as -C, -M, or -P.

-Idir

Include dir in list of directories to search for include files. If dir is -, search those directories specified by -I before the -I- only when #include "file" is specified, not #include <file>.

-Ldir

Search dir in addition to standard directories.

-O[level]

Optimize. level should be 1, 2, 3, or 0 (the default is 1). 0 turns off optimization; 3 optimizes the most.

-S

Compile source files into assembler code, but do not assemble.

-V version

Attempt to run gcc version version.

-Wa,options

Pass options to the assembler. Multiple options are separated by commas.

-Wl,options

Pass options to the linker. Multiple options are separated by commas.

-Wp,options

Pass options to the preprocessor. Multiple options are separated by commas.

-Xlinker options

Pass options to the linker. A linker option with an argument requires two -Xlinkers, the first specifying the option and the second specifying the argument. Similar to -Wl.

Preprocessor options

gcc will pass the following options to the preprocessor:

-$

Do not allow $ in identifiers.

-dD, -dI, -dM, -dN

Suppress normal output; print preprocessor instructions instead. See cpp for details.

-idirafter dir

Search dir for header files when a header file is not found in any of the included directories.

-imacros file

Process macros in file before processing main files.

-include file

Process file before main file.

-iprefix prefix

When adding directories with -iwithprefix, prepend prefix to the directory’s name.

-isystem dir

Search dir for header files after searching directories specified with -I but before searching standard system directories.

-iwithprefix dir

Append dir to the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory’s name.

-iwithprefixbefore dir

Insert dir at the beginning of the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory’s name.

-nostdinc

Search only specified, not standard, directories for header files.

-nostdinc++

Suppress searching of directories believed to contain C++-specific header files.

-trigraphs

Convert special three-letter sequences, meant to represent missing characters on some terminals, into the single character they represent.

-undef

Suppress definition of all nonstandard macros.

-A name[=def]

Assert name with value def as if defined by #assert. To turn off standard assertions, use -A-.

-A -name[=def]

Cancel assertion name with value def.

-C

Retain all comments except those found on cpp directive lines. By default, the preprocessor strips C-style comments.

-Dname[=def]

Define name with value def as if by #define. If no =def is given, name is defined with value 1. -D has lower precedence than -U.

-H

Print pathnames of included files, one per line, on standard error.

-M, -MG, -MF, -MD, -MMD, -MQ, -MT

Suppress normal output and print Makefile rules describing file dependencies. Print a rule for make that describes the main source file’s dependencies. If -MG is specified, assume that missing header files are actually generated files, and look for them in the source file’s directory. Most of these options imply -E. See cpp for further details.

-Uname

Remove definition of symbol name.

Linker options

gcc will pass the following options to the linker:

-llib

Link to lib.

-nostartfiles

Force linker to ignore standard system startup files.

-nostdlib

Suppress linking to standard library files.

-s

Remove all symbol table and relocation information from the executable.

-shared

Create a shareable object.

-shared-libgcc

Link to a shared version of libgcc if available.

-static

Suppress linking to shared libraries.

-static-libgcc

Link to a static version of libgcc if available.

-u symbol

Force the linker to search libraries for a definition of symbol and to link to the libraries found.

Warning options

-pedantic

Warn verbosely.

-pedantic-errors

Produce a fatal error in every case in which -pedantic would have produced a warning.

-w

Don’t print warnings.

-W

Warn more verbosely than normal.

-Waggregate-return

Warn if any functions that return structures or unions are defined or called.

-Wall

Enable -W, -Wchar-subscripts, -Wcomment, -Wformat, -Wimplicit, -Wmain, -Wmissing-braces, -Wparentheses, -Wreturn-type, -Wsequence-point, -Wswitch, -Wtemplate-debugging, -Wtrigraphs, -Wuninitialized, -Wunknown-pragmas, -Wstrict-aliasing, and -Wunused.

-Wcast-align

Warn when encountering instances in which pointers are cast to types that increase the required alignment of the target from its original definition.

-Wcast-qual

Warn when encountering instances in which pointers are cast to types that lack the type qualifier with which the pointer was originally defined.

-Wchar-subscripts

Warn when encountering arrays with subscripts of type char.

-Wcomment

Warn when encountering the beginning of a nested comment.

-Wconversion

Warn in particular cases of type conversions.

-Werror

Exit at the first error.

-Wformat

Warn about inappropriately formatted printfs and scanfs.

-Wimplicit

Warn when encountering implicit function or parameter declarations.

-Winline

Warn about illegal inline functions.

-Wmain

Warn about malformed main functions.

-Wmissing-braces

Enable more verbose warnings about omitted braces.

-Wmissing-declarations

Warn if a global function is defined without a previous declaration.

-Wmissing-prototypes

Warn when encountering global function definitions without previous prototype declarations.

-Wnested-externs

Warn if an extern declaration is encountered within a function.

-Wno-import

Don’t warn about use of #import.

-Wparentheses

Enable more verbose warnings about omitted parentheses.

-Wpointer-arith

Warn when encountering code that attempts to determine the size of a function or void.

-Wredundant-decls

Warn if anything is declared more than once in the same scope.

-Wreturn-type

Warn about violations of sequence point rules defined in the C standard.

-Wreturn-type

Warn about functions defined without return types or with improper return types.

-Wshadow

Warn when a local variable shadows another local variable.

-Wstrict-prototypes

Insist that argument types be specified in function declarations and definitions.

-Wswitch

Warn about switches that skip the index for one of their enumerated types.

-Wtraditional

Warn when encountering code that produces different results in ANSI C and traditional C.

-Wtrigraphs

Warn when encountering trigraphs.

-Wuninitialized

Warn when encountering uninitialized automatic variables.

-Wundef

Warn when encountering a nonmacro identifier in an #if directive.

-Wunknown-pragmas

Warn when encountering a #pragma directive not understood by gcc.

-Wunused

Warn about unused variables, functions, labels, and parameters.

Pragma directives

#pragma interface [header-file]

Used in header files to force object files to provide definition information via references instead of including it locally in each file. C++-specific.

#pragma implementation [header-file]

Used in main input files to force generation of full output from header-file (or, if it is not specified, from the header file with the same basename as the file containing the pragma directive). This information will be globally visible. Normally the specified header file contains a #pragma interface directive.

Name

gdb

Synopsis

gdb [options] [program [core|pid]]

GDB (GNU DeBugger) allows you to step through the execution of a program in order to find the point at which it breaks. It fully supports C and C++, and provides partial support for FORTRAN, Java, Chill, assembly, and Modula-2. The program to be debugged is normally specified on the command line; you can also specify a core or, if you want to investigate a running program, a process ID.

Options

-b bps

Set line speed of serial device used by GDB to bps.

-batch

Exit after executing all the commands specified in .gdbinit and -x files. Print no startup messages.

-c file, -core=file

Consult file for information provided by a core dump.

-cd=directory

Use directory as gdb’s working directory.

-d directory, -directory=directory

Include directory in path that is searched for source files.

-e file, -exec=file

Use file as an executable to be read in conjunction with source code. May be used in conjunction with -s to read the symbol table from the executable.

-f, -fullname

Show full filename and line number for each stack frame.

-h, -help

Print help message, then exit.

-n, -nx

Ignore .gdbinit file.

-q, -quiet

Suppress introductory and copyright messages.

-s file, -symbols=file

Consult file for symbol table. With -e, also uses file as the executable.

-tty=device

Set standard in and standard out to device.

-write

Allow gdb to write into executables and core files.

-x file, -command=file

Read gdb commands from file.

Common commands

These are just some of the more common gdb commands; there are too many to list them all.

bt

Print the current location within the program and a stack trace showing how the current location was reached. (where does the same thing.)

break

Set a breakpoint in the program.

cd

Change the current working directory.

clear

Delete the breakpoint where you just stopped.

commands

List commands to be executed when a breakpoint is hit.

c

Continue execution from a breakpoint.

delete

Delete a breakpoint or a watchpoint; also used in conjunction with other commands.

display

Cause variables or expressions to be displayed when program stops.

down

Move down one stack frame to make another function the current one.

frame

Select a frame for the next continue command.

info

Show a variety of information about the program. For instance, info breakpoints shows all outstanding breakpoints and watchpoints.

jump

Start execution at another point in the source file.

kill

Abort the process running under gdb’s control.

list

List the contents of the source file corresponding to the program being executed.

next

Execute the next source line, executing a function in its entirety.

print

Print the value of a variable or expression.

ptype

Show the contents of a datatype, such as a structure or C++ class.

pwd

Show the current working directory.

quit

Exit gdb.

reverse-search

Search backward for a regular expression in the source file.

run

Execute the program.

search

Search for a regular expression in the source file.

set variable

Assign a value to a variable.

signal

Send a signal to the running process.

step

Execute the next source line, stepping into a function if necessary.

undisplay

Reverse the effect of the display command; keep expressions from being displayed.

until

Finish the current loop.

up

Move up one stack frame to make another function the current one.

watch

Set a watchpoint (i.e., a data breakpoint) in the program.

whatis

Print the type of a variable or function.

Name

genisoimage

Synopsis

genisoimage [options] [-o filename] pathspec...

Generate an ISO9660/Joliet/HFS hybrid filesystem for writing a CD with a program such as wodim. (HFS is the native Macintosh Hierarchical File System.) genisoimage takes a snapshot of a directory tree and generates a binary image that corresponds to an ISO9660 or HFS filesystem when it is written to a block device. Each specified pathspec describes the path of a directory tree to be copied into the ISO9660 filesystem; if multiple paths are specified, the files in all the paths are merged to form the image.

Options

-abstract file

Specify the abstract filename. Overrides an ABST=file entry in .genisoimagerc.

-allow-leading-dots, -idots

Allow ISO9660 filenames to start with a period instead of replacing it with an underscore. Violates the ISO9660 standard.

-allow-lowercase

Allow ISO9660 filenames to be lowercase. Violates the ISO9660 standard.

-allow-multidot

Allow more than one dot in ISO9660 filenames. Violates the ISO9660 standard.

-A id, -appid id

Specify a text string id that describes the application to be written into the volume header.

-b image

Specify the path and filename of the boot image to be used for making a bootable CD based on the El Torito specification.

-biblio file

Specify bibliographic filename. Overrides a BIBL=file entry in .genisoimagerc.

-boot-info-table

Specify that a 56-byte table with information on the CD layout is to be patched in at offset 8 of the boot file. If specified, the table is patched into the source boot file, so make a copy if the file isn’t recreatable.

-boot-load-seg addr

Specify the load segment address of the boot image for a no-emulation El Torito CD.

-boot-load-size size

Specify the number of virtual 512-byte sectors to load in no-emulation mode. The default is to load the entire boot file. The number may need to be a multiple of 4 to prevent problems with some BIOSes.

-c catalog

Specify the path, relative to the source pathspec, and the filename of the boot catalog for an El Torito bootable CD. Required for making an El Torito bootable CD.

-C last-start,next-start

Required for creating a CDExtra or a second or higher-level session for a multisession CD. last-start is the first sector number in the last session on the disk, and next-start is the first sector number for the new session. Use the command:

wodim -msinfo

to get the values. Use -C with -M to create an image that is a continuation of the previous session; without -M, create an image for a second session on a CDExtra (a multisession CD with audio data in the first session and an ISO9660 filesystem image in the second).

-[no-]cache-inodes

Cache [do not cache] inode and device numbers to find hard links to files. The default on Linux is to cache. Use -no-cache-inodes for filesystems that do not have unique inode numbers.

-check-oldnames

Check all filenames imported from old sessions for genisoimage compliance with ISO9660 file-naming rules. If not specified, check only those files with names longer than 31 characters.

-check-session file

Check all old sessions for genisoimage compliance with ISO9660 file-naming rules. This option is the equivalent of:

-M file -C 0,0 -check-oldnames

where file is the pathname or SCSI device specifier that would be specified with -M.

-copyright file

Specify the name of the file that contains the copyright information. Overrides a COPY=file entry in .genisoimagerc.

-d

Omit trailing period from files that do not have one. Violates the ISO9660 standard, but works on many systems.

-D

Do not use deep directory relocation. Violates the ISO9660 standard, but works on many systems.

-dir-mode mode

Specify the mode for directories used to create the image. Automatically enables the Rock Ridge extensions.

-eltorito-alt-boot

Start with a new set of El Torito boot parameters. Allows putting more than one El Torito boot image on a CD (maximum is 63).

-exclude-list file

Check filenames against the globs contained in the specified file and exclude any that match.

-f

Follow symbolic links when generating the filesystem.

-file-mode mode

Specify the mode for files used to create the image. Automatically enables the Rock Ridge extensions.

-force-rr

Do not use automatic Rock Ridge detection for the previous session.

-G image

Specify the path and filename of the generic boot image for making a generic bootable CD.

-gid gid

Set the group ID to gid for the source files. Automatically enables the Rock Ridge extensions.

-graft-points

Allow the use of graft points for filenames, which permits paths to be grafted at locations other than the root directory. -graft-points checks all filenames for graft points and divides the filename at the first unescaped equals sign (=).

-gui

Switch the behavior for a GUI. Currently, the only effect is to make the output more verbose.

-hard-disk-boot

Specify that the boot image to be used to create an El Torito bootable CD is a hard disk image that must begin with a master boot record containing a single partition.

-hidden glob

Set the hidden (existence) ISO9660 directory attribute for paths or filenames matching the shell-style pattern glob. To match a directory, the path must not end with a trailing /. May be specified more than once.

-hidden-list file

Specify a file containing a list of globs that are to be hidden with -hidden.

-hide glob

Find paths or files that match the shell-style pattern glob and hide them from being seen on the ISO9660 or Rock Ridge directory. The files are still included in the image file. If the pattern matches a directory, the contents of the directory are hidden. To match a directory, the path must not end with a trailing /. See also the -hide-joliet option and the file README.hide. May be specified more than once.

-hide-joliet glob

Hide paths or files that match the shell-style pattern glob so they will not be seen in the Joliet directory. If the pattern matches a directory, the contents of the directory are hidden. To match a directory, the path must not end with a trailing /. Usually used with -hide. See also the README.hide file. May be specified more than once.

-hide-joliet-list file

Specify a file containing a list of globs to be hidden with -hide-joliet.

-hide-joliet-trans-tbl

Hide the TRANS.TBL files from the Joliet tree.

-hide-list file

Specify a file containing a list of globs to be hidden with -hide.

-hide-rr-moved

Rename the directory RR_MOVED to .rr_moved to hide it as much as possible from the Rock Ridge directory tree. Use the -D option to omit the file entirely.

-input-charset charset

Specify the character set for characters used in local filenames. Specify help in place of a charset for a list of valid character sets.

-iso-level level

Set the ISO9660 conformance level. Possible values are:

1

Filenames are restricted to 8.3 characters, and files may have only one section.

2

Files may have only one section.

3

No restrictions.

4

genisoimage maps level 4 to ISO-9660:1999 (ISO9660 version 2).

-J

Generate Joliet directory records in addition to regular ISO9660 filenames.

-jcharset charset

The equivalent of -input-charset -J.

-l

Allow full 31-character filenames instead of restricting them to the MS-DOS-compatible 8.3 format.

-log-file file

Send all messages to the specified logfile.

-m glob

Exclude files matching the shell-style pattern glob. May be specified multiple times.

-M path, -dev device

Specify the path to an existing ISO9660 image to be merged. path (or the device given with -dev) can also be a SCSI device specified in the same syntax as wodim’s dev= parameter. May be used only with -C.

-max-iso9660-filenames

Allow up to 37 characters in ISO9660 filenames. Forces -N. Violates the ISO9660 standard.

-N

Omit version numbers from ISO9660 filenames. Violates the ISO9660 standard. Use with caution.

-new-dir-mode mode

Specify the four-digit chmod-style mode to use for new directories in the image. The default is 0555.

-nobak, -no-bak

Do not include backup files on the ISO9660 filesystem.

-no-boot

Mark the El Torito CD to be created as not bootable.

-no-emul-boot

Specify that the boot image for creating an El Torito bootable CD is a no-emulation image.

-no-iso-translate

Do not translate the # and ˜ characters. Violates the ISO9660 standard.

-no-rr

Do not use Rock Ridge attributes from previous sessions.

-o file

Specify the filename of the output ISO9660 filesystem image.

-output-charset charset

Specify the output character set for Rock Ridge filenames. The default is the input character set.

-p prepid

Specify a text string of up to 128 characters describing the preparer of the CD. Overrides a PREP= parameter set in the file .genisoimagerc.

-publisher pubid

Specify a text string of up to 128 characters describing the publisher of the CD to be written to the volume header. Overrides a PUBL= parameter set in .genisoimagerc.

-[no -]pad

Pad [do not pad] the ISO9660 filesystem by 150 sectors (300 KB). If used with -B, force the first boot partition to start on a sector number that is a multiple of 16. The default is -pad.

-path-list file

Specify a file that contains a list of pathspec directories and filenames to add to the ISO9660 filesystem. Note that at least one pathspec must be given on the command line. If file is -, read from standard input.

-print-size

Print estimated filesystem size and exit.

-quiet

Run in quiet mode; do not display progress output.

-r

Like -R, but set UID and GID to zero, set all file read bits to write, and turn off all file write bits. If any execute bit is set for a file, set all execute bits; if any search bit is set for a directory, set all search bits; if any special mode bits are set, clear them.

-R

Generate SUSP (System Use Sharing Protocol) and Rock Ridge records using the Rock Ridge protocol.

-relaxed-filenames

Allow ISO9660 filenames to include seven-digit ASCII characters except lowercase characters. Violates the ISO9660 standard.

-sort file

Sort file locations according to the rules in the specified file, which contains pairs of filenames and weights, with one space or tab between them. A higher weight puts the file closer to the beginning of the media.

-sysid id

Specify the system ID of up to 32 characters. Overrides a SYSI= parameter set in the file .genisoimagerc.

-T

Generate the file TRANS.TBL in each directory for establishing the correct filenames on non-Rock Ridge-capable systems.

-table-name table

Use table as the translation table name instead of TRANS.TBL. Implies -T. For a multisession image, the table name must be the same as the previous session.

-U

Allow untranslated filenames. Violates the ISO9660 standard. Forces the following options: -d, -l, -N, -allow-leading-dots, -relaxed-filenames, -allow-lowercase, -allow-multidot, -no-iso-translate. Use with extreme caution.

-ucs-level num

Set the Unicode conformance level to the specified number, which can be between 1 and 3 (default is 3).

-use-fileversion

Use file version numbers from the filesystem. The version number is a string from 1 to 32767. The default is to set a version of 1.

-v

Run in verbose mode. Specify twice to run even more verbosely.

-V volid

Specify the volume ID (volume name or label) of up to 32 characters to be written to the master block. Overrides a VOLI= parameter specified in the file .genisoimagerc.

-volset id

Specify the volume set ID of up to 128 characters. Overrides a VOLS= parameter specified in .genisoimagerc.

-volset-seqno num

Set the volume set sequence number to num. Must be specified after -volset-size.

-volset-size num

Set the volume set size (the number of CDs in a set) to num. Must be specified before -volset-seqno.

HFS options

-apple

Create an ISO9660 CD with Apple’s extensions.

-auto file

Set file as the Autostart file to make the HFS CD use the QuickTime 2.0 Autostart feature. file must be the name of an application or document at the top level of the CD and must be less than 12 characters long.

-boot-hfs-file file

Install file as the driver file that may make the CD bootable on a Macintosh.

-cluster-size size

Specify the size in bytes of a cluster or allocation units of PC Exchange files. Implies --exchange (see --format in getent).

-hfs

Create a hybrid ISO9660/HFS CD. Use with -map, -magic, and/or the various --HFS options (see manpage).

-hfs-bless folder

“Bless” the specified directory (folder), given as the full pathname as genisoimage sees it. This is usually the System Folder and is used in creating HFS bootable CDs. The pathname must be in quotes if it contains spaces.

-hfs-creator creator

Set the four-character default creator for all files.

-hfs-type type

Set the four-character default type for all files.

-hfs-unlock

Leave the HFS volume unlocked so other applications can modify it. The default is to lock the volume.

-hfs-volid id

Specify the volume name for the HFS partition. This name is assigned to the CD on a Macintosh and replaces the ID set with the -V option.

-hide-hfs glob

Hide files or directories matching the shell-style pattern glob from the HFS volume, although they still exist in the ISO9660 and/or Joliet directory. May be specified multiple times.

-hide-hfs-list file

The specified file contains a list of globs to be hidden.

-input-hfs-charset charset

Specify the input character set used for HFS filenames when used with the -mac-name option. The default is cp10000 (Mac Roman).

-mac-name

Use the HFS filename as the starting point for the ISO9660, Joliet, and Rock Ridge filenames.

-magic file

Use the specified magic file to set a file’s creator and type information based on the file’s magic number, which is usually the first few bytes of the file. The magic file contains entries consisting of four tab-separated columns specifying the byte offset, type, test, and a message.

-map file

Use the specified mapping file to set a file’s creator and type information based on the filename extension. Only files that are not known Apple or Unix file types need to be mapped. The mapping file consists of five-column entries specifying the extension, file translation, creator, type, and a comment. Creator and type are both four-letter strings.

-no-desktop

Do not create empty Desktop files. The default is to create such files.

-output-hfs-charset charset

Specify the output character set used for HFS filenames. Defaults to the input character set.

-part

Generate an HFS partition table. The default is not to generate the table.

-probe

Search the contents of files for known Apple or Unix file types.

--format

Look for Macintosh files of the specified file format type. The valid formats are cap (Apple/Unix File System (AUFS) CAP files), netatalk, double, ethershare, ushare, exchange, sgi, xinet, macbin, single, dave, sfm, osx-double, and osx-hfs.

Name

getent

Synopsis

getent [options] database key

Search the specified database for the specified key. The database may be any one of passwd, group, hosts, services, protocols, or networks.

Options

-s CONFIG, --service=CONFIG

Specify the service configuration to be used. See nsswitch.conf(5) for information about name-service switching.

-?, --help

Display a help message.

--usage

Display a very short syntax synopsis.

-V, --version

Print version information and quit.

Name

getkeycodes

Synopsis

getkeycodes

Print the kernel’s scancode-to-keycode mapping table.

Name

gpasswd

Synopsis

gpasswd [options] group

Administer /etc/group and /etc/gshadow entries. May only be used by an administrator. When used with a group name only, prompts for new group password. Defaults such as minimum and maximum group id values are specified in /etc/login.defs.

Options

-a

Add a new group.

-A users

Add administrative members.

-d

Delete a group.

-M users

Add group members.

-R

Disable access to the group. Also prevent creation of a new group with the same name.

-r

Remove the password entirely.

Name

gpg

Synopsis

gpg [options] command [options]

The GNU Privacy Guard application allows you to encrypt and decrypt information, create public and private encryption keys, and use or verify digital signatures. GPG is based on the use of a pair of keys, one public and one private (or “secret”). Data encrypted with one key can only be decrypted with the other. To encrypt a message to you, someone would use your public key to create a message that could only be unlocked with your private key. To sign information, you would lock it with your private key, allowing anyone to verify that it came from you by unlocking it with your public key.

GPG has dozens of additional options that fine-tune its available options. For a complete list, plus a guide to careful use of encryption and a deeper explanation of how public-key encryption works, visit www.gnupg.org.

Key commands

--check-sigs [keyname]

Lists keys and signatures like --list-sigs, but also verifies the signatures.

--delete-key keyname

Delete the specified key from the keyring.

--delete-secret-key keyname

Delete the named secret key from the secret and public keyring.

--delete-secret-and-public-key keyname

Delete the secret (if any) and then the public key for the specified name.

--desig-revoke keyname

Create a revocation certificate for a key pair and designate authority to issue it to someone else. This allows the user to permit someone else to revoke the key, if necessary.

--edit-key [keyname]

Edit key options using a menu-driven tool. Key options are too numerous to list here, but include everything from trust settings to images attached to keys for user identification purposes.

--export [keyname]

Output the specified key or, if no key is named, the entire keyring. Use the --output flag to send the key information to a file, and --armor to make the key mailable as ASCII text.

--export-secret-keys [keyname]

Outputs the specified secret key or keys. Operation is the same as --export, except with secret keys. This is a security risk and should be used with caution.

--export-secret-subkeys [keyname]

Outputs the specified secret subkeys. Operation is the same as --export, except with secret keys. This is a security risk and should be used with caution.

--fingerprint [keyname]

List keys and their fingerprints for keys named, or all keys if no name is specified. If repeated, shows fingerprints of secondary keys.

--gen-key

Generate a new pair of keys, prompting for several preferences and a passphrase. For most purposes, the default answers to the questions about algorithm and key length are fine.

--gen-revoke keyname

Create a revocation certificate for a key pair. A revocation certificate is designed to assure all parties that the key pair is no longer valid and should be discarded.

--keyserver keyserver

Specifies the name of the keyserver holding the key.

--list-keys [keyname]

List keys with the specified name, or all keys if no name is specified.

--list-public-keys [keyname]

List public keys with the specified name, or all public keys if no name is specified.

--list-secret-keys [keyname]

List secret keys with the specified name, or all secret keys if no name is specified.

--list-sigs [keyname]

List keys as --list-keys does, but also list the signatures.

--gen-revoke keyname

Delete the secret key (if any) and then the public key for the specified name.

--import file

Read keys from a file and add them to your keyring. This is most often used with public keys that are sent by email, but can also be used to move private keys from one system to another. Combined with the --merge-only option, adds only new signatures, subkeys, and user IDs, not keys.

--lsign-key keyname

Sign a public key, but mark it as nonexportable.

--recv-keys keyname

Download and import keys from a keyserver. The key name here should be the key ID as known to the keyserver, and you must specify the server with the --keyserver option.

--refresh-keys [keyname]

Check the keyserver for updates to keys already in the keyring. You can specify which keys to check for updates using the key IDs known to the server, and you must specify the server with the --keyserver option.

--search-keys [keyname]

Search the names of keys on the keyserver. Specify the keyserver with --keyserver.

--send-keys [keyname]

Send one or more keys to a keyserver. Specify the keyserver with --keyserver.

--sign-key keyname

Sign a public key using your private key. Often used to send the public key to a third party. This is the same as selecting “sign” from the --edit-key menu.

Signature commands

-b, --detach-sign

Create a signature that is not attached to anything.

--clearsign

Create a signature in cleartext.

-s, --sign

Create a signature. May be combined with --encrypt and/or --symmetric.

--verify [detached-signature] [signed-file]

Verify the signature attached to a file. If the signature and data are in the same file, only one file needs to be specified. For detached signatures, the first file should be the .sig or .asc signature file, and the second the datafile. If you wish to use stdin instead of a file for the nonattached data, you must specify a single dash (-) as the second filename.

--verify-files [files]

Verify one or more files entered on the command line or to stdin. Signatures must be part of the files submitted, and files sent to stdin should be one file per line. This is designed to check many files at once.

Encryption commands

-e, --encrypt

Encrypt data. May be used with --sign to create signed, encrypted data.

--encrypt-files [files]

Encrypt files one after another, either at the command line or sent to stdin one per line.

-c, --symmetric

Encrypt using a symmetric cipher. The cipher is encrypted using the CAST5 algorithm unless you specify otherwise using the --cipher-algo flag.

--store

Create a PGP message packet (RFC 1991). This does not encrypt data; it just puts it into the right packet format.

Decryption commands

-d, --decrypt [file]

Decrypt a file. If no file is specified, stdin is decrypted. Decrypted data is sent to stdout or to the file specified with the --output flag. If the encrypted data is signed, the signature is also verified.

--decrypt-files [files]

Decrypt files one after another, either at the command line or sent to stdin one per line.

Other commands

--check-trustdb

Check the list of keys with defined trust levels to see if they have expired or been revoked.

--export-ownertrust

Create a backup of the trust values for keys.

--h, --help

Display a help message.

--import-ownertrust [file]

Import trust values from a file or stdin. Overwrites existing values.

--list-packets

Display packet sequence for an encrypted message. Used for debugging.

--update-trustdb

Update the database of trusted keys. For each key that has no defined level of trust, --update-trustdb prompts for an estimate of how much the key’s owner can be trusted to certify other keys. This builds a web of more-trusted and less-trusted keys by which the overall security of a given key can be estimated.

--version

Display version information and quit.

--warranty

Display warranty information. There is no warranty.

Name

gpgsplit

Synopsis

gpgsplit [options] [files]

Split an OpenPGP-format message into individual packets. If no file is specified, the message is read from stdin. The split packets are written as individual files.

Options

-h, -?, --help

Display a short help message.

--no-split

Write to stdout instead of splitting the packets into individual files.

-p string, --prefix string

Begin each filename with the specified string.

--secret-to-public

Convert any secret keys in the message to public keys.

--uncompress

Uncompress any compressed packets.

-v, --verbose

Verbose mode. More informative.

Name

gpgv

Synopsis

gpgv [options] [detached-signature] [signed-files]

Check the signature of one or more OpenPGP-signed files. This is similar in operation to gpg --verify but uses a different keyring, ˜/.gnupg/trustedkeys.gpg by default. Also, gpgv assumes that the keyring is trusted, and it cannot edit or update it. By contrast, gpg --verify can go to a keyserver to verify signatures that are not in the local keyring, and offers various levels of trust. In both cases, you can use a detached signature file

Options

-h, -?, --help

Display a short help message.

--ignore-time-conflict

Use this flag to ignore incorrect dates on signatures. An incorrect date can be a sign of fraud, but is often just a result of an incorrectly set clock.

--keyring file

Use the specified file as a keyring, in addition to the default ~/.gnupg/trustedkeys.gpg.

--homedir dir

Use the specified directory as the GPG home directory, instead of the default (set in the GNUPGHOME variable, or, if that is unset, ˜/.gnupg).

--logger-fd FD

Send log output to the specified file descriptor. By default, log output goes to stderr. Use of file descriptors is described in the DETAILS section of the GPG documentation.

-q, --quiet

Minimal output.

--status-fd FD

Send special status messages to the specified file descriptor.

-v, --verbose

Verbose mode. More informative.

Name

gpm

Synopsis

gpm [options]

System administration command. Provide a mouse server and cut-and-paste utility for use on the Linux console. gpm acts like a daemon, responding to both mouse events and client input. If no clients are connected to the active console, gpm provides cut-and-paste services.

Options

−2

Force two buttons. If there is a middle button, it is treated as the right button.

−3

Force three buttons. With a three-button mouse, the left button makes a selection, the right button extends the selection, and the middle button pastes it. Using this option with a two-button mouse results in being unable to paste.

-a accel

Set the acceleration for a single motion longer than the delta specified with the -d option.

-A [limit]

Start up with pasting disabled for security. If specified, limit gives the time in seconds during which a selection can be pasted. If too much time has passed, the paste is not allowed.

-b baud

Specify the baud rate.

-B seq

Set a three-digit button sequence, mapping the left, middle, and right buttons to buttons 1, 2, and 3. The default is 123. The sequence 321 is useful if you are left-handed, or 132 for a two-button mouse.

-d delta

Set the delta value for use with -a. When a mouse motion event is longer than the specified delta, use accel as a multiplier. delta must be 2 or greater.

-D

Debugging mode. When set, gpm does not put itself into the background, and it logs messages to standard error instead of syslog.

-g num

For a glidepoint device, specify the button to be emulated by a tap. num must be 1, 2, or 3 and refers to the button number before any remapping is done by the -B option. Applies to mman and ps2 protocol decoding.

-h

Print a help message and exit.

-i interval

Specify the upper time limit, in milliseconds, between mouse clicks for the clicks to be considered a double or triple click.

-k

Kill a running gpm. For use with a bus mouse to kill gpm before running X. See also -R.

-l charset

Specify the inword( ) lookup table, which determines which characters can appear in a word. charset is a list of characters. The list can include only printable characters. Specify a range with -, and use \ to escape the following character or to specify an octal character.

-m filename

Specify the mouse file to open. The default is /dev/mouse.

-M

Enable the use of more than one mouse. Options appearing before -M apply to the first mouse; those appearing after it apply to the second mouse. Forces the use of -R.

-o extra-options

Specify a comma-separated list of additional mouse-specific options. See the gpm info page for a description of the mouse types and the possible options.

-p

Keep the pointer visible while text is being selected. The default is not to show the pointer.

-r num

Specify the responsiveness. A higher number causes the cursor to move faster.

-R name

Act as a repeater and pass any mouse data received while in graphical mode to the fifo /dev/gpmdata in the protocol specified by name (default is msc). In addition to certain protocol types available with -t, you can specify raw to repeat the data with no protocol translation.

-s num

Specify the sample rate for the mouse device.

-S [commands]

Enable special-command processing (see the next section). Custom commands can be specified as a colon-separated list to associate commands with the left button, middle button, and right button. If a command is omitted, it defaults to sending a signal to init.

-t type

Specify the mouse protocol type. Use -t help for a list of types; those marked with an asterisk (*) can be used with -R.

-v

Print version information and exit.

-V [increment]

Make gpm more or less verbose by the specified increment. The default verbosity level is 5, and the default increment is 1. A larger value of increment causes more messages to be logged. The increment can be negative, but must be specified with no space (e.g., -V-3).

Special commands

Special commands, activated with the -S option, are associated with each mouse button. You can also use -S to customize the commands. To execute a special command, triple-click the left and right buttons (hold down one of the buttons and triple-click the other). A message appears on the console, and the speaker beeps twice. At this point, release the buttons and press the desired button within three seconds to activate the associated special command. The default special commands are:

Left button

Reboot by signaling init.

Middle button

Shut down the system with /sbin/shutdown -h now.

Right button

Reboot with /sbin/shutdown -r now.

Name

gprof

Synopsis

gprof [options] [object_file]

Display the profile data for an object file. The file’s symbol table is compared with the call graph profile file gmon.out (previously created by compiling with gcc -pg). Many of gprof’s options take a symbol-specification argument, or symspec, to limit the option to specified files or functions. The symspec may be a filename, a function, or a line number. It can also be given as filename:function or filename:linenumber to specify a function or line number in a specific file. gprof expects filenames to contain a period and functions to not contain a period.

Options

-a, --no-static

Do not display statically declared functions. Since their information might still be relevant, append it to the information about the functions loaded immediately before.

-b, --brief

Do not display information about each field in the profile.

-c, --static-call-graph

Consult the object file’s text area to attempt to determine the program’s static call graph. Display static-only parents and children with call counts of 0.

--demangle[=style], --no-demangle

Specify whether C++ symbols should be demangled or not. They are demangled by default. If profiling a program built by a different compiler, you may need to specify the mangling style.

--function-ordering

Print suggested function order based on profiling data.

--file-ordering file

Print suggested link line order for .o files based on profiling data. Read function name to object file mappings from file. This file can be created using the nm command.

-i, --file-info

Print summary information on datafiles, then exit.

-k from to

Remove arcs between the routines from and to.

-m n, --min-count[=n]

Don’t print count statistics for symbols executed less than n times.

-n[symspec], --time[=symspec]

Propagate time statistics in call graph analysis.

-p[symspec], --flat-profile[=symspec]

Print profile statistics.

-q[symspec], --graph[=symspec]

Print call graph analysis.

-s, --sum

Summarize profile information in the file gmon.sum.

-v, --version

Print version and exit.

-w n, --width=n

Print function index formatted to width n.

-x, --all-lines

When printing annotated source, annotate every line in a basic block, not just the beginning.

-y, --separate-files

Print annotated-source output to separate files instead of standard output. The annotated source for each source file is printed to filename-ann.

-z, --display-unused-functions

Include zero-usage calls.

-A[symspec], --annotated-source[=symspec]

Print annotated source code.

-C[symspec], --exec-counts[=symspec]

Print statistics on the number of times each function is called. When used with option -l, count basic-block execution.

-F routine

Print only information about routine. Do not include time spent in other routines.

-I dirs, --directory-path=dirs

Set directory path to search for source files. The dirs argument may be given as a colon-separated list of directories.

-J[symspec], --no-annotated-source[=symspec]

Don’t print annotated source code.

-L, --print-path

Print the path information when printing filenames.

-N[symspec], --no-time[=symspec]

Don’t propagate time statistics in call graph analysis.

-P[symspec], --no-flat-profile[=symspec]

Don’t print profile statistics.

-Q[symspec], --no-graph[=symspec]

Don’t print call graph analysis.

-T, --traditional

Print output in BSD style.

-Z[symspec], --no-exec-counts[=symspec]

Don’t print statistics on the number of times each function is called.

Name

grep

Synopsis

grep [options] pattern [files]

Search one or more files for lines that match a regular expression pattern. Regular expressions are described in Chapter 7. Exit status is 0 if any lines match, 1 if none match, and 2 for errors. See also egrep and fgrep.

Options

-a, --text

Don’t suppress output lines with binary data; treat as text.

-A num, --after-context=num

Print num lines of text that occur after the matching line.

-b, --byte-offset

Print the byte offset within the input file before each line of output.

-B num, --before-context=num

Print num lines of text that occur before the matching line.

-c, --count

Print only a count of matched lines. With -v or --revert-match, count nonmatching lines.

-C[num], --context[=num], -num

Print num lines of leading and trailing context. Default context is 2 lines.

-d action, --directories=action

Define an action for processing directories. Possible actions are:

read

Read directories like ordinary files (default).

skip

Skip directories.

recurse

Recursively read all files under each directory. Same as -r.

-D action, --directories=action

Define an action for processing an input file that is a device, FIFO, or socket. Possible actions are read (default) and skip, as in -d.

-e pattern, --regexp=pattern

Search for pattern. Same as specifying a pattern as an argument, but useful in protecting patterns beginning with -.

-E, -extended-regexp

Act like egrep, recognizing extended regular expressions such as (UN|POS)IX to find UNIX and POSIX.

-f file, --file=file

Take a list of patterns from file, one per line.

-F, --fixed-strings

Act like fgrep, recognizing only fixed strings instead of regular expressions. Useful when searching for characters that grep normally recognizes as metacharacters.

-G, --basic-regexp

Expect the regular expressions traditionally recognized by grep (the default).

-h, --no-filename

Print matched lines but not filenames (inverse of -l) when multiple files are searched.

-H, --with-filename

Display, before each line found, the name of the file containing the line. This is done by default if multiple files are submitted to a single grep command.

-i, --ignore-case

Ignore uppercase and lowercase distinctions.

-l, --files-with-matches

Print the names of files with matches but not individual matched lines. Scanning per file stops on the first match.

-L, --files-without-match

Print only the names of files with no matches. Scanning per file stops on the first match.

-m num, --max-count=num

Stop looking after num matches are found.

--mmap

Try to use memory mapping (mmap) to read input in order to save time.

-n, --line-number

Print lines and their line numbers.

-q, --quiet, --silent

Suppress normal output in favor of quiet mode; scanning stops on the first match.

-r, --recursive

Recursively read all files under each directory. Same as -d recurse.

-s, --no-messages

Suppress error messages about nonexistent or unreadable files.

-v, --invert-match

Print all lines that don’t match pattern.

-V, --version

Print the version number and then exit.

-w, --word-regexp

Match on whole words only. Words are divided by characters that are not letters, digits, or underscores.

-x, --line-regexp

Print lines only if pattern matches the entire line.

-Z, --null

When displaying filenames, follow each with a zero byte instead of a colon.

Examples

List the number of users who use tcsh:

grep -c /bin/tcsh /etc/passwd

List header files that have at least one #include directive:

grep -l '^#include' /usr/include/*

List files that don’t contain pattern:

grep -c pattern files | grep :0

Name

groff

Synopsis

groff [options] [files]
troff [options] [files]

Frontend to the groff document-formatting system, which normally runs troff along with a postprocessor appropriate for the selected output device. Options without arguments can be grouped after a single dash (-). A filename of - denotes standard input.

Options

-a

Generate an ASCII approximation of the typeset output.

-b

Print a backtrace.

-C

Enable compatibility mode.

-dcs, -dname=s

Define the character c or string name to be the string s.

-e

Preprocess with eqn, the equation formatter.

-E

Don’t print any error messages.

-ffam

Use fam as the default font family.

-Fdir

Search dir for subdirectories with DESC and font files before searching the default directory /usr/lib/groff/font.

-h, --help

Print a help message.

-i

Read standard input after all files have been processed.

-l

Send the output to a print spooler (as specified by the print command in the device description file).

-Larg

Pass arg to the spooler. Each argument should be passed with a separate -L option.

-mname

Read the macro file tmac.name.

-Mdir

Search directory dir for macro files before searching the default directory /usr/lib/groff/tmac.

-nnum

Set the first page number to num.

-N

Don’t allow newlines with eqn delimiters; equivalent to eqn’s -N option.

-olist

Output only pages specified in list, a comma-separated list of page ranges.

-p

Preprocess with pic.

-Parg

Pass arg to the postprocessor. Each argument should be passed with a separate -P option.

-rcn, -name=n

Set the number register c or name to n. c is a single character, and n is any troff numeric expression.

-R

Preprocess with refer.

-s

Preprocess with soelim.

-S

Use safer mode (that is, pass the -S option to pic and use the -msafer macros with troff).

-t

Preprocess with tbl.

-Tdev

Prepare output for device dev; the default is ps.

-v, --version

Make groff and programs run by it print out their version numbers.

-V

Print the pipeline on stdout instead of executing it.

-wname

Enable warning name. You can specify multiple -w options. See the troff manpage for a list of warnings.

-Wname

Disable warning name. You can specify multiple -W options. See the troff manpage for a list of warnings.

-z

Suppress troff output (except error messages).

-Z

Do not postprocess troff output. Normally groff automatically runs the appropriate postprocessor.

Devices

ascii

Typewriter-like device.

dvi

TEX DVI format.

html

HTML output.

latin1

Typewriter-like devices using the ISO Latin-1 character set.

lj4

HP LaserJet4-compatible (or other PCL5-compatible) printer.

ps

PostScript.

utf8

Unicode (ISO 10646) character set with UTF-8 encoding.

X75

75-dpi X11 previewer.

X100

100-dpi X11 previewer.

Environment variables

GROFF_COMMAND_PREFIX

If set to X, groff runs Xtroff instead of troff.

GROFF_FONT_PATH

Colon-separated list of directories to search for the devname directory.

GROFF_TMAC_PATH

Colon-separated list of directories to search for the macro files.

GROFF_TMPDIR

If set, temporary files are created in this directory; otherwise, they are created in TMPDIR (if set) or /tmp (if TMPDIR is not set).

GROFF_TYPESETTER

Default device.

PATH

Search path for commands that groff executes.

Name

groupadd

Synopsis

groupadd [options] group

System administration command. Create a new user group.

Options

-f, --force

This option is useful for scripts. When specified the command will exit without error if the group being added already exists. If a gid requested with -g already exists and the -o option has not been specified, assign a different gid as if -g had not been specified. This option is not available on all distributions.

-g gid, --gid gid

Assign numerical group ID. (By default, the first available number above 500 is used.) The value must be unique, unless the -o option is used.

-K key=value, --key key=value

Override defaults in /etc/login.defs.

-o

Accept a nonunique gid with the -g option.

-p string, --password string

Set the password for the group. string must already be encrypted appropriately for the system.

-r, --system

Add a system account. Assign the first available number lower than 499.

--usage

Display a very short list of acceptable options for the command.

Name

groupdel

Synopsis

groupdel group

System administration command. Remove group from system account files. You may still need to find and change permissions on files that belong to the removed group.

Name

groupmod

Synopsis

groupmod [options] group

System administration command. Modify group information for group.

Options

-g gid, --gid gid

Assign numerical group ID. (By default, the first available unreserved number is used. Many distributions reserve the first 500 IDs for system groups, some the first 1000.) The value must be unique, unless the -o option is used.

-n name

Change the group name to name.

-o

Override. Accept a nonunique gid.

-p string, --password string

Set the initial password for the group. string must already be encrypted appropriately for the system.

Name

groups

Synopsis

groups [options] [users]

Show the groups that each user belongs to (default user is the owner of the current group). Groups are listed in /etc/passwd and /etc/group.

Options

--help

Print help message.

--version

Print version information.

Name

grpck

Synopsis

grpck [option] [files]

System administration command. Remove corrupt or duplicate entries in the /etc/group and /etc/gshadow files. Generate warnings for other errors found. grpck will prompt for a “yes” or “no” before deleting entries. If the user replies “no,” the program will exit. If run in a read-only mode, the reply to all prompts is “no.” Alternate group and gshadow files can be checked. If other errors are found, the user will be encouraged to run the groupmod command.

Option

-r

Read-only mode.

-s

Sort entries by GID.

Exit codes

0

Success.

1

Syntax error.

2

One or more bad group entries found.

3

Could not open group files.

4

Could not lock group files.

5

Could not write group files.

Name

grpconv

Synopsis

grpconv
grpunconv

System administration command. Like pwconv, the grpconv command creates a shadowed group file to keep your encrypted group passwords safe from password-cracking programs. grpconv creates the /etc/gshadow file based on your existing /etc/groups file and replaces your encrypted password entries with x. If you add new entries to the /etc/groups file, you can run grpconv again to transfer the new information to /etc/gshadow. It will ignore entries that already have a password of x and convert those that do not. grpunconv restores the encrypted passwords to your /etc/groups file and removes the /etc/gshadow file.

Name

gs

Synopsis

gs [options] [files]

GhostScript, an interpreter for Adobe Systems’ PostScript and PDF (Portable Document Format) languages. Used for document processing. With - in place of files, standard input is used.

Options

-- filename arg1 ...

Take the next argument as a filename, but use all remaining arguments to define ARGUMENTS in userdict (not systemdict) as an array of those strings before running the file.

-Dname=token, -dname=token

Define a name in systemdict with the given definition. The token must be exactly one token (as defined by the token operator) and must not contain any whitespace.

-Dname, -dname

Define a name in systemdict with a null value.

-gnumber1xnumber2

Specify width and height of device; intended for systems like the X Window System.

-Idirectories

Add a list of directories at the head of the search path for library files.

-q

Quiet startup.

-rnumber, -rnumber1xnumber2

Specify X and Y resolutions (for the benefit of devices, such as printers, that support multiple X and Y resolutions). If only one number is given, it is used for both X and Y resolutions.

-Sname=string, -sname=string

Define a name in systemdict with a given string as value.

Special names

-dDISKFONTS

Cause individual character outlines to be loaded from the disk the first time they are encountered.

-dNOBIND

Disable the bind operator. Useful only for debugging.

-dNOCACHE

Disable character caching. Useful only for debugging.

-dNODISPLAY

Suppress the normal initialization of the output device. May be useful when debugging.

-dNOPAUSE

Disable the prompt and pause at the end of each page.

-dNOPLATFONTS

Disable the use of fonts supplied by the underlying platform (e.g., the X Window System).

-dSAFER

Disable the deletefile and renamefile operators, and the ability to open files in any mode other than read-only.

-dWRITESYSTEMDICT

Leave systemdict writable.

-sDEVICE=device

Select an alternate initial output device.

-sOUTPUTFILE=filename

Select an alternate output file (or pipe) for the initial output device.

Name

gunzip

Synopsis

gunzip [options] [files]

Uncompress files compressed by gzip. See gzip for a list of options.

Name

gzexe

Synopsis

gzexe [option] [files]

Compress executables. When run, these files automatically uncompress, thus trading time for space. gzexe creates backup files with a tilde at the end (filename˜). These backup files can be deleted once you are sure the compression has worked properly.

Option

-d

Decompress files.

Name

gzip

Synopsis

gzip [options] [files]
gunzip [options] [files]
zcat [options] [files]

Compress specified files (or data read from standard input) with Lempel-Ziv coding (LZ77). Rename compressed file to filename.gz; keep ownership modes and access/modification times. Ignore symbolic links. Uncompress with gunzip, which takes all of gzip’s options except those specified. zcat is identical to gunzip -c and takes the options -fhLV, described here. Files compressed with the compress command can be decompressed using these commands.

Options

-n, --fast, --best

Regulate the speed of compression using the specified digit n, where −1 or --fast indicates the fastest compression method (less compression), and −9 or --best indicates the slowest compression method (most compression). The default compression level is −6.

-c, --stdout, --to-stdout

Print output to standard output, and do not change input files.

-d, --decompress, --uncompress

Same as gunzip.

-f, --force

Force compression. gzip normally prompts for permission to continue when the file has multiple links, its .gz version already exists, or it is reading compressed data to or from a terminal.

-h, --help

Display a help screen and then exit.

-l, --list

Expects to be given compressed files as arguments. Files may be compressed by any of the following methods: gzip, deflate, compress, lzh, or pack. For each file, list uncompressed and compressed sizes (the former is always −1 for files compressed by programs other than gzip), compression ratio, and uncompressed name. With -v, also print compression method, the 32-bit CRC of the uncompressed data, and the timestamp. With -N, look inside the file for the uncompressed name and timestamp.

-L, --license

Display the gzip license and quit.

-n, --no-name

When compressing, do not save the original filename and timestamp by default. When decompressing, do not restore the original filename if present, and do not restore the original timestamp if present. This option is the default when decompressing.

-N, --name

Default. Save original name and timestamp. When decompressing, restore original name and timestamp.

-q, --quiet

Print no warnings.

-r, --recursive

When given a directory as an argument, recursively compress or decompress files within it.

-S suffix, --suffix suffix

Append .suffix. Default is gz. A null suffix while decompressing causes gunzip to attempt to decompress all specified files, regardless of suffix.

-t, --test

Test compressed file integrity.

-v, --verbose

Print name and percent size reduction for each file.

-V, --version

Display the version number and compilation options.

Name

halt

Synopsis

halt [options]

System administration command: turns off the computer. Inserts a note in the file /var/log/wtmp; if the system is in runlevel 0 or 6, stops all processes; otherwise, calls shutdown -h.

Options

-d

Suppress writing to /var/log/wtmp.

-f

Call halt even when shutdown -nf would normally be called (i.e., force a call to halt, even when not in runlevel 0 or 6).

-h

Place hard drives in standby mode before halt or power off.

-i

Shut down network interfaces before halt.

-n

No sync before reboot or halt.

-p

Perform power-off when halting system.

Name

hdparm

Synopsis

hdparm [options] [device]

System administration command. Read or set the hard drive parameters. This command can be used to tune hard drive performance. It is primarily used with IDE drives, but some can be used with SCSI drives as well.

Options

The hdparm command accepts many option flags, including some that can result in filesystem corruption if misused. Flags can be used to set or get a parameter. To get a parameter, just pass the flag without a value. To set a parameter, follow the flag with a space and the appropriate value.

-a [n]

Get or set the number of sectors to read ahead in the disk. The default is 8 sectors (4 KB); a larger value is more efficient for large, sequential reads, and a smaller value is better for small, random reads. Many IDE drives include this functionality in the drive itself, so this feature is not always necessary.

-A

Enable or disable the IDE read-ahead feature. Usually on by default.

-b [n]

Get or set the bus state for the drive.

-B

Set the Advanced Power Management (APM) data if the drive supports it.

-c [n]

Get or set 32-bit I/O values for IDE drives. Acceptable values are 0 (32-bit support off), 1 (32-bit support on), and 3 (on, but only with a sync sequence).

-C

Check the power status of the drive. This will tell you unknown, active/idle, standby, or sleeping. Use -S, -y, -Y, and -Z to set the power status.

-d [n]

Get or set the using_dma flag for the drive, which may be 0 (not using DMA) or 1 (using DMA).

-D

Enable or disable defect-handling features that are controlled by the hard drive itself.

-E n

Set CD-ROM read speed to n times normal audio playback speed. Not normally necessary.

-f

Flush and sync the buffer cache on exit.

-F

Flush write cache buffer on-drive.

-g

Query and display drive size and geometry information, such as number of cylinders, heads, and sectors.

-h

Display a short help message.

-i

Display the drive identification information obtained at boot time. If the drive has changed since boot, this information may not be current.

-I

Display more detailed identification information for the drive.

--Istdin

Read identify data from standard input.

--Istdout

Write identify data to standard output.

-k [n]

Get or set the keep_settings_over_reset variable. Valid settings are 0 and 1, and a value of 1 will keep the -dmu options when rebooting (soft reset only).

-K [n]

Get or set the keep_features_over_reset variable. Valid settings are 0 and 1, and a value of 1 will keep settings for the flags -APSWXZ over a soft reset.

-L n

Set the door lock flag for the drive. Used for Syquest, ZIP, and JAZ drives.

-m [n]

Get or set the number of sectors used for multiple sector count reading. A value of 0 disables the feature, and values of 2, 4, 8, 16, and 32 are common. Drives that try to support this feature and fail may suffer corruption and data loss.

-M [n]

Get or set the level for Automatic Acousting Management (AAM) features. Newer drives support this feature, which can slow down head movements to reduce hard disk noise. Values range from 128 (quiet, but slow) to 254 (fast, but loud). Some drives support only 128 and 254, while others support multiple levels between the extremes. At the time of writing, this feature was still considered experimental and not recommended for production use.

-n [n]

Set to 0 or 1 to disable or enable, respectively, the “ignore write errors” flag. This can cause massive data loss if used incorrectly, and is for development purposes only.

-N [n]

Get or set visible number of sectors. Without a parameter this will display the current maximum sectors and the hardware limit for the disk. The invisible sectors form the Host Protected Area (HPA) commonly used to hold diagnostic software or the original copy of the operating system. Changing this value will usually result in data loss.

-p n

Tune the IDE interface to use PIO mode n, usually an integer between 0 and 5. Incorrect values can result in massive data loss. Support for the PIO mode-setting feature varies between IDE chips, so tuning it is not for the faint of heart.

-P n

Set the internal prefetch sector count. Not all drives support the feature.

-q

Suppress output for the flag after this one, unless it is the -i, -v, -t, or -T flag.

-Q [n]

Set the depth of tagged queues. 0 disables tagged queues. This is supported only on specific drives, and only for kernels 2.5.x and later.

-r [n]

Get or set the flag for read-only on the device. A value of 1 marks the device as read-only.

-R

This option should be used by experts only. It registers an IDE interface. See the -U option for further details.

-S n

Set the amount of time a disk is inactive before it spins down and goes into standby mode. Settings from 1 to 240 represent chunks of five seconds (for timeout values between 5 seconds and 20 minutes); values from 241 to 251 are increments of 30 minutes (for 30 minutes to 5.5 hours). A value of 252 sets the timeout to 21 minutes, 253 to the vendor default, and 255 to 20 minutes and 15 seconds.

-t

Time device reads to determine performance.

-T

Time cache reads to determine performance.

-u [n]

Get or set the interrupt-unmask value for the drive. A value of 1 lets the drive unmask other interrupts and can improve performance; when used with older kernels and hardware, it can cause data loss.

-U

Unregister an IDE interface. Use this feature and the -R feature only with hot-swappable hardware, such as very high-end servers and some laptops. It can damage or hang other systems, and should be used with caution.

-v

Display all appropriate settings for device except -i. This is the same as the default behavior with no flags.

-w

Reset the device. Use as a last resort only; may cause data loss.

-W

Enable or disable the write-cache feature for the drive. The default varies among drive manufacturers.

-x

Sets tristate. Use only for hot-swappable devices. See the -R and -U entries.

-X n

Set the IDE transfer mode. Possible values include 34 (multiword DMA mode2 transfers) and 66 (UltraDMA mode2 transfers), or any PIO mode number plus 8. This option is suggested for experts only, and is useful only with newer EIDE/IDE/ATA2 drives. Often used in combination with -d.

-y

Put the IDE drive into standby (spin-down) mode, saving power.

-Y

Put the IDE drive into sleep mode.

-z

Force the kernel to reread the partition table.

-Z

Disable automatic powersaving on some drives, which can prevent them from idling or spinning down at inconvenient moments. This will increase the electrical power consumption of your system.

Name

head

Synopsis

head [options] [files]

Print the first few lines (default is 10) of one or more files to standard output. If files is missing or -, read from standard input. With more than one file, print a header for each file showing the filename.

Options

-c num[b|k|m], --bytes num[b|k|m]

Print first num bytes or, if num is followed by b, k, or m, first num 512-byte blocks, 1-kilobyte blocks, or 1-megabyte blocks.

--help

Display help and then exit.

-n num, --lines num, -num

Print first num lines. Default is 10.

-q, --quiet, --silent

Quiet mode; never print headers giving filenames.

-v, --verbose

Print filename headers, even for only one file.

--version

Output version information and then exit.

Examples

Display the first 20 lines of phone_list:

head −20 phone_list

Display the first 10 phone numbers having a 202 area code:

grep '(202)' phone_list | head

Name

hexdump

Synopsis

hexdump [options] file

Display specified file or input in hexadecimal, octal, decimal, or ASCII format. Option flags are used to specify the display format.

Options

-b

Use a one-byte octal display; show the input offset in hexadecimal, followed by 16 three-column octal data bytes, filled with zeroes and separated by spaces.

-c

Use a one-byte character display; show the input offset in hexadecimal, followed by 16 three-column entries, filled with zeroes and separated by spaces.

-C

Canonical mode. Display hexadecimal offset, two sets of eight columns of hexadecimal bytes, then a | followed by the ASCII representation of those same bytes.

-d

Use a two-byte decimal display. The input offset is again in hexadecimal, but the display has only eight entries per line, of five columns each, containing two bytes of unsigned decimal format.

-e format_string

Choose a format string to be used to transform the output data. Format strings consist of:

Iteration count

The iteration count is optional. It determines the number of times to use the transformation string. The number is followed by a slash (/) to distinguish it from the byte count.

Byte count

The number of bytes to be interpreted by the conversion string, preceded by a slash character to distinguish it from the iteration count. The byte count is optional.

Format characters

The actual format characters are required. They are surrounded by quotation marks and are interpreted as fprintf (see printf) formatting strings, although the *, h, l, n, p, and q options will not work as expected. Format string usage is discussed at greater length in the hexdump manpage.

-f filename

Choose a file that contains several format strings, separated by newlines; the # character marks a line as a comment.

-n length

Limit the number of bytes of input to be interpreted.

-o

Two-byte octal display; show a hexadecimal offset followed by eight five-column data entries of two bytes each, in octal format.

-s offset

Skip to specified offset. The offset number is assumed to be decimal unless it starts with 0x or 0X (hexadecimal), or 0 (octal). Numbers may also be designated in megabytes, kilobytes, or half-kilobytes with the addition of m, k, or b at the end of the number.

-v

Display all input data, even if it is the same as the previous line. Normally, a duplicate line is replaced by an asterisk (*).

-x

Display data in a two-byte hexadecimal format. The offset is in hexadecimal, and is followed by eight space-separated entries, each of which contains four-column, two-byte chunks of data in hexadecimal format.

Name

host

Synopsis

host [options] name [server]

System administration command. Print information about hosts or zones in DNS. Hosts may be IP addresses or hostnames; host converts IP addresses to hostnames by default and appends the local domain to hosts without a trailing dot. Default servers are determined in /etc/resolv.conf. For more information about hosts and zones, read Chapter 1 and Chapter 2 of Paul Albitz’s and Cricket Liu’s DNS and BIND (O’Reilly).

Options

-a

Same as -t ANY.

-c class

Search for specified resource record class (IN, CH, CHAOS, HS, HESIOD, or ANY). Default is IN.

-d

Verbose output. Same as -v.

-l

List mode. This also performs a zone transfer for the named zone. Same as -t AXFR.

-n

Perform reverse lookups for IPv6 addresses using IP6.INT domain and “nibble” labels instead of IP6.ARPA and binary labels.

-r

Do not ask contacted server to query other servers, but require only the information that it has cached.

-s

Stop querying nameservers upon receiving a SERVFAIL response.

-t type

Look for type entries in the resource record. type may be any recognized query type, such as A, AXFR, CNAME, NS, SOA, SIG, or ANY. If name is a hostname, host will look for A records by default. If name is an IPv4 or IPv6 address, it will look for PTR records.

-v

Verbose. Include all fields from resource record, even time-to-live and class, as well as “additional information” and “authoritative nameservers” (provided by the remote nameserver).

-w

Never give up on queried server.

-C

Display SOA records from all authoritative nameservers for the specified zone.

-N n

Consider names with fewer than n dots in them to be relative. Search for them in the domains listed in the search and domain directives of /etc/resolv.conf. The default is usually 1.

-R n

Retry query a maximum of n times. The default is 1.

-T

Use TCP instead of UDP to query nameserver. This is implied in queries that require TCP, such as AXFR requests.

-W n

Wait a maximum of n seconds for reply.

Name

hostid

Synopsis

hostid

Print the ID number in hexadecimal of the current host.

Name

hostname

Synopsis

hostname [option] [nameofhost]

Set or display name of current host system. A privileged user can set the hostname with the nameofhost argument.

Options

-a, --alias

Display the alias name of the host (if used).

-d, --domain

Display DNS domain name.

-f, --fqdn, --long

Display fully qualified domain name.

-F file, --file file

Consult file for hostname.

-h, --help

Display a help message and then exit.

-i, --ip-address

Display the IP address(es) of the host.

-s, --short

Trim domain information from the display output.

-v, --verbose

Verbose mode.

-V, --version

Display version information and then exit.

-y, --yp, --nis

Display the NIS domain name. A privileged user can set a new NIS domain name with nameofhost.

Name

htdigest

Synopsis

htdigest [-c] filename realm username

Create or update user authentication files used by the Apache web server. The -c option is used if you wish to create the file, and will overwrite any existing files rather than update them. The three arguments are the file you wish to use as the authentication file, the realm name to which the user belongs, and the username you will update in the password file. You will be prompted for a password when you run the command.

The Apache manual contains information about authentication mechanisms, including more detail about using htdigest and the ways in which you can control access to the resources served by Apache.

Name

hunspell

Synopsis

hunspell [options] [files]

A spell checker modeled after ispell. With no files specified, hunspell reads from standard input. See ispell for details of the available options and commands. Commands are single-character and case-insensitive; use them to tell hunspell what to do with a misspelled word.

Name

hwclock

Synopsis

hwclock [option]

System administration command. Read or set the hardware clock. This command maintains change information in /etc/adjtime, which can be used to adjust the clock based on how much it drifts over time. hwclock replaces the clock command. The single-letter options are included for compatibility with the older command.

Options

You may specify only one of the following options:

-a, --adjust

Adjust the hardware clock based on information in /etc/adjtime and set the system clock to the new time.

--getepoch

Print the kernel’s hardware clock epoch value, then exit.

-r, --show

Print the current time stored in the hardware clock.

-s, --hctosys

Set the system time in accordance with the hardware clock.

--setepoch, --epoch=year

Set the hardware clock’s epoch to year.

--set --date=date

Set the hardware clock to the specified date, a string appropriate for use with the date command.

-v, --version

Print version and exit.

-w, --systohc

Set the hardware clock in accordance with the system time.

The following may be used with the above options:

--debug

Print information about what hwclock is doing.

--localtime

The hardware clock is stored in local time.

--noadjfile

Disable /etc/adjtime facilities.

--test

Do not actually change anything. This is good for checking syntax.

-u, --utc

The hardware clock is stored in Universal Coordinated Time.

Name

icedax

Synopsis

icedax [options] [output.wav]

Retrieve audio tracks in CDDA (Compact Disc Digital Audio) format and convert to WAV format. icedax stands for InCrEdible Digital Audio eXtractor. The manpage has full details as well as hints on the options and on usage.

Options

Some of the following options use sectors as a unit of measurement. Each sector of data on a CD represents approximately 1/75 second of play time.

-a n, --divider n

Set the sample rate to a value equal to 44100/n samples per second. The -R option, used by itself, lists the possible values.

-A drivename, --auxdevice drivename

Specify a different drive for ioctl purposes.

-b n, --bits-per-sample n

Set the quality of samples to n bits per sample per channel. Possible values are 8, 12, and 16.

-B, --bulk, --alltracks

Copy each track into its own file. This is the most commonly used flag.

-c channel, --channels channel

Set stereo instructions. Set channel to 1 for mono; 2 for stereo; or s for stereo, but swapped left-to-right. You can also use -s (--stereo) to record in stereo and -m (--mono) to record in mono.

-C byteorder, --cdrom-endianness byteorder

Set the byte order, or “endianness” of the input data. You may set the order to little, big, or guess. This is useful when your CD-ROM drive uses an unexpected or unusual byte order for your platform.

--cddbp-server=servername

Set the name of the CD lookup server used. The default server is freedb.freedb.org.

--cddbp-port=portnumber

Select the port on which to access the CD lookup server. The servers at freedb.org use cddbp on port 8880, and http on port 80.

-d duration, --duration

Set the number of seconds duration, or follow with f to set the duration in frames (sectors). Set duration to zero to record an entire track.

-D devicename, --device devicename

Specify the device. The device must work with the -I (--interface) settings.

-e, --echo

Copy output to an audio output device. Use -K (--sound-device) to set the device (usually /dev/dsp).

-E byteorder, --output-endianness byteorder

Set the byte order or “endianness” of the output data. As with -C, you may set the order to little, big, or guess.

-g, --gui

Format all text output for easy parsing by GUI frontends.

-h, --help

Print usage information and exit.

-H, --no-infofile

Do not copy any info or CDDB files, only the audio files.

-i n, --index n

Set the start index to n when recording.

-I ifname, --interface ifname

Specify the type of interface, generic_scsi or cooked_ioctl. It’s usually safest to use generic_scsi.

-J, --info-only

Use this option by itself to display information about the disc, but do nothing else.

-K device, --sound-device device

Set the sound device to use with -e.

-l n, --buffers-in-ring n

Use a ring of n buffers.

-L n, --cddb n

icedax looks up CD information online, if possible. This option determines what happens when there are multiple entries identifying the CD. If the mode is 0, the user is prompted to select an entry. If the mode is 1, the application uses the first entry returned.

-M n, --md5 n

Create MD5 checksums for the first n bytes of each track copied.

-n n, --sectors-per-request n

Read n sectors in each request.

-N, --no-write

For debugging purposes, this option suppresses writing an output file.

-o n, --offset n

Start recording n sectors before the beginning of the first track.

-O format, --output-format=format

Choose the output file format. Normal file options are wav, aiff, aifc, au, and sun. You can also use cdr and raw for headerless files dumped into recording devices.

-p n, --set-pitch n

Adjust the pitch by n percent when copying data to an audio device.

-P n, --set-overlap n

Use n sectors of overlap for jitter correction. Very fast systems with absolutely perfect drives and unscratched CDs can set this to 0.

--paranoia

Read and interpret the CD using the paranoia library instead of the icedax code.

-q, --quiet

Quiet mode; the program sends no data to the screen.

-r n, --rate n

Set the sample rate in samples per second. To get a list of possible values, use the -R option by itself.

-R, --dump-rates

Output a list of possible sample rates and dividers. This option is typically used with no other option flags or arguments.

-S n, --speed n

Specify the speed at which your system will read the CD-ROM. Set the value to the multiple of normal playback speed given as your CD-ROM drive speed (4, 16, 32, and so forth). Setting the speed lower than the maximum can prevent errors in some cases.

-t m[+n], --track m[+n]

Set start track to n. Optionally, use + and a second track number for the end track: 1+10 copies tracks one through ten.

-v list, --verbose-level list

Specify CD information to display in a comma-separated list. The options are: for no information, use disable; for all information, use all. Specify toc for the table of contents, summary for a summary of recording parameters, indices for index offsets, catalog for the media catalog number (MCN), trackid for track IDs, sectors for the table of contents in start sector notation, and titles for title information, if available.

--version

Display version and quit.

-w, --wait

Wait for a signal before recording anything.

-x, --max

Set recording quality (and amount of hard disk usage) to maximum.

Name

iconv

Synopsis

iconv [options] files

Convert the contents of one or more files from one character encoding to another and write the results to standard output. Use -l to print a list of possible encodings.

Options

-c

Omit invalid output characters.

-f code1, --from-code=code1

Convert input characters from the code1 encoding.

-?, --help

Print help message and exit.

-l, --list

Print a list of valid encodings to standard output.

-o file, --output=file

Write the converted output to file instead of standard output.

-s, --silent

Operate silently; don’t print warning messages.

-t code2, --to-code=code2

Convert input characters to the code2 encoding.

--usage

Print a brief usage message showing only the command syntax and then exit.

-V, --version

Print version information and exit.

--verbose

Operate verbosely; print progress messages.

Name

id

Synopsis

id [options] [username]

Display information about yourself or another user: user ID, group ID, effective user ID and group ID if relevant, and additional group IDs.

Options

-g, --group

Print effective group ID only.

-G, --groups

Print supplementary groups only.

-n, --name

With -u, -g, or -G, print user or group name, not number.

-r, --real

With -u, -g, or -G, print real, not effective, user ID or group ID.

-u, --user

Print user ID only.

-Z, --context

Print security context of the current user.

--help

Print help message and then exit.

--version

Print version information.

Name

ifconfig

Synopsis

ifconfig [interface]
ifconfig [interface address_family parameters addresses]

TCP/IP command. Assign an address to a network interface and/or configure network interface parameters. ifconfig is typically used at boot time to define the network address of each interface on a machine. It may be used at a later time to redefine an interface’s address or other parameters. Without arguments, ifconfig displays the current configuration for a network interface. With the single option -a and no other arguments, it will display all current interfaces. Used with a single interface argument, ifconfig displays that particular interface’s current configuration. Note that interfaces are usually numbered starting at zero: eth0, eth1, eth2, and so forth. Wireless network interfaces may begin with ath0 or wlan0. On some systems the ifconfig command is deprecated in favor of the ip command.

Arguments

interface

String of the form name unit: for example, en0.

address_family

Since an interface may receive transmissions in differing protocols, each of which may require separate naming schemes, you can specify the address_family to change the interpretation of the remaining parameters. You may specify inet (for TCP/IP, the default), ax25 (AX.25 Packet Radio), ddp (Appletalk Phase 2), or ipx (Novell).

parameters

The following parameters may be set with ifconfig:

add address/prefixlength

Add an IPv6 address and prefix length.

address address

Assign the specified IP address to the interface.

allmulti/-allmulti

Enable/disable sending of incoming frames to the kernel’s network layer.

arp/-arp

Enable/disable use of the Address Resolution Protocol in mapping between network-level addresses and link-level addresses.

broadcast/-broadcast [address]

(inet only) Set or clear the address to use to represent broadcasts to the network. Default is the address with a host part of all ones (i.e., x.y.z.255 for a class C network).

debug/-debug

Enable/disable driver-dependent debugging code.

del address/prefixlength

Delete an IPv6 address and prefix length.

down

Mark an interface “down” (unresponsive).

hw class address

Set the interface’s hardware class and address. class may be ether (Ethernet), ax25 (AX.25 Packet Radio), or ARCnet.

io_addr addr

I/O memory start address for device.

irq addr

Set the device’s interrupt line.

metric n

Set routing metric of the interface to n. Default is 0.

mem_start addr

Shared memory start address for device.

media type

Set media type. Common values are 10base2, 10baseT, and AUI. If auto is specified, ifconfig will attempt to autosense the media type.

mtu n

Set the interface’s Maximum Transfer Unit (MTU).

multicast

Set the multicast flag.

netmask mask

(inet only) Specify how much of the address to reserve for subdividing networks into subnetworks. mask can be specified as a single hexadecimal number with a leading 0x, with a dot notation Internet address, or with a pseudo-network name listed in the network table /etc/networks.

pointopoint/-pointopoint [address]

Enable/disable point-to-point interfacing, so that the connection between the two machines is dedicated.

promisc/-promisc

Enable/disable promiscuous mode. Promiscuous mode allows the device to receive all packets on the network.

txqueuelen n

Specify the transmit queue length.

tunnel addr

Create an IPv6-in-IPv4 (SIT) device, tunneling to IPv4 address addr.

up

Mark an interface “up” (ready to send and receive).

addresses

Each address is either a hostname present in the hostname database (/etc/hosts), or an Internet address expressed in the Internet standard dot notation.

Examples

To list all interfaces:

ifconfig -a

To add a second IP address to wlan0:

ifconfig wlan0:1 192.168.2.41 netmask 255.255.255.0

To change the hardware address (MAC address) assigned to eth0 (useful when setting up a router for a DSL or cable modem):

ifconfig eth0 hw ether 01:02:03:04:05:06

Name

imapd

Synopsis

imapd [options]

TCP/IP command. The Interactive Mail Access Protocol (IMAP) server daemon. imapd is often invoked by xinetd and listens on port 143 for requests from IMAP clients. IMAP allows mail programs to access remote mailboxes as if they were local. IMAP is a richer protocol than POP because it allows a client to retrieve message-level information from a server mailbox instead of the entire mailbox. IMAP can be used for online and offline reading. The popular Pine mail client contains support for IMAP. There are several versions of imapd available. Here we document the Cyrus IMAP server with its most common command options.

Options

-C file

Read configuration options from file instead of /etc/imapd.conf.

-s

Encrypt data using the Secure Socket Layer (SSL).

-T n

Wait n seconds for a new connection before closing the process. The default is 60.

-U n

Reuse process for new connections no more than n times.

Name

inetd

Synopsis

inetd [options] [configuration_file]

TCP/IP command. The Internet services daemon. This is an older daemon usually replaced with xinetd. See xinetd.

Name

info

Synopsis

info [options] [topics]

GNU hypertext reader. Display online documentation previously built from Texinfo input. Info files are arranged in a hierarchy and can contain menus for subtopics. When entered without options, the command displays the top-level info file (usually /usr/local/info/dir or /usr/local/share/dir). When topics are specified, find a subtopic by choosing the first topic from the menu in the top-level info file, the next topic from the new menu specified by the first topic, and so on. The initial display can also be controlled by the -f and -n options. If a specified topic has no info file but does have a manpage, info displays the manpage; if there is neither, the top-level info file is displayed.

Options

-d directories, --directory directories

Search directories, a colon-separated list, for info files. If this option is not specified, use the INFOPATH environment -variable or the default directory (usually /usr/local/info or /usr/share/info).

--dribble file

Store each keystroke in file, which can be used in a future session with the --restore option to return to this place in info.

-f file, --file file

Display specified info file.

--help

Display brief help message and exit.

--index-search string

Display node pointed to by index entry string.

-k string, --apropos string

Search all info topics for string and display the results.

-n node, --node node

Display specified node in the info file.

-o file, --output file

Copy output to file instead of displaying it on the screen.

-O, --show-options, --usage

Display the node with the command-line options.

--restore file

When starting, execute keystrokes stored in file.

--subnodes

Display subtopics.

--version

Display version.

--vi-keys

Use vi-like key bindings.

Name

init

Synopsis

init

System administration command. The init daemon is the parent of all processes on Linux. Traditionally Linux has used a System V Unix style boot process (SysVinit) that calls this daemon at system startup. The SysVinit daemon starts or stops other programmings depending on run level. Newer Linux distributions use a more flexible process called Upstart, but for backward compatibility many still group processes into run levels. For a System V init process use the telinit program to change run levels. For Upstart use initctl to communicate with the init daemon. For more information, see the section Starting and Stopping the System in Starting and Stopping the System.

Name

initctl

Synopsis

initctl [options] command

System administration command. initctl sends commands to the Upstart init daemon. Use it to monitor jobs or events, call jobs directly, or send custom events to the daemon.

Options

--show-ids

Show unique process id (pid) as well as the job id.

--by-id

Parameter passed to command is a job id.

--no-wait

When using start, stop, or emit, exit immediately instead of waiting for the request to finish.

--quiet

Only show errors when running the given command.

Commands

These generally apply to upstart jobs. Jobs are usually defined in files located in the /etc/event.d directory. Most commands will accept multiple job names given in a space separated list.

emit event [arguments]

Emit a custom event to which init should respond. Event arguments may be passed in a comma separated list. If any job status changes as a result of the event, print each change.

events

Monitor system events.

list [pattern]

Print a list of all known jobs. If an optional shell style matching pattern is given, only those jobs matching the pattern will be shown.

log-priority priority

Change init message logging priority to one of debug, info, message, warn, error, or fatal.

start job...

Start and print job status changes to screen.

status job...

Print status. The job name, goal (to start or stop) and the current status of the job are shown, along with any associated pids.

stop job...

Stop and print job status changes to screen.

jobs

Monitor job changes, printing changes to the screen.

version

Print version of running init daemon.

Name

insmod

Synopsis

insmod filename [module-options]

System administration command. Load the module filename into the kernel. Simpler but less flexible than the modprobe command. Error messages from insmod may be vague, because the kernel performs module operations internally and therefore sends error information to the kernel log instead of standard output; see dmesg.

Name

install

Synopsis

install [options] [source] destination

System administration command. Used primarily in Makefiles to update files. install copies files into user-specified directories. Similar to cp, but attempts to set permission modes, owner, and group. The source may be a file or directory, or a list of files and directories. The destination should be a single file or directory.

Options

-b, --backup[=control]

Back up any existing files. When using the long version of the command, the optional control parameter controls the kind of backup. When no control is specified, install will attempt to read the control value from the VERSION_CONTROL environment variable. Accepted values are:

none, off

Never make backups.

numbered, t

Make numbered backups.

existing, nil

Match existing backups, numbered or simple.

simple, never

Always make simple backups.

-C

Do not overwrite file when the target exists and is identical to the new file. Preserve original timestamp.

-d, --directory

Create any missing directories.

-D

Create leading components of destination except the last, then copy source to destination.

-g group, --group group

Set group ID of new file to group (privileged users only).

--help

Print help information and exit.

-m mode, --mode mode

Set permissions of new file to mode (octal or symbolic). By default, the mode is 0755.

-o [owner], --owner[=owner]

Set ownership to owner or, if unspecified, to root (privileged users only).

-p, --preserve-timestamps

Preserve access and modification times on source files and directories.

-P, --preserve-context

Preserve SELinux security context.

-s, --strip

Strip symbol tables.

-S suffix, --suffix=suffix

Use suffix instead of the default backup suffix, usually ˜.

-t directory, --target-directory directory

Copy SOURCE arguments into the specified directory.

-T, --no-target-directory

Treat destination as a normal file.

-v, --verbose

Print name of each directory as it is created.

--version

Print version, then exit.

Name

ionice

Synopsis

ionice [options] [program [arg]]

Set the I/O scheduling class and priority for a program. The three possible scheduling classes are idle, best effort, and real time. The default is best effort. With no arguments or just -p, query the current class and priority for the process. Without -p, the program is run with the specified parameters.

Options

-c n

Set the scheduling class, where n is 1 for real time, 2 for best effort, and 3 for idle.

-h

Print help information and exit.

-n n

Define the scheduling class data for classes that accept it. For real time and best effort, n can be in the range 0–7.

-p pid

Specify the process id of a running program to be changed.

Name

ip

Synopsis

ip [options] object command [arguments]
ip [object [command]] help

System administration command. Show and manipulate network devices and routing. This command is a part of the iproute2 utilities for controlling TCP and UDP IP networking and traffic control. It’s meant to replace the ifconfig, route, and arp commands among others. On some distributions these utilities may be deprecated in favor of ip.

ip’s subcommand syntax is very similar to the Cisco’s IOS syntax used on many Cisco routers and switches. The ip command can be used to configure tunnels, load balancing and other traffic shaping. For brevity, we won’t cover all of its features here. For more in-depth coverage, we recommend iproute2’s Linux Foundation web pages at: http://www.linuxfoundation.org/en/Net:Iproute2.

Options

-s, --stats, --statistics

Print statistics or time values. Use multiple times to increase the verbosity of output even more.

-f protocol_family, --family protocol_family

Specify the protocol_family to use for the commands given. This may be inet, inet6, or link. The protocol_family link may be used to indicate no protocol is involved. The ip command also accepts shortcut options of −4, −6, and −0 for families inet, inet6, and link.

-o, --oneline

Format output as one line, replacing linefeeds with the '\' character. This is useful when piping output of ip to another command.

-r, --resolve

Resolve IP addresses to host names. The default is to use IP addresses.

Commands

We will only cover commands for address, link, neighbor and route objects, and the syntax of the help command. These are the commands that replace ifconfig, arp, and route. (In IPv4 the neighbor table is known as the arp table.) Most objects and commands have a long name (or two) as well as one or more abbreviations. For example, the object address can be given as address, addr, or a. The commands show and list are interchangeable and can be abbreviated as sh, s, li, or l. Here we show the most commonly used form in examples and documentation:

help

List command syntax, including applicable arguments. The syntax is given in a form similar to BNF grammar notation.

addr add address[/netmask] arguments

Add a new protocol address to a device. The format of the address depends on the protocol (inet or inet6). A netmask may be given in CIDR notation. If no netmask is given, a mask of /32 is assumed.

addr del address[/netmask] [arguments]

Remove a protocol address.

addr show [arguments]

Print current addresses.

link set device_name [arguments]

Define or change settings on a network device.

link show [device_name]

Print current settings for network devices.

neigh add address [arguments]

Add a new entry to the neighbor table for the IPv4 or IPv6 address.

neigh chg address [arguments]

Change an existing entry in the neighbor table.

neigh del address [arguments]

Mark as invalid then remove an entry from the neighbor table when released from all clients.

neigh list [address] [arguments]

Add a new entry or change an existing one in the neighbor table.

neigh repl address [arguments]

Add a new entry or change an existing one in the neighbor table.

neigh flush arguments

Flush the specified entries from neighbors table. This command requires an argument, either an address, address prefix, dev, nud, or unused argument.

route add address [arguments]

Add a new entry to the routing table.

route chg address [arguments]

Change an existing entry in the routing table.

route del address [arguments]

Remove an entry from the routing.

route list [arguments]

Show current routing table entries. Use arguments to limit the entries shown.

route repl address [arguments]

Add a new entry or change an existing one in the routing table.

Common arguments

The following are common arguments for the above commands:

address address[/netmask]

Set a link layer address (i.e., MAC address) for a network device.

arp on, arp off

Set the arp flag of a network device on or off.

brd address

Set the broadcast address. Addresses for address objects may also be given as the symbols + or - meaning to set all the host bits of the broadcast address to 1 or 0. When used with a link object, this argument sets the link layer broadcast address instead.

dev name

The name of the network device to which the command applies (e.g., lo or eth0.) For link object commands you can omit dev and just pass the name as the first argument.

down, up

Change the state of a network device, disabling or enabling it (or limit shown devices to those with the specified state).

dynamic on, dynamic off

Set the dynamic flag of a network device on or off.

label name

Assign a label string of name to an address.

local address

The IPv4 or IPv6 address to use with addr object commands. For these commands you can omit local and just pass the address as the first argument.

lladdr address

Set a link layer address for a neighbors table entry.

mtu n

Set the maximum transfer unit (MTU) for a network device to n.

multicast on, multicast off

Set the multicast flag of a network device on or off.

nud state

Set the neighbor unreachability detection (nud) state of a neighbor entry. State values include:

noarp

Mark the entry as valid and not to be checked. It may be removed when it expires.

permanent

Like noarp, but a permanent entry can only be removed by an administrator.

reachable

Mark the entry as valid until its reachability timeout expires.

stale

Mark a new or changed entry as valid, but suspicious. The kernel will check stale entries at the first transmission.

promisc on, promisc off

Turn promiscuous mode on or off for a network device.

proto protocol

Set the routing protocol. The protocol identifies how a route was entered. If you are manually entering a route, the appropriate value for protocol should be static. If not specified the protocol defaults to boot.

scope value

Set the valid scope of an address or route entry. Valid values include global, site, link, and host. If used with the show command, only addresses of the given scope will be shown.

src address

The preferred IPv4 or IPv6 source address for a routing table entry.

to address

The IPv4 or IPv6 address or address prefix for a neighbor table or routing table entry. For neigh and route object commands you can omit the to and pass the address as the first argument. For route object commands you may also use the special address default, which is equivalent to an address of 0/0 or /0.

tos key

An 8-bit hexadecimal number or the IPv4 or IPv6 address or address prefix for a neighbor table or routing table entry. For neigh and route object commands you can omit the to and pass the address as the first argument.

txqlen n

Set the transmit queue length of a network device to n.

unused

When given with neigh show, show only unused entries.

via address

The address of the nexthop router (e.g., the Ipv4 or IPv6 address of the gateway). Used with route commands.

Examples

Show all configured network cards:

# ip link show

Bring down eth0:

# ip link set eth0 down

Add an IP address to device eth0 and label it “internal”:

# ip addr add 192.186.0.32/24 brd + dev eth0 label internal

Show current routing table entries for device eth1:

# ip route list dev eth1

Add a router table entry for a private network on eth1 with gateway via 192.168.0.254:

# ip route add 10.0.0.1/8 via 192.168.0.254 dev eth1

Put eth0 into promiscuous mode in order to sniff traffic:

# ip link set eth0 promisc on

Add a permanent entry to the neighbors table (arp table) for eth1:

# ip neigh add 10.0.0.5 lladdr 52:54:00:32:5e:20 dev eth1 nud permanent

Name

ipcrm

Synopsis

ipcrm [options]

System administration command. Remove interprocess communication (IPC) message queues, shared memory segments, or semaphore arrays. These may be specified either by numeric identifier or by key, using the following options.

Options

-m identifier, -M key

Remove specified shared memory segment and its associated data structures after the last detach is performed.

-q identifier, -Q key

Remove specified message queue and its associated data structures.

-s identifier, -S key

Remove specified semaphore array and its associated data structures.

Name

ipcs

Synopsis

ipcs [options]

System administration command. Print report on interprocess communication (IPC) message queues, shared memory segments, and semaphore arrays for which the current process has read access. Options can be used to specify the type of resources to report on and the output format of the report.

Options

Resource specification options:

-a

Report on all IPC facilities: shared memory segments, message queues, and semaphore arrays. This is the default.

-m

Report on shared memory segments.

-q

Report on message queues.

-s

Report on semaphore arrays.

Output format options:

-c

Print creator and owner user IDs for IPC facilities.

-l

Print resource maximum and minimum limits.

-p

Print creator and last operation process identifiers.

-t

Print attach, detach, and change times for shared memory segments; last operation and change times for semaphore arrays; and send, receive, and change times for message queues.

-u

Print summary of current resource usage.

Other options:

-h

Print help message, then exit.

-i identifier

Used in combination with the -m, -q, or -s options. Report only on the resource specified by numeric identifier.

Name

iptables

Synopsis

iptables command [options]

System administration command. Configure netfilter filtering rules for kernels 2.4 and later. Rules for iptables consist of some matching criteria and a target, a result to be applied if the packet matches the criteria. The rules are organized into chains. You can use these rules to build a firewall, masquerade your local area network, or just reject certain kinds of network connections.

There are three built-in tables for iptables: one for network filtering (filter), one for Network Address Translation (nat), and the last for specialized packet alterations (mangle). Firewall rules are organized into chains, ordered checklists of rules that the kernel works through looking for matches. The filter table has three built-in chains: INPUT, OUTPUT, and FORWARD. The INPUT and OUTPUT chains handle packets originating from or destined for the host system. The FORWARD chain handles packets just passing through the host system. The nat table also has three built-in chains: PREROUTING, POSTROUTING, and OUTPUT. mangle has only two chains: PREROUTING and OUTPUT.

netfilter checks packets entering the system. After applying any PREROUTING rules, it passes them to the INPUT chain, or to the FORWARD chain if the packet is just passing through. Upon leaving, the system packets are passed to the OUTPUT chain and then on to any POSTROUTING rules. Each of these chains has a default target (a policy) in case no match is found. User-defined chains can also be created and used as targets for packets but do not have default policies. If no match can be found in a user-defined chain, the packet is returned to the chain from which it was called and tested against the next rule in that chain.

iptables changes only the rules in the running kernel. When the system is powered off, all changes are lost. You can use the iptables-save command to make a script you can run with iptables-restore to restore your firewall settings. Such a script is often called at bootup. Many distributions have an iptables initialization script that uses the output from iptables-save.

Commands

iptables is almost always invoked with one of the following commands:

-A chain rules, --append chain rules

Append new rules to chain.

-D chain rules, --delete chain rules

Delete rules from chain. Rules can be specified by their ordinal number in the chain as well as by a general rule description.

-E old-chain new-chain, --rename-chain old-chain new-chain

Rename old-chain to new-chain.

-F [chain], --flush [chain]

Remove all rules from chain, or from all chains if chain is not specified.

-I chain number rules, --insert chain number rules

Insert rules into chain at the ordinal position given by number.

-L [chain], --list [chain]

List the rules in chain, or all chains if chain is not specified.

-N chain, --new-chain chain

Create a new chain. The chain’s name must be unique. This is how user-defined chains are created.

-P chain target, --policy chain target

Set the default policy for a built-in chain; the target itself cannot be a chain.

-R chain number rule, --replace chain number rule

Replace a rule in chain. The rule to be replaced is specified by its ordinal number.

-X [chain], --delete-chain [chain]

Delete the specified user-defined chain, or all user-defined chains if chain is not specified.

-Z [chain], --zero [chain]

Zero the packet and byte counters in chain. If no chain is specified, all chains will be reset. When used without specifying a chain and combined with the -L command, list the current counter values before they are reset.

Targets

A target may be the name of a chain or one of the following special values:

ACCEPT

Let the packet through.

DROP

Drop the packet.

QUEUE

Send packets to the user space for processing.

RETURN

Stop traversing the current chain and return to the point in the previous chain from which this one was called. If RETURN is the target of a rule in a built-in chain, the built-in chain’s default policy is applied.

Rule specification parameters

These options are used to create rules for use with the preceding commands. Rules consist of some matching criteria and usually a target to jump to (-j) if the match is made. Many of the parameters for these matching rules can be expressed as a negative with an exclamation point (!) meaning “not.” Those rules will match everything except the given parameter.

-c packets bytes, --set-counters packets bytes

Initialize packet and byte counters to the specified values.

-d [!] address[/mask] [!] [port], --destination [!] address[/mask] [port]

Match packets from the destination address. The address may be supplied as a hostname, a network name, or an IP address. The optional mask is the netmask to use and may be supplied either in the traditional form (e.g., /255.255.255.0) or in the modern form (e.g., /24).

[!] -f, [!]--fragment

The rule applies only to the second or further fragments of a fragmented packet.

-i [!] name[+], --in-interface name[+]

Match packets being received from interface name. name is the network interface used by your system (e.g., eth0 or ppp0). A + can be used as a wildcard, so ppp+ would match any interface name beginning with ppp.

-j target, --jump target

Jump to a special target or a user-defined chain. If this option is not specified for a rule, matching the rule only increases the rule’s counters, and the packet is tested against the next rule.

-o [!] name[+], --out-interface name[+]

Match packets being sent from interface name. See the description of -i for the syntax for name.

-p [!] name, --protocol [!] name

Match packets of protocol name. The value of name can be given as a name or number, as found in the file /etc/protocols. The most common values are tcp, udp, icmp, or the special value all. The number 0 is equivalent to all, and this is the default value when this option is not used. If there are extended matching rules associated with the specified protocol, they will be loaded automatically. You need not use the -m option to load them.

-s [!] address[/mask] [!] [port], --source [!] address[/mask] [!] [port]

Match packets with the source address. See the description of -d for the syntax of this option.

Options

-h [icmp], --help [icmp]

Print help message. If icmp is specified, a list of valid ICMP type names will be printed. -h can also be used with the -m option to get help on an extension module.

--line-numbers

Used with the -L command. Add the line number to the beginning of each rule in a listing, indicating its position in the chain.

-m module, --match module

Explicitly load matching rule extensions associated with module. See the next section.

--modprobe=command

Use specified command to load any necessary kernel modules while adding or inserting rules into a chain.

-n, --numeric

Print all IP address and port numbers in numeric form. By default, text names are displayed when possible.

-t name, --table name

Apply rules to the specified table. Rules apply to the filter table by default.

-v, --verbose

Verbose mode.

-x, --exact

Expand all numbers in a listing (-L). Display the exact value of the packet and byte counters instead of rounded figures.

Match extensions

Several modules extend the matching capabilities of netfilter rules. Using the -p option will cause iptables to load associated modules implicitly. Others need to be loaded explicitly with the -m or --match options. Here we document those modules used most frequently.

icmp

Loaded when -p icmp is the only protocol specified:

--icmp-type [!] type

Match the specified ICMP type. type may be a numeric ICMP type or one of the ICMP type names shown by the command iptables -p icmp -h.

multiport

Loaded explicitly with the -m option. The multiport extensions match sets of source or destination ports. These rules can be used only in conjunction with -p tcp and -p udp. Up to 15 ports can be specified in a comma-separated list:

--source-port [ports]

Match the given source ports.

--destination-port [ports]

Match the given destination ports.

--port [ports]

Match if the packet has the same source and destination port and that port is one of the given ports.

state

Loaded explicitly with the -m option. This module matches the connection state of a packet:

--state states

Match the packet if it has one of the states in the comma-separated list states. Valid states are INVALID, ESTABLISHED, NEW, and RELATED.

tcp

Loaded when -p tcp is the only protocol specified:

--source-port [!] [port][:port], --sport [!] [port][:port]

Match the specified source ports. Using the colon specifies an inclusive range of services to match. If the first port is omitted, 0 is the default. If the second port is omitted, 65535 is the default. You can also use a dash instead of a colon to specify the range.

--destination-port [!] [port][:port], --dport [!] [port][:port]

Match the specified destination ports. The syntax is the same as for --source-port.

--mss n[:n]

Match if TCP SYN or SYN/ACK packets have the specified MSS value or fall within the specified range. Use this to control the maximum packet size for a connection.

[!] --syn

Match packets with the SYN bit set and the ACK and FIN bits cleared. These are packets that request TCP connections; blocking them prevents incoming connections. Shorthand for --tcp-flags SYN,RST,ACK SYN.

--tcp-flags [!] mask comp

Match the packets with the TCP flags specified by mask and comp. mask is a comma-separated list of flags that should be examined. comp is a comma-separated list of flags that must be set for the rule to match. Valid flags are SYN, ACK, FIN, RST, URG, PSH, ALL, and NONE.

--tcp-option [!] n

Match if TCP option is set.

udp

Loaded when -p udp is the only protocol specified:

--source-port [!] [port][:port], --sport [!] [port][:port]

Match the specified source ports. The syntax is the same as for the --source-port option of the TCP extension.

--destination-port [!] [port][:port], --dport [!] [port][:port]

Match the specified destination ports. The syntax is the same as for the --source-port option of the TCP extension.

Target extensions

Extension targets are optional additional targets supported by separate kernel modules. They have their own associated options. We cover the most frequently used target extensions below.

DNAT

Modify the destination address of the packet and all future packets in the current connection. DNAT is valid only as a part of the POSTROUTING chain in the nat table:

--to-destination address[-address][port-port]

Specify the new destination address or range of addresses. The arguments for this option are the same as the --to-source argument for the SNAT extension target.

LOG

Log the packet’s information in the system log:

--log-level level

Set the syslog level by name or number (as defined by syslog.conf).

--log-prefix prefix

Begin each log entry with the string prefix. The prefix string may be up to 30 characters long.

--log-tcp-sequence

Log the TCP sequence numbers. This is a security risk if your log is readable by users.

--log-tcp-options

Log options from the TCP packet header.

--log-ip-options

Log options from the IP packet header.

MASQUERADE

Masquerade the packet so it appears that it originated from the current system. Reverse packets from masqueraded connections are unmasqueraded automatically. This is a legal target only for chains in the nat table that handle incoming packets and should be used only with dynamic IP addresses (like dial-up.) For static addresses use DNAT:

--to-ports port[-port]

Specify the port or range of ports to use when masquerading. This option is valid only if a tcp or udp protocol has been specified with the -p option. If this option is not used, the masqueraded packet’s port will not be changed.

REJECT

Drop the packet and, if appropriate, send an ICMP message back to the sender indicating the packet was dropped. If the packet was an ICMP error message, an unknown ICMP type, or a nonhead fragment, or if too many ICMP messages have already been sent to this address, no message is sent:

--reject-with type

Send specified ICMP message type. Valid values are icmp-net-unreachable, icmp-host-unreachable, icmp-port-unreachable, or icmp-proto-unreachable. If the packet was an ICMP ping packet, type may also be echo-reply.

SNAT

Modify the source address of the packet and all future packets in the current connection. SNAT is valid only as a part of the POSTROUTING chain in the nat table:

--to-source address[-address][port-port]

Specify the new source address or range of addresses. If a tcp or udp protocol has been specified with the -p option, source ports may also be specified. If none is specified, map the new source to the same port if possible. If not, map ports below 512 to other ports below 512, those between 512 and 1024 to other ports below 1024, and ports above 1024 to other ports above 1024.

Examples

To reject all incoming ICMP traffic on eth0:

iptables -A INPUT -p ICMP -i eth0 -j  REJECT

Name

iptables-restore

Synopsis

iptables-restore [options]

System administration command. Restore firewall rules from information provided on standard input. iptables-restore takes commands generated by iptables-save and uses them to restore the firewall rules for each chain. This is often used by initialization scripts to restore firewall settings on boot.

Options

-c, --counters

Restore packet and byte counter values.

-n, --noflush

Don’t delete previous table contents.

Name

iptables-save

Synopsis

iptables-save [options]

System administration command. Print the IP firewall rules currently stored in the kernel to stdout. Output may be redirected to a file that can later be used by iptables-restore to restore the firewall.

Options

-c, --counters

Save packet and byte counter values.

-t name, --table name

Print data from the specified table only.

Name

isodump

Synopsis

isodump isoimage

Interactively display the contents of the ISO9660 image isoimage. Used to verify the integrity of the directory inside the image. isodump displays the first portion of the root directory and waits for commands. The prompt shows the extent number (zone) and offset within the extent, and the contents display at the top of the screen.

Commands

+

Search forward for the next instance of the search string.

a

Search backward within the image.

b

Search forward within the image.

f

Prompt for a new search string.

g

Prompt for a new starting block and go there.

q

Exit.

Name

isoinfo

Synopsis

isoinfo [options]

Display information about ISO9660 images. You can use isoinfo to list the contents of an image, extract a file, or generate a find-like file list. The -i option is required to specify the image to examine.

Options

-d

Print information from the primary volume descriptor (PVD) of the ISO9660 image, including information about Rock Ridge and Joliet extensions if they are present.

dev=target

Set the SCSI target for the drive.

-f

Generate output similar to the output of a find . -print command. Do not use with -l.

-h

Print help information and exit.

-i isoimage

Specify the path for the ISO9660 image to examine.

-j charset

Convert any Joliet filenames to the specified character set.

-J

Extract filename information from any Joliet extensions.

-l

Generate output similar to the output of an ls -lR command. Do not use with -f.

-N sector

To help examine single-session CD files that are to be written to a multisession CD. Specify the sector number at which the ISO9660 image is to be written when sent to the CD writer.

-p

Display path table information.

-R

Extract permission, filename, and ownership information from any Rock Ridge extensions.

-T sector

To help examine multisession images that have already been burned to a multisession CD. Use the specified sector number as the start of the session to display.

-x path

Extract the file at the specified path to standard output.

Name

isosize

Synopsis

isosize [option] iso9660-img-file

Display the length of an ISO9660 filesystem contained in the specified file. The image file can be a normal file or a block device such as /dev/sr0. With no options, the length is displayed in bytes. Only one of the two options can be specified.

Options

-d num

Display the size in bytes divided by num.

-x

Display the number of blocks and the block size (although the output refers to blocks as sectors).

Name

isovfy

Synopsis

isovfy isoimage

Verify the integrity of the specified ISO9660 image and write the results to standard output.

Name

ispell

Synopsis

ispell [options] [files]

Compare the words of one or more named files with the system dictionary. Display unrecognized words at the top of the screen, accompanied by possible correct spellings, and allow editing via a series of single-character commands that are case-insensitive.

Options

-b

Back up original file in filename.bak.

-B

Count two correctly spelled words without a space between them as a spelling error.

-C

Count two correctly spelled words without a space between them as a legitimate compound word.

-d file

Search file instead of standard dictionary file.

-H

File is in HTML/XML format.

-L number

Show number lines of context.

-m

Suggest combinations of known roots and affixes, even if the result is not known. For example, “generous” and “ly” are known, so “generously” would be suggested as a word, even if it were not in the dictionary.

-M

List interactive commands at bottom of screen.

-n

Expect nroff or troff input file.

-N

Suppress printing of interactive commands.

-p file

Search file instead of personal dictionary file.

-P

Do not guess new words using known roots and affixes. The opposite of -m.

-S

Sort suggested replacements by likelihood that they are correct.

-t

Expect TEX or LATEX input file.

-T type

Expect all files to be formatted by type.

-V

Use hat notation (^L) to display control characters, and M- to display characters with the high bit set.

-w chars

Consider chars to be legal, in addition to a-z and A-Z.

-W n

Never consider words that are n characters or fewer to be misspelled.

-x

Do not back up original file.

Interactive commands

?

Display help screen.

space

Accept the word in this instance.

number

Replace with suggested word that corresponds to number.

!command

Invoke shell and execute command in it. Prompt before exiting.

a

Accept word as correctly spelled, but do not add it to personal dictionary.

i

Accept word and add it (with any current capitalization) to personal dictionary.

l

Search system dictionary for words.

q

Exit without saving.

r

Replace word.

u

Accept word and add lowercase version of it to personal dictionary.

x

Skip to the next file, saving changes.

^L

Redraw screen.

^Z

Suspend ispell.

Name

join

Synopsis

join [options] file1 file2

Join lines of two sorted files by matching on a common field. If either file1 or file2 is -, read from standard input. Often used to merge data stored in text-based file formats such as comma-separated-value formatted spreadsheets.

Options

−1 fieldnum1

The join field in file1 is fieldnum1. Default is the first field.

−2 fieldnum2

The join field in file2 is fieldnum2. Default is the first field.

-a filenum

Print a line for each unpairable line in file filenum, in addition to the normal output.

--check-order, --nocheck-order

Check or do not check that the files are correctly sorted on the join fields.

-e string

Replace missing input fields with string.

-i, --ignore-case

Ignore case differences when comparing fields.

-o fieldlist

Order the output fields according to fieldlist, where each entry in the list is in the form filenum.fieldnum. Entries are separated by commas or blanks.

-t char

Specifies the field-separator character (default is whitespace).

-v filenum

Print only unpairable lines from file filenum.

--help

Print help message and then exit.

--version

Print the version number and then exit.

Name

kbd_mode

Synopsis

kbd_mode [option]

Print or set the current keyboard mode, which may be RAW, MEDIUMRAW, XLATE, or UNICODE.

Options

-a

Set mode to XLATE (ASCII mode).

-k

Set mode to MEDIUMRAW (keycode mode).

-s

Set mode to RAW (scancode mode).

-u

Set mode to UNICODE (UTF-8 mode).

Name

kbdrate

Synopsis

kbdrate [options]

System administration command. Control the rate at which the keyboard repeats characters, as well as its delay time. Using this command without options sets a repeat rate of 10.9 characters per second; the default delay is 250 milliseconds. On boot, most Linux systems set the keyboard rate to 30 characters per second.

Options

-d delay

Specify the delay, which must be one of the following (in milliseconds): 250, 500, 750, or 1000.

-r rate

Specify the repeat rate, which must be one of the following numbers (all in characters per second): 2.0, 2.1, 2.3, 2.5, 2.7, 3.0, 3.3, 3.7, 4.0, 4.3, 4.6, 5.0, 5.5, 6.0, 6.7, 7.5, 8.0, 8.6, 9.2, 10.0, 10.9, 12.0, 13.3, 15.0, 16.0, 17.1, 18.5, 20.0, 21.8, 24.0, 26.7, or 30.0.

-s

Suppress printing of messages.

-V

Print version number and exit.

Name

kill

Synopsis

kill [options] [pids]

Send a signal to terminate one or more process IDs. You must own the process or be a privileged user. If no signal is specified, TERM is sent.

This entry describes the /bin/kill command. There are also built-in shell commands of the same name; the bash version is described in Chapter 6.

In some Linux distributions, /bin/kill allows you to specify a command name, such as gcc or xpdf, instead of a process ID (PID). All processes running that command with the same UID as the process issuing /bin/kill are sent the signal.

If /bin/kill is issued with a pid of 0, it sends the signal to all processes of its own process group. If /bin/kill is issued with a pid of −1, it sends the signal to all processes except process 1 (the system’s init process).

Options

-a

Kill all processes of the given name (if privileges allow), not just processes with the same UID. To use this option, specify the full path (e.g., /bin/kill -a gcc).

-l

List all signals.

-p

Print the process ID of the named process, but don’t send it a signal. To use this option, specify the full path (e.g., /bin/kill -p).

-s SIGNAL, -SIGNAL

The signal number (from /usr/include/sys/signal.h) or name (from kill -l). With a signal number of 9 (KILL), the kill cannot be caught by the process; use this to kill a process that a plain kill doesn’t terminate. The default signal is TERM. The letter flag itself is optional: both kill −9 1024 and kill -s 9 1024 terminate process 1024.

Name

killall

Synopsis

killall [options] names

Kill processes by command name. If more than one process is running the specified command, kill all of them. Treats command names that contain a / as files; kill all processes that are executing that file.

Options

-e, --exact

Require an exact match to kill very long names (i.e., longer than 15 characters). Normally, killall kills everything that matches within the first 15 characters. With -e, such entries are skipped. (Use -v to print a message for each skipped entry.)

-g, --process-group

Kill the process group to which the process belongs.

-i, --interactive

Prompt for confirmation before killing processes.

-I, --ignore-case

Ignore case when matching process names.

-l, --list

List known signal names.

-q, --quiet

Quiet; do not complain of processes not killed.

-r, --regexp

Interpret process name as an extended regular expression.

-s signal, --signal signal

Send signal to named processes. signal may be a name or a number. The most commonly used signal is 9, which terminates processes no matter what. The default signal is SIGTERM.

-u user, --user user

Kill only processes owned by the specified user.

-v, --verbose

Verbose; after killing process, report success and process ID.

-V, --version

Print version information.

-w, --wait

Wait for all killed processes to die. Note that killall may wait forever if the signal was ignored or had no effect, or if the process stays in zombie state.

Name

klogd

Synopsis

klogd [options]

System administration command. Control which kernel messages are displayed on the console, prioritize all messages, and log them through syslogd. On many operating systems, syslogd performs all the work of klogd, but on Linux the features are separated. Kernel messages are gleaned from the /proc filesystem and from system calls to syslogd. By default, no messages appear on the console. Messages are sorted into eight levels, 0–7, and the level number is prepended to each message.

Priority levels

0

Emergency situation (KERN_EMERG).

1

A crucial error has occurred (KERN_ALERT).

2

A serious error has occurred (KERN_CRIT).

3

An error has occurred (KERN_ERR).

4

A warning message (KERN_WARNING).

5

The situation is normal but should be checked (KERN_NOTICE).

6

Information only (KERN_INFO).

7

Debugging message (KERN_DEBUG).

Options

-c level

Print all messages of a higher priority (lower number) than level to the console.

-d

Debugging mode.

-f file

Print all messages to file; suppress normal logging.

-i

Signal executing daemon to reload kernel module symbols.

-I

Signal executing daemon to reload both static kernel symbols and kernel module symbols.

-k file

Use file as source of kernel symbols.

-n

Avoid auto-backgrounding. This is needed when klogd is started from init.

-o

One-shot mode. Prioritize and log all current messages, then immediately exit.

-p

Reload kernel-module symbol information whenever an Oops string is detected.

-P file

Use file as the source for kernel messages instead of /proc/kmsg.

-s

Suppress reading of messages from the /proc filesystem. Read from kernel message buffers instead.

-v

Print version, then exit.

-x

Don’t translate instruction pointers (EIP). klogd will not read the System.map file.

−2

Print two lines for each symbol, one showing the symbol and the other showing its numerical value (address).

Files

/usr/include/linux/kernel.h, /usr/include/sys/syslog.h

Sources for definitions of each logging level.

/proc/kmsg

A file examined by klogd for messages.

/var/run/klogd.pid

klogd’s process ID.

Name

last

Synopsis

last [options] [username] [ttynumber]

Display a list of the most recent logins, taken from the file /var/log/wtmp by default. If you specify a tty number or username, the output displays only the logins for that user or terminal.

Options

-a

Display the hostname from which logins originated in the last column.

-d

For remote logins, display both IP address and hostname.

-f filename

Get the list of logins from filename. The default source is /var/log/wtmp.

-i

Like -d, but display the IP address in numbers-and-dots notation.

-n number, -number

Choose how many lines of logins to display. Thus, last −7 or last -n 7 displays seven lines.

-R

Do not show the hostname.

-x

Display shutdown messages and runlevel messages.

Name

lastb

Synopsis

lastb [options] [username] [ttynumber]

Display a list of recent bad login attempts (from the /var/log/btmp file). Accepts the same option flags and arguments as last.

Name

lastlog

Synopsis

lastlog [options]

System administration command. Print the last login times for system accounts. Login information is read from the file /var/log/lastlog.

Options

-tn, --timen

Print only logins more recent than n days ago.

-uname, --username

Print only login information for user name.

Name

ld

Synopsis

ld [options] objfiles

Combine several objfiles, in the specified order, into a single executable object module (a.out by default). ld is the link editor and is often invoked automatically by compiler commands. ld accepts many options, the most common of which are listed here.

Options

-b format, --format=format

If ld is configured to accept more than one kind of object file, this option can be used to specify the input format. format should be a GNU Binary File Descriptor (BFD), as described in the BFD library. Use objdump -i to list available formats.

-call_shared

Link with dynamic libraries.

-d, -dc, -dp

Force the assignment of space to common symbols.

-defsym symbol=expression

Create the global symbol with the value expression.

-demangle[=style]

Force demangling of symbol names. Optionally set the demangling style. Turn off demangling with -nodemangle.

-e symbol

Set symbol as the address of the output file’s entry point.

-f name

Set the DT_AUXILIARY field of ELF shared object to name.

-fini name

Set the DT_FINI field of ELF shared object to the address of function name. The default function is _fini.

-h name

Set the DT_SONAME field of ELF shared object to name.

--help

Print help message, then exit.

-i

Produce a linkable output file; attempt to set its magic number to OMAGIC.

-init name

Set the DT_INIT field of ELF shared object to the address of function name. The default function is _init.

-larch, --library=archive

Include the archive file arch in the list of files to link.

-m linker

Emulate linker. List supported emulations with the -V option.

-n

Make text read-only; attempt to set NMAGIC.

-o output

Place output in output, instead of in a.out.

-oformat format

Specify output format.

-q

Retain relocation sections and contents in linked executables.

-r

Produce a linkable output file; attempt to set its magic number to OMAGIC.

-rpath dir

Add directory dir to the runtime library search path. Ignore additional paths normally read from the LD_RUN_PATH environment variable.

-rpath-link dirs

Specify path to search for shared libraries required by another shared library. The dirs argument can be a single directory, or multiple directories separated by colons. This overrides search paths specified in shared libraries themselves.

-s

Do not include any symbol information in output.

-shared

Create a shared library.

-static

Do not link with shared libraries.

-sort-common

Do not sort global common symbols by size.

-t

Print each input file’s name as it is processed.

--target-help

Print target-specific options, then exit.

-u symbol

Force symbol to be undefined.

-v, --version

Show version number.

--verbose

Print information about ld; print the names of input files while attempting to open them.

--warn-common

Warn when encountering common symbols combined with other constructs.

--warn-once

Provide only one warning per undefined symbol.

-x

With -s or -S, delete all local symbols. These generally begin with L.

-z keyword

Mark the object for special behavior specified by keyword. ld recognizes the following keywords:

combreloc

Object combines and sorts multiple relocation sections for dynamic symbol lookup caching.

defs

Disallow undefined symbols.

initfirst

Initialize object first at runtime.

execstack

Marks the object as requiring an executable stack.

interpose

Interpose object’s symbol table before all but the primary executable’s symbol table.

loadfltr

Process object’s filter immediately at runtime.

multidefs

Allow multiple definitions of a single symbol. Use the first definition.

nocombreloc

Disable combining multiple relocation sections.

nocopyreloc

Disable copy relocation.

nodefaultlib

Ignore default library search path when seeking dependencies for object.

nodelete

Do not unload object at runtime.

nodlopen

Object is not available to dlopen.

nodump

Object cannot be dumped by dldump.

now

Non-lazy runtime binding.

origin

Object may contain $ORIGIN.

relro

Create an ELF PT_GNU_RELRO segment header in the object.

-E, --export-dynamic

Add all symbols to dynamic symbol table, not just those referenced by linked objects.

-EB

Link big-endian objects.

-EL

Link little-endian objects.

-F name

Set DT_FILTER field of ELF shared object to name.

-Ldir, --library-path=dir

Search directory dir before standard search directories (this option must precede the -l option that searches that directory).

-M

Display a link map on standard output.

-Map file

Print a link map to file.

-N

Allow reading of and writing to both data and text. Mark ouput if it supports Unix magic numbers. Do not page-align data.

-O level

Optimize. level should be 1, 2, 3, or 0. The default is 1. 0 turns off optimization; 3 optimizes the most.

-R file

Obtain symbol names and addresses from file, but suppress relocation of file and its inclusion in output.

-S

Do not include debugger symbol information in output.

-T file

Execute script file instead of the default linker script.

-Tbss address

Begin bss segment of output at address.

-Tdata address

Begin data segment of output at address.

-Ttext address

Begin text segment of output at address.

-Ur

Synonymous with -r except when linking C++ programs, where it resolves constructor references.

-X

With -s or -S, delete local symbols beginning with L.

-V

Show version number and emulation linkers for -m option.

Name

ldconfig

Synopsis

ldconfig [options] directories

System administration command. Examine the libraries in the given directories, /etc/ld.so.conf.d, /usr/lib, and /lib; update links and cache where necessary. Usually run in startup files or after the installation of new shared libraries.

Options

-C filename

Use filename instead of /etc/ld.so.cache.

-f filename

Use filename instead of /etc/ld.so.conf.

-l

Library mode. Expect libraries as arguments, not directories. Manually link specified libraries.

-n

Suppress examination of /usr/lib and /lib and reading of /etc/ld.so.conf; do not cache.

-N

Do not cache; only link.

-p

Print all directories and candidate libraries in the cache. Used without arguments.

-v

Verbose mode. Include version number, and announce each directory as it is scanned and links as they are created.

-X

Do not link; only rebuild cache.

Files

/lib/ld.so

Linker and loader.

/etc/ld.so.conf

List of directories that contain libraries.

/etc/ld.so.cache

List of the libraries found in those libraries mentioned in /etc/ld.so.conf.

Name

ldd

Synopsis

ldd [options] programs

Display a list of the shared libraries each program requires.

Options

-d, --data-relocs

Process data relocations. Report missing objects (for ELF objects only).

-r, --function-relocs

Process relocations for both data objects and functions. Report any that are missing (for ELF objects only).

-v, --verbose

Verbose mode. Display extra information, including symbol versions.

--help

Print help message, then exit.

--version

Display the linker’s version, then exit.

Name

less

Synopsis

less [options] [filename]

less is a program for paging through files or other output. It was written in reaction to the perceived primitiveness of more (hence its name) and allows backward as well as forward paging. Some commands may be preceded by a number.

Options

-[z]num, --window=num

Set number of lines to scroll to num. Default is one screenful. A negative num sets the number to num lines less than the current number.

+[+]command

Run command on startup. If command is a number, jump to that line. The option ++ applies this command to each file in the command-line list.

-?, --help

Print help screen.

-a, --search-skip-screen

When searching, begin after last line currently displayed. (Default is to search from second line displayed.)

-bbuff, --buffers=buff

Specify the amount of buffer space to use for each file in 1 KB units. (Default is to use 64 KB per file.)

-B, --auto-buffers

Do not automatically allocate buffer space to hold all data read from a pipe. If -b is specified, allocate that amount of space, or default to 64 KB. If necessary, allow information from previous screens to be lost.

-c, --clear-screen

Redraw screen from top, not bottom.

-f, --force

Force opening of directories and devices; do not print warning when opening binaries.

-F, --quit-if-one-screen

Exit without displaying anything if first file can fit on a single screen.

-g, --hilite-search

Highlight only string found by past search command, not all matching strings.

-G, --HILITE-SEARCH

Never highlight matching search strings.

-hnum, --max-back-scroll=num

Never scroll backward more than num lines at once.

-i, --ignore-case

Make searches case-insensitive, unless the search string contains uppercase letters.

-I, --IGNORE-CASE

Make searches case-insensitive, even when the search string contains uppercase letters.

-jnum, --jump-target=num

Position target line on line num of screen. Target line can be the result of a search or a jump. Count lines beginning from 1 (top line). A negative num is counted back from bottom of screen.

-kfile, --lesskey-file=file

Read file to define special key bindings. See lesskey for more information.

-K, --quit-on-intr

Exit immediately on interrupt (usually ^-C).

-m, --long-prompt

Display more-like prompt, including percent of file read.

-M, --LONG-PROMPT

Prompt more verbosely than with -m, including percentage, line number, and total lines.

-n, --line-numbers

Do not calculate line numbers. Affects -m and -M options and = and v commands (disables passing of line number to editor).

-N, --LINE-NUMBERS

Print line number before each line.

-ofile, --log-file=file

When input is from a pipe, copy output to file as well as to screen. (Prompt for overwrite authority if file exists.)

-O file, --LOG-FILE=file

Similar to -o, but do not prompt when overwriting file.

-ppattern, --pattern=pattern

At startup, search for first occurrence of pattern.

-P[mM=]prompt

Set the prompt displayed by less at the bottom of each screen to prompt. The m sets the prompt invoked by the -m option, the M sets the prompt invoked by the -M option, and the = sets the prompt invoked by the = command. Special characters (described in the less manpage), can be used to print statistics and other information in these prompts.

-q, --quiet, --silent

Disable ringing of bell on attempts to scroll past EOF or before beginning of file. Attempt to use visual bell instead.

-Q, --QUIET, --SILENT

Never ring terminal bell.

-r, --raw-control-chars

Display “raw” control characters instead of using ^x notation. This sometimes leads to display problems, which might be fixed by using -R instead.

-R, --RAW-CONTROL-CHARS

Like r, but only output “raw” ANSI color escape characters.

-s, --squeeze-blank-lines

Print successive blank lines as one line.

-S, --chop-long-lines

Cut, do not fold, long lines.

-ttag, --tag=tag

Edit file containing tag. Consult ./tags (constructed by ctags).

-T file, --tag-file=file

With the -t option or :t command, read file instead of ./tags.

-u, --underline-special

Treat backspaces and carriage returns as printable input characters.

-U, --UNDERLINE-SPECIAL

Treat backspaces, tabs and carriage returns as control characters.

-V, --version

Display version and exit.

-w, --hilite-unread

Show the line to which a movement command has skipped, phrases displayed by a search command, or the first unread line during a normal scroll by highlighting text in reverse video.

-W, --HILITE-UNREAD

Show phrases displayed by a search command, or the first unread line of any forward movement that is more than one line, by highlighting text in reverse video.

-x n..., --tabs=n...

Set tab stops to every n characters. Default is 8. If multiple values are given for n in a comma-separated list, set the tab stops to those values.

-X, --no-init

Do not send initialization and deinitialization strings from termcap to terminal.

-y n, --max-forw-scroll=n

Never scroll forward more than n lines at once.

Commands

Many commands can be preceded by a numeric argument, referred to as number in the command descriptions.

SPACE, ^V, f, ^F

Scroll forward the specified number of lines (default one windowful).

ESC-SPACE

Like SPACE, but scroll forward a complete screenful.

z

Similar to SPACE, but if number is specified, reset the default to that number.

RETURN, ^N, e, ^E, j, ^J

Scroll forward. Default is one line. Display all lines, even if the default is more lines than the screen size.

d, ^D, PageDown

Scroll forward. Default is one-half the screen size. The number of lines may be specified, in which case the default is reset.

b, ^B, ESC-v

Scroll backward, but if number is specified, scroll back that number of lines. Default is one windowful.

w

Like b, but if number is specified, reset the default to that number.

y, ^Y, ^P, k, ^K

Scroll backward. Default is one line. Display all lines, even if the default is more lines than the screen size.

u, ^U, PageUp

Scroll backward. Default is one-half the screen size. The number of lines may be specified, in which case the default is reset.

r, ^R, ^L

Redraw screen.

R

Like r, but discard buffered input.

F

Scroll forward. On EOF, continue trying to find more output, behaving similarly to tail -f.

g, <, ESC-<

Skip to a line. Default is 1.

G, >, ESC->

Skip to a line. Default is the last line.

p, %

Skip to a position number percent of the way into the file.

{

If the top line on the screen includes a {, find its matching }. If the top line contains multiple {s, use number to determine which one to use in finding a match.

}

If the bottom line on the screen includes a }, find its matching {. If the bottom line contains multiple }s, use number to determine which one to use in finding a match.

(

If the top line on the screen includes a (, find its matching ). If the top line contains multiple (s, use number to determine which one to use in finding a match.

)

If the bottom line on the screen includes a ), find its matching (. If the bottom line contains multiple )s, use number to determine which one to use in finding a match.

[

If the top line on the screen includes a [, find its matching ]. If the top line contains multiple [s, use number to determine which one to use in finding a match.

]

If the bottom line on the screen includes a ], find its matching [. If the bottom line contains multiple ]s, use number to determine which one to use in finding a match.

ESC-^F char1 char2

Behave like { but substitute char1 and char2 for { and } in the search.

ESC-^B char1 char2

Behave like } but substitute char1 and char2 for { and } in the search.

m let

Use the specified lowercase letter to mark the current position.

' (single apostrophe) let

Use the specified lowercase letter and to return to the position marked by that letter. With a second apostrophe, return to the previous position where the last “large” movement began. With ^, return to the beginning of the file; with $, return to the end of the file.

^X^X

Same as ‘.

/pattern

Find next occurrence of pattern, starting at second line displayed. Some special characters can be entered before pattern:

!, ^N

Find lines that do not contain pattern.

*, ^E

If current file does not contain pattern, continue through the rest of the files in the command-line list.

@, ^F

Search from the first line in the first file specified on the command line, no matter what the screen currently displays.

^K

Hightlight matching text on the current screen, but do not move there.

^R

Use text comparison; do not interpret regular expressions.

?pattern

Search backward, beginning at the line before the top line. The use of special characters is the same as for /pattern.

ESC-/pattern

Same as /*.

ESC-?pattern

Same as ?*.

n

Repeat last pattern search.

N

Repeat last pattern search in the reverse direction.

ESC-n

Repeat previous search command, but as though it were prefaced by *.

ESC-N

Repeat previous search command, but as though it were prefaced by * and in the reverse direction.

ESC-u

Toggle search highlighting.

&pattern

Display only lines that match the pattern. With ^N or !, display lines that do not match; with ^R, do not interpret regular expressions.

:d

Remove the current file from the list of files.

:e [filename]

Read in filename and insert it into the command-line list of filenames. Without filename, reread the current file. Replace a percent sign (%) in the filename with the name of the current file; replace a hash mark (#), with the name of the previous file.

^X^V, E

Same as :e.

:n

Read in next file in command-line list or the file indicated by number, if specified.

:p

Read in previous file in command-line list or the file indicated by number, if specified.

:x

Read in first file in command-line list or the file indicated by number, if specified.

s filename

If input is a pipe, save to the specified file.

t

Go to the next tag. See the -t option.

T

Go to the previous tag. See the -T option.

:f, =, ^G

Print filename, position in command-line list, line number on top of window, total lines, byte number, and total bytes.

- (single dash)

Expects to be followed by a command-line option letter. Toggle the value of that option or, if appropriate, prompt for its new value.

--

Like -, but takes a long option name.

-+

Expects to be followed by a command-line option letter. Reset that option to its default.

--+

Like -+, but takes a long option name.

_ (underscore)

Expects to be followed by a command-line option letter. Display that option’s current setting.

_ _

Like _, but takes a long option name.

+command

Execute command each time a new file is read in.

q, :q, :Q, ZZ

Exit.

v

Not valid for all versions. Invoke editor specified by $VISUAL or $EDITOR, or vi if neither is set.

! [command]

Not valid for all versions. Invoke $SHELL or sh. If command is given, run it and then exit. Replace % with the name of the current file, # with the name of the previous file, and !! with the last shell command.

| mark-letter command

Not valid for all versions. Pipe fragment of file (from first line on screen to mark-letter) to command. mark-letter may be ^ for the beginning of the file, $ for the end of the file, or . or newline to pipe the current screen.

Prompts

The prompt interprets certain sequences specially. Those beginning with % are always evaluated. Those beginning with ? are evaluated if certain conditions are true. Some prompts determine the position of particular lines on the screen. These sequences require that a method of determining that line be specified. See the -P option and the manpage for more information.

Name

lesskey

Synopsis

lesskey [-o output-file | --output=output-file] [input-file]

Configure keybindings for the less command using a configuration file. The input file defaults to ˜/.lesskey and the output file to ˜/.less unless you specify otherwise.

Configuration file format

The configuration file for lesskey has one to three sections. These are marked by a line containing a # symbol and the name of the section: #command, #line-edit, and #env.

The #command section

The command section determines the keys used for actions within less. Each line should contain the key or key combination you wish to define, a space or tab, and the name of the action to perform. You may also add an extra string at the end, which will be performed at the end of the first action.

Keys you define should be entered as you plan to type them, with the following exceptions:

Backspace: \b

Backslash: \\

Caret: \^

Escape: \e

Newline: \n

Return: \r

Tab: \t

Up arrow: \ku

Down arrow: \kd

Right arrow: \kr

Left arrow: \kl

Page up: \kU

Page down: \kD

Home: \kh

End: \ke

Delete: \kx

The actions that can be defined are:

invalid (creates error)

noaction

forw-line

back-line

forw-line-force

forw-scroll

back-scroll

forw-screen

back-screen

forw-window

back-window

forw-screen-force

forw-forever

repaint-flush

repaint

undo-hilite

goto-line

percent

left-scroll

right-scroll

forw-bracket

back-bracket

goto-end

status

forw-search

back-search

repeat-search

repeat-search-all

reverse-search

reverse-search-all

filter

set-mark

goto-mark

examine

next-file

index-file

prev-file

next-tag

previous-tag

remove-file

toggle-option

display-option

pipe

visual

shell

firstcmd

help

version (display version)

digit (display number)

quit

The #line-edit section

The line editing section lets you choose keys for the line-editing capabilities of less in a similar manner to the #command section, although without the “extra” string after the command. The line editing actions that can be defined are:

forw-complete

back-complete

expand

literal

right

left

word-left

word-right

insert

delete

word-delete

word-backspace

home

end

up

down

The #env section

The third section, like the second, is optional, and you can use it to override environment variables that affect less. Each line consists of a variable, the equals sign (=), and the value to which you wish to set the variable. The most important ones are LESS, which allows you to select additional flags to pass to less when you run it, and LESSCHARSET, which lets you choose a character set. See the less manpage for a complete list of environment variables that affect the program.

Name

lftp

Synopsis

lftp [options] [url]

File transfer program with more features than ftp. The lftp command allows FTP and HTTP protocol transfers, plus other protocols including FISH (SSH based), FTPS, and HTTPS. It uses a shell-like command interface and offers job control in a manner similar to bash. lftp has two important reliability features: it resumes failed or interrupted transactions, and it goes into the background automatically if it is quit in the middle of a file transfer.

Options

-d

Run in debug mode.

-e commands

Start, execute the specified commands, and then wait for further instructions.

-p portnumber

Connect to the specified port number.

-u user[,pass]

Login to the server with the username (and, optionally, password) you specify.

-f scriptfile

Run the specified script file of lftp commands, then exit.

-c commands

Run the commands specified, then exit.

Commands

The lftp commands are similar to those for ftp. However, lftp lacks or uses different mechanisms for a number of commands, including $, ascii, binary, case, and macdef. It also adds the following:

alias [name [value]]

Create an alias for a command. For example, you could set dir to be an alias for ls -lf.

anon

Set the username to anonymous. This is the default username.

at

Execute a command at a given time, as with the at command in an actual shell.

bookmark [arguments]

The lftp bookmark command used with the following arguments will add, delete, edit, import, or list bookmarks, respectively:

- add name url

- del name

- edit

- import type

- list

cache

Work with the local memory cache. This command should be followed by the arguments:

stat

Display the status for the cache.

on|off

Turn caching on or off.

flush

Empty the cache.

size n

Set the maximum size for the cache. Setting it to −1 means unlimited.

expire nu

Set the cache to expire after n units of time. You can set the unit (u) to seconds (s), minutes (m), hours (h), or days (d). For example, for a cache that expires after an hour, use the syntax cache expire 1h.

close

Close idle connections with the current server. This differs from ftp, which closes all connections. If you have connections to multiple servers and wish to close all idle connections, add the -a flag.

command cmd args

Execute the specified lftp command, with the specified arguments, ignoring any aliases created with the alias command.

mirror [options] [remotedir [localdir]]

Copy a directory exactly. The mirror command accepts the following arguments:

-c, --continue

If mirroring was interrupted, resume it.

-e, --delete

Delete local files that are not present at the remote site.

-s, --allow-suid

Keep the suid/sgid bits as set on the remote site.

-n, --only-newer

Get only those files from the remote site that have more recent dates than the files on the local system. Cannot be used with the -c argument.

-r, --no-recursion

Do not get any subdirectories.

--no-umask

Do not use umask when getting file modes. See umask for more information about file modes.

-R, --reverse

Mirror files from the local system to the remote system. With this argument, make sure that you specify the local directory first and the remote directory second. If you do not specify both directories, the second is assumed to be the same as the first. If you choose neither, the operation occurs in the current working directories.

-L, --dereference

When mirroring a link, download the file the link points to rather than just the link.

-N filename, --newer-than filename

Get all files newer than the file filename.

-P n, --parallel[=n]

Download n files in parallel.

-i regex, --include regex

Get only the files whose names match the regular expression regex. See Chapter 7 for information about regular expressions.

-x regex, --exclude regex

Do not get the files whose names match regex. See Chapter 7 for information about regular expressions.

-v n, --verbose=n

Set the verbose level. You can set n from 0 (no output) to 3 (full output) using a number or by repeating the v. For example, -vvv is level 3 verbose mode.

--use-cache

Use the cache to get directory listings.

--remove-source-files

Move, rather than copy, files when mirroring.

set [variable | value]

Set a preference variable for lftp. With no arguments, list the variables that have been changed; with no arguments and with the -a or -d flags, list all values or default values, respectively.

See the lftp manpage for a complete list of preference variables that can be set.

wait [n | all]

Wait for the job or jobs you specify by number, or all jobs, to terminate.

Name

lftpget

Synopsis

lftpget [options] url

Uses the lftp program to fetch the specified URL, which may be HTTP, FTP, or any of the protocols supported by lftp.

Options

-c

Continue or restart a paused transaction.

-d

Display debugging output.

-v

Verbose mode; display more information about transactions.

Name

link

Synopsis

link file1 file2

Create a link between two files. This is the same as the ln command, but it has no error checking because it uses the link( ) system call directly.

Name

ln

Synopsis

ln [options] sourcename [destname]
ln [options] sourcenames destdirectory

Create pseudonyms (links) for files, allowing them to be accessed by different names. Links may be “hard” or “soft.” A hard link creates two names for the same file, and a soft, or symbolic, link creates a second file which acts as a shortcut to the first. The default is to create hard links; use -s or --symbolic to create symbolic links.

The first form links sourcename to destname, where destname is usually either a new filename or (by default) a file in the current directory with the same name as sourcename. If destname is an existing file, it is overwritten; if destname is an existing directory, a link named sourcename is created in that directory. The second form creates links in destdirectory, each link having the same name as the file specified.

Options

-b, --backup[=control]

Back up any existing files. With the long version of the command, the optional control parameter controls the kind of backup. When no control is specified, ln attempts to read the control value from the VERSION_CONTROL environment variable. Accepted values are:

none, off

Never make backups.

numbered, t

Make numbered backups.

existing, nil

Match existing backups, numbered or simple.

simple, never

Always make simple backups.

-d, -F, --directory

Allow hard links to directories. Available to privileged users.

-f, --force

Force the link (don’t prompt for overwrite permission).

--help

Print a help message and then exit.

-i, --interactive

Prompt for permission before removing files.

-n, --no-dereference

Replace symbolic links to directories instead of dereferencing them. --force is useful with this option.

-s, --symbolic

Create a symbolic link. This lets you link across filesystems, and also see the name of the link when you run ls -l (otherwise, there’s no way to know the name that a file is linked to).

-S suffix, --suffix=suffix

Append suffix to files when making backups, instead of the default ˜.

-t directory, --target-directory=directory

Create links in the specified directory.

-v, --verbose

Verbose mode.

--version

Print version information and then exit.

Name

loadkeys

Synopsis

loadkeys [options] [filename]

Load a keymap from a specified file, usually one of the keymaps stored in /lib/kbd/keymaps. If you create your own keymap file, the related commands showkey, keymaps, and dumpkeys will be useful as well. Note that loadkeys applies only to virtual consoles; to change your X keyboard configuration, use xmodmap or set--xkbmap, or the graphical keyboard-layout switching tools that are included with your desktop environment.

Options

-c, --clearcompose

Clear the compose, or accent, table in the kernel.

-d, --default

Load the default keymap. The same as running loadkeys defkeymap.

-h, --help

Display help and usage information.

-m, --mktable

Instead of loading the table, output maps as C language declarations.

-s, --clearstrings

Clear the string table in the kernel.

-v, --verbose

Operate verbosely. For extra effect, repeat.

Name

locale

Synopsis

locale [options] [names]

Print report on current locale settings. Locales determine the country-specific settings for a system, including character encodings, the formatting of dates, honorifics, diagnostic messages, currency, printer-paper sizes, and default measurements. Locale settings are essentially a dictionary of settings specified by keyword. The keywords are grouped together into related categories whose names begin with LC_. Each category has a related environment variable of the same name from which it reads its locale setting. Supply keyword or category names as names to examine their values. You can also use the special keyword charmap to see the current character mapping. When executed with no arguments, locale prints the value of all locale-related environment variables.

Options

-a, --all-locales

Print all available locale settings installed on the system.

-c, --category-name

Print the category related to each name argument.

-k, --keyword-name

Print keywords along with their settings for each name argument.

-m, --charmaps

Print all available character maps.

Environment variables

LANG

The default value for unset internationalization variables. If not set, the system’s default value is used.

LC_ADDRESS

Postal settings, country, and language names and abbreviation.

LC_COLLATE

String and character sorting and comparison settings.

LC_CTYPE

Character attributes, including case conversion mappings, and categories of characters (whitespace, digit, lower, upper, punctuation, etc.).

LC_IDENTIFICATION

Information related to the current locale definition, including its title, source, revision, and contact information for its author.

LC_MEASUREMENT

Measurement units, metric or other.

LC_MESSAGES

Settings for yes/no prompts and other informative and diagnostic messages.

LC_MONETARY

Currency formats and symbols.

LC_NAME

Formats for names and honorifics.

LC_NUMERIC

Nonmonetary number formats.

LC_PAPER

Default paper sizes for printing and pagination.

LC_TELEPHONE

Telephone number formats.

LC_TIME

Date and time formats.

LC_ALL

When set, overrides the values of all other internationalization variables.

Examples

Print the category name and all keywords for date and time settings:

locale -ck LC_TIME

Print the strings used for days of the week and months of the year:

locale day mon

Name

locate

Synopsis

locate [options] pattern

Search database(s) of filenames and print matches. Matches include all files that contain pattern unless pattern includes metacharacters, in which case locate requires an exact match. *, ?, [, and ] are treated specially; / and . are not. Searches are conducted against a database of system contents that is updated periodically. To update the database, use the updatedb command.

Options

-b, --basename

Look only at the basename when searching for matches.

-c, --count

List only the match count, not the individual filenames.

-d path, --database=path

Search databases in path. path must be a colon-separated list.

-h, --help

Print a help message and then exit.

-i, --ignore-case

Ignore case when performing matches.

-q, --quiet

Run quietly, printing no error messages.

-r regexp, --regexp regexp

Search for a basic regular expression, with no patterns allowed. May be issued more than once.

--regex

Treat all patterns as extended regular expressions.

-S, --statistics

Print statistics about each database and then exit.

-V, --version

Print version information and then exit.

-w, --wholename

Look at the entire pathname when searching for matches (the default).

Name

lockfile

Synopsis

lockfile [options] filenames

Create semaphore file(s), used to limit access to a file. When lockfile fails to create some of the specified files, it pauses for eight seconds and retries the last one on which it failed. The command processes flags as they are encountered (i.e., a flag that is specified after a file will not affect that file). This command is most often used by scripts and applications as a way to avoid multiple users changing the same file at once.

Options

-sleeptime

Number of seconds lockfile waits before retrying after a failed creation attempt. Default is 8.

-!

Invert return value. Useful in shell scripts.

-l lockout_time

Time (in seconds) after a lockfile was last modified at which it will be removed by force. See also -s.

-ml, -mu

If the permissions on the system mail spool directory allow it or if lockfile is suitably setgid, lockfile can lock and unlock your system mailbox with the options -ml and -mu, respectively.

-r retries

Stop trying to create files after this many retries. The default is −1 (never stop trying). When giving up, remove all created files.

-s suspend_time

After a lockfile has been removed by force (see -l), a suspension of 16 seconds takes place by default. (This is intended to prevent the inadvertent immediate removal of any lockfile newly created by another program.) Use -s to change the default suspend time.

Name

logger

Synopsis

logger [options] [message...]

TCP/IP command. Add entries to the system log (via syslogd). If no message is given on the command line, standard input is logged.

Options

-d

When writing to a socket with -s, use a datagram instead of a stream.

-f file

Read message from file.

-i

Include the process ID of the logger process.

-p pri

Enter message with the specified priority pri. Default is user.notice.

-s

Log message to standard error as well as to the system log.

-t tag

Mark every line in the log with the specified tag.

-u socket

Write log to socket instead of to the syslog.

--

Accept no further options. Consider whatever is to the right of the hyphens as the message to be logged.

Name

login

Synopsis

login [name | option]

Log into the system. login asks for a username (name can be supplied on the command line) and password (if appropriate).

If successful, login updates accounting files, sets various environment variables, notifies users if they have mail, and executes startup shell files.

Only the root user can log in when /etc/nologin exists. That file is displayed before the connection is terminated. Furthermore, root may connect only on a tty that is listed in /etc/securetty. If ˜/.hushlogin exists, execute a quiet login. If /var/adm/lastlog exists, print the time of the last login.

Options

-f

Suppress second login authentication.

-h host

Specify name of remote host. Normally used by servers, not humans; may be used only by root.

-p

Preserve previous environment.

Name

logrotate

Synopsis

logrotate [options] config_files

System administration command. Manipulate logfiles according to commands given in config_files.

Options

-d, --debug

Debug mode. No changes will be made to logfiles.

-f, --force

Force rotation of logfiles.

-h, --help

Describe options.

-m command, --mail command

Use the specified command to mail logfiles. The default command is /bin/mail -s.

-s file, --state file

Save state information in file. The default is /var/lib/logrotate.status.

--usage

Show syntax and options.

-v, --verbose

Describe what is being done and what logfiles are affected.

Configuration commands

Logrotate directives may appear on their own or as part of logfile definitions--instructions for specific logfiles. You may use wildcards to specify those files. Enclose directives for logfile definitions in a beginning and ending curly brace. For example:

compress
/var/log/messages {
rotate 5
weekly
}

compress

Compress old versions of logfiles with gzip.

compresscmd command

Use command to compress logfiles. Default is gzip.

compressext extension

Append filename extension to compressed files instead of the compress command’s default.

compressoptions options

Specify options to pass to the compress command. Default for gzip is −9 for maximum compression.

copy

Copy logfile, but do not change the original.

copytruncate

Copy logfile, then truncate it in place. For use with programs whose logging cannot be temporarily halted.

create [permissions] [owner] [group]

After rotation, re-create logfile with the specified permissions, owner, and group. permissions must be in octal. If any of these parameters is missing, the logfile’s original attributes will be used.

daily

Rotate logfiles every day.

delaycompress

Don’t compress logfile until the next rotation.

endscript

End a postrotate or prerotate script.

extension extension

Give rotated logfiles the specified extension. Any compression extension will be appended to this.

firstaction

May only be used as part of a logfile definition. Begin a shell script to execute once if any files match. The script ends when the endscript directive is read.

ifempty

Rotate logfile even if it is empty. Overrides the default notifempty option.

include file

Read the file into current file. If file is a directory, read all files in that directory into the current file.

lastaction

May only be used as part of a logfile definition. Begin a shell script to execute once after rotating all matching files and running any postrotate script. The script ends when the endscript directive is read.

mail address

Mail any deleted logs to address.

mailfirst

When using the mail command, mail the newly rotated log instead of the one being deleted.

maillast

When using the mail command, mail the log that is about to expire. This is the default behavior.

missingok

Skip missing logfiles. Do not generate an error.

monthly

Rotate logfiles only the first time logrotate is run in a month.

nocompress

Override compress.

nocopy

Override copy.

nocopytruncate

Override copytruncate.

nocreate

Override create.

nodelaycompress

Override delaycompress.

nomail

Override mail.

nomissingok

Override missingok.

noolddir

Override olddir.

nosharedscripts

Override sharedscripts. Run prerotate and postrotate scripts for each log rotated. This is the default.

notifempty

Override ifempty.

olddir directory

Move logs into directory for rotation. directory must be on the same physical device as the original logfiles.

postrotate

May only be used as part of a logfile definition. Begin a shell script to apply after the logfile is rotated. The script ends when the endscript directive is read.

prerotate

May only be used as part of a logfile definition. Begin a shell script to apply before a logfile is rotated. The script ends when the endscript directive is read.

rotate number

The number of times to rotate a logfile before removing it.

size n[k|M]

Rotate logfile when it is greater than n bytes. n can optionally be followed by k for kilobytes or M for megabytes.

sharedscripts

Run prescript and postscript only once for the session.

start n

Use n as the starting number for rotated logs. Default is 0.

tabooext [+] extlist

Replace taboo extension list with the given extlist. If + is specified, add to existing list. The default list is .rpmorig .rpmsave, v .swp .rpmnew ~.

weekly

Rotate logfiles if more than a week has passed since their last rotation.

uncompresscmd command

Use command to uncompress logfiles. Default is gunzip.

Name

look

Synopsis

look [options] string [file]

Search for lines in file (/usr/dict/words by default) that begin with string.

Options

-a

Use alternate dictionary, /usr/dict/web2.

-d

Compare only alphanumeric characters.

-f

Search is not case-sensitive.

-t character

Stop checking after the first occurrence of character.

Name

losetup

Synopsis

losetup [options] loopdevice [file]

System administration command. Set up and control loop devices. Attach a loop device to a regular file or block device, detach a loop device, or query a loop device. A loop device can be used to mount an image file as if it were a normal device.

Options

-d

Detach specified loopdevice.

-e encryption, -Enumber

Use specified kernel encryption module when performing writes and reads. (Usually NONE, DES, and XOR.) You may also specify the encryption module by number. When using DES encryption, you will be prompted for an initialization passphrase.

-o offset

Start reading data at offset bytes from the beginning of file.

-p fd

Read the passphrase from file descriptor fd.

Name

lpadmin

Synopsis

lpadmin [options]

System administration command. Configure CUPS printer queues. The command requires one of the following options: -d, -p, or -x. When a queue is configured to require a password, the lpadmin command will prompt for one.

Options

-d queue

Set the default destination for CUPS commands like lp and lpr to the specified queue.

-E

Always use encryption when connecting to the server.

-h server

Apply configuration commands remotely to the specified CUPS server.

-p printer print-options

Apply print-options (documented below) to the specified printer.

-x queue

Delete the specified queue. Abort any current print job and discard any pending print jobs.

Print options

Use these additional options with the -p option just listed:

-c class

Add printer to the specified class. Create class if it does not already exist.

-D description

Set the text description of the printer.

-E

Enable printer.

-L location

Set the printer location text.

-i script

Use the specified System V-style interface script.

-m filename

Use the specified System V interface script or PPD file found in the model directory.

-o name=value

Set the value of PPD or server option name. For a list of available PPD options, use the lpoptions command.

-P filename

Use the PPD specified by filename. This option overrides the -i printer option.

-r class

Remove printer from the specified class. Remove class if it has no printer entries.

-u allow:[@]name, -u deny:[@]name

Set user level access control. To specify a group instead of a user name, preface the name with @. You may also use the special names all and none.

-v uri

Set the device universal resource indicator, uri. If given as a filename, the command will automatically convert it to a file URI.

Name

lpinfo

Synopsis

lpinfo options

System administration command. Print information on available printer devices and drivers.

Options

-E

Force the use of encryption connecting to the server.

-l

Show a long, or verbose, listing.

-m

List available printer drivers.

-v

List available printer devices.

Name

lpmove

Synopsis

lpmove [option] jobdestination

System administration command. Move the specified print job to a new destination.

Option

-E

Force the use of encryption connecting to the server.

Name

lpq

Synopsis

lpq [options] [+interval]

Check the print spool queue for status of print jobs. For each job, display username, rank in the queue, filenames, job number, and total file size (in bytes). We document the CUPS printing system here; other versions will vary slightly.

Options

-a

Report on all printers listed in the server’s printcap database.

-E

Use encryption when connecting to a print server.

-h server[:port]

Specify an alternate server and optional port.

-l

Verbose mode. Print information about each file composing a job. Use -l multiple times to increase the information provided.

-P printer

Specify which printer to query. Without this option, lpq uses the default printer, normally set through lpadmin.

-U username

Specify an alternate username.

+interval

Check the queue every interval seconds until it is empty. For example, +10 reloads the queue every ten seconds.

Name

lpr

Synopsis

lpr [options] [files]

Send files to be printed. If no files are given, accept standard input. We document the CUPS printing system here; the older LPRng and BSD systems will vary slightly. CUPS lpr, for example, does not accept the options c, d, f, g, i, m, n, t, v, or w, used by LPRng.

Options

-# copies

Set the number of copies to print, from 1 to 100.

-C, J, T name

Set a name for the print job.

-E

Use encryption when connecting to a print server.

-H server[:port]

Specify an alternate server and optional port.

-l

Expect a binary or literal file on which minimal processing should be done. The same as -o raw.

-m

Send email when printing is complete.

-o option[=value]

Set printer-specific options. These vary by printer, but may include paper type and orientation, paper-tray selection, output order, and so forth. Check the complete CUPS user manual and your printer’s PPD file for the full list.

-p

Pretty-print a text document. Provides a shaded header containing page numbers, the job name, and the time and date of printing. Equivalent to -o prettyprint.

-P printername

Print to the specified printer. If no printer is given, prints to the default printer, usually set with lpadmin.

-q

Hold job for printing.

-r

Delete files after printing them.

-U username

Specify an alternate username.

Example

Print a simple file:

Lpr filename.txt

Name

lprm

Synopsis

lprm [options] [jobid]

Cancel print jobs. Job IDs can be obtained from lpq; if no job is specified, cancels the current job on the default printer.

Options

-

Remove all jobs available to the user. Same as specifying jobid as ALL.

-E

Use encryption.

-h server[:port]

Specify an alternate server and optional port.

-P printer

Specify printer queue. If no printer is specified, the default printer is used.

-U username

Specify an alternate username.

Name

lpstat

Synopsis

lpstat [options] [queues]

Show the status of the print queue or queues. With options that take a list argument, omitting the list produces all information for that option. list can be separated by commas or, if enclosed in double quotes, by spaces. For the LPRng print service, lpstat is a frontend to the lpq program. With no arguments, lpstat shows jobs queued by the current user.

Options

-a [list]

Show whether the list of printer or class names is accepting requests.

-c [list]

Show information about printer classes named in list.

-d

Show the default printer destination.

-E

Use encryption when connecting to the print server.

-I

When showing printers, classes, or jobs, print a long listing.

-o [list]

Show the status of output requests. list contains printer names, class names, or request IDs.

-p [list]

Show the status of printers named in list.

-r

Show whether the print scheduler is on or off.

-s

Summarize the print status (show almost everything).

-t

Show all status information (report everything).

-u [list]

Show request status for users on list. Use all to show information on all users.

-U username

Specify an alternate username.

-v [list]

Show printers and the devices they are attached to.

Name

ls

Synopsis

ls [options] [names]

List contents of directories. If no names are given, list the files in the current directory. With one or more names, list files contained in a directory name or that match a file name. names can include filename metacharacters. The options let you display a variety of information in different formats. The most useful options include -F, -R, -l, and -s. Some options don’t make sense together (e.g., -u and -c).

Options

−1, --format=single-column

Print one entry per line of output.

-a, --all

List all files, including the normally hidden files whose names begin with a period.

-A, --almost-all

List all files, including the normally hidden files whose names begin with a period. Does not include the . and .. directories.

-b, --escape

Display nonprinting characters in octal and alphabetic format.

-B, --ignore-backups

Do not list files ending in ˜ unless given as arguments.

-c, --time=ctime, --time=status

List files by status change time (ctime), not creation/modification time. With -l, show ctime and sort by filename; with -lt, show and sort by ctime; otherwise, sort by ctime.

-C, --format=vertical

List files in columns (the default format).

--color[=when]

Colorize the names of files depending on the type of file. Accepted values for when are never, always, or auto.

-d, --directory

Report only on the directory, not its contents; do not dereference symbolic links.

-D, --dired

List in a format suitable for Emacs dired mode.

-f

Print directory contents in order, without attempting to sort them.

-F, --classify, --indicator-style=classify

Flag filenames by appending / to directories, * to executable files, @ to symbolic links, | to FIFOs, and = to sockets.

--full-time

List times in full, rather than using the standard abbreviations.

-g

Long listing like -l, but don’t show file owners.

-G, --no-group

In long format, do not display group name.

--group-directories-first

Display directories before files.

-h, --human-readable

Print sizes in kilobytes and megabytes.

-H, --dereference-command-line

When symbolic links are given on the command line, follow the link and list information from the actual file.

--help

Print a help message and then exit.

-i, --inode

List the inode for each file.

-I, --ignore pattern

Do not list files whose names match the shell pattern pattern, unless they are given on the command line.

--indicator-style=none

Display filenames without the flags assigned by -p or -f (default).

-k

If file sizes are being listed, print them in kilobytes. This option overrides the environment variable POSIXLY_CORRECT.

-l, --format=long, --format=verbose

Long format listing (includes permissions, owner, size, modification time, etc.).

-L, --dereference

List the file or directory referenced by a symbolic link rather than the link itself.

-m, --format=commas

Merge the list into a comma-separated series of names.

-n, --numeric-uid-gid

Like -l, but use group ID and user ID numbers instead of owner and group names.

-N, --literal

Display special graphic characters that appear in filenames.

-o

Long listing like -l, but don’t show group information.

-p, --indicator-style=slash

Mark directories by appending / to them.

-q, --hide-control-chars

Show nonprinting characters as ? (default for display to a terminal).

-Q, --quote-name

Quote filenames with “; quote nongraphic characters.

-r, --reverse

List files in reverse order (by name or by time).

-R, --recursive

List directories and their contents recursively.

-s, --size

Print file size in blocks.

-S, --sort=size

Sort by file size, largest to smallest.

--show-control-chars

Show nonprinting characters verbatim (default for printing to a file).

--si

Similar to -h, but uses powers of 1000 instead of 1024.

-t, --sort=time

Sort files according to modification time (newest first).

-u, --time=atime, --time=access, --time=use

Sort files according to file-access time. With -l, show access time and sort by filename; with -lt, show and sort by access time; otherwise sort by access time.

-U, sort=none

Do not sort files.

-v, --sort=version

Interpret the digits in names such as file.6 and file.6.1 as versions, and order filenames by version.

--version

Print version information on standard output, then exit.

-w n, --width=n

Format output to fit n columns.

-x, --format=across, --format=horizontal

List files in rows going across the screen.

-X, sort=extension

Sort by file extension, then by filename.

Name

lsattr

Synopsis

lsattr [options] [files]

Print attributes of files on a Linux Second Extended File System. See also chattr.

Options

-a

List all files in specified directories.

-d

List attributes of directories, not of contents.

-R

List directories and their contents recursively.

-v

List version of files.

-V

List version of lsattr and then exit.

Name

lspci

Synopsis

lspci [options]

System administration command. List all Peripheral Component Interconnect (PCI) devices. This command has many options that are useful for debugging device drivers. Here we document some of the more common options:

Options

-b

Show IRQ and addresses as seen by the cards instead of the kernel.

-t

Print a tree showing connections between devices.

-m

Print information with quoted strings suitable for use by scripts.

-n

Print vendor and device codes as numbers.

-v, -vv

List devices verbosely. Use the second form for very verbose listings.

Name

lsmod

Synopsis

lsmod

System administration command. List all loaded modules: name, size (in 4 KB units), and, if appropriate, a list of referring modules. The same information is available in /proc/modules if the /proc directory is enabled on the system.

Name

lsusb

Synopsis

lsusb [options]

System administration command. List all Universal Serial Bus (USB) devices. This command has many options of use for debugging device drivers. Here we document some of the more common options.

Options

-b

Show IRQ and addresses as seen by the cards instead of the kernel.

-D device

Only show information about the specified device. This should be given as a file in the /proc/bus/usb directory--e.g., /proc/bus/usb/001/001.

-t

Print a tree showing connections between devices.

-v, -vv

List devices verbosely. Use the second form for very verbose listings.

Name

m4

Synopsis

m4 [options] [macros] [files]

Macro processor for C and other files.

Options

-e, --interactive

Operate interactively, unbuffered, ignoring interrupts.

-dflags, --debug=flags

Specify flag-level debugging.

--help

Print help message, then exit.

-ln, --arglength=n

Specify the length of debugging output.

-o file, --error-output=file

Place output in file. Despite the name, print error messages on standard error.

-P, --prefix-built-ins

Prepend m4_ to all built-in macro names.

-s, --synclines

Insert #line directives for the C preprocessor.

-tname, --trace=name

Insert name into symbol table as undefined. Trace macro from the point it is defined.

--version

Print version, then exit.

-Bn

Set the size of the pushback and argument collection buffers to n (default is 4096).

-Dname[=value], --define=name[=value]

Define name as value or, if value is not specified, define name as null.

-E, --fatal-warnings

Consider all warnings to be fatal, and exit after the first of them.

-Ffile, --freeze-state=file

Record m4’s frozen state in file for later reloading.

-G, --traditional

Behave like traditional m4, ignoring GNU extensions.

-Hn, --hashsize=n

Set symbol-table hash array to n (default is 509).

-Idirectory, --include=directory

Search directory for include files.

-Ln, --nesting-limit=n

Change artificial nesting limit to n.

-Q, --quiet, --silent

Suppress warning messages.

-Rfile, --reload-state=file

Load state from file before starting execution.

-Uname, --undefine=name

Undefine name.

Name

mail

Synopsis

mail [options] [users]

Read mail or send mail to other users. mail is now generally a symbolic link to mailx.

Name

mailq

Synopsis

mailq [options]

List all messages in the sendmail mail queue. Equivalent to sendmail -bp.

Options

-Ac

Show queue specified in /etc/mail/submit.cf instead of queue specified in /etc/mail/sendmail.cf.

-q[!]Isubstring

Show items in mail queue with queue ids containing substring. In this, and in similar options below, invert the match when ! is specified.

-qL

Show lost items in mail queue.

-qQ

Show quarantined items in the mail queue.

-q[!]Qsubstring

Show quarantined messages with quarantine reasons containing substring.

-q[!]Rsubstring

Show items in mail queue with recipients containing substring.

-q[!]Ssubstring

Show items in mail queue with senders containing substring.

-v

Verbose mode.

Name

mailstats

Synopsis

mailstats [options]

System administration command. Display a formatted report of the current sendmail mail statistics.

Options

-c

Use configuration in /etc/mail/submit.cf instead of /etc/mail/sendmail.cf.

-C file

Use sendmail configuration file file instead of the default sendmail.cf file.

-f file

Use sendmail statistics file file instead of the file specified in the sendmail configuration file.

-o

Don’t show the name of the mailer in the report.

-p

Print stats without headers or separators. Output suitable for use by other programs. Reset statistics.

-P

Print stats without headers or separators. Output suitable for use by other programs. Do not reset statistics.

Name

mailx

Synopsis

mailx [options] [users]

Read mail or send mail to other users. mailx is based on the traditional mail command, extended to provide support for MIME, IMAP, POP3, SMTP, and S/MIME. The mailx command allows you to compose, send, receive, forward, and reply to mail. mailx has two main modes: compose mode, in which you create a message, and command mode, in which you manage your mail.

mailx is most commonly seen nowadays in scripts. Most Linux distributions include several utilities that are richer in features and easier to use: mailers built into browsers such as Mozilla and Firefox, graphical mail programs distributed with GNOME (Evolution) and KDE (Kmail), and the terminal-based, full-screen utilities pine and elm. The GNU Emacs editor can also send and receive mail.

To get you started, here are two of the most basic commands.

To enter interactive mail-reading mode, type:

mailx

To begin writing a message to user, type:

mailx user

Enter the text of the message, one line at a time, pressing Enter at the end of each line. To end the message, enter a single period (.) in the first column of a new line and press Enter.

You can also provide much of the information on the command line, as shown in the following example:

mailx james -s "System Log" </var/log/messages

This command sends a message to the user james, with a subject line of System Log, and the text of the message read from the system logfile, /var/log/messages.

mailx has many more options and commands than we can describe here. For complete details, as well as a full description of managing and using the command, see the manpage.

Command-line options

-~

Allow tilde escapes even when not in interactive mode.

-a file

Attach the specified file to the message.

-A account

Run the account command for the specified email account after the startup files have been read.

-b list

Set blind-carbon-copy field to comma-separated list.

-c list

Set carbon-copy field to comma-separated list.

-D

Start disconnected.

-e

Check for presence of mail in the system mailbox, but do not read. Returns exit status of 0 if there is mail, otherwise returns nonzero.

-E

Discard an outgoing message with no text in its first or only part.

-f [file]

Process contents of file instead of /var/spool/mail/$user. If file is omitted, process mbox in the user’s home directory.

-H

Print message header summaries and exit.

-i

Do not respond to tty interrupt signals.

-I

Show Newsgroup: or Article-Id: fields in the header summary; used with -f.

-n

Do not consult /etc/mail.rc when starting up.

-N

When printing a mail message or entering a mail folder, do not display message headers.

-q file

In compose mode, insert the contents of file at the beginning of the message.

-R

Open folders read-only.

-s subject

Set subject to subject. Use quotes around subjects that contain spaces.

-S var[=value]

Set the internal option var. If var is a string variable, assign the given value to it.

-t

Expect the message to contain To:, Cc:, and/or Bcc: fields to identify recipients and ignore any set on the command line.

-uuser

Process contents of /var/spool/mail/$user for the specified user.

-v

Verbose; print information about mail delivery to standard output.

Compose-mode commands

The following commands are known as tilde escapes and are only recognized at the beginning of a line in the message:

~!command

Execute a shell escape from compose mode and run the specified command.

~<!command

Execute a shell escape and run the specified command, then insert its standard output into the message.

~?

List tilde escapes.

~| command

Pipe message through command.

~: mailx-command

Execute mailx-command.

~~string

Insert string in text of message, prefaced by a single tilde (˜). If string contains a ˜, it must be escaped with a \.

~b names

Add names to or edit the Bcc: header.

~c names

Add names to or edit the Cc: header.

~d

Read in the dead.letter file.

~e

Invoke text editor.

~f messages

Insert messages into message being composed. Only the first printable part of a MIME multipart message is inserted.

~F messages

Similar to ˜f, but include message headers and all MIME parts.

~h

Add to or change To:, Cc:, Bcc:, and Subject: headers interactively.

~H

Like ˜h but edit From:, Reply-To:, Sender:, and Organization: headers.

˜m messages

Similar to ˜f, but indent with a tab.

˜M messages

Similar to ˜m, but include message headers and all MIME parts.

˜p

Print message header fields, message being sent, and attachment list.

˜q

Abort current message composition, and save to dead.letters file.

˜r filename

Include file in current message.

˜s string

Change Subject: header to string.

˜t names

Add names to or edit the To: list.

˜v

Invoke editor specified with the VISUAL environment variable.

˜w filename

Write the message to the named file, appending it if the file already exists.

˜x

Like ˜q, but don’t save the message to dead.letters file.

Command-mode commands

?

List summary of commands (help screen).

!

Execute a shell command.

- [num]

Print numth previous message; defaults to immediately previous.

account (ac)

Create, select, or list an email account.

alias (a)

Print or create alias lists.

alternates (alt)

Specify remote accounts on remote machines that are yours. Tell mailx not to reply to them.

cache

For IMAP mailboxes only, read specified messages into the IMAP cache.

chdir (c)

cd to home or specified directory.

classify

Check contents of messages for junk mail, using Bayesian filtering, and mark as junk.

copy (co)

Similar to save, but do not mark message for deletion.

delete (d)

Delete message.

dp (dt)

Delete current message and display next one.

edit (e)

Edit message.

exit (ex, x)

Exit mailx without updating folder or user’s system mailbox.

file (fi)

Switch folders.

folder (fold)

Read messages saved in a file. If no file is specified, display the name of the current file. In addition to filenames, the following are allowed:

#

Previous file

%

System mailbox

%user

user’s system mailbox

&

mbox

+folder

File in folder directory.

folders

List folders, and subfolders with an existing folder as argument.

forward (fwd)

Forward a message to a recipient.

from (f)

Print headers for messages.

good (go)

Mark messages as good (not junk mail).

headers (h)

List message headers in groups of 18 at current prompt.

headers+ (h+)

Move forward one window of headers.

headers- (h-)

Move back one window of headers.

help

Same as ?.

hold (ho)

Hold messages in system mailbox.

ignore

Append list of fields to ignored fields. With no arguments, list currently ignored fields.

imap

Send commands to the current IMAP server.

junk (j)

Mark messages as junk mail.

list

Print list of available commands.

mail user (m)

Compose message to user.

mbox

Move specified messages to mbox on exiting (the default).

move (mv)

Like copy, but mark messages for deletion after the move.

next (n)

Type next message or next message that matches argument.

pipe (pi), |

Pipe messages through a shell command.

preserve (pre)

Synonym for hold.

print [list] (p)

Display each message in list. For MIME multipart messages, display parts that are labeled “text” or “message”.

Print [list] (P)

Similar to print, but include ignored header fields and all parts of MIME multipart messages.

quit (q)

Exit mailx and update folder.

remove (rem)

Remove named folders.

rename (ren)

Rename an existing folder.

reply (r)

Send mail to all on distribution list.

Reply (R)

Send mail to author only.

replyall

Reply to all recipients.

respond

Same as reply.

retain

Always include this list of header fields when printing messages. With no arguments, list retained fields.

save (s)

Save message to folder.

saveignore

Remove ignored fields when saving.

saveretain

Override saveignore to retain specified fields.

seen

Mark list of messages as read.

set (se)

Set or print mailx options.

shell (sh)

Enter a new shell.

show (Sh)

Like print, but show raw message text, with no decoding, for MIME or encrypted messages.

size

Print size of each specified message.

source

Read commands from specified file.

thread (th)

Show current folder in threaded format.

top

Print first few lines of each specified message.

touch

Mark messages to be saved in mbox.

type (t)

Same as print.

Type (T)

Same as Print.

unalias

Discard previously defined aliases.

unanswered

Mark specified messages as unanswered.

uncollapse (unc)

Uncollapse threaded messages so the messages and replies are visible in header summaries again.

undelete (u)

Restore specified deleted messages.

ungood

Undo the effect of an earlier good command.

unjunk

Undo the effect of an earlier junk command.

unread (U)

Mark specified messages as unread.

unset (uns)

Unset mailx options.

verify (verif)

Verify that specified messages are S/MIME signed messages.

visual (v)

Edit message with editor specified by the VISUAL environment variable.

write (w)

Write message, without headers, to file.

xit (x)

Same as exit.

z

Move mailx’s attention to next windowful of text. Use z- to move it back.

Configuration options

These options are set inside the user’s .mailrc configuration file. The syntax is set option or unset option. The system default configuration is in /etc/mail.rc.

append

Append (do not prepend) messages to mbox.

ask, asksub

Prompt for subject.

askattach

Prompt at end of message for attachments.

askbcc

Prompt for blind-carbon-copy recipients.

askcc

Prompt for carbon-copy recipients.

asksign

Ask if message is to be signed.

autobcc list

Specify recipients who are always to receive a blind carbon copy.

autocc list

Specify recipients who are always to receive a carbon copy.

autoprint

Print next message after a delete.

autothread

Always enter threaded mode when a folder is opened.

cmd command

Specify the default command for a pipe.

crt num

Use the default pager to display a message of more than num lines. Defaults to the height of the terminal screen.

debug

Same as -d on command line.

dot

Interpret a solitary . as an EOF.

encoding value

The default MIME encoding to use for outgoing messages. Possible values are 8bit (the default) or quoted-printable.

escape char

Specify escape character to use instead of a tilde (˜).

folder dir

Define directory to hold mail folders.

from addr

The default address to put in the From: field.

hold

Keep message in system mailbox upon quitting.

ignore

Ignore interrupt signals from terminal. Print them as @.

ignoreeof

Do not treat ^D as an EOF.

indentprefix string

Use the specified string with ˜m as the prefix for indented messages.

junkdb addr

Location of the junk mail database.

keep

Do not delete user’s system mailbox when empty.

metoo

Do not remove sender from groups when mailing to them.

noheader

Same as -N on command line.

nosave

Do not save aborted letters to dead.letter.

pop3-use-apop

If set, connection to POP3 server uses APOP authentication.

quiet

Do not print version at startup.

record file

Use file as the path to record outgoing mail. If not set, outgoing mail is not saved.

Replyall

Switch roles of Reply and reply.

replyto list

Specify addresses for the Reply-To: field.

searchheaders

When given the specifier /x:y, expand all messages that contain the string y in the x header field.

sender addr

Specify the address to put into the Sender: field.

showlast

Start at the last message, not the first, when folder is opened.

toplines num

Print num lines of message with the top command. Default value is 5.

verbose

Same as -v on command line.

Name

make

Synopsis

make [options] [targets] [macro definitions]

Update one or more targets according to dependency instructions in a description file in the current directory. By default, this file is called makefile or Makefile. Options, targets, and macro definitions can be in any order. Macro definitions are typed as:

name=string

For more information on make, see Robert Mecklenburg’s Managing Projects with GNU Make (O’Reilly).

Options

-d, --debug

Print detailed debugging information.

-e, --environment-overrides

Override Makefile macro definitions with environment variables.

-f Makefile, --file=Makefile, --makefile=Makefile

Use Makefile as the description file; a filename of - denotes standard input.

-h, --help

Print options to make command.

-i, --ignore-errors

Ignore command error codes (same as .IGNORE).

-j [jobs], --jobs [=jobs]

Attempt to execute this many jobs simultaneously or, if no number is specified, as many jobs as possible.

-k, --keep-going

Abandon the current target when it fails, but keep working with unrelated targets.

-l [load], --load-average [=load], --max-load [=load]

Attempt to keep load below load, which should be a floating-point number. Used with -j.

-n, --just-print, --dry-run, --recon

Print commands but don’t execute (used for testing).

-o file, --old-file=file, --assume-old=file

Never remake file or cause other files to be remade on account of it.

-p, --print-data-base

Print rules and variables in addition to normal execution.

-q, --question

Query; return 0 if file is up to date, nonzero otherwise.

-r, --no-built-in-rules

Do not use default rules.

-s, --silent, --quiet

Do not display command lines (same as .SILENT).

-t, --touch

Touch the target files without remaking them.

-v, --version

Show version of make.

-w, --print-directory

Display the current working directory before and after execution.

--warn-undefined-variables

Print warning if a macro is used without being defined.

-C directory, --directory directory

cd to directory before beginning make operations. A subsequent -C directive will cause make to attempt to cd into a directory relative to the current working directory.

-I directory, --include-dir directory

Include directory in list of directories containing included files.

-S, --no-keep-going, --stop

Cancel previous -k options. Useful in recursive makes.

-W file, --what-if file, --new-file file, --assume-new file

Behave as though file has been recently updated.

Description-file lines

Instructions in the description file are interpreted as single lines. If an instruction must span more than one input line, use a backslash (\) at the end of the line so that the next line is considered a continuation. The description file may contain any of the following types of lines:

Blank lines

Blank lines are ignored.

Comment lines

A pound sign (#) can be used at the beginning of a line or anywhere in the middle. make ignores everything after the #.

Dependency lines

Depending on one or more targets, certain commands that follow will be executed. Possible formats include:

targets : dependencies
targets : dependencies ; command

Subsequent commands are executed if dependency files (the names of which may contain wildcards) do not exist or are newer than a target. If no prerequisites are supplied, then subsequent commands are always executed (whenever any of the targets are specified). No tab should precede any targets.

Conditionals

Conditionals are evaluated when the Makefile is first read and determine what make sees — i.e., which parts of the Makefile are obeyed and which parts are ignored. The general syntax for a conditional is:

Conditional
Text if true
Else
Text if false
endif

ifeq (arg1, arg2), ifeq "arg1" "arg2"

True if the two arguments are identical. The arguments should either be placed in parentheses and separated by a comma — (arg1, arg2) — or individually quoted with either single or double quotes.

ifneq (arg1, arg2), ifneq "arg1" "arg2"

True if the two arguments are not identical. The arguments should either be placed in parentheses and separated by a comma, or individually quoted with either single or double quotes.

ifdef variable

True if variable has a nonempty value.

ifndef variable

True if variable has an empty value.

Suffix rules

These specify that files ending with the first suffix can be prerequisites for files ending with the second suffix (assuming the root filenames are the same). Either of these formats can be used:

.suffix.suffix:
.suffix:

The second form means that the root filename depends on the filename with the corresponding suffix.

Commands

Commands are grouped below the dependency line and are typed on lines that begin with a tab. If a command is preceded by a hyphen (-), make ignores any error returned. If a command is preceded by an at sign (@), the command line won’t echo on the display (unless make is called with -n).

Macro definitions

These have the following form:

name =string

or:

define name
string
endef

Blank space is optional around the =.

Include statements

Similar to the C include directive, these have the form:

include files

Internal macros

$?

The list of prerequisites that have been changed more recently than the current target. Can be used only in normal description-file entries, not in suffix rules.

$@

The name of the current target, except in description-file entries for making libraries, where it becomes the library name. Can be used both in normal description-file entries and in suffix rules.

$<

The name of the current prerequisite that has been modified more recently than the current target.

$*

The name (without the suffix) of the current prerequisite that has been modified more recently than the current target. Can be used only in suffix rules.

$%

The name of the corresponding .o file when the current target is a library module. Can be used both in normal description-file entries and in suffix rules.

$^

A space-separated list of all dependencies with no duplications.

$+

A space-separated list of all dependencies, which includes duplications.

Pattern rules

These are a more general application of the idea behind suffix rules. If a target and a dependency both contain %, GNU make will substitute any part of an existing filename. For instance, the standard suffix rule:

$(cc) -o $@ $<

can be written as the following pattern rule:

%.o : %.c
$(cc) -o $@ $<

Macro modifiers

D

The directory portion of any internal macro name except $?. Valid uses are:

$(*D)   $$(@D)   $(?D)   $(<D)
$(%D)   $(@D)    $(^D)

F

The file portion of any internal macro name except $?. Valid uses are:

$(*F)   $$(@F)   $(?F)   $(<F)
$(%F)   $(@F)    $(^F)

Functions

$(subst from,to,string)

Replace all occurrences of from with to in string.

$(patsubst pattern,to,string)

Similar to subst, but treat % as a wildcard within pattern. Substitute to for any word in string that matches pattern.

$(strip string)

Remove all extraneous whitespace.

$(findstring substring,mainstring)

Return substring if it exists within mainstring; otherwise, return null.

$(filter pattern,string)

Return those words in string that match at least one word in pattern. pattern may include the wildcard %.

$(filter-out pattern,string)

Remove those words in string that match at least one word in pattern. pattern may include the wildcard %.

$(sort list)

Return list, sorted in lexical order.

$(dir list)

Return the directory part (everything up to the last slash) of each filename in list.

$(notdir list)

Return the nondirectory part (everything after the last slash) of each filename in list.

$(suffix list)

Return the suffix part (everything after the last period) of each filename in list.

$(basename list)

Return everything but the suffix part (everything up to the last period) of each filename in list.

$(addsuffix suffix,list)

Return each filename given in list with suffix appended.

$(addprefix prefix,list)

Return each filename given in list with prefix prepended.

$(join list1,list2)

Return a list formed by concatenating the two arguments word by word (e.g., $(join a b,.c .o) becomes a.c b.o).

$(word n,string)

Return the nth word of string.

$(wordlist start,end,string)

Return words in string between word start and word end, inclusive.

$(words string)

Return the number of words in string.

$(firstword list)

Return the first word in the list list.

$(wildcard pattern)

Return a list of existing files in the current directory that match pattern.

$(foreach variable,list,string)

For each whitespace-separated word in list, expand its value and assign it to variable; then expand string, which usually contains a function referencing variable. Return the list of results.

$(if condition,then-string[,else-string])

Expand string condition if it expands to a nonempty string, then expand the then-string. If condition expands to an empty string, return the empty string or, if specified, expand and return the else-string.

$(call variable,parameters)

Expand each item in comma-separated list parameters and assign it to a temporary variable, $(n), where n is an incremented number beginning with 0. Then expand variable, a string referencing these temporary variables, and return the result.

$(origin variable)

Return one of the following strings that describes how variable was defined: undefined, default, environment, environment override, file, command line, override, or automatic.

$(shell command)

Return the results of command. Any newlines in the result are converted to spaces. This function works similarly to backquotes in most shells.

$(error string)

When evaluated, generate a fatal error with the message string.

$(warning string)

When evaluated, generate a warning with the message string.

Macro string substitution

$(macro:s1=s2)

Evaluates to the current definition of $(macro), after substituting the string s2 for every occurrence of s1 that occurs either immediately before a blank or tab, or at the end of the macro definition.

Special target names

.DEFAULT:

Commands associated with this target are executed if make can’t find any description-file entries or suffix rules with which to build a requested target.

.DELETE_ON_ERROR:

If this target exists in a Makefile, delete the target of any rule whose commands return a nonzero exit status.

.EXPORT_ALL_VARIABLES:

If this target exists, export all macros to all child processes.

.IGNORE:

Ignore error codes. Same as the -i option.

.INTERMEDIATE:

This target’s dependencies should be treated as intermediate files.

.NOTPARALLEL:

If this target exists in a Makefile, run make serially, ignoring option -j.

.PHONY:

Always execute commands under a target, even if it is an existing, up-to-date file.

.PRECIOUS:

Files you specify for this target are not removed when you send a signal (such as an interrupt) that aborts make or when a command line in your description file returns an error.

.SECONDARY:

Like .INTERMEDIATE, this target’s dependencies should be treated as intermediate files, but never automatically deleted.

.SILENT:

Execute commands, but do not echo them. Same as the -s option.

.SUFFIXES:

Suffixes associated with this target are meaningful in suffix rules. If no suffixes are listed, the existing list of suffix rules is effectively “turned off.”

Name

makedbm

Synopsis

makedbm [options] infile outfile
makedbm [option]

NFS/NIS command. Create or dump an NIS dbm file. makedbm will take a text infile and convert it to a gdbm database file named outfile. This file is suitable for use with ypserv. Each line of the input file is converted to a single record. All characters up to the first TAB or SPACE form the key, and the rest of the line is the data. If a line ends with \&, the data for that record is continued onto the next line. The # character is given no special treatment. infile can be -, in which case the standard input is read.

makedbm generates two special keys: the YP_M*ER_NAME key, which is the value of the current host (unless another name is specified with -m), and the YP_L*_MODIFIED key, which is the date of infile (or the current time if infile is -).

Options

-a

Add support for mail aliases.

-b

Insert YP_INTERDOMAIN key into map. This indicates that ypserv should fall back to DNS lookups when a host’s address is not found in NIS.

-c

Send a YPPROC_CLEAR signal to ypserv, causing it to clear all cached entries.

-i file_name

Create a YP_INPUT_NAME key with the value file_name.

-l

Convert keys of the given map to lowercase.

-m master_name

Specify the value of the YP_M*ER_NAME key. The default value is the current hostname.

--no-limit-check

Don’t enforce NIS size limits for keys or data.

-o file_name

Create a YP_OUTPUT_NAME key with the value file_name.

-r

Treat lines beginning with # as comments. Do not include them in the datafile.

-s

Add the key YP_SECURE, indicating that ypserv should accept connections to the database only from secure NIS networks.

-u filename

Undo a gdbm file: print out a dbm file, one entry per line, with a single space separating keys from values.

Example

It’s easy to write shell scripts to convert standard files such as /etc/passwd to the key-value form used by makedbm. For example, the awk program:

BEGIN { FS =":";OFS = "\t";}{ print $1, $0}

takes the /etc/passwd file and converts it to a form that can be read by makedbm to make the NIS file passwd.byname. That is, the key is a username and the value is the remaining line in the /etc/passwd file.

Name

makemap

Synopsis

makemap [options] typename

System administration command. Create database maps for use by sendmail in keyed map lookups. makemap will read from standard input and create a database file of type type with filename name.db. If the TrustedUser option is set in /etc/sendmail.cf and makemap is invoked as root, the ouput file will be owned by TrustedUser.

Input should be formatted as:

key value

Comment lines with #. Indicate parameter substitution with %n. Specify a literal % character by entering it twice: %%. The type may be btree or hash.

Options

-c size

Specify hash or B-Tree cache size.

-C file

Look up TrustedUser in the specified sendmail configuration file.

-d

Allow duplicate entries. Valid only with btree type maps.

-D x

Treat x as the comment marker instead of #.

-e

Allow empty value data fields.

-f

Suppress conversion of uppercase to lowercase.

-l

List supported map types.

-N

Append the zero-byte string terminator specified in sendmail’s configuration file to mapped entries.

-o

Append to existing file instead of replacing it.

-r

If some keys already exist, replace them. (By default, makemap will exit when encountering a duplicated key.)

-s

Ignore safety checks.

-t delimiter

Use delimiter instead of whitespace.

-u

Undo a map: print out the specified database file, one entry per line.

-v

Verbose mode.

Name

man

Synopsis

man [options] [section] [title]

Display information from the online reference manuals. man locates and prints the named title from the designated reference section.

Traditionally, manpages are divided into nine sections, where section 1 consists of user commands, section 2 contains system calls, and so forth (see Section names, coming up, for the full list). By default, all sections are consulted, so the section option serves to bypass the most common entry and find an entry of the same name in a different section (e.g., man 2 nice).

Numerous other utilities — such as info, xman, and the Konqueror browser--can also display manpages.

Options

-a

Show all pages matching title.

-B

Specify the browser to use on HTML files. Overrides the BROWSER environment variable. The default is /usr/bin/less -is.

-c

Reformat output even if there is a current cat file.

-C file

Specify a configuration file to use. Default is /etc/man.config.

-d

Display debugging information but not the manpage.

-D

Display debugging information and also display the manpage.

-f

Same as whatis command.

-F, --preformat

Format the manpage but do not display it.

-h, --help

Print a help message and exit.

-H command

Specify a command to render HTML files as text. Overrides the HTMLPAGER environment variable. The default is /bin/cat.

-k

Same as apropos command.

-K directory

A kind of super-k option. Search for a term in all manpages and display the name of each page, along with a prompt asking whether you want to view the page. This can be very slow.

-m systems

Search manual pages on the specified system or systems. systems should be a comma-separated list.

-M path

Search for manual pages in path. Ignore -m option.

-p preprocessors

Preprocess manual pages with preprocessors before turning them over to nroff, troff, or groff. Always runs soelim first to read in files to be included in the one currently being processed. preprocessors can be any combination of e for eqn, g for grap, p for pic, r for refer, t for tbl, and v for vgrind.

-P pager

Specify the pager to use. Overrides the MANPAGE environment variable. The default is /usr/bin/less -is.

-S sections

Colon-separated list of sections to look in for an entry.

-t

Format the manual page with /usr/bin/groff -Tgv -mandoc.

-w, -W, --path

Print only the pathnames of entries on standard output, one per line.

Section names

Manual pages are divided into sections for various audiences:

1. Executable programs or shell commands.

2. System calls (functions provided by the kernel).

3. Library calls (functions within system libraries).

4. Special files (usually found in /dev).

5. File formats and conventions (e.g., /etc/passwd).

6. Games.

7. Macro packages and conventions.

8. System administration commands (usually only for a privileged user).

9. Kernel routines (nonstandard).

Name

manpath

Synopsis

manpath [options]

Attempt to determine path to manual pages. Check $MANPATH first; if that is not set, consult /etc/man.conf, user environment variables, and the current working directory. The manpath command is a symbolic link to man and is equivalent to man --path. Most of the options are ignored for manpath.

Options

-d, --debug

Print debugging information.

-h

Print help message and then exit.

Name

md5sum

Synopsis

md5sum [option] [files]
md5sum [option] --check [file]

Compute or check 128-bit MD5 checksums. Used to verify that no change has been made to a file. With no files or - specified, read from standard input. The exit status is 0 for success and nonzero for failure.

Options

-b, --binary

Read the files in binary mode.

-c, --check

Check the MD5 sum and file information in the file argument (or standard input) against the corresponding files and verify that they are consistent. The input must have been generated by an earlier md5sum command.

--help

Print usage information and exit.

--status

Don’t generate output messages; the exit code indicates success or failure. Used only with --check.

--string=string

Compute the MD5 sum for the specified string. This option does not take a file argument. Put quotes around the string if it contains spaces.

-t, --text

Read files in text mode. The default.

--version

Print version information and exit.

-w, --warn

Warn about improperly formatted checksum lines. Used only with --check.

Name

merge

Synopsis

merge [options] file1 file2 file3

Perform a three-way file merge, putting the result in file1. The effect is easiest to understand if file2 is considered the original version of a file, file3 an altered version of file2, and file1 a later altered version of file2.

After the merge, file1 contains both the changes from file2 to file1 and the changes from file2 to file3. In other words, file1 keeps its changes and incorporates the changes in file3 as well. merge does not change file2 or file3.

If a line from file2 was changed in different ways in both file1 and file3, merge recognizes a conflict. By default, the command outputs a warning and puts brackets around the conflict, with lines preceded by <<<<<<< and >>>>>>>. A typical conflict looks like this:

<<<<<<< file1
relevant lines from file1
=======
relevant lines from file3
>>>>>>> file3

If there are conflicts, the user should edit the result and delete one of the alternatives.

Options

-A

Output conflicts using the -A style of diff3. This merges all changes leading from file2 to file3 into file1 and generates the most verbose output.

-e

Don’t warn about conflicts.

-E

Output conflict information in a less verbose style than -A; this is the default.

-L label

Specify up to three labels to be used in place of the corresponding filenames in conflict reports. That is:

merge -L x -L y -L z file_a file_b file_c

generates output that looks as if it came from x, y, and z instead of from file_a, file_b, and file_c.

-p

Send results to standard output instead of overwriting file1.

-q

Quiet; do not warn about conflicts.

-V

Print version number.

Name

mesg

Synopsis

mesg [option]

Change the ability of other users to send write messages to your terminal. With no options, display the permission status.

Options

n

Forbid write messages.

y

Allow write messages (the default).

Name

mkdir

Synopsis

mkdir [options] directories

Create one or more directories. You must have write permission in the parent directory in order to create a directory. See also rmdir. The default mode of the new directory is 0777, modified by the system or user’s umask.

Options

-m mode, --mode mode

Set the access mode for new directories. See chmod for an explanation of acceptable formats for mode.

-p, --parents

Create intervening parent directories if they don’t exist.

-v, --verbose

Print a message for each directory created.

--help

Print help message and then exit.

--version

Print version number and then exit.

-Z context, --context=context

Set security context in SELinux.

Examples

Create a read-only directory named personal:

mkdir -m 444 personal

The following sequence:

mkdir work; cd work
mkdir junk; cd junk
mkdir questions; cd ../..

can be accomplished by typing this:

mkdir -p work/junk/questions

Name

mkdosfs

Synopsis

mkdosfs [options] device [blocks]
mkfs.msdos [options] device [blocks]

System administration command. Format device as an MS-DOS filesystem. You may specify the number of blocks on the device or allow mkdosfs to guess.

Options

-A

Create an Atari MS-DOS filesystem.

-b backup-sector

Specify sector for backup boot sector. The default value depends on the number of reserved sectors, but is usually sector 6.

-c

Scan device for bad blocks before execution.

-C

Create and format a file suitable for use on a floppy disk. The device given on the command line should be a filename, and the number of blocks must also be specified.

-f n

Specify number of File Allocation Tables (FATs) to create (either 1 or 2).

-F fat-size

Create File Allocation Tables (FATs) of size fat-size. By default this will be between 12 and 16 bits. Set to 32 to create a FAT32 filesystem.

-i volume-id

Use the specified 32-bit hexadecimal volume-id instead of calculating a number based on the time of creation.

-I

Force installation to a device without partitions. This is useful when formating magneto-optical disks.

-l file

Read list of bad blocks from file.

-m message-file

Set the message to be used when the filesystem is booted without an installed operating system to the contents of the file message-file. The message may be up to 418 bytes in size. If filename is a hyphen, read text from standard input.

-n label

Set volume name for filesystem to label. The volume name may be up to 11 characters long.

-r maximum-entries

Set the maximum-entries allowed in the root directory. The default is 112 or 224 for floppies, and 512 for hard disks.

-R reserved-sectors

Create the specified number of reserved-sectors. The default depends on the size of the File Allocation Table (FAT). For 32-bit FAT, the default is 32; for all other sizes, the default is 1.

-s sectors

Set the number of disk sectors per cluster. The number must be a power of 2.

-S sector-size

Create logical sectors of sector-size bytes. Size must be a power of 2 and at least 512 bytes.

-v

Print verbose information about progress.

Name

mke2fs

Synopsis

mke2fs [options] device [blocks]
mkfs.ext2 [options] device [blocks]

System administration command. Format device as a Linux Second Extended Filesystem. You may specify the number of blocks on the device or allow mke2fs to guess.

Options

-b block-size

Specify block size in bytes.

-c

Scan device for bad blocks before execution.

-E featurelist

Specify extended features. This option’s parameters may be given in a comma-separated list:

stride=size

Configure filesystem for a RAID array. Set stride size to size blocks per stripe.

resize=blocks

Reserve descriptor table space to grow filesystem to the specified number of blocks.

-f fragment-size

Specify fragment size in bytes.

-F

Force mke2fs to run even if filesystem is mounted or device is not a block special device. This option is probably best avoided.

-i bytes-per-inode

Create an inode for each bytes-per-inode of space. bytes-per-inode must be 1024 or greater; it is 4096 by default.

-j

Create an ext3 journal. This is the same as invoking mkfs.ext3.

-J parameterlist

Use specified parameterlist to create an ext3 journal. The following two parameters may be given in a comma-separated list:

size=journal-size

Create a journal of journal-size megabytes. The size may be between 1024 filesystem blocks and 102,400 filesystem blocks in size (e.g., 1–100 megabytes if using 1K blocks, 4–400 megabytes if using 4K blocks).

device=journal-device

Use an external journal-device to hold the filesystem journal. The journal-device can be specified by name, by volume label, or by UUID.

-l filename

Consult filename for a list of bad blocks.

-L label

Set volume label for filesystem.

-m percentage

Reserve percentage percent of the blocks for use by privileged users.

-M directory

Set the last mounted directory for filesystem to directory.

-n

Don’t create the filesystem; just show what would happen if it were run. This option is overridden by -F.

-N inodes

Specify number of inodes to reserve for filesystem. By default, this number is calculated from the number of blocks and the inode size.

-o os

Set filesystem operating system type to os. The default value is usually Linux.

-O featurelist

Use specified featurelist to create filesystem. The sparse_super and filetype features are used by default on kernels 2.2 and later. The following parameters may be given in a comma-separated list:

dir_index

Use hashed B-trees to index directories.

filetype

Store file type information in directory entries.

has_journal

Create an ext3 journal. Same as using the -j option.

journal_dev

Prepare an external journaling device by creating an ext3 journal on device instead of formatting it.

sparse_super

Save space on a large filesystem by creating fewer superblock backup copies.

-q

Quiet mode.

-r revision

Set filesystem revision number to revision.

-S

Write only superblock and group descriptors; suppress writing of inode table and block and inode bitmaps. Useful only when attempting to salvage damaged systems.

-T use

Set bytes-per-inode based on the intended use of the filesystem. Supported filesystem usage types are defined in /etc/mke2fs.conf. Common types include:

news

Four kilobytes per inode.

largefile

One megabyte per inode.

largefile4

Four megabytes per inode.

-v

Verbose mode.

-V

Print version number, then exit.

Name

mkfifo

Synopsis

mkfifo [option] names

Make one or more named pipes (FIFOs) with the specified names.

Options

-m mode, --mode=mode

Set permission mode. Default is 666, with the bits in the umask subtracted.

--help

Print help information and exit.

--version

Print version information and exit.

Name

mkfs

Synopsis

mkfs [options] [fs-options] filesys [blocks]

System administration command. Construct a filesystem on a device (such as a hard disk partition). filesys is either the name of the device or the mountpoint. mkfs is actually a frontend that invokes the appropriate version of mkfs according to a filesystem type specified by the -t option. For example, a Linux Second Extended Filesystem uses mkfs.ext2 (which is the same as mke2fs); MS-DOS filesystems use mkfs.msdos. fs-options are options specific to the filesystem type. blocks is the size of the filesystem in 1024-byte blocks.

Options

-V

Produce verbose output, including all commands executed to create the specific filesystem.

-t fs-type

Tells mkfs what type of filesystem to construct.

Filesystem-specific options

These options must follow generic options and cannot be combined with them. Most filesystem builders support these three options:

-c

Check for bad blocks on the device before building the filesystem.

-l file

Read the file file for the list of bad blocks on the device.

-v

Produce verbose ouput.

Name

mkfs.ext3

Synopsis

mkfs.ext3 [options] devicesize

Create a journaling ext3 filesystem. Options are identical to mke2fs. See mkfs.

Name

mkisofs

Synopsis

mkisofs [options] -o pathspecs

Generate an ISO9660/Joliet/HFS filesystem for writing to a CD. (HFS is the native Macintosh Hierarchical File System.) mkisofs takes a snapshot of a directory tree and generates a binary image that corresponds to an ISO9660 or HFS filesystem when it is written to a block device. Each specified pathspec describes the path of a directory tree to be copied into the ISO9660 filesystem; if multiple paths are specified, the files in all the paths are merged to form the image.

mkisofs is now generally a symbolic link to genisoimage.

Name

mklost+found

Synopsis

mklost+found

System administration command. Create a lost+found directory in the current working directory. Intended for Linux Second Extended Filesystems.

Name

mknod

Synopsis

mknod [options] name type [major minor]

Create a special file (a file that can send or receive data). Special files can be character files (read one character at a time), block files (read several characters at a time), or FIFO pipes (see mkfifo).

To choose which type of device to create, use one of the following arguments:

p

Create a FIFO file (named pipe). You do not need to specify the major and minor device numbers.

b

Create a block file. You must specify the major and minor device numbers the file represents.

c or u

Create a character file. You must specify the major and minor device numbers the file represents.

Linux’s /dev/MAKEDEV utility is useful for creating one or more devices of a given type in a single command.

Options

--help

Print usage information and exit.

-m mode, --mode=mode

Set the file mode of the device, as with chmod. The default mode is a=rw unless you have chosen other settings via umask.

--version

Print version information and exit.

Name

mkswap

Synopsis

mkswap [options] device

System administration command. Prepare swapspace on device: a disk partition or a prepared file. This command can create old and new style swap areas. The older style provides backward compatibility with 2.2 kernels, but is less efficient and more limited in size. The mkswap command has some dangerous options we have omitted here. They provide backward compatibility and solutions to problems with older libraries, but can destroy a disk if specified incorrectly.

Options

-c

Check for bad blocks before creating the swapspace.

-L label

Create a label for use with swapon.

-v0

Create an old style swap area.

-v1

Create a new style swap area. (The default behavior on newer kernels.)

Name

mktemp

Synopsis

mktemp [options] [template]

Generate a unique temporary filename for use in a script. The filename is based on the specified template, which may be any filename with at least six Xs appended (e.g., /tmp/mytemp.XXXXXX). mktemp replaces the Xs with the current process number and/or a unique letter combination. The file is created with mode 0600 (unless -u is specified), and the filename is written to standard output. With no template specified, the default file tmp.XXXXXXXXXX is created.

Options

-d, --directory

Make a directory, not a file.

--help

Print usage information and exit.

-q, --quiet

Fail silently in case of error. Useful to prevent error output from being sent to standard error.

-u, --dryrun

Operate in “unsafe” mode and unlink the temporary file before mktemp exits. Use of this option is not recommended.

-V, --version

Print version information and exit.

Name

modinfo

Synopsis

modinfo [options] object-file

System administration command. Print information about kernel module object-file. Information is read from tag names in the mod-info section of the module file. By default, it will print the module’s filename, description, author, license, and parameters.

Options

−0, --null

Separate fields with the null character instead of newlines.

-F fieldname, --field fieldname

Print only the value of the specified fieldname (e.g., author, license, depends, etc.).

-h, --help

Print usage message, then exit.

-k kernel

Specify kernel to use (e.g., a kernel other than the running kernel).

-V, --version

Print version number of the module.

Name

modprobe

Synopsis

modprobe [options] [modules] [moduleoptions]

System administration command. With no options, attempt to load the specified module, as well as all modules on which it depends. If more than one module is specified, attempt to load further modules only if the previous module failed to load. When specifying a module, use only its name without its path or trailing .o. modprobe will pass to the kernel any options following the module name.

Options

-a, --all

Load all modules matching the given wildcard.

-c, --showconfig

Print modprobe’s current configuration.

-C file, --config file

Read additional configuration from file instead of /etc/modules.conf.

-f, --force

Ignore all versioning information during module insertion. Even if the module does not match the running kernel, modprobe will try to insert it anyway.

--force-modversion

Ignore module versioning mismatches.

--force-vermagic

Ignore kernel versioning mismatches.

--first-time

Return failure if told to insert a module that is already present or remove a module that is not loaded. Normally, modprobe will return success if asked to perform an unnecessary action.

-i, --ignore-install, --ignore-remove

Ignore any install and remove directives in the configuration file.

-l, --list

List modules matching the given wildcard (or “*” if no wildcard is given).

-n, --dry-run

Perform all of the actions except actually inserting or removing the module.

-q, --quiet

Suppress warnings during failure to load a module and continue processing other modules.

-r, --remove

Remove the specified modules, as well as the modules on which they depend.

-s, --syslog

Send error messages to syslogd instead of to standard error.

-ttype, --type type

Load only a specific type of module.

-v, --verbose

Print commands as they are executed.

-V, --version

Print version, then exit.

Name

more

Synopsis

more [options] [files]

Display the named files on a terminal, one screenful at a time. See less for an alternative to more.

Options

+num

Begin displaying at line number num.

-num number

Set screen size to number lines.

+/pattern

Search for pattern and begin displaying at that point.

-c

Repaint screen from top instead of scrolling.

-d

Display the prompt “[Press space to continue, ‘q’ to quit]” instead of ringing the bell. Also display “[Press ‘h’ for instructions]” in response to illegal commands.

-f

Count logical rather than screen lines. Useful when long lines wrap past the width of the screen.

-l

Ignore form-feed (Ctrl-L) characters.

-p

Page through the file by clearing each window instead of scrolling. This is sometimes faster.

-s

Squeeze; display multiple blank lines as one.

-u

Suppress underline characters.

Commands

All commands in more are based on vi commands. You can specify a number before many commands to have them executed multiple times. For instance, 3:p causes more to skip back three files, the same as issuing :p three times. The optional number is indicated by num in the following list:

SPACE

Display next screen of text.

z

Display next num lines of text, and redefine a screenful to num lines. Default is one screenful.

RETURN

Display next num lines of text, and redefine a screenful to num lines. Default is one line.

d, ^D

Scroll num lines of text, and redefine scroll size to num lines. Default is one line.

q, Q, INTERRUPT

Quit.

s

Skip next num lines of text. Default is one line.

f

Skip forward num screens of text. Default is one screen.

b, ^B

Skip backward num screens of text. Default is one screen. Does not work on pipes.

'

Return to point where previous search began.

=

Print number of current line.

/pattern

Search for pattern, skipping to numth occurrence if an argument is specified.

?, h

Display a summary of commands.

n

Repeat last search, skipping to numth occurrence if an argument is specified.

!cmd, :!cmd

Invoke shell and execute cmd in it.

v

Invoke an editor on the file at the current line. Use the editor in the environment variable VISUAL if defined, or EDITOR if that is defined; otherwise, default to vi.

^L

Redraw screen.

:n

Skip to next file, or numth file if an argument is specified.

:p

Skip to previous file, or numth previous if an argument is specified.

:f

Print current filename and line number.

.

Reexecute previous command.

Examples

Page through file in “clear” mode, and display prompts:

more -cd file

Format doc to the screen, removing underlines:

nroff doc | more -u

View the manpage for the more command; begin at the first appearance of the word “scroll”:

man more|more +/scroll

Name

mount

Synopsis

mount [options] [[device] directory]

System administration command. Mount a file structure. The file structure on device is mounted on directory. If no device is specified, mount looks for an entry in /etc/fstab to find out what device is associated with the given directory. The directory, which must already exist and should be empty, becomes the name of the root of the newly mounted file structure. If mount is invoked with no arguments, it displays the name of each mounted device, the directory on which it is mounted, its filesystem type, and any mount options associated with the device.

Options

-a

Mount all filesystems listed in /etc/fstab. Use -t to limit this to all filesystems of a particular type.

--bind olddirectory newdirectory

Bind a mounted subtree to a new location. The tree will be available from both the old and new directory. This binding does not include any volumes mounted below the specified directory.

-f

Fake mount. Go through the motions of checking the device and directory, but do not actually mount the filesystem.

-F

When used with -a, fork a new process to mount each system.

-h

Print help message, then exit.

-l

When reporting on mounted filesystems, show filesystem labels for filesystems that have them.

-L label

Mount filesystem with the specified label.

--move olddirectory newdirectory

Move a mounted device to a new location. Maintains options and submounts.

-n

Do not record the mount in /etc/mtab.

-o option

Qualify the mount with a mount option. Many filesystem types have their own options. The following are common to most filesystems:

async

Read input and output to the device asynchronously.

atime

Update inode access time for each access. This is the default behavior.

auto

Allow mounting with the -a option.

defaults

Use all options’ default values (async, auto, dev, exec, nouser, rw, suid).

dev

Interpret any special devices that exist on the filesystem.

dirsync

Perform all directory updates to the filesystem synchronously.

exec

Allow binaries to be executed.

_netdev

Filesystem is a network device requiring network access.

noatime

Do not update inode access time for each access.

noauto

Do not allow mounting via the -a option.

nodev

Do not interpret any special devices that exist on the filesystem.

noexec

Do not allow the execution of binaries on the filesystem.

nofail

Do not report errors if device doesn’t exist.

nosuid

Do not acknowledge any suid or sgid bits.

nouser

Only privileged users will have access to the filesystem.

remount

Expect the filesystem to have already been mounted, and remount it.

ro

Allow read-only access to the filesystem.

rw

Allow read/write access to the filesystem.

suid

Acknowledge suid and sgid bits.

sync

Read input and output to the device synchronously.

user

Allow unprivileged users to mount or unmount the filesystem. The defaults on such a system will be nodev, noexec, and nosuid, unless otherwise specified.

users

Allow any user to mount or unmount the filesystem. The defaults on such a system will be nodev, noexec, and nosuid, unless otherwise specified.

-O option

Limit systems mounted with -a by -O’s filesystem options (as used with -o). Use a comma-separated list to specify more than one option, and prefix an option with no to exclude filesystems with that option. Options -t and -O are cumulative.

-r

Mount filesystem read-only.

--bind olddirectory newdirectory

Bind a mounted subtree to a new location. The tree will be available from both the old and new directory. Include any volumes mounted below the specified directory.

-s

Where possible, ignore mount options specified by -o that are not supported by the filesystem.

-t type

Specify the filesystem type. Possible values include adfs, affs, autofs, coda, cramfs, devpts, efs, ext2, ext3, hfs, hpfs, iso9660, jfs, minix, msdos, ncpfs, nfs, nfs4, ntfs, proc, qnx4, reiserfs, romfs, smbfs, sysv, tmpfs, udf, ufs, umsdos, vfat, xfs, and xiafs. The default type is iso9660. The type auto may also be used to set mount to autodetect the filesystem. When used with -a, this option can limit the types mounted. Use a comma-separated list to specify more than one type to mount. Prefix a list (or type) with no to exclude those types.

-U uuid

Mount filesystem with the specified uuid.

-v

Display mount information verbosely.

-V

Print version, then exit.

-w

Mount filesystem read/write. This is the default.

Files

/etc/fstab

List of filesystems to be mounted and options to use when mounting them.

/etc/mtab

List of filesystems currently mounted and the options with which they were mounted.

/proc/partitions

Used to find filesystems by label and uuid.

Name

mountd

Synopsis

rpc.mountd [options]

NFS/NIS command. NFS mount request server. mountd reads the file /etc/exports to determine which filesystems are available for mounting by which machines. It also provides information about which filesystems are mounted by which clients. See also nfsd.

Options

-d kind, --debug kind

Specify debugging facility. Accepted values for kind are general, call, auth, parse, and all.

-f file, --exports-file file

Read the export permissions from file instead of /etc/exports.

-F, --foreground

Run mountd in the foreground.

-h, --help

Print help message, then exit.

-n, --no-tcp

Use UDP for mounts.

-N n, --no-nfs-version n

Do not offer NFS version n.

-o n, --descriptors n

Allow no more than n open file descriptors. The default is 256.

-p n, --port n

Bind to specified port instead of accepting a port from portmapper.

-r, --reverse-lookup

Perform a reverse lookup on ip address when requested to report mounting hosts (a DUMP request).

-v, --version

Print the version number, then exit.

-V n, --nfs-version n

Explicity offer NFS version n.

Files

/etc/exports

Information about mount permissions.

/var/lib/nfs/rmtab

List of filesystems currently mounted by clients.

Name

mt

Synopsis

mt [option] operation [count | arguments]

Control a magnetic tape drive used to back up or restore system data. The version of the mt command documented here is the GNU version of mt. The operation argument determines what action will be taken, and, unless the -f or -t option is used, the action is applied to the default tape drive named in the TAPE -environment variable. The count argument determines how many times the operation is to be repeated. If not specified, it defaults to 1. Some operations take one or more arguments other than a count, as noted in the descriptions below.

Options

-f device, -t device

Name the tape device to use. This may be a local device, a character special file (see mknod), or a remote device, named in the format host:/path/to/drive or user@host:path/to/drive.

--help

Print usage message and exit.

-V, --version

Print version number and exit. Also tells you if you are running the GNU version of mt or the mt-st version.

Operations

mt can perform the following operations on tape drives. Unique abbreviations are allowed.

asf n

Move to file number n on the tape. This is the same as rewinding the tape and moving forward n files with fsf.

bsf n

Move backward n files, positioning the tape at the last block of the previous file.

bsfm n

Move backward n file marks, to a position on the side of the file mark closer to the beginning of the tape.

bsr n

Move backward n records.

eof, weof n

Write n end-of-file (EOF) notations at the current location on the tape.

erase

Erase the tape.

fsf n

Move forward n files, positioning the tape at the first block of the next file.

fsfm n

Move forward n file marks, to a position on the side of the file mark closer to the beginning of the tape.

fsr n

Move forward n records.

offline, rewoffl

Rewind and unload the tape (if drive supports unload).

retension

Used when the tape has become loosely wound, usually because it has been dropped, shaken, or transported. Rewinds the tape, moves forward to the end of the tape, then rewinds again.

rewind

Return to the beginning of the tape.

seek n

Seek to block n on the tape.

status

Display the status of the tape drive.

Name

mv

Synopsis

mv [option] sources target

Move or rename files and directories. The source (first column) and target (second column) determine the result (third column).

Source

Target

Result

File

name (nonexistent)

Rename file to name.

File

Existing file

Overwrite existing file with source file.

Directory

name (nonexistent)

Rename directory to name.

Directory

Existing directory

Move directory to be a subdirectory of existing directory.

One or more files

Existing directory

Move files to directory.

The mv command is often aliased as mv -i in the .bashrc file, especially for the root account, to prevent inadvertently overwriting files.

Options

-b

Back up existing files before removing.

--backup[=type]

Like -b, but can take an argument specifying the type of version-control file to use for the backup. The value of type overrides the VERSION_CONTROL environment variable, which determines the type of backups made. The acceptable values for version control are:

t, numbered

Always make numbered backups.

nil, existing

Make numbered backups of files that already have them, and make simple backups of the others. This is the default.

never, simple

Always make simple backups.

none, off

Never make backups.

-f, --force

Force the move, even if target file exists; suppress messages about restricted access modes. Same as --reply=yes.

--help

Print a help message and then exit.

-i, --interactive

Query user before removing files. Same as --reply=query.

--reply=prompt

Specify how to handle prompt if the destination exists already. Possible values are yes, no, and query.

--strip-trailing-slashes

Remove trailing slashes from source paths.

-S suffix, --suffix=suffix

Override the SIMPLE_BACKUP_SUFFIX environment variable, which determines the suffix used for making simple backup files. If the suffix is not set either way, the default is a tilde (˜).

-T, --no-target-directory

Treat the destination as a file.

--target-directory=dir

Move all source files and directories into the specified directory.

-u, --update

Do not remove a file or link if its modification date is the same as or newer than that of its replacement.

-v, --verbose

Print the name of each file before moving it.

--version

Print version information and then exit.

Name

named

Synopsis

named [options]

TCP/IP command. Internet domain nameserver. named is used by resolver libraries to provide access to the Internet distributed naming database. With no arguments, named reads /etc/named.conf for any initial data and listens for queries on a privileged port. See RFC 1034 and RFC 1035 for more details.

There are several named binaries available at different Linux archives, displaying various behaviors. Here we describe named as provided by Internet Software Consortium’s Berkeley Internet Name Domain (BIND) version 9.2.x.

Options

-c file

Read configuration information from file instead of /etc/named.conf.

-d debuglevel

Print debugging information. debuglevel is a number indicating the level of messages printed.

-f

Run named in the foreground.

-g

Run named in the foreground and send all log messages to standard error.

-n n

Specify the number of processors in a multiprocessor system. Normally named can autodetect the number of CPUs.

-p port

Use port as the port number. Default is 53.

-t dir

Change root to specified directory after reading command arguments but before reading the configuration file. Useful only when running with option -u.

-u user

Set the user ID to user after completing any privileged operations.

-v

Print version, then exit.

File

/etc/named.conf

Read when named starts up.

Name

namei

Synopsis

namei [options] pathname [pathname . . .]

Follow a pathname until a terminal point is found (e.g., a file, directory, char device, etc.). If namei finds a symbolic link, it shows the link and starts following it, indenting the output to show the context. namei prints an informative message when the maximum number of symbolic links has been exceeded, making it helpful for resolving errors resulting from too many levels of links.

Options

-m

Show mode bits of each file type in the style of ls (e.g., “rwxr-xr-x”).

-x

Show mountpoint directories with a D rather than a d.

File-type characters

For each line of output, namei prints the following characters to identify the file types found:

-

A regular file.

?

An error of some kind.

b

A block device.

c

A character device.

d

A directory.

f:

The pathname namei is currently trying to resolve.

l

A symbolic link (both the link and its contents are output).

p

A FIFO (named pipe).

s

A socket.

Name

nameif

Synopsis

nameif [options] [name macaddress]

System administration command. Assign an interface name to a network device specified by macaddress, the unique serial number that identifies a network card. If no name and macaddress are given, nameif will attempt to read addresses from the configuration file /etc/mactab. Each line of the configuration file should contain either a comment beginning with # or an interface name and MAC address.

Options

-c filename

Read interface names and MAC addresses from filename instead of /etc/mactab.

-s

Send any error messages to syslog.

Name

nc

Synopsis

nc [options] [host] [port]

TCP/IP command. nc (also known as netcat) is a versatile networking utility that reads and writes data across network connections using TCP or UDP. It’s a simple tool that has many uses. Unlike telnet, you can easily script nc. It can also be used to listen for as well as make connections.

Options

-C

Send CRLF as line ending.

-i seconds

Send and read data one line at a time with a delay of the specified interval in seconds. By default netcat reads and writes in 8 KB blocks.

-k

Listen for further connections when a current connection ends. Used with -l.

-l

Listen for an incoming connection on the specified port or ports.

-n

Don’t perform any DNS lookups.

-o file

Hex-dump data sent and received to file.

-p [port]

Read from the specified source port.

-r

Choose ports randomly.

-s [address]

Read from the specified source IP address.

-u

Use UDP instead of the default TCP.

-U

Use Unix Domain Sockets instead of the default TCP.

-v

Verbose output. Use multiple times to increase verbosity. If not using -n, include reports on forward/reverse DNS mismatches.

-w seconds

Set the inactivity timeout for a connection. Silently close a connection if idle for more than the specified seconds.

-x address[:port]

Use the proxy found at the specified IP address and port. If no port is specified, the well-known port for the protocol is used.

-X protocol

Use the specified proxy protocol. Valid values are 4 (SOCKS v. 4), 5 (SOCKS v. 5) and connect (HTTPS proxy). The default value is 5.

-z

Scan for listening daemons. With this option port can be given as a port range or sets of ranges.

Examples

Connect to an SMTP port reporting connection information and timing out after 2 seconds of inactivity:

$ nc -w 2 -v remotehost 25

Copy a directory over the network, preserving permissions. On the receiving server, use this:

$ nc -l -p 1234 | tar xzfp -

On the server sending the directory files, use this:

$ tar czfp - /dir/ |  nc -w 3 remotehost 1234

Perform a simple port scan:

$ nc -w 1 -z remotehost 20-80 400-500

Name

netstat

Synopsis

netstat [options] [delay]

TCP/IP command. Show network status. Print information on active sockets, routing tables, interfaces, masquerade connections, or multicast memberships. By default, netstat lists open sockets. When a delay is specified, netstat will print new information every delay seconds.

Options

The first five options (-g, -i, -M, -r, and -s) determine what kind of information netstat should display.

-g, --groups

Show multicast group memberships.

-i, --interface[=name]

Show all network interfaces, or just the interface specified by name.

-M, --masquerade

Show masqueraded connections.

-r, --route

Show kernel routing tables.

-s, --statistics

Show statistics for each protocol.

-a, --all

Show all entries.

-A family, --protocol=family

Show connections only for the specified address family. Accepted values are inet, unix, ipx, ax25, netrom, and ddp. Specify multiple families in a comma-separated list.

-c, --continuous

Display information continuously, refreshing once every second.

-C

Print routing information from the route cache.

-e, --extend

Increase level of detail in reports. Use twice for maximum detail.

-F

Print routing information from the forward information database (FIB). This is the default.

-l, --listening

Show only listening sockets.

-n, --numeric

Show network addresses, ports, and users as numbers.

--numeric-hosts

Show host addresses as numbers, but resolve others.

--numeric-ports

Show ports as numbers, but resolve others.

--numeric-users

Show user ID numbers for users, but resolve others.

-N, --symbolic

Where possible, print symbolic host, port, or usernames instead of numerical representations. This is the default behavior.

-o, --timers

Include information on network timers.

-p, --program

Show the process ID and name of the program owning the socket.

-t, --tcp

Limit report to information on TCP sockets.

-u, --udp

Limit report to information on UDP sockets.

-v, --verbose

Verbose mode.

-w, --raw

Limit report to information on raw sockets.

Name

newaliases

Synopsis

newaliases

Rebuild the mail aliases database, /etc/aliases, after a change. Return 0 on success, or a number greater than 0 if there was an error. newaliases must be run whenever /etc/aliases has been changed for the change to take effect. newaliases is a sendmail command and is identical to sendmail -bi.

Name

newgrp

Synopsis

newgrp [-
] [group]

Change user’s current group ID to the specified group. If no group is specified, change to the user’s login group. The new group is then used for checking permissions. If - is specified, also reinitialize the user’s environment.

Name

newusers

Synopsis

newusers file

System administration command. Create or update system users from entries in file. Each line in file has the same format as an entry in /etc/passwd, except that passwords are unencrypted and group IDs can be given as a name or number. During an update, the password age field is ignored if the user already exists in the /etc/shadow password file. If a group name or ID does not already exist, it will be created. If a home directory does not exist, it will be created.

Name

nfsd

Synopsis

rpc.nfsd [options] n

System administration command. Launch n kernel threads for the Network File System (NFS) kernel module. The threads will handle client filesystem requests. By default, only one thread is launched. Most systems require eight or more, depending on the number of NFS clients using the system. Use nfsstat to check NFS performance.

Option

-H hostname, --host hostname

Specify the hostname or address that will accept NFS requests. The default is to accept on all addresses.

-N version, --no-nfs-version version

Do not provide support for the specified NFS version. By default support is provided for versions 2, 3, and 4.

-p port, --port hostname

Listen for NFS requests on port instead of the default port 2049.

-T, --no-tcp

Do not accept TCP requests.

-U, --no-udp

Do not accept UDP requests.

Name

nfsstat

Synopsis

nfsstat [options]

System administration command. Print statistics on NFS and remote procedure call (RPC) activity for both clients and server.

Options

−2, −3, −4

Shows server statistics for version 2, 3, or 4.

-c

Display only client-side statistics.

-m, --mounts

Show statistics for mounted filesystems.

-n

Display only NFS statistics.

-o facility

Only display statistics for the specified facility. The following are valid values for facility:

all

All of the following facilities.

fh

Server file handle cache.

net

Network layer statistics.

nfs

Same as -n.

rc

Server request reply cache.

rpc

Same as -r.

-r

Display only RPC statistics.

-s

Display only server-side statistics.

-z

Reset statistics to zero. Use with above options to zero out specific sets of statistics (e.g., -zr to reset the RPC statistics).

-Z, --sleep

Take a snapshot of current stats then sleep until receiving a SIGINT signal (e.g., Ctrl-C) then take another snapshot and display a diff of the two.

Name

nice

Synopsis

nice [option] [command [arguments]]

Execute a command (with its arguments) with lower priority (i.e., be “nice” to other users). With no command, nice prints the current scheduling priority (niceness). If nice is a child process, it prints the parent process’s scheduling priority. Niceness has a range of −20 (highest priority) to 19 (lowest priority).

Options

--help

Print a help message and then exit.

-n adjustment, -adjustment, --adjustment=adjustment

Run command with niceness incremented by adjustment (1–19); default is 10. A privileged user can raise the priority by specifying a negative adjustment (e.g., −5).

--version

Print version information and then exit.

Name

nm

Synopsis

nm [options] [objfiles]

Print the symbol table in alphabetical order from one or more object files. If no object files are specified, perform operations on a.out. Output includes each symbol’s value, type, size, name, and so on. A key letter categorizing the symbol can also be displayed.

Options

-a, --debug-syms

Print debugger symbols.

--defined-only

Display only defined symbols.

-f format, --format=format

Specify output format (bsd, sysv, or posix). Default is bsd.

-g, --extern-only

Print external symbols only.

--help

Print help message, then exit.

-l, --line-numbers

Print source filenames and line numbers for each symbol from available debugging information.

-n, -v, --numeric-sort

Sort the external symbols by address.

-p, --no-sort

Don’t sort the symbols at all.

-r, --reverse-sort

Sort in reverse, alphabetically or numerically.

-s, --print-armap

Include mappings stored by ar and ranlib when printing archive symbols.

--size-sort

Sort by size.

-t radix, --radix=radix

Use the specified radix for printing symbol values. Accepted values are d for decimal, o for octal, and x for hexadecimal.

--target=format

Specify an object code format other than the system default.

-u, --undefined-only

Report only the undefined symbols.

-A, -o, --print-file-name

Print input filenames before each symbol.

-B

Same as --format=bsd.

-C, --demangle[=style]

Translate low-level symbol names into readable versions. You may specify a style to use when demangling symbol names from a foreign compiler.

-D, --dynamic

Print dynamic, not normal, symbols. Useful only when working with dynamic objects (some kinds of shared libraries, for example).

-P, --portability

Same as -f posix.

-S, --print-size

Print the size of defined symbols.

-V, --version

Print nm’s version number on standard error.

Name

nohup

Synopsis

nohup command [arguments]
nohup option

Run the named command with its optional command arguments, continuing to run it even after you log out (make command immune to hangups — i.e., no hangup). Terminal output is appended to the file nohup.out by default, or $HOME/nohup.out if nohup.out can’t be written to. Modern shells preserve background commands by default; this command is necessary only in the original Bourne shell.

Options

--help

Print usage information and exit.

--version

Print version information and exit.

Name

nslookup

Synopsis

nslookup

TCP/IP command. Query Internet domain nameservers. nslookup is deprecated; its functionality is replaced by the dig and host commands. nslookup may not be included in some distributions.

Name

nsupdate

Synopsis

nsupdate [options] [filename]

System administration command. Interactively submit dynamic DNS update requests to a nameserver. Use nsupdate to add or remove records from a zone without manually editing the zone file. Commands may be entered interactively or read from filename. An update message is built from multiple commands, some establishing prerequisites, some adding or deleting resource records. Messages are executed as a single transaction. A blank line or the send command will send the current message. Lines beginning with a semicolon are treated as comments. For additional information on dynamic DNS updates, see RFC 2136.

Options

-d

Print additional tracing information usable for debugging.

-k keyfile

Read encrypted transaction signature key from keyfile. The key should be encrypted using the HMAC-MD5 algorithm. Keyfiles are generated by the dnssec-keygen command.

-r n

Retry UDP n times. Default is 3.

-t seconds

Set request timeout. Default is 300 seconds. 0 disables timeout.

-u seconds

Set UDP retry interval. Default is 3 seconds. If 0, then interval is computed from the time out and retry values.

-v

Use TCP instead of UDP to send update requests.

-y keyname:secret

Generate transaction signature from specified keyname and secret.

Interactive commands

answer

Print answer.

class classname

Set default class to classname instead of the normal default IN.

key keyname secret

Generate transaction signature from specified keyname and secret. This command overrides command-line options -k or -y.

local address [port]

Use local address and, if specified, port to send updates.

prereq criteria

Specify prerequisites for updating a domain. Provide the criteria in one of the following forms:

nxdomain domain-name

Perform updates only if there are no preexisting records with the name domain-name.

nxrrset domain-name [class] type

Perform updates only if there is no preexisting record of the specified type and class for domain-name. When no class is given, IN is assumed.

yxdomain domain-name

Perform updates only if there is a preexisting record with the name domain-name.

yxrrset domain-name [class] type [data]

Perform updates only if there is a preexisting record of the specified type and class for domain-name. If data is given, the RDATA of the specified resource must match it exactly. When no class is given, IN is assumed.

send

Send the current message. Same as entering a blank line.

server servername [port]

Update records on DNS server servername instead of the master server listed in the MNAME field of the appropriate zone’s SOA record.

show

Print all commands in current message.

update command

Update the records according to one of the following commands:

add domain-name [ttl] [class] type data

Add a resource record with the specified values.

delete domain-name [ttl] [class] [type [data]]

Delete resource records for domain-name. The ttl field is always ignored, but if other fields are given, only delete records that match all criteria.

zone zonename

Apply updates to the specified zonename. If no zone command is given, nsupdate attempts to determine the correct zone based on other input.

Name

objcopy

Synopsis

objcopy [options] infile [outfile]

Copy the contents of the input object file to another file, optionally changing the file format in the process (but not the endian-ness). If outfile is not specified, objcopy creates a temporary file and renames it to infile when the copy is complete, destroying the original input file. The GNU Binary File Descriptor (BFD) library is used to read and write the object files.

Options

--add-section section=file

Add a new section to the output object file with the specified section name and the contents taken from the specified file. Available only for formats that allow arbitrarily named sections.

--alt-machine-code=n

If the output architecture has alternate machine codes, use the nth code instead of the default.

-b n, --byte=n

Copy only every nth byte. Header data is not affected. The value of n can be from 0 to interleave−1, where interleave is specified by -i (default is 4). This option is useful for creating files to program ROM and is typically used with srec as the output format.

-B bfdarch, --binary-architecture=bfdarch

Set the output architecture to bfdarch (e.g., i386) for transforming a raw binary file into an object file. Otherwise, this option is ignored. After the conversion, your program can access data inside the created object file by referencing the special symbols _binary_objfile_start, _binary_objfile_end, and _binary_objfile_size.

--change-addresses=incr, --adjust-vma=incr

Change the VMA and LMA addresses of all sections, plus the start address, by adding incr. Changing section addresses is not supported by all object formats. Sections are not relocated.

--change-leading-char

For object formats that use a special character (such as an underscore) to begin symbols, change the leading character when converting between formats. If the character is the same in both formats, the option has no effect. Otherwise, it adds, removes, or changes the leading character as appropriate for the output format.

--change-section-address section{=|+|-}val,
--adjust-section-vma section{=|+|-}val

Set or change the VMA and LMA addresses of the specified section. With =, set the section address to the specified value; otherwise, add or subtract the value to get the new address.

--change-section-lma section{=|+|-}val

Set or change the LMA address of the specified section. With =, set the section address to the specified value; otherwise, add or subtract the value to get the new address.

--change-section-vma section{=|+|-}val

Set or change the VMA address of the specified section. With =, set the section address to the specified value; otherwise, add or subtract the value to get the new address.

--change-start incr, --adjust-start incr

Add incr to the start address to get a new start address. Not supported by all object formats.

--change-warnings, --adjust-warnings

Issue a warning if the section that is specified in one of the options --change-section-address, --change-section-lma, or --change-section-vma does not exist.

--debugging

Convert debugging information if possible.

-F bfdname, --target=bfdname

Set the binary format for both input and output files to the binary file descriptor name bfdname. No format translation is done. Use the -h option for a list of supported formats for your system.

-g, --strip-debug

Do not copy debugging information.

-G symbol, --keep-global-symbol=symbol

Copy only the specified global symbol, making all other symbols local to the file. May be specified multiple times.

--gap-fill=val

Fill gaps between sections with the specified value; applies to the load address (LMA) of the sections.

-h, --help

Print help information, including a list of supported target object formats, then exit.

- interleave, --interleave=interleave

Copy one out of every interleave bytes. Use -b to set the byte to copy (default is 4). This option is ignored if -b is not specified.

-I bfdname, --input-target=bfdname

Set the binary file format of the input file using its binary file descriptor name, bfdname.

-j section, --only-section=section

Copy only the specified section. May be specified multiple times.

-K symbol, --keep-symbol=symbol

Copy only the specified symbol from the source file. May be specified multiple times.

--keep-global-symbols=filename

Apply the option --keep-global-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.

--keep-symbols=file

Apply the option --keep-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.

-L symbol, --localize-symbol=symbol

Make the specified symbol local. May be specified multiple times.

--localize-symbols=filename

Apply the option --localize-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.

-N symbol, --strip-symbol=symbol

Do not copy the specified symbol. May be specified multiple times.

--no-change-warnings, --no-adjust-warnings

Do not issue a warning even if the section specified in one of the options --change-section-address, --change-section-lma, or --change-section-vma does not exist.

-O bfdname, --output-target=bfdname

Set the binary file format of the output file using its binary file descriptor name, bfdname. The format srec generates S-records (printable ASCII versions of object files), and binary generates a raw binary file. Use -h for other available formats.

-p, --preserve-dates

Preserve the input file’s access and modification dates in the output file.

--pad-to=addr

Pad the output file up to the load address. Use the fill value specified by --gap-fill (default is 0).

-R section, --remove-section=section

Do not copy any section with the specified name. May be specified multiple times.

--redefine-sym old=new

Change the name of the symbol old to new.

--remove-leading-char

If the first character of a global symbol is a special character (such as an underscore) used by the input object file format, remove it. Unlike --change-leading-char, this option always changes the symbol name when appropriate, regardless of the output object format.

--rename-section oldname=newname[,flags]

Rename a section from oldname to newname, optionally also changing the flags to flags.

-S, --strip-all

Do not copy relocation and symbol information.

--set-section-flags section=flags

Set flags for the specified section as a comma-separated string of flag names. Not all flags are meaningful for all object formats. The possible flags are alloc, code, contents, data, debug, load, noload, readonly, rom, and share.

--set-start=val

Set the start address of the new file to the specified value. Not supported by all object formats.

--srec-forceS3

Force all srec output records to be type S3 records.

--srec-len=ival

Set the maximum length of srec output records to the specified value. The length includes the address, data, and crc fields.

--strip-symbols=filename

Apply the option --strip-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.

--strip-unneeded

Strip all symbols not needed for relocation processing.

-v, --verbose

Run in verbose mode, listing all object files modified; for archives, list all archive members.

-V, --version

Print version information and exit.

-W symbol, --weaken-symbol=symbol

Make the specified symbol weak. May be specified multiple times.

--weaken

Make all global symbols weak.

--weaken-symbols=filename

Apply the option --weaken-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.

-x, --discard-all

Do not copy nonglobal symbols.

-X, --discard-locals

Do not copy compiler-generated local symbols (usually those starting with L or ..).

Name

objdump

Synopsis

objdump [options] objfiles

Display information about one or more object files. If an archive is specified, objdump displays information on each object file in the archive. At least one of the options -a, -d, -D, -f, -g, -G, -h, -H, -p, -r, -S, -t, -T, -V, or -x must be given to tell objdump what information to show.

Options

-a, --archive-header

If any input files are archives, display the archive header information. The output includes the object file format of each archive member.

--adjust-vma=offset

Add offset to all section headers before dumping information. Useful if the section addresses do not correspond to the symbol table.

-b bfdname, --target=bfdname

Set the binary file format using its binary file descriptor name, bfdname. Use the -h option for a list of supported formats for your system.

-C [style], --demangle[=style]

Decode (demangle) low-level symbol names into user-level names, optionally specifying a mangling style. Removes any initial underscores and makes C++ function names readable.

-d, --disassemble

Display assembler mnemonic names for the machine instructions. Disassemble only sections that are expected to contain instructions.

-D, --disassemble-all

Disassemble all sections, not just those expected to contain instructions.

-EB, --endian=big
-EL, --endian=little

Specify whether the object files are big- or little-endian, for disassembling. Useful for disassembling formats such as S-records (printable ASCII versions of object files) that do not include that information.

-f, --file-header

Display overall header summary information.

--file-start-context

When using -S and displaying source code from a file that hasn’t been displayed yet, include context from the start of the file.

-g, --debugging

Display debugging information.

-G, --stabs

Display any stabs (debugging symbol table entries) information, in addition to the contents of any sections requested.

-h, --section-header, --header

Display section-header summary information.

-H, --help

Display help information and exit.

-i, --info

Display the architectures and object formats available on your system for use with -b or -m.

-j name, --section=name

Display information for section name.

-l, --line-numbers

Label the display with filename and source code line numbers corresponding to the object code or relocation entries shown. Use with -d, -D, or -r.

-m arch, --architecture=arch

Specify the architecture for disassembling object files. Useful when disassembling files such as S-records that do not include this information.

-M options, --disassembler-options=options

Pass target-specific information to the disassembler. Supported only on some targets.

--no-show-raw-insn

Do not show instructions in hexadecimal when disassembling. This is the default with --prefix-addresses.

-p, --private-headers

Display information specific to the object format. For some formats, no additional information is displayed.

--prefix-addresses

When disassembling, print the complete address on each line.

-r, --reloc

Display relocation entries. With -b or -D, the entries are intermixed with the disassembly.

-R, --dynamic-reloc

Print dynamic relocation entries. Meaningful only for dynamic objects such as certain types of shared libraries.

-s, --full-contents

Display the full contents of any requested sections.

-S, --source

Display source code intermixed with disassembly, if possible. Implies -d.

--show-raw-insn

When disassembling, show instructions in hexadecimal as well as symbolic form. This is the default, except with --prefix-addresses.

--start-address=addr

Start displaying data at the specified address. Applies to -d, -r, and -s.

--stop-address=addr

Stop displaying data at the specified address. Applies to -d, -r, and -s.

-t, --syms

Print symbol table entries.

-T, --dynamic-syms

Print dynamic symbol table entries. Meaningful only for dynamic objects such as certain types of shared libraries.

-V, --version

Print version information and exit.

-w, --wide

Format lines for output devices wider than 80 characters, and do not truncate symbol table names.

-x, --all-headers

Display all available header information. Equivalent to specifying -a -f -h -r -t.

-z, --disassemble-zeroes

Disassemble blocks of zeroes. The default is to skip such blocks.

Name

od

Synopsis

od [options] [files]
od --traditional [file] [[+]offset [[+]label]]

Dump the specified files to standard output. The default is to dump in octal format, but other formats can be specified. With multiple files, concatenate them in the specified order. If no files are specified or file is -, read from standard input. With the second form, using the --traditional option, only one file can be specified.

Options

For the following options, see the upcoming Arguments section for an explanation of the arguments bytes, size, and type. If no options are specified, the default is -A o -t d2 -w 16.

-a

Print as named characters. Same as -t a.

-A radix, --address-radix=radix

Specify the radix (base) for the file offsets printed at the beginning of each output line. The possible values are:

d

Decimal.

n

None; do not print an offset.

o

Octal; the default.

x

Hexadecimal.

-b

Print as octal bytes. Same as -t o1.

-c

Print as ASCII characters or backslash escapes. Same as -t c.

-d

Print as unsigned decimal shorts. Same as -t u2.

-f

Print as floating-point. Same as -t fF.

--help

Display a usage message and exit.

-i

Print as decimal integers. Same as -t dI.

-j bytes, --skip-bytes=bytes

Skip the specified number of input bytes before starting.

-l

Print as decimal longs. Same as -t dL.

-N bytes, --read-bytes=bytes

Format and print only the specified number of input bytes.

-o

Print as octal shorts. Same as -t o2.

-s

Print as decimal shorts. Same as -t d2.

-S bytes, --strings[=bytes]

Output strings that are at least bytes ASCII graphic characters long (default is 3 if bytes is not specified for --strings).

-t type, --format=type

Format the output according to type, where type is a string of one or more of the characters listed in the Arguments section. If more than one type is specified, each output line is written once in each specified format. If a trailing z is appended to type, od appends any printable characters to the end of each output line.

--traditional

Accept arguments in the traditional form, which takes a single file specification with an optional offset and label, as shown in the second form of the command. offset is an octal number indicating how many input bytes to skip over. label specifies an initial pseudo-address, which is printed in parentheses after any normal address. Both the offset and the label can begin with an optional plus sign (+), and can have a trailing decimal point (.) to force the offset to be interpreted as a decimal number and/or a trailing b to multiply the number of bytes skipped by offset by 512.

-v, --output-duplicates

Print all lines, including duplicates. By default, only the first of a series of identical lines is printed, and an asterisk is printed at the beginning of the following line to indicate that there were duplicates.

--version

Display version information and exit.

-w bytes, --width[=bytes]

Dump bytes input bytes to each output line. Defaults to 16 if this option is omitted. If --width is specified but bytes is omitted, the default is 32.

-x

Print as hexadecimal shorts. Same as -t x2.

Arguments

bytes

Specify a number of bytes. Treated as hexadecimal if it begins with 0x or 0X, as octal if it begins with 0, or as decimal otherwise. Append b to multiply by 512, k to multiply by 1024, or m to multiply by 10,248,576.

size

Specified as part of type to indicate how many bytes to use in interpreting each number. Types a and c do not take a size. For other types, size is a number. For type f, size can also be one of the following:

D

Double.

F

Float.

L

Long double.

For the remaining types (d, o, u, x), size can be one of the following in addition to a number:

C

Character.

I

Integer.

L

Long.

S

Short.

type

Specify the format type. The possible types are:

a

Named character.

c

ASCII character or backslash escape.

dsize

Signed decimal, with size bytes per integer.

fsize

Floating point, with size bytes per integer.

osize

Octal, with size bytes per integer.

usize

Unsigned decimal, with size bytes per integer.

xsize

Hexadecimal, with size bytes per integer.

Name

openvt

Synopsis

openvt [options] [--
] [command] [arguments]

Locate the first available virtual terminal (VT) and run command with any arguments given. If no command is specified, the shell $SHELL is started.

Options

--

Indicates the end of openvt options. Required before the command name to pass options to the command.

-c vt

Use the specified VT number instead of the first available. You must have write access to vt.

-e

Execute command without forking. For use in /etc/inittab, rather than on the command line.

-l

Run the command as a login shell, prepending a dash (-) to the command name.

-s

Switch to the new VT when the command is started and make it the current VT.

-u

Determine the owner of the current VT, and log in as that user. You must be root to use this option, which is also suitable for calling by init. Don’t use with -l.

-v

Verbose mode.

-w

Wait for the command to complete. If used with -s, switch back to the controlling terminal when the command is done.

Name

passwd

Synopsis

passwd [options] [user]

Create or change a password associated with a user name. Only the owner or a privileged user may change a password. Owners need not specify their user name. Users can change their own passwords. For all other operations, you must be root.

Options

-d, --delete

Delete the password for the user’s account.

-f, --force

Force the operation. Overrides -u.

-?, --help

Display a help message describing the options. See also --usage.

-i days, --inactive=days

Set the number of days after a password has expired before the account is disabled.

-k, --keep-tokens

Keep passwords (authentication tokens) that have not expired.

-l, --lock

Lock the user’s account.

-n days, --minimum=days

Set the minimum number of days that the password is valid.

-S, --status

Print the status of the user’s password.

--stdin

Read new passwords from standard input.

-u, --unlock

Unlock the user’s account

--usage

Display a brief usage message. See also --help.

-w days, --warning=days

Set the number of days of warning users will get before their password expires.

-x days, --maximum=days

Set the maximum number of days that the password is valid.

Name

paste

Synopsis

paste [options] files

Merge corresponding lines of one or more files into tab-separated vertical columns and write to standard output. Use - to read from standard input, instead of specifying a file. See also cut, join, and pr.

Options

-dchar, --delimiters=char

Separate columns with char instead of a tab. You can separate columns with different characters by supplying more than one char.

--help

Print a help message and then exit.

-s, --serial

Merge lines from one file at a time.

--version

Print version information and then exit.

Examples

Create a three-column file from files x, y, and z:

paste x y z > file

List users in two columns:

who | paste - -

Merge each pair of lines into one line:

paste -s -d"\t\n" list

Name

patch

Synopsis

patch [options] [original [patchfile]]

Apply the patches specified in patchfile to original. Replace the original with the new, patched version; move the original to original.orig or original˜. The patch file is a difference listing produced by the diff command.

Options

-b, --backup

Back up the original file.

-B prefix, --prefix=prefix

Prepend prefix to the backup filename.

--backup-if-mismatch, --no-backup-if-mismatch

When not backing up all original files, these options control whether a backup should be made when a patch does not match the original file. The default is to make backups unless --posix is specified.

-c, --context

Interpret patchfile as a context diff.

-d dir, --directory=dir

cd to directory dir before beginning patch operations.

-D string, --ifdef=string

Mark all changes with:

#ifdef
string
#endif

--dry-run

Print results of applying a patch, but don’t change any files.

-e, --ed

Treat the contents of patchfile as ed commands.

-E, --remove-empty-files

If patch creates any empty files, delete them.

-f, --force

Force all changes, even those that look incorrect. Skip patches if the original file does not exist; force patches for files with the wrong version specified; assume patches are never reversed.

-F num, --fuzz=num

Specify the maximum number of lines that may be ignored (fuzzed over) when deciding where to install a hunk of code. The default is 2. Meaningful only with context diffs.

-g num, --get num

Specify whether to check the original file out of source control if it is missing or read-only. If num is a positive number, get the file. If it is negative, prompt the user. If it is 0, do not check files out of source control. The default is negative or the value of the PATCH_GET environment variable when set, unless the --posix option is given. In that case, the default is 0.

--help

Print help message, then exit.

-i file, --input=file

Read patch from file instead of stdin.

-l, --ignore-whitespace

Ignore whitespace while pattern matching.

-n, --normal

Interpret patch file as a normal diff.

-N, --forward

Ignore patches that appear to be reversed or to have already been applied.

-o file, --output=file

Print output to file.

-p num, --strip=num

Specify how much of preceding pathname to strip. A num of 0 strips everything, leaving just the filename. 1 strips the leading /. Each higher number after that strips another directory from the left.

--posix

Conform more strictly to the POSIX standard.

--quoting-style=style

Set the quoting style used when printing names. The default style is shell, unless set by the environment variable QUOTING_STYLE. style may be one of the following:

c

Quote as a C language string.

escape

Like c, but without surrounding double-quote characters.

literal

Print without quoting.

shell

Quote for use in shell when needed.

shell-always

Quote for use in shell even if not needed.

-r file, --reject-file=file

Place rejects (hunks of the patch file that patch fails to place within the original file) in file. Default is original.rej.

-R, --reverse

Do a reverse patch: attempt to undo the damage done by patching with the old and new files reversed.

-s, --silent, --quiet

Suppress commentary.

-t, --batch

Force changes as with -f but make different decisions. Skip patches if headers don’t contain filenames; skip patches for files with the wrong version specified; assume patches are reversed if they look like they are. Also see -Z.

-T, --set-time

When original file timestamps match the times given in the patch header, set timestamps for patched files according to the context diff headers. Use option -f to force date changes. Assume timestamps are in local time.

-u, --unified

Interpret patch file as a unified context diff.

-v, --version

Print version number and exit.

-V method, --version-control=method

Specify method for creating backup files (overridden by -B):

t, numbered

Make numbered backups.

nil, existing

Back up files according to preexisting backup schemes, with simple backups as the default. This is patch’s default behavior.

never, simple

Make simple backups.

--verbose

Verbose mode.

-Y prefix, --basename-prefix=prefix

Use the specified prefix with a file’s basename to create backup filenames. Useful for specifying a directory.

-z suffix, --suffix=suffix

Back up the original file in original.suffix.

-Z, --set-utc

When original file timestamps match the times given in the patch header, set timestamps for patched files according to the context diff headers. Use option -f to force date changes. Assume timestamps are in Coordinated Universal Time (UTC). Also see -T.

Name

pathchk

Synopsis

pathchk [options] filenames

Determine validity and portability of filenames. Specifically, determine if all directories within the path are searchable and if the length of the filenames is acceptable.

Options

--help

Print a help message and then exit.

-p

Check for most POSIX systems.

-P

Check for empty names and names that start with -.

--portability

Check portability for all POSIX systems. Equivalent to -p -P.

--version

Print version information and then exit.

Name

pccardctl

Synopsis

pccardctl command

System administration command. Monitor and control PCMCIA sockets. Commands operate on a named card socket number, or all sockets if no number is given.

Commands

config [socket]

Display current socket configuration.

eject [socket]

Prepare the system for the card(s) to be ejected.

ident [socket]

Display card identification information.

info [socket]

Display card identification information as Bourne shell variable definitions for use in scripts.

insert [socket]

Notify system that a card has been inserted.

resume [socket]

Restore power to socket and reconfigure for use.

status [socket]

Display current socket status.

suspend [socket]

Shut down device and cut power to socket.

Name

pidof

Synopsis

pidof [options] programs

Display the process IDs of the listed program or programs. pidof is actually a symbolic link to killall5.

Options

-c

Return only processes running in the same root directory. Ignored for nonroot users.

-o pid

Omit all processes with the specified process ID. Can be specified more than once to omit multiple IDs.

-s

Return a single process ID.

-x

Also return process IDs of shells running the named scripts.

Name

ping

Synopsis

ping [options] host

System administration command. Confirm that a remote host is online and responding. ping is intended for use in network testing, measurement, and management. Because of the load it can impose on the network, it is unwise to use ping during normal operations or from automated scripts.

Options

-a

Make ping audible. Beep each time response is received.

-A

Adapt to return interval of packets. Like -f ping, sends packets at approximately the rate at which they are received. This option may be used by an unprivileged user.

-b

Ping a broadcast address.

-B

Bind to original source address and do not change.

-c count

Stop after sending (and receiving) count ECHO_RESPONSE packets.

-f

Flood ping-output packets as fast as they come back or 100 times per second, whichever is greater. This can be very hard on a network and should be used with caution. Only a privileged user may use this option.

-i wait

Wait wait seconds between sending each packet. Default is to wait one second between each packet. This option is incompatible with the -f option.

-I name

Set source address to interface name. name may also be specified as an IP address.

-l preload

Send preload number of packets as fast as possible before falling into normal mode of behavior.

-L

If destination is a multicast address, suppress loopback.

-M hint

Specify Path MTU Discovery strategy. Accepted values are do, want, or dont.

-n

Numeric output only. No attempt will be made to look up symbolic names for host addresses.

-p digits

Specify up to 16 pad bytes to fill out packet sent. This is useful for diagnosing data-dependent problems in a network. digits are in hex. For example, -p ff will cause the sent packet to be filled with all 1s.

-q

Quiet output--nothing is displayed except the summary lines at startup time and when finished.

-Q tos

Set Quality of Service on ICMP datagrams.

-r

Bypass the normal routing tables and send directly to a host on an attached network.

-R

Set the IP record route option, which will store the route of the packet inside the IP header. The contents of the record route will be printed if the -v option is given, and will be set on return packets if the target host preserves the record route option across echoes or if the -l option is given.

-s packetsize

Specify number of data bytes to be sent. Default is 56, which translates into 64 ICMP data bytes when combined with the 8 bytes of ICMP header data.

-S size

Set send buffer (SNDBUF) size. The default is the size of one packet.

-t n

Set the IP Time to Live to n seconds.

-T option

Set IP timestamp options. Accepted option values are:

tsonly

Timestamps only.

tsandaddr

Timestamps and addresses.

tsprespec hosts

Timestamps with prespecified hops of one or more hosts.

-U

Use older ping behavior and print full user-to-user latency instead of network round-trip time.

-v

Verbose; list ICMP packets received other than ECHO_RESPONSE.

-V

Print version, then exit.

-w n

Exit ping after n seconds.

-W n

When waiting for a response, time out after n seconds.

Name

pmap

Synopsis

pmap [options] pids

Display the memory maps of a process.

Options

-d

Display the offset and device number of each mapping.

-q

Be more quiet. Displays less header and footer information.

-x

Provide a more detailed and verbose display.

-V

Display the version number and exit.

Name

portmap

Synopsis

rpc.portmap [options]

NFS/NIS command. RPC program number to IP port mapper. portmap is a server that converts RPC program numbers to IP port numbers. It must be running in order to make RPC calls. When an RPC server is started, it tells portmap which port number it is listening to and which RPC program numbers it is prepared to serve. When a client wishes to make an RPC call to a given program number, it first contacts portmap on the server machine to determine the port number where RPC packets should be sent. portmap must be the first RPC server started. On newer systems portmap is deprecated. Use rpcbind instead.

Options

-d

Run portmap in debugging mode. Does not allow portmap to run as a daemon.

-l

Bind to loopback device. This only works from the localhost.

-v

Verbose mode.

Name

poweroff

Synopsis

poweroff [options]

System administration command. Close out filesystems, shut down the system, and power off. Because this command immediately stops all processes, it should be run only in single-user mode. If the system is not in runlevel 0 or 6, poweroff calls shutdown -h, then performs a poweroff.

Options

-d

Suppress writing to /var/log/wtmp.

-f

Call reboot or halt and not shutdown, even when shutdown would normally be called. This option is used to force a hard halt or reboot.

-h

Place hard drives in standby mode before halt or poweroff.

-i

Shut down network interfaces before reboot.

-n

Suppress normal call to sync.

-w

Suppress normal execution; simply write to /var/log/wtmp.

Name

pppd

Synopsis

pppd [tty] [speed] [options]

System administration command. PPP stands for the Point-to-Point Protocol; it allows datagram transmission over a serial connection. pppd attempts to configure tty for PPP (searching in /dev) or, by default, the controlling terminal. You can also specify a baud rate of speed. pppd accepts many options. Only the most common options are listed here.

Options

[local_IP_address]:[remote_IP_address]

Specify the local and/or remote interface IP addresses, as hostnames or numeric addresses.

asyncmap map

Specify which control characters cannot pass over the line. map should be a 32-bit hex number, where each bit represents a character to escape. For example, bit 00000001 represents the character 0x00; bit 80000000 represents the character 0x1f or _. You may specify multiple characters.

auth

Require self-authentication by peers before allowing packets to move.

call file

Read options from file in /etc/ppp/peers/. Unlike the file option, call file may contain privileged options, even when pppd is not run by root.

connect command

Connect as specified by command, which may be a binary or shell command.

crtscts

Use hardware flow control.

debug

Log contents of control packets to syslogd.

defaultroute

Add a new default route in which the peer is the gateway. When the connection shuts down, remove the route.

nodetach

Operate in the foreground. By default, pppd forks and operates in the background.

disconnect command

Close the connection as specified by command, which may be a binary or shell command.

escape character-list

Escape all characters in character-list, which should be a comma-separated list of hex numbers. You cannot escape 0x20-0x3f or 0x5e.

file file

Consult file for options.

init script

Run specified command or shell script to initialize the serial line.

lock

Allow only pppd to access the device.

mru bytes

Refuse packets of more than bytes bytes.

mtu bytes

Do not send packets of more than bytes bytes.

passive, -p

Do not exit if peer does not respond to attempts to initiate a connection. Instead, wait for a valid packet from the peer.

silent

Send no packets until after receiving one.

Files

/var/run/pppn.pid

pppd’s process ID. The n in pppn.pid is the number of the PPP interface unit corresponding to this pppd process.

/etc/ppp/ip-up

Binary or script to be executed when the PPP link becomes active.

/etc/ppp/ip-down

Binary or script to be executed when the PPP link goes down.

/etc/ppp/pap-secrets

Contains usernames, passwords, and IP addresses for use in PAP authentication.

/etc/ppp/options

System defaults. Options in this file are set before the command-line options.

~/.ppprc

The user’s default options. These are read before command-line options but after the system defaults.

/etc/ppp/options.ttyname

Name of the default serial port.

Name

pr

Synopsis

pr [options] [files]

Convert a text file or files to a paginated or columned version, with headers, suitable for printing. If - is provided as the filename, read from standard input.

Options

+beg_pag[:end-pag], --pages=beg_pag[:end-pag]

Begin printing on page beg_pag and end on end-pag if specified.

-num_cols, --columns=num_cols

Set the number of columns to print, balancing the number of lines in the columns on each page. Print vertical columns, except with -a.

-a, --across

Print columns horizontally, not vertically.

-c, --show-control-chars

Convert control characters to hat notation (such as ^C), and other unprintable characters to octal backslash format.

-d, --double-space

Double space.

-D format, --date-format=format

Format the header date using format. See the date command for the possible formats.

-e[tab-char[width]], --expand-tabs[=tab-char[width]]

Convert tabs (or tab-chars) to spaces. If width is specified, convert tabs to width characters (default is 8).

-f, -F, --form-feed

Separate pages with form feeds, not newlines. With -F, print a three-line page header; otherwise, print a five-line header and trailer.

-h header, --header=header

Use header for the header instead of the filename. The header is centered.

--help

Print a help message and then exit.

-i[out-tab-char[out-tab-width]],
--output-tabs[=out-tab-char[out-tab-width]]

Replace spaces with tabs on output. You can specify an alternative tab character (default is tab) and width (default is 8).

-J, --join-lines

Merge full lines; ignore -W if set.

-l lines, --length=lines

Set page length to lines (default is 66). If lines is less than 10, omit headers and footers. Thus the default number of lines of text (i.e., not header or trailer) is 56, or 63 with -F.

-m, --merge

Print all files, one per column.

-n[delimiter[digits]], --number-lines[=delimiter[digits]]

Number columns, or, with the -m option, number lines. Append delimiter to each number (default is a tab) and limit the size of numbers to digits (default is 5).

-N num, --first-line-number=num

Start counting with num at the first line of the first page printed. Also see +beg_page.

-o width, --indent=width

Indent left margin to width. Does not affect the page width set with -w or -W.

-r, --no-file-warnings

Continue silently when unable to open an input file.

-s[delimiter], --separator[=delimiter]

Separate columns with the single-character delimiter (default is a tab) instead of spaces.

-S[string], --sep-string[=string]

Separate columns with string. Default is a tab with -J and a space otherwise.

-t, --omit-header

Suppress headers, footers, and fills at end of pages.

-T, --omit-pagination

Like -t but also suppress form feeds.

-v, --show-non-printing

Convert unprintable characters to octal backslash format.

-w page_width, --width=page_width

Set the page width to page_width characters for multicolumn output. Default is 72.

-W page_width, --page-width=page_width

Set the page width to always be page_width characters. Lines longer than the specified width are truncated unless -J is also specified. Default is 72.

--version

Print version information and then exit.

Name

praliases

Synopsis

praliases [options] [keys]

System administration command. praliases prints the current sendmail mail aliases. (Usually defined in the /etc/aliases or /etc/aliases.db file.) Limit output to the specified keys when given.

Options

-f file

Read the aliases from the specified file instead of sendmail’s default alias files.

-C file

Read sendmail configuration from the specified file instead of from /etc/mail/sendmail.cf.

Name

printenv

Synopsis

printenv [variables]
printenv option

Print values of all environment variables or, optionally, only the specified variables.

Options

--help

Print usage information and exit.

--version

Print version information and exit.

Name

printf

Synopsis

printf formats [strings]
printf option

Print strings using the specified formats. formats can be ordinary text characters, C-language escape characters, C format specifications ending with one of the letters diouxXfeEgGcs or, more commonly, a set of conversion arguments listed here.

Options

--help

Print usage information and exit.

--version

Print version information and exit.

Arguments

%%

Print a single %.

%b

Print string with \ escapes interpreted.

%s

Print the next string.

%n$s

Print the nth string.

%[-]m[.n]s

Print the next string, using a field that is m characters wide. Optionally, limit the field to print only the first n characters of string. Strings are right-adjusted unless the left-adjustment flag, -, is specified.

Examples

printf '%s %s\n' "My files are in" $HOME
printf '%-25.15s %s\n' "My files are in" $HOME

Name

ps

Synopsis

ps [options]

Report on active processes. ps has three types of options. GNU long options start with two hyphens, which are required. BSD options may be grouped and do not start with a hyphen, while Unix98 options may be grouped and require an initial hyphen. The meaning of the short options can vary depending on whether or not there is a hyphen. In options, list arguments should either be comma-separated or space-separated and placed inside double quotes. In comparing the amount of output produced, note that e prints more than a and l prints more than f for each entry.

Options

nums, p nums, -p nums, --pid=nums

Include only specified processes, which are given in a space-delimited list.

-nums, -s nums, --sid=nums

Include only specified session IDs, which are given in a space-delimited list.

[-]a

As a, list all processes on a terminal. As -a, list all processes except session leaders and processes not associated with a terminal.

[-]c

As -c, show different scheduler information with -l. As c, show the true command name.

-C cmds

Select by command name.

--cols=cols, --columns=cols

Set the output width (the number of columns to display).

-d

Select all processes except session leaders.

-e, -A

Select all processes.

e

Include environment information after the command.

[-]f, --forest

As -f, display full listing. As f or --forest, display “forest” family tree format, with ASCII art showing the relationships.

-F

Set extra-full format; implies -f.

-g list, -G list, --group=groups, --Group=groups

For -g, select by session leader if list contains numbers, or by group if it contains group names. For -G, select by the group IDs in list. --group selects by effective group and --Group selects by real group, where groups can be either group names or group IDs.

h, --no-headers

Suppress header. If you select a BSD personality by setting the environment variable PS_PERSONALITY to bsd, then h prints a header on each page.

-H

Display “forest” family tree format, but without ASCII art.

H

Display threads as if they were processes.

--headers

Repeat headers on every output page.

--help

Display help information and exit.

--info

Print debugging information.

[-]j

Jobs format. j prints more information than -j.

k spec, --sort spec

Specify sort order. Syntax for the specification is:

[+|-]key[,[+|-]key...]]

The default direction is +, for increasing numerical or alphabetic order. See Format and sort specifiers in Format and sort specifiers for possible keys.

[-]l

Produce a long listing. -l prints more information than l and is often used with -y.

L

Print list of field specifiers that can be used for output formatting or for sorting.

-L

Show threads, possibly with LWP and NLWP columns.

--lines=num, --rows=num

Set the screen height to num lines. If --headers is also set, the headers repeat every num lines.

[-]m

Show threads after processes.

n

Print user IDs and WCHAN numerically.

-n file, N file

Specify the System.map file for ps to use as a namelist file. The map file must correspond to the Linux kernel--e.g., /boot/System.map-2.6.27.5-117.fc10.x86_64.

-N, --deselect

Negate the selection, selecting all processes that do not meet the specified conditions.

[-]o fields, --format=fields

Specify user-defined format with a list of fields to display.

[-]O fields

As -O, this option is like -o, but some common fields are predefined. As O, this option can be either the same as -O in specifying fields to display, or can specify single-letter fields for sorting. For sorting, each field specified as a key can optionally have a leading + (return to default sort direction on key) or - (reverse the default direction).

--ppid=nums

Select by parent process IDs.

r

Show only processes that are currently running.

s

Display signal format.

S, --cumulative

Include some dead child process data in parent total.

[-]t ttys, --tty=ttys

Display processes running on the specified terminals. t with no terminal list displays processes for the terminal associated with ps. Specify - to select processes not associated with any terminal.

T

Display all processes on this terminal. Like t with no argument.

-T

Display threads, possibly with SPID column,

[-]u [users], U users, --user=users

As u with no argument, display user-oriented output. As -u, U, or --user, display by effective user ID (and also support names), showing results for users. With no argument, -u displays results for the current user.

-U users, --User=users

Display processes for users by real user ID (and also support names).

v

Display virtual memory format.

[-]V, --version

Display version information and then exit.

[-]w

Wide format. Don’t truncate long lines. Use twice to set an unlimited width.

--width=cols

Set screen width.

x

Display processes without an associated terminal.

-y

Do not show flags; show rss instead of addr. Requires -l.

Format and sort specifiers

The following are the keywords for formatting and for sorting with --sort, followed by a desciption and the output column header in parentheses:

%cpu, pcpu

Percent of CPU time used recently. (%CPU)

%mem, pmem

Percent of memory used. (%MEM)

args, cmd, command

The command the process is running with all its arguments. (CMD for cmd; otherwise COMMAND)

blocked, sig_block, sigmask

Mask, in hexadecimal, of blocked signals. (BLOCKED)

bsdstart

Command start time. (START)

bsdtime

Accumulated CPU time for user plus system. (TIME)

c

Integer value of %cpu. (C)

caught, sig_catch, sigcatch

Mask, in hexadecimal, of caught signals. (CAUGHT)

class, cls, policy

Scheduling class. (POL for policy, otherwise CLS). Possible values are:

-

Unreported

?

Unknown value

FF

SCHED_FIFO (first in, first out)

RR

SCHED_RR (round robin)

TS

SCHED_OTHER (standard time-sharing)

comm, ucmd, ucomm

Name of the command executable. (CMD for ucmd; otherwise, COMMAND)

cp

Per-mill CPU usage, where mill is 1000. Equivalent to %cpu with no decimal point. (CP)

cputime, time

Cumulative CPU time. (TIME)

egid, gid

Effective group ID number in decimal. (EGID or GID, respectively)

egroup, group

Effective group ID; as text value if it is available and if it fits, otherwise shown as decimal value. (EGROUP or GROUP, respectively)

eip

Effective instruction pointer. (EIP)

esp

Effective stack pointer. (ESP)

etime

Elapsed time since the start of the process. (ELAPSED)

euid, uid

Effective user ID. (EUID or UID, respectively)

euser, uname, user

Effective username; as text value if it is available and if it fits, otherwise shown as decimal value. (EUSER for euser; otherwise, USER)

f, flag, flags

Process flags. Can be summed. (F) Possible values are 1 (the process forked but didn’t exec) and 4 (the process used super-user privileges).

fgid, fsgid

Filesystem access group ID. (FGID)

fgroup, fsgroup

Filesystem access group ID; as text if available and if it fits, otherwise as a decimal number. (FGROUP)

fname

First eight bytes of the executable’s basename. (COMMAND)

fuid, fsuid

Filesystem access user ID. (FUID)

fuser

Filesystem access user ID; as text if available and if it fits, otherwise as a decimal number. (FUSER)

ignored, sig_ignore, sigignore

Mask of ignored signals in hexadecimal format. (IGNORED)

lstart

Command start time. (STARTED)

lwp, spid, tid

Light-weight process, or thread, ID. (LWP, SPID, TID, respectively)

ni, nice

The nice value of the process. A higher number indicates less CPU time. (NI)

nlwp, thcount

Number of LWPs, or threads, in the process. (NLWP or THCNT, respectively)

nwchan

Address of kernel function where process is sleeping. See also wchan to get the function by name. (WCHAN)

pending, sig, sig_pend

Mask of pending signals. Use with the m or -m option to see both signals pending on the process and on individual threads. (PENDING)

pgid, pgrp

Process group ID or ID of process group leader, which are equivalent. (PGID or PGRP, respectively)

pid

Process ID. (PID)

ppid

Parent process ID. (PPID)

pri

Process’s scheduling priority. A higher number indicates lower priority. (PRI)

psr

Current processor that the process is running on. (PSR)

rgid

Real group ID. (RGID)

rgroup

Real group name; as text if available and it fits, otherwise as a decimal number. (RGROUP)

rss, rssize, rsz

Resident set size (the amount of physical memory), in kilobytes. (RSZ for rsz; otherwise RSS)

rtprio

Real-time priority. (RTPRIO)

ruid

Real user ID number. (RUID)

ruser

Real user ID; as text if available and it fits, otherwise as a decimal number. (RUSER)

s, state

A single-character state display. See stat for the possible characters or for a multicharacter display. (S)

sched

Scheduling policy. Also see class. (SCH) Possible values are:

0

SCHED_OTHER

1

SCHED_FIFO

2

SCHED_RR

sess, session, sid

Session ID, or the process ID of the session leader, which is equivalent. (SID for sid; otherwise SESS)

sgi_p

Processor on which the process is currently running, or “*” if the process is not running. (P)

sgid, svgid

Saved group ID. (SGID or SVGID, respectively)

sgroup

Saved group name; as text if available and it fits, otherwise as a decimal number.

size

Size of virtual image. Provides a rough estimate of the swapspace required to swap the process out. Note that sz uses the same column header, but has a different meaning. (SZ)

stackp

Address of the stack bottom (start of the stack). (STACKP)

start

Start time of the command. (STARTED)

start_time

Starting time or date of the process. (START)

stat

Status. Multiple status characters can appear. See also s to display a single character. (STAT)

+

Part of foreground process group.

<

High priority (not “nice”).

D

Asleep and not interruptible.

l

Multithreaded.

L

Pages locked into memory.

N

Low priority (“nice”).

R

Running or runnable.

s

Session leader.

S

Asleep.

T

Stopped.

Z

Zombie.

suid, svuid

Saved user ID. (SUID or SVUID, respectively)

suser, svuser

Saved username; as text if it is available and it fits, otherwise as a decimal number. (SUSER or SVUSER, respectively)

sz

Physical page size of the core image of the process, including text, data and stack space. (SZ)

tpgid

ID of the foreground process group on the associated terminal for the process, or −1 if not connected to a terminal. (TPGID)

tt, tty, tname

Associated (controlling) terminal. (TTY for tname; otherwise TT)

vsz, vsize

Virtual memory size, in kilobytes of the entire process. (VSZ)

wchan

Kernel function in which process is sleeping, or “-” if running, or “*” if multithreaded process and ps is not displaying threads. (WCHAN)

Name

ptx

Synopsis

ptx [options] [infiles]
ptx -G [options] [infile [outfile]]

Create a permuted index, including context, from the contents of the specified input files. If the input files are omitted, or are -, read from standard input. The results are written to standard output. In the second form, with the -G option, ptx behaves like the System V version rather than the GNU version; you specify only one input file, and you can also specify an output file. Because they show words in context, permuted indexes are often used in such places as bibliographic or medical databases, thesauruses, or websites to aid in locating entries of interest.

Options

-A, --auto-reference

Produce automatically generated references, consisting of the filename and line number, separated by a colon, and print them at the beginning of each line.

-b file, --break-file=file

The specified file contains word-break characters--characters that are not part of words, but separate them.

-f, --ignore-case

Ignore case when sorting, by folding lowercase into uppercase.

-F string, --flag-truncation=string

Use string to flag line truncations.

-g num, --gap-size=num

Specify the number of spaces between output columns.

-G, --traditional

Behave like System V ptx; don’t use the GNU extensions. If an output file is specified, any existing contents are lost.

--help

Display a help message and exit.

-i file, --ignore-file=file

Read the list of words that are not to be used as keywords in the concordance output from file.

-M string, --macro-name=string

Select a string for use when generating output suitable for nroff, troff or TEX. The default is xx.

-o file, --only-file=file

Specify the “only” file, which contains a list of words to be used in the concordance output. Any words not in file are ignored. If both an only file and an ignore file are specified, a word must appear in the only file and not appear in the ignore file to be used as a keyword.

-O [roff], --format=roff

Format the output as roff directives suitable to be used as input to nroff or troff. Use -T for TEX output.

-r, --references

Use the first field of each line as a reference to identify the line in the permuted index.

-R, --right-side-refs

Put references on the right, instead of the left. Used with -r and -A. The space taken up by the references is not taken into account by -w, even if -R is specified without -r or -A.

-S regexp, --sentence-regexp=regexp

Specify a regular expression to identify the end of a line or a sentence. Without -G and without -r, the end of a sentence is used. With -G, or with -r, the end of a line is used. An empty regex disables end-of-line or end-of-sentence recognition.

-T [tex], --format=tex

Format the output as TEX directives suitable to be used as TEX input. Use -O for roff output.

--version

Print version information and exit.

-w num, --width=num

Select the maximum output-line width (excluding the width of any reference if -R is specified).

-W regexp, --word-regexp=regexp

Use the specified regular expression to match each keyword.

Name

pwck

Synopsis

pwck [options] [files]

System administration command. Remove corrupt or duplicate entries in the /etc/passwd and /etc/shadow files. pwck will prompt for a “yes” or “no” before deleting entries. If the user replies “no,” the program will exit. Alternate passwd and shadow files can be checked. If correctable errors are found, the user will be encouraged to run the usermod command.

Option

-q

Run in quiet mode. Only report serious problems.

-r

Run in noninteractive read-only mode, answering all questions no.

-s

Don’t check integrity, just sort entries by UID.

Exit status

0

Success.

1

Syntax error.

2

One or more bad password entries found.

3

Could not open password files.

4

Could not lock password files.

5

Could not write password files.

Name

pwconv

Synopsis

pwconv
pwunconv

System administration command. Convert unshadowed entries in /etc/passwd into shadowed entries in /etc/shadow. Replace the encrypted password in /etc/password with an x. Shadowing passwords keeps them safer from password-cracking programs. pwconv creates additional expiration information for the /etc/shadow file from entries in your /etc/login.defs file. If you add new entries to the /etc/passwd file, you can run pwconv again to transfer the new information to /etc/shadow. Already shadowed entries are ignored. pwunconv restores the encrypted passwords to your /etc/passwd file and removes the /etc/shadow file. Some expiration information is lost in the conversion. See also grpconv and grpunconv.

Name

pwd

Synopsis

pwd

Print the full pathname of the current working directory. See also the dirs shell command built into bash.

Name

quota

Synopsis

quota [options] [user|group]

Display disk usage and total space allowed for a designated user or group. With no argument, the quota for the current user is displayed. Most users can display only their own quota information, but the superuser can display information for any user. This command reports quotas for all filesystems listed in /etc/mtab. For NFS-mounted filesystems, quota calls rpc.rquotad on the server machine for the information.

Options

-A, --all-nfs

Report quotas for all NFS filesystems.

-F format, --format=format

Check quota files for the specified format.

-g, --group

Given with a user argument, display the quotas for the groups of which the user is a member, instead of the user’s quotas. With no argument, shows group quotas for the current user.

-i, --no-autofs

Igonore mountpoints that are mounted by the automounter.

-l, --local-only

Only report quotas on local filesystems.

-p, --raw-grace

When user is in a grace period, print a timestamp (seconds since epoch) marking when the grace period expires.

-q, --quiet

Display information only for filesystems in which the user is over quota.

-Q, --quiet-refuse

For NFS-mounted filesystems. do not print an error message if the connection to rpc.rquotad is refused (usually because it is not running on the server).

-s, --human-readable

Try to choose units for displaying limits, space used, and inodes used.

-u, --user

The default behavior. When used with -g, display both user and group quota information.

-v, --verbose

Display quotas for filesystems even if no storage is currently allocated.

-w, --no-wrap

Do not wrap line for long device names.

Formats

rpc

Quota over NFS.

vfsold

Version 1 quota.

vfsv0

Version 2 quota.

xfs

Quota on XFS filesystem.

Name

quotacheck

Synopsis

quotacheck [options] [filesystems]

System administration command. Audit and correct quota information by building a table of current disk usage and comparing it to the recorded usage in both the kernel and the quota files. quotacheck will update quota information when possible and prompt the user if it requires input. Most systems that support quotas run this command at system startup. To prevent damage to filesystems or loss of quota data, turn off quotas with quotaoff and umount the system. quotacheck will attempt to remount any mounted filesystem as read-only before scanning.

Options

-a, --all

Check all non-NFS filestystems in /etc/mtab.

-b, --backup

Back up quota files before writing new data to them.

-c, --create-files

Skip reading existing quota information; just write new files.

-f, --force

Force checking on filesystems with quotas currently enabled.

-Fformat , --format=format

Check quota files for the specified format. (See quota for valid formats.)

-g, --group

Only check group quotas.

-i, --interactive

Prompt user for input upon finding errors.

-m, --no-remount

Don’t try to remount mounted filesystems.

-M, --try-remount

Force check to run in read-write mode if it cannot successfully remount the filesystem in read-only mode.

-n, --use-first-dquot

If multiple entries for a user or group are found in a corrupt quota file, use the first entry found.

-R, --exclude-root

Don’t check the root filesystem when using the -a option.

-u, --user

Only check user quotas. This is the default.

-v, --verbose

Print information on the progress of the command.

Name

quotaon

Synopsis

quotaon [options] [filesystems]

System administration command. Turn on enforcement of filesystem quotas. To work, the filesystems must have a gpquota, quota, or usrquota option listed in the /etc/fstab file. On most filesystems, user and group quota files must also exist. XFS filesystems store quota information as metadata instead of as files. Use edquota or setquota to create the appropriate quota information.

Options

-a, --all

Turn on quotas for all autoloading filesystems in /etc/fstab that support them.

-f, --off

Invoke quotaoff instead of quotaon.

-F format, --format=format

Check quota files for the specified format. (See quota for valid formats.)

-g, --group

Turn group quotas on.

-p, --print-state

Print current quota status, then exit.

-u, --user

Turn user quotas on.

-v, --verbose

Print a message for each filesystem affected by the command.

Name

quotaoff

Synopsis

quotaoff [options] [filesystems]

System administration command. Turn off enforcement of filesystem quotas. This command is a synonym for quotaon -f.

Options

-a, --all

Turn off quotas for all filesystems in /etc/fstab.

-F format, --format=format

Check quota files for the specified format. (See quota for valid formats.)

-g, --group

Turn group quotas off.

-p, --print-status

Print current quota status, then exit.

-u, --user

Turn user quotas off.

-v, --verbose

Print a message for each filesystem affected by the command.

-xcommand, -xfs-command command

On an XFS system, perform one of the following commands:

delete

Remove quota metadata from the XFS filesystem.

enforcement

Turn off limit enforcement on an XFS filesystem.

Name

quotastats

Synopsis

quotastats

System administration command. Print a report of quota system statistics gathered from the kernel.

Name

ranlib

Synopsis

ranlib filename
ranlib option

Generate an index for archive file filename. This is equivalent to running ar -s.

Option

-v, -V, --version

Print version information and exit.

Name

rcp

Synopsis

rcp [options] file1 file2
rcp [options] file ... directory

Copy files between two machines. Each file or directory is either a remote filename of the form rname@rhost:path, or a local filename. Files can be copied between two remote machines, where neither file1 nor file2 is on the local machine. Use of rcp has generally been replaced by scp, which offers better security.

Options

-p

Preserve modification times and modes of the source files.

-r

If any of the source files are directories, descend into each directory and recursively copy all files and directories within it. The destination must be a directory.

Name

rdate

Synopsis

rdate [options] [host...]

TCP/IP command. Retrieve the date and time from a host or hosts on the network and optionally set the local system time.

Options

-l

Send errors and output to syslogd.

-p

Print the retrieved dates.

-s

Set the local system time from the host; must be specified by root.

-t n

Timeout each retrieval attempt after n seconds.

-u

Use UDP instead of TCP.

Name

rdist

Synopsis

rdist [options] [names]

System administration command. Remote file distribution client program. rdist maintains identical copies of files over multiple hosts. It reads commands from a file named distfile to direct the updating of files and/or directories. An alternative distfile can be specified with the -f option or the -c option.

Options

-a num

Do not update filesystems with fewer than num bytes free.

-A num

Specify the minimum number of inodes that rdist requires.

-c name [login@]host[:dest]

Interpret the arguments as a small distfile, where login is the user to log in as, host is the destination host, name is the local file to transfer, and dest is the remote name where the file should be installed.

-d var=value

Define var to have value. This option defines or overrides variable definitions in the distfile. Set the variable var to value.

-D

Debugging mode.

-f file

Read input from file (by default, distfile). If file is -, read from standard input.

-F

Execute all commands sequentially, without forking.

-l options

Specify logging options on the local machine.

-L options

Specify logging options on the remote machine.

-m machine

Update only machine. May be specified multiple times for multiple machines.

-M num

Do not allow more than num child rdist processes to run simultaneously. Default is 4.

-n

Suppress normal execution. Instead, print the commands that would have been executed.

-ooptions

Specify one or more options, which must be comma-separated.

chknfs

Suppress operations on files that reside on NFS filesystems.

chkreadonly

Check filesystem to be sure it is not read-only before attempting to perform updates.

chksym

Do not update files that exist on the local host but are symbolic links on the remote host.

compare

Compare files; use this comparison rather than age as the criteria for determining which files should be updated.

follow

Interpret symbolic links, copying the file to which the link points instead of creating a link on the remote machine.

ignlnks

Ignore links that appear to be unresolvable.

nochkgroup

Do not update a file’s group ownership unless the entire file needs updating.

nochkmode

Do not update file mode unless the entire file needs updating.

nochkowner

Do not update file ownership unless the entire file needs updating.

nodescend

Suppress recursive descent into directories.

noexec

Suppress rdist of executables that are in a.out format.

numchkgroup

Check group ownership by group ID instead of by name.

numchkowner

Check file ownership by user ID instead of by name.

quiet

Quiet mode; do not print commands as they execute.

remove

Remove files that exist on the remote host but not the local host.

savetargets

Save updated files in name.old.

sparse

Check for sparse files--for example, ndbm files.

verify

Print a list of all files on the remote machine that are out of date, but do not update them.

whole

Preserve directory structure by creating subdirectories on the remote machine. For example, if you rdist the file /foo/bar into the directory /baz, it would produce the file /baz/foo/bar instead of the default /baz/bar.

younger

Do not update files that are younger than the master files.

-p path

Specify the path to search for rdistd on the remote machine.

-P path

Specify path to the transport command to use on the local machine. This is normally rsh, but may also be ssh. The path argument may also be specified as a colon-separated list of acceptable transports to use in order of preference.

-t seconds

Specify the timeout period (default 900 seconds) after which rdist will sever the connection if the remote server has not yet responded.

-V

Display version, then exit.

Name

rdistd

Synopsis

rdistd options

System administration command. Start the rdist server. Note that you must specify the -S option unless you are simply querying for version information with -V.

Options

-D

Debugging mode.

-S

Start the server.

-V

Display the version number and exit.

Name

readcd

Synopsis

readcd dev=device [options]

Read or write compact discs. readcd is now generally a link to readom.

Name

readelf

Synopsis

readelf option[...] elffiles

Display information about one or more ELF (Executable and Linking Format) object files. At least one option is required to specify the information to be displayed for each file.

Options

-a, --all

Display all. Equivalent to -A -d -h -I -l -r -s -S -V.

-A, --arch-specific

Display architecture-specific information, if any.

-d, --dynamic

Display the dynamic section.

-D, --use-dynamic

When displaying symbols, use the symbol table in the dynamic section, not the symbols section.

-e, --headers

Display all headers. Equivalent to -h -l -s.

-h, --file-header

Display the ELF header at the beginning of the file.

-H, --help

Display help information and exit.

-I, --histogram

Display a histogram of bucket bit lengths when displaying the symbol tables.

-l, --program-headers, --segments

Display the segment headers, if any.

-n, --notes

Display the NOTE segment, if any.

-r, --relocs

Display the relocation segment, if any.

-s, --symbols, --syms

Display entries in symbol table sections, if any.

-S, --section-headers, --sections

Display the section headers, if any.

-u, --unwind

Display the unwind section, if any (currently applies only to IA64 ELF files).

-v, --version

Display version information and exit.

-V, --version-info

Display the version sections, if any.

-w[option], --debug-dump[=option]

Display the debug sections. If specified with an option, display only that section. The options shown here in parentheses are for -w; the words preceding them are for --debug-dump. The options are abbrev (a), frames (f), frames-interp (F), info (i), line (l), loc (o), macro (m), pub-names (p), ranges (r), and str (s).

-W, --wide

Don’t break output lines at 80 columns. The default is to break them. Useful for wide terminals.

-x num, --hex-dump=num

Display a hexadecimal dump of the section number.

Name

readlink

Synopsis

readlink file
readlink option

Print the contents of the symbolic link file — that is, the name of the file to which the link points.

Options

-f, --canonicalize

Canonicalize by recursively following symbolic links.

--help

Print usage information and exit.

-n, --no-newline

Do not output a trailing newline.

-q, --quiet, -s, --silent

Suppress most error messages.

-v, --verbose

Print all error messages.

--version

Print version information and exit.

Name

readom

Synopsis

readom dev=device [options]

Read or write compact discs. The device is usually specified as dev=scsibus/target/lun or dev=target/lun if the device is on the default SCSI bus. The default SCSI bus is bus 0, the target is the ID number, and the lun is the logical unit number.

Options

-c2scan

Do a C2 error scan. If any C2 errors are found, specifying the speed= option to reduce the speed may help.

-clone

Read all data and the table of contents, and put the table-of-contents data into a file with the same filename as specified with f= but with a .toc extension.

-d, debug=num

Increment the debugging level by 1 with -d or set the level to num with debug. Specifying -dd is the equivalent of debug=2.

dev=target

Set the SCSI target.

f=filename

Specify the file from which input should be read, or to which output should be written. If the filename is given as -, use standard input or standard output, respectively.

-factor

Print the speed factor for the meshpoints= option, based on the current medium’s single speed. Works only if readom can determine the current medium type.

-fulltoc

Read the full table of contents from the current CD and display it in hexadecimal.

kd=num, kdebug=num

Modify the kernel debugging level while SCSI commands are running, to do kernel debugging.

meshpoints=num

Print the read speed at num locations, and produce a list of values suitable for plotting. The output is written to standard output.

-nocorr

Ignore read errors, doing no error correction. Switches the drive into a mode to ignore the errors; if readom completes, it switches the drive back to the previous mode.

-noerror

Do not abort if an uncorrectable error is found in the data stream.

-notrunc

Do not truncate the output file on open.

-overhead

Measure SCSI command overhead. The measurement is done by running several commands 1000 times and printing the total time used for each.

retries=num

Set the retry count to num. The default is 128.

-s, -silent

Do not print a status report for SCSI command failures.

-scanbus

Scan all SCSI devices on all SCSI buses, print the results, and exit. Useful for finding the SCSI addresses of devices.

sectors=range

Specify the range of sectors to read.

speed=num

Set the reading and writing speed, as an integer value. Useful only for MMC-compliant drives. Defaults to maximum speed.

timeout=num

Set the default SCSI command timeout to num seconds. Defaults to 40 seconds.

ts=num

Set the maximum transfer size for a single SCSI command to num. Defaults to 256 KB.

-v, -verbose

Increment the general verbosity level by 1. Useful for displaying progress.

-V, -Verbose

Increment the verbosity level for SCSI command transport by 1. Useful for debugging. Specifying -VV adds data-buffer content to the output.

-version

Print version information and exit.

-w

Switch to write mode. The default is to read from the device.

Name

reboot

Synopsis

reboot [options]

System administration command. Close out filesystems, shut down the system, then reboot. Because this command immediately stops all processes, it should be run only in single-user mode. If the system is not in runlevel 0 or 6, reboot calls shutdown -r.

Options

-f

Call reboot even when shutdown would normally be called.

-i

Shut down network interfaces before reboot.

-n

Suppress normal call to sync.

-w

Suppress normal execution; simply write to /var/log/wtmp.

Name

reject

Synopsis

reject [options] destination

System administration command. Instruct printing system to reject jobs for the specified print queue destinations. Depending on queue settings, the system may prompt for a password. Also invoked as cupsreject.

Options

-E

Require encryption when connecting.

-h server

Apply command remotely to the specified CUPS server.

-r reason

Reject with the specified reason instead of the default “Reason Unknown.”

Name

rename

Synopsis

rename from to files

Rename files by replacing the first occurrence of from in each filename with to.

Example

Rename files that start with test so they start with mytest:

$ rename test mytest test*

Name

renice

Synopsis

renice [priority] [options] [target]

Control the scheduling priority of running processes. May be applied to a process, process group, or user (target). A privileged user may alter the priority of other users’ processes. priority must, for ordinary users, lie between 0 and the environment variable PRIO_MAX (normally 20), with a higher number indicating increased niceness. A higher niceness value means that the process will run at a lower priority. A privileged user may set a negative priority, as low as PRIO_MIN (normally −20), to speed up processes. See the nice command for setting the scheduling priority for processes when they are initially run.

Options

+num

Specify number by which to increase current priority of process, rather than an absolute priority number.

-num

Specify number by which to decrease current priority of process, rather than an absolute priority number.

-g, --pgrp

Interpret target parameters as process group IDs.

-p, --pid

Interpret target parameters as process IDs (default).

-u, --user

Interpret target parameters as usernames.

Name

repquota

Synopsis

repquota [options] [filesystem]

System administration command. Generate a report on disk usage and quotas for the specified filesystem.

Options

-a, --all

Generate report for all filesystems in /etc/mtab that support quotas.

-c, --batch-translation

Translate UIDs and GIDs in batches. (Faster for /etc/passwd.)

-C, --no-batch-translation

Translate UIDs and GIDs individually. (Faster for database lookups.)

-F format, --format=format

Report on quotas for the specified format. (See quota for valid formats.)

-g, --group

Report group quotas.

-i, --no-autofs

Ignore automount mount points.

-n, --no-names

Use UIDs and GIDs instead of names. (Generates faster reports.)

-p, --raw-grace

When user is in a grace period, print a timestamp (seconds since epoch) marking when the grace period expires.

-s, --human-readable

Report sizes in more human-readable units.

-t, --truncate-names

Truncate user and group names to nine characters.

-u, --user

Report user quotas. (This is the default.)

Name

reset

Synopsis

reset [options] [terminal]

Clear screen (reset terminal). If terminal is specified on the command line, the value is used as the terminal type. reset is a symbolic link to the tset command. Invoking the command as reset is useful for clearing your terminal when a program dies and leaves the terminal in an abnormal state. You may have to run the command with a linefeed character (usually Ctrl-J) before and after it:

Ctrl-JresetCtrl-J

See the tset command for the available options.

Name

resize2fs

Synopsis

resize2fs [options] device [size]

System administration command. Enlarge or shrink an ext2 filesystem on device so it has size blocks. The filesystem size cannot be larger than the underlying partition. This command changes only the filesystem size, not the underlying partition. To change the partition, use fdisk.

Options

-d flags

Print debugging information on resize activity. The value of the flags parameter determines what activity is reported. Compute its value by summing the numbers of the items you wish to debug:

2

Block relocations.

4

Inode relocations.

8

Inode table movement.

-f

Force resize, overriding safety checks.

-M

Shrink filesystem to minimum size.

-p

Print progress information for each resize task.

-P

Print maximum filesystem size then exit.

Name

restore

Synopsis

restore flag [options] [files]

System administration command. Restore backed-up files from a dump archive. Execute this command with one of the following flags.

Flags

-C

Compare files on disk to files in the backup and print report.

-i

Restore files interactively. This will open a shell-like interface that accepts the following commands.

add [name]

Add the current working directory, or the specified file or directory name to the list of files to extract.

cd directory

Change the current working directory.

delete [name]

Remove the current working directory or the specified file or directory name from the list of files to extract.

extract

Extract selected files. This will prompt for the volume on which the files to be extracted can be found. Once the files are extracted, the system will prompt if you want to change the ownership and mode of the current directory (the one to which you extracted the files) to match the settings on the dump’s original base directory.

help

Print a command summary.

ls [name]

Like the shell command, list files in the current working directory, or the specified file or directory name. A * before a name indicates items marked for extraction. In verbose mode, the listing will include each item’s inode.

pwd

Like the shell command, print the working directory.

quit

Exit the command.

setmodes

Set ownership and mode of the directory to which you extract the files to match the settings on the dump’s original base directory.

quit

Exit the command.

verbose

Verbose mode. Print inodes along with file and directory names when using ls.

-P filename

Create a Quick File Access file suitable for use with the -Q option.

-r

Fully restore the backup to a clean, newly created ext2 filesystem. Execute this command in the root directory of the new filesystem.

-R

Prompt for the tape volume to fully restore.

-t

Print files if they exist in the archive or an error if they do not. If no files are specified, list all files in the archive.

-x

Recursively extract files if they exist in the archive. Restore owner, modification times, and modes. If no files are specified, restore the entire backup.

Options

-a

Read all volumes to find the files to extract, beginning with volume 1. This will skip any volume prompts.

-A file

Read the table of contents from the specified archive file.

-bblocksize

Specify the block size in kilobytes used for a block in the archive. Restore can usually determine this when reading the dump media.

-c

Read dumps made prior to version 4.4.

-d

Print debugging information.

-D filesystem

When using the -C flag, compare the dump to files on the specified filesystem.

-f file

Read the backup from the specified file: a device file, an ordinary file, or - to read from standard input. Use host:file or user@host:file to read from a networked host using either the rmt program or the program specified by the RMT environment variable.

-F script

Run the specified script at the beginning of each volume. restore will pass the current device and volume number to the script. The script should return 0 to continue, 1 to prompt for a new tape, or any other exit value to abort the restore. The script will run with the process’s real user and group ID.

-h

Do not recursively restore directory. Only restore the specified directory.

-k

Use Kerberos authentication when connecting to a remote server.

-l

Treat file as a regular file instead of a tape device. Use this option when restoring from remote compressed files.

-L n

Used with the -C flag. Abort the comparison after encountering n errors.

-m

Expect filenames to be given as inodes.

-M

Restore from a multivolume backup. Treat any filename provided with -f as a prefix.

-N

Perform all actions indicated by other flags and options, but don’t write anything to the disk.

-o

Automatically set ownership and mode of the current directory to match the original base directory of the dump.

-Q file

Read tape positions from the specified Quick File Access mode file.

-S n

Read from volume n of a multifile backup.

-u

Unlink (remove) any existing files before writing a file with the same name.

-v

Verbose mode. Print information about files being restored.

-V

Enable multivolume mode for devices other than tapes.

-X file

Read list of files and directories to extract from the specified file. Use - to retrieve list of files from standard input.

-y

Attempt to skip over errors without prompting for operator input.

Name

rev

Synopsis

rev [files]

Reverse the order of characters on each line of the specified files and print the results on standard output. If no files are specified, rev reads from standard input.

Name

rexec

Synopsis

rexec [options] rhost command

Execute commands remotely. This client program connects to a remote host running rexecd, and passes it command. It uses a login name and password for authentication. These can be passed on the command line using the options below, provided through the $HOME/.netrc file or the environment variables REXEC_USER and REXEC_PASS. If it cannot determine the username and password, rexec prompts the user for the information. Note that because rexec sends passwords to the remote system in cleartext, you should use it only on a secure network. See ssh for a more secure alternative.

Options

-a

Send both error messages and output to standard output.

-b

When received locally, only echo signals SIGINT, SIGQUIT and SIGTERM to the remote process.

-c

Leave remote standard input open when the local input closes.

-d

Debugging mode. Echo commands sent locally.

-l username

Specify a different username for the remote login. Default is the same as your local username.

-n

Prompt user for name and password even if otherwise provided.

-p password

Specify the password for the remote account.

-s

Do not echo any signals to the remote process.

Name

rexecd

Synopsis

rexecd command-line

TCP/IP command. Server for the rexec routine, providing remote execution facilities with authentication based on usernames and passwords. rexecd is started by inetd and must have an entry in inetd’s configuration file, /etc/inetd.conf.

Option

-D

Disable reverse DNS lookup; use IP addresses in logs.

Name

rlogin

Synopsis

rlogin [options] rhost

Remote login. rlogin connects the terminal on the current local host to the remote host rhost. The remote terminal type is the same as your local terminal type. The terminal or window size is also copied to the remote system if the server supports it. Use of rlogin has generally been replaced with ssh, which offers better security.

Options

−8

Allow an 8-bit input data path at all times.

-d

Debugging mode.

-ec

Specify escape character c (default is ~).

-E

Do not interpret any character as an escape character.

-l username

Specify a different username for the remote login. Default is the same as your local username.

-L

Allow rlogin session to be run without any output postprocessing (i.e., run in litout mode).

Name

rlogind

Synopsis

in.rlogind [options]

TCP/IP command. Server for the rlogin program, providing a remote login facility, with authentication based on privileged port numbers from trusted hosts. rlogind is invoked by inetd when a remote login connection is requested. The login process propagates the client terminal’s baud rate and terminal type as found in the TERM environment variable.

Options

-a

Verify hostname.

-h

Permit superuser .rhosts files to be used. Ignored if pluggable authentication module (PAM) support is enabled. Control through /etc/pam.conf instead.

-l

Do not authenticate hosts via a nonroot .rhosts file. Ignored if pluggable authentication module (PAM) support is enabled. Control through /etc/pam.conf instead.

-L

Do not authenticate hosts via .rhosts or hosts.equiv files. Ignored if pluggable authentication module (PAM) support is enabled. Control through /etc/pam.conf instead.

-n

Suppress keep-alive messages.

Name

rm

Synopsis

rm [options] files

Delete one or more files. To remove a file, you must have write permission in the directory that contains the file, but you need not have permission on the file itself. If you do not have write permission on the file, you will be prompted (y or n) to override. rm is often aliased to rm -i, especially for the root user, to protect against inadvertently deleting files.

Options

-d, --directory

Remove directories, even if they are not empty. Available only to a privileged user.

-f, --force

Remove write-protected files without prompting.

--help

Print a help message and then exit.

-i

Prompt for y (remove the file) or n (do not remove the file) for each file.

--interactive[=when]

Specify when to prompt. The possible values for when are never, no, none, once, always, yes.

-I

Prompt only once before deleting recursively or before deleting more than three files.

--no-preserve-root

Do not treat root (/) specially. This is the default.

--one-file-system

When removing recursively, only remove files on the same filesystem as files.

--preserve-root

Do not remove root (/).

-r, -R, --recursive

If file is a directory, remove the entire directory and all its contents, including subdirectories. Be forewarned: use of this option can be dangerous.

-v, --verbose

Verbose mode (print the name of each file before removing it).

--version

Print version information and then exit.

--

Mark the end of options. Use this when you need to supply a filename beginning with -.

Name

rmail

Synopsis

rmail [options] users

TCP/IP command. Handle remote mail received via uucp. rmail transforms trace information from mail in UUCP format to the equivalent RFC 822 format, then forwards messages to sendmail.

Options

-D domain

Use domain instead of UUCP as the UUCP hostname in From fields.

-T

Print debugging information.

Name

rmdir

Synopsis

rmdir [options] directories

Delete the named directories (not the contents). directories are deleted from the parent directory and must be empty (if not, rm -r can be used instead). See also mkdir.

Options

--help

Print a help message and then exit.

--ignore-fail-on-non-empty

Ignore failure to remove directories that are not empty.

-p, --parents

Remove directories and any intervening parent directories that become empty as a result. Useful for removing subdirectory trees.

-v, --verbose

Verbose mode; print message for each directory as it is processed.

--version

Print version information and then exit.

Name

rmmod

Synopsis

rmmod [options] modules

System administration command. Unload a module or list of modules from the kernel. This command is successful only if the specified modules are not in use and no other modules are dependent on them. This simplified program provides some backward compatibility. In general, use modprobe -r instead.

Options

-s, --syslog

Write messages to syslogd instead of to the terminal.

-v, --verbose

Verbose mode.

-V, --version

Print version number, then exit.

-w, --wait

If module is in use, disable it so no new processes can use it. Remove the module when it is no longer in use.

Name

rndc

Synopsis

rndc [options] [command]

TCP/IP command. Send commands to a BIND DNS server via a TCP connection (see the named command.) This command reads authentication and connection information from the file /etc/rndc.conf, and its authentication key from /etc/rndc.key. If entered without a command, display a help message listing the available commands.

Options

-c file

Read configuration information from file instead of /etc/rndc.conf.

-k file

Perform command on the routing cache instead of the forwarding information base (FIB) routing table.

-p port

Connect to the specified port instead of the default control channel port, 953.

-s server

Send command to the specified server. There must be an entry for server in the configuration file.

-V

Use verbose log messages.

-y keyname

Specify the key to use by keyname. There must be a key entry for keyname in the /etc/rndc.conf file.

Commands

You can send the following commands to a BIND nameserver:

dumpdb

Dump current cache to the dump file (specified in /etc/named.conf), or to named_dump.db when not specified.

flush [view]

Flush all server caches, or only the cache for the specified view.

halt

Stop server immediately.

querylog

Toggle query logging.

reconfig

Reload the configuration file and any new zones.

reload [zone [class [view]]]

Reload configuration file and zones. When specified, limit the reload to the given zone, class, or view.

refresh zone

Refresh database information for zone.

stats

Write statistics to the statistics file (specified in /etc/named.conf).

status

Display server status.

stop

Save any recent dynamic zone transfer updates (IXFR) to the master files, then stop the server.

trace [debuglevel], notrace

Increase the server’s debug level by 1, or set it to the specified debuglevel. Use the notrace command to set the level to 1.

Name

route

Synopsis

route [options] [command]

TCP/IP command. Add or remove entries in the routing tables maintained by routed. route accepts two commands: add, to add a route, and del, to delete a route. The two commands have the following syntax:

add [-net | -host] address [modifiers]
del [-net | -host] address [modifiers]

address is treated as a plain route, unless -net is specified or address is found in /etc/networks. -host can be used to specify that address is a plain route whether or not it is found in /etc/networks. Using route modifiers, you can specify the gateway through which to route packets headed for that address, its netmask, TCP mss, or the device with which to associate the route; you can also mask certain routes. Only a privileged user may modify the routing tables.

If no command is specified, route prints the routing tables.

Options

-A family, --family

Specify an address family to use with an add or del command. family may be inet, inet6, ax25, netrom, ipx, ddp, or x25.

-C, --cache

Perform command on the routing cache instead of the forwarding information base (FIB) routing table.

-e, --extend

Use netstat -r format to print routing table. Use twice to print extended information. Same as netstat -ree.

-F, --fib

Perform command on the forwarding information base (FIB) routing table. This is the default behavior.

-h, --help

Print help message, then exit.

-n, --numeric

Show numerical addresses; do not look up hostnames. (Useful if DNS is not functioning properly.)

-v, --verbose

Verbose mode.

-V, --version

Print version and configuration options, then exit.

Route modifiers

[dev] interface

Associate route with specified device. When the interface is given as the last argument on a command line, the word dev is optional.

netmask mask

Use netmask mask.

gw gateway

Route packets through gateway.

metric n

Set routing metric to n.

mss bytes

Set maximum segment size for connections over this route.

reject

Cause route lookup for target to fail. Used to mask out networks from a default route.

Example

Add a default gateway for interface eth0:

route add default gw 192.168.0.1 dev eth0

Name

rpcbind

Synopsis

rpcbind [options]

NFS/NIS command. portmap is renamed rpcbind in newer Linux systems. It maps RPC program numbers into universal addresses. This server must be running in order to make RPC calls. RPC servers run on a host register their program number with rpcbind. Clients wishing to make an RPC call first check with rpcbind to find the address for a given program number.

-a

Abort on errors if debugging (-d).

-d

Run in debug mode. Do not fork.

-h [address]

Bind to the specified IP address for UDP requests. This option may be given multiple times. You need not specify the localhost. When using this option rpcbind automatically binds to 127.0.0.1 and ::1 (if using IPv6) as well.

-i

Insecure mode. Allow calls to SET and UNSET from any host.

-l

Enable libwrap connection logging (tcp wrappers).

-s

Change to user daemon sooner. Bind to nonprivileged ports for outgoing connections, refuse connections to privileged ports from nonprivileged clients.

-w

Warm start. Read stat from a previous rpcbind.

Name

rpcgen

Synopsis

rpcgen [options] file

Parse file, which should be written in the RPC (Remote Procedural Call) language, and produce a program written in C that implements the RPC code. Place header code generated from file.x in file.h, XDR routines in file_xdr.c, server code in file_svc.c, and client code in file_clnt.c. Lines preceded by % are not parsed. By default, rpcgen produces Sun OS 4.1-compatible code.

-a

Produce all files (client and server).

-b

Produce SunOS 4.1-compatible code. This is the default.

−5

Produce SVR4-compatible code.

-c

Create XDR routines. Cannot be used with other options.

-C

Produce ANSI C code (the default).

-k

Produce K&R C code.

-Dname[=value]

Define the symbol name, and set it equal to value or 1.

-h

Produce a header file. With -T, make the file support RPC dispatch tables. Cannot be used with other options.

-I

Produce an inetd-compatible server.

-K secs

Specify amount of time that the server should wait after replying to a request and before exiting. Default is 120. Setting secs to −1 prevents the program from ever exiting.

-l

Produce client code. Cannot be used with other options.

-m

Produce server code only, suppressing creation of a “main” routine. Cannot be used with other options.

-N

New style. Allow multiple arguments for procedures. Not necessarily backward-compatible.

-o [file]

Print output to file or standard output.

-Sc

Print sample client code to standard output.

-Ss

Create skeleton server code only.

-t

Create RPC dispatch table. Cannot be used with other options.

-T

Include support for RPC dispatch tables.

Name

rpcinfo

Synopsis

rpcinfo [options] [host] [program] [version]

NFS/NIS command. Report RPC information. program can be either a name or a number. If a version is specified, rpcinfo attempts to call that version of the specified program. Otherwise, it attempts to find all the registered version numbers for the specified program by calling version 0, and then attempts to call each registered version.

Options

-b

Make an RPC broadcast to the specified program and version using UDP, and report all hosts that respond.

-d

Delete the specified version of program’s registration. Can be executed only by the user who added the registration or by a privileged user.

-n portnum

Use portnum as the port number for the -t and -u options, instead of the port number given by the portmapper.

-p

Probe the portmapper on host and print a list of all registered RPC programs. If host is not specified, it defaults to the value returned by hostname.

-t

Make an RPC call to program on the specified host using TCP, and report whether a response was received.

-u

Make an RPC call to program on the specified host using UDP, and report whether a response was received.

Name

rpm

Synopsis

rpm [options]

The Red Hat Package Manager. A freely available packaging system for software distribution and installation. RPM packages are built, installed, and queried with the rpm and rpmbuild commands. For detailed information on RPM, see Chapter 5.

Name

rsh

Synopsis

rsh [options] host [command]

Execute command on remote host, or, if no command is specified, begin an interactive shell on the remote host using rlogin. The options can be specified before or after host. Use of rsh has generally been replaced with ssh, which offers better security.

Options

-d

Enable socket debugging.

-l username

Attempt to log in as username. By default, the name of the user executing rsh is used.

-n

Redirect the input to rsh from the special device /dev/null. (This should be done when backgrounding rsh from a shell prompt, to direct the input away from the terminal.)

Name

rshd

Synopsis

rshd [options]

TCP/IP command. Remote shell server for programs such as rcmd and rcp, which need to execute a noninteractive shell on remote machines. rshd is started by inetd and must have an entry in inetd’s configuration file, /etc/inetd.conf.

All options are exactly the same as those in rlogind, except for -L, which is unique to rshd.

Option

-L

Log all successful connections and failed attempts via syslogd.

Name

rsync

Synopsis

rsync [options] sources dest

Transfer files; used frequently for updating files across a network. File transfer with rsync is fast and efficient because it checks local files against remote files in small chunks, or blocks, and transfers only the blocks that differ between the files.

sources and the final dest are in the form of:

user@host:port/filename

If the file is on the local host, a plain filename can be specified. If the file is on a remote host, the host must also be specified. user can optionally be specified to log in as a different user on the remote site (in which case a password prompt might appear) and port can optionally be specified with a remote host to make rsync use a TCP port other than its default, 873.

Relative filenames (names without initial slashes) are handled relative to the user’s home directory. If a source directory is listed with a trailing slash, the whole directory is transferred and will appear under the destination directory; if the directory is listed without the slash, its files and subdirectories will appear directly under the destination directory. Normally, regular directories and files are transferred, but not symbolic links or other special files such as sockets and FIFOs.

Two other formats for sources and dest, which refer to files on an rsync server (rsyncd), are:

user@host::filename
rsync://user@host:port/filename

rsync servers are beyond the scope of this book.

Options

−0, --from0

Specify that the file specified in options such as --files-from is formatted with null characters to separate the filenames; when this option is not used, the file must include each filename on a separate line.

−4, --ipv4, −6, --ipv6

Opt for IPv4 or IPv6 when creating sockets.

−8, --8-bit-output

Leave high-bit characters unescaped in output.

-a, --archive

Transfer recursively, reproducing most characteristics of the files and directories being transferred, such as modification times, symbolic links, ownership, and permissions. Equivalent to -rlptgoD. With --files-from, transfer is not recursive.

--address=addr

Specify the IP address of an rsync server to connect to; useful when multiple servers are running on the same host.

--append

Append new data to the end of an existing file. Implies --inplace.

--append-verify

Like --append, but include existing data in full-file checksum verification.

-b, --backup

Preserve existing files at the destination by appending a suffix such as ˜ while transferring new versions of those files.

-B n, --block-size=n

Change block size used for transfers.

--backup-dir

Specify where files created by the --backup option are stored.

--blocking-io

Use blocking I/O when starting the remote shell used for transfer.

--bwlimit=n

Set a limit to the speed of transfer, specified in kilobytes per second.

-c, --checksum

Perform a full checksum on each file transferred.

-C, --cvs-exclude

Don’t transfer files that are normally considered temporary or otherwise uninteresting; obeys the same rules for ignoring files as CVS (Concurrent Versions Systems).

--compare-dest=dir

Compare source files to files of the same name in dir as well as the destination directory.

--compress-level=num

Set the compression level to num. If nonzero, -z/--compress is implied.

--config=configfile

When running as server, take configuration from configfile instead of /etc/rsyncd.conf.

--contimeout=n

Set time in seconds to wait for a connection to an rsync daemon.

--copy-unsafe-links

If files to which symbolic links point are being transferred, copy even those files that exist outside the directories being transferred.

-d, --dirs

Transfer directories with no recursion unless the directory name is . or ends in a trailing slash (/).

-D

Equivalent to --devices --specials.

--daemon

Run rsync as server.

--devices

Transfer device (/dev) files; requires superuser permission on both systems.

--delete-after

After transferring files from a source directory, delete any files from the destination directory that do not exist in the source directory.

--delete

Before transferring files from a source directory, delete any files from the destination directory that do not exist in the source directory.

--delete-excluded

Invoke --delete, and additionally delete from the destination directory any files that match exclude options.

-e shell, --rsh=shell

Use shell (which can be a complete command with arguments, enclosed in quotes) to create the connection between two systems for file transfer. rsync uses rsh by default. Nowadays, most users prefer the secure shell ssh. This can be made the default by setting the environment variable RSYNC_RSH=ssh.

--exclude=glob-pattern

Don’t transfer files whose names match glob-pattern. Rules for glob-pattern are complex and are described in the manpage. In general, filenames can include the shell globbing characters * to match everything, ? to match a single character, and [] to enclose a set of matching characters. Furthermore, to specify the beginning of a filename, start the name with a / character (it does not mean the file has to be an absolute pathname).

--exclude-from=file

Like --exclude, but globbing patterns are taken from file; each pattern on a separate line.

--existing, --ignore-non-existing

Transfer only files that already exist on the destination host.

--files-from=file

Take names of files to transfer from file.

--force

Allow a file to replace a nonempty directory of the same name.

-g, --group

Set the group (normally identified by name, not number) of the destination file to match that of the source file, instead of using the group running the rsync program.

-H, --hard-links

Set hard links on destination system to match source system.

--help

Display command syntax and options, then exit.

-h, --human-readable

Output numbers in a more easily read format, using larger units with a K, M, or G suffix.

--ignore-errors

Delete files even when there are I/O errors.

--ignore-existing

Do not transfer files to replace existing files of the same name.

-I, --ignore-times

Consider files for transfer even if they have the same size and timestamp as destination files.

--include=glob-pattern

Specify files to be transferred even if further exclude options would cause them to be ignored. rsync processes the include and exclude options in the order they appear on the command line, so earlier include options override later exclude options.

--include-from=file

Like --include, but take globbing patterns from file, which has each pattern listed on a separate line.

--inplace

Update files in place instead of creating a new copy and then moving it.

-l, --links

Set symbolic links on destination system to match source system.

-L, --copy-links

Transfer the files to which symbolic links are made instead of just the pointer information in the links.

--log-file=file

Write log data to the specified file.

--log-format=format

Display information about each file transferred in a format specified by % sequences; see rsyncd.conf manpage for formats. Used with --log-file.

--max-delete=n

Delete at most n files when deleting from destination host.

--max-size=n, --min-size=n

Don’t transfer files that are larger than or smaller than the specified size.

-n, --dry-run

Display the names of files that would be transferred and statistics related to a transfer, without performing a transfer.

--no-blocking-io

Do not use blocking I/O when starting the remote shell used for transfer.

--no-detach

When running as a daemon, do not restart as a background process.

--no-implied-dirs

When preserving directory structures with --relative, do not force the creation of new directories or symbolic links if the destination host is set up differently from the source host.

--no-relative

Transfer only the plain files without preserving the entire directory structure of files whose names include directories; otherwise, --files-from would create the entire directory structure to contain the file.

--no-whole-file

Use rsync’s block checks to transfer parts of files where possible.

--numeric-ids

Set user and group IDs on destination files by number rather than name.

-o, --owner

Set the user (normally identified by name, not number) of the destination file to match that of the source file, instead of settng it to the user running the rsync program.

-O, --omit-dir-times

When using --times to preserve modification times, don’t preserve directory times.

-p, --perms

Set the permissions of the destination file to match that of the source file, instead of using the existing file’s permissions or the default umask of the destination user.

-P

Combination of --partial and --progress.

--partial

Preserve partial files transferred if rsync is interrupted. The default is to delete them.

--partial-dir=dir

Specify a directory for keeping partial files instead of using --partial. Useful for speeding up the resumption of the transfer later. The file is deleted from dir once the transfer is complete.

--password-file=file

Take password for accessing a remote rsync server from file.

--port=n

Use port n instead of default rsync port.

--progress

Display ongoing statistics about the progress of the transfer of each file.

-q, --quiet

Do not display statistics or server error messages.

-r, --recursive

Copy directories with all their contents.

-R, --relative

Preserve the entire path of a specified source file or directory, instead of creating the file directly under the destination directory. That is, if project/tmp/main.c is specified, create project/tmp/main.c instead of just main.c. Create intermediate directories if needed.

--read-batch=file

Apply all changes stored in the specified file, written by a preceding --write-batch.

--remove-source-files

After files have been successfully transferred, remove them from the source system. Directories are not removed.

--rsync-path=file

Use the rsync binary located in file on the destination system.

--safe-links

Don’t copy links that point to absolute paths or to files outside the directories being transferred.

-s, --protect-args

Protect arguments sent to the remote system from intrepretation by the remote shell.

-S, --sparse

Perform special optimizations on sparse files (files that contain holes and actually contain less data than their sizes indicate).

--size-only

Skip files that have the same size on the source and destination hosts, even if their timestamps differ; usually, this check is based on both size and timestamp.

--specials

Transfer special files such as named sockets and FIFOs.

--stats

Like -v, but also prints a number of statistics about each file transferred, such as the number of bytes actually transferred and the number transferred to compare the files on the two hosts.

--suffix=string

Set the suffix placed on backup files to string. Default is a tilde (~).

-t, --times

Set the timestamps of the destination file to match those of the source file, instead of using the time of transfer (that is, reflecting the existence of a new file on the destination host).

-T dir, --temp-dir=dir

Use dir as rsync’s temporary directory instead of the destination directory.

--timeout=n

Stop rsync if n seconds pass with no data being transferred.

-u, --update

Don’t change a destination file if it is newer than the source file.

--version

Display rsync’s version and compiled-in features, then exit.

-v, --verbose

Display the names of files transferred and statistics related to the transfer.

-W, --whole-file

Transfer the entire files, instead of using rsync’s block checks to transfer just parts of files where possible.

--write-batch=prefix

Prepare to synchronize systems by writing files, whose names start with prefix, that describe the transfers to take place.

-x, --one-file-system

When traversing directories, do not transfer files on directories that are mounted on other filesystems.

-z, --compress

Use compression during transmission.

Examples

Transfer the entire directory proj to the /planning directory on remote host ourhub:

$ rsync -r proj/ ourhub:/planning

Transfer the files and subdirectories under proj to the /planning directory on remote host ourhub:

$ rsync -r proj ourhub:/planning

Return files from local directory active to the /tmp/active directory on remote host ourhub. Files to be transferred are listed in active/current_work.txt:

$ cat active/current_work.txt
workplan.doc
workplan.sxw
$ rsync -v --files-from=active/current_work.txt active \
ourhub:/tmp/active
building file list ... done
workplan.doc
workplan.sxw
...

Copy the source directory’s OpenOffice.org (.sxw) files and Kim’s status report, but exclude the other status reports.

$ ls proj
conclusion.sxw    Status_joem  Status_leigh
incentives.sxw    Status_kim   unified.sxw
$ rsync -rv --include=*kim --exclude=/proj/Status* proj \  ourhub:tmp
building file list ... done
proj/Status_kim
proj/conclusion.sxw
proj/incentives.sxw
proj/unified.sxw
...

Name

rsyslogd

Synopsis

rsyslogd [options]

System administration command. rsyslogd provides local and remote logging functions. It is based on sysklogd and on some systems replaces that program. It adds support for logging over TCP, SSL, TLS, logging to databases and more. By default rsyslogd is command-line compatible with sysklogd and can be used as a drop-in replacement. In native mode, some of the old command line options have been moved to the configuration file. rsyslogd will log warnings for these deprecated commands. Its compatibility mode can be changed with the -c3 option.

rsyslogd logs system messages into a set of files described by the configuration file /etc/rsyslog.conf. Each message is one line. A message can contain a priority code, marked by a number in angle brackets at the beginning of the line.

Options

−4

Listen on IPV4 addresses only.

−6

Listen on IPV6 addresses only.

-A

If there are multiple paths to a UDP target, send to all paths.

-cmode

Set compatibility mode. Values for mode are 0, for sysklogd and 3 to enable native rsyslogd options. The default value is 0 though this also generates a warning that you are not using native mode.

-d

Turn on debugging. Don’t fork.

-f configfile

Specify alternate configuration file.

-i pidfile

Specify alternate pid file.

-l hostlist

Specify hostnames that should be logged with just the hostname, not the fully qualified domain name (fqdn). Multiple hosts should be separated by a colon (:).

-n

Avoid auto-backgrounding. This is needed when starting syslogd from init.

-p socket

Send log to socket instead of /dev/log.

-q

If DNS is not available when determining which systems are AllowedSenders (from the configuration file), use the hostname instead of the hosts IP address.

-Q

Don’t resolve hostnames to IP addresses when determining AllowedSenders.

-s domainlist

Strip off domain names specified in domainlist before logging. Multiple domain names should be separated by a colon (:).

-v

Print version number, then exit.

-w

Don’t warn when receiving messages from systems not in the AllowedSender list.

-x

Don’t perform DNS lookups for remote hosts sending logs.

Name

runlevel

Synopsis

runlevel [utmp]

System administration command. Display the previous and current system runlevels as reported in the utmp file. The default utmp file is /var/run/utmp. See Starting and Stopping the System in Starting and Stopping the System.

Name

sane-find-scanner

Synopsis

sane-find-scanner [options]

Locate SCSI and USB scanners and print their device files, to be sure the scanners can be detected by SANE (Scanner Access Now Easy) backends.

Options

devname

Check only the specified device for a scanner.

-f

Force the opening of any SCSI and USB devices specified with devname, in case the command is wrong in determining the device type.

-h, -?

Print a usage message and exit.

-p

Test for parallel-port scanners. Note that most parallel-port scanners won’t be detected, even with this option.

-q

Run quietly, printing only the devices.

-v

Run verbosely. When specified as -v, show every device name and test result; as -vv, also print SCSI inquiry information and USB device descriptors.

Name

scanimage

Synopsis

scanimage [options]

Read images from devices such as scanners and cameras, writing the images to standard output in one of the PNM (Portable aNyMap) formats. scanimage uses the SANE interface to access the scanner and can support any device for which there is a SANE backend.

Formats

PBM

Black-and-white

PGM

Grayscale

PPM

Color

TIFF

Black-and-white, grayscale, or color

Options

--accept-md5-only

Only accept MD5 authorization requests.

-b [format], --batch[=format]

Work in batch mode, using a document feeder. Each page is written to a file, as specified by format, using a printf-type string. The default format is out%d.pnm for the PNM formats and out%d.tif for TIFF.

-B, --buffersize

Change the buffersize from the default 32 KB to 1 MB.

--batch-count=num

The number of pages to scan in batch mode. Use this option for scanners that do not signal when they are empty; the default is to continue scanning until such a signal is received.

--batch-double

Increment the page number by 2 in batch mode. Used for scanning two-sided originals on a single-sided scanner.

--batch-increment=num

Increment the number in the filename by num in batch mode.

--batch-prompt

In batch mode, prompt the user to press Return before scanning a page. Useful for manually feeding multiple pages.

--batch-start=num

Specify the page number in batch mode to use in the first filename. The default is 0.

-d device, --device-name=device

Specify the scanner device to use. See -L to show the available devices.

-f format, --formatted-device-list=format

Show the available scanner devices, as with -L, but also format the output. Possible format specifications are:

%d

Device name

%i

Index number

%m

Model

%t

Scanner type

%v

Vendor

--format=format

Specify the file format of the output file. The possible values are pnm (default) and tiff.

-h, --help

Print a help message and exit. You can get device-specific help by running scanimage as follows:

scanimage -h -d device

-i profile, --icc-profile=profile

Include the specified ICC profile in the TIFF output file.

-L, --list-devices

Display a list of available devices. The list may not be complete, particularly when accessing scanners across the network. Only scanners listed in a configuration file (typically in the directory /etc/sane.d) are displayed. A scanner with no configuration file entry must be accessed by its full device name.

-n, --dont-scan

Set the specified options, but don’t actually scan anything.

-p, --progress

Print progress information.

-T, --test

Run some sanity tests to be sure the backend works as defined by the SANE API.

-v, --verbose

Run in verbose mode, providing additional messages.

-V, --version

Print version information and exit.

Name

scp

Synopsis

scp [options] file1 [...] file2

Securely copy files between hosts on a network, using ssh. Part of the OpenSSH suite of network tools. scp requests a password or passphrase if required. The transfer can be between two remote hosts. If more than one file is specified for file1, file2 should be a directory; otherwise, only the last file in the list is copied. file1 and file2 can be specified in any of the following ways:

file
host:file
user@host:file

The first format is used for a local file; a remote file can be specified in either of the other two formats.

Options

−1

Force the use of SSH protocol 1.

−2

Force the use of SSH protocol 2

−4

Use IPv4 addresses.

−6

Use IPv6 addresses.

-B

Run in batch mode. Don’t ask for passwords or passphrases.

-c cipher

Specify the cipher to be used for encrypting the data.

-C

Enable ssh compression.

-F config

Specify an ssh user configuration file (default is $HOME/.ssh/config).

-i file

Specify the file that contains the identity (private key) for RSA authentication.

-l limit

Limit bandwidth used to limit, specified in kilobits/second.

-o option

Specify an option to pass to ssh.

-p

Preserve modification time, access time, and mode.

-P port

Connect to port on the remote host.

-q

Don’t display the progress meter or messages.

-r

Copy directories recursively.

-S program

Specify the program to use for the encrypted connection. The program must understand ssh options.

-v

Verbose mode.

Example

Copy the local file user.server1.pub to the remote system server2, putting it in james’s home directory:

$ scp user.server1.pub james@server2:/home/james/

Name

screen

Synopsis

screen [options] [command [args]]

Provide ANSI/VT100 terminal emulation, making it possible to run multiple full-screen pseudo-terminals from one real terminal, and letting you manipulate and save your screen input and output, copy and paste between windows, etc. screen allows you to detach from a running session without interrupting the processing, and reattach to it later.

Options

-a

Include all capabilities in each window’s termcap.

-A

Adapt all windows to the size of the current terminal. Default is to try to use the previous window size.

-c file

Use file as the configuration file instead of the default $HOME/.screenrc.

-d [pid.tty.host]

Detach session running elsewhere. With -r, reattach to this terminal. With -R, reattach to this terminal or create it if it doesn’t already exist. With -RR, use the first session when reattaching if more than one session is available.

-D [pid.tty.host]

Detach session running elsewhere, logging out before detaching. With -r, reattach to this terminal. With -R, reattach to this terminal or create it if it doesn’t already exist. With -RR, do whatever is necessary to create a new session.

-e xy

Change command characters. Specify x as the command character (default Ctrl-a) and y as the character that generates a literal command character (default a). Specify in caret notation (e.g., -e ^Pp to set Ctrl-p as the command character, which is useful for emacs-mode shell).

-f, -fn, -fa

Turn flow control on, off, or to automatic-switching mode.

-h num

Specify the size of the history scrollback buffer.

-i

Cause the interrupt key (usually Ctrl-c) to interrupt the display immediately when flow control is on. Use of this option is discouraged.

-l, -ln

Turn login mode on or off for /etc/utmp updating.

-ls, -list

Print list of pid.tty.host strings identifying screen sessions.

-L

Turn on automatic output logging.

-m

Ignore the $STY environment variable and create a new session. With -d, start session in detached mode; useful for scripts. With -D, start session in detached mode but don’t fork a new process; the command exits if the session terminates.

-O

Use optimal output mode for terminal rather than true VT100 emulation.

-p window

Preselect the specified window by number or name if it exists.

-q

Suppress error message printing on startup. Exit with nonzero return code if unsuccessful.

-r

[pid.tty.host]

-r sessionowner/[pid.tty.host]

Resume detached session. No other options except -d or -D can be specified. With sessionowner, resume another user’s detached session; requires setuid root.

-R

Attempt to resume the first session found, or start a new session with the specified options. Set by default if screen is run as a login shell.

-s shell

Set the default shell, overriding the $SHELL environment variable.

-S name

Specify a name for the session being started, for use with the -list and -r options.

-t name

Set the window’s title.

-T term

Set $TERM to term instead of “screen”.

-U

Run in UTF-8 mode and set the default for new windows to utf8.

-v

Print version information and exit.

-wipe [match]

Like -ls, but remove destroyed sessions instead of marking them dead. If a match is specified, it should be in the same form as the argument to the -r option.

-x

Attach to a session that is not detached. Requires multi-display mode.

-X

Run specified command in specified session. Requires multi-display mode, and session must not be password-protected.

Key bindings

screen commands consist of a command character (Ctrl-a by default) followed by another character. For many of the commands, you can also specify the character as Ctrl-character--e.g., Ctrl-a Ctrl-d as well as Ctrl-a d. The default key bindings are listed here. You can change the bindings for yourself in the $HOME/.screenrc configuration file, or for all users in /etc/screenrc. The term in parentheses that follows the description is the equivalent configuration-file command for changing the key binding.

Ctrl-a '

Prompt for window name or number to switch to. (select)

Ctrl-a "

List all windows for selection. (windowlist -b)

Ctrl-a num

Switch to window num, where num is a digit in the range 0–9 or - (the blank window). (select num)

Ctrl-a Tab

Switch input focus to next region. (focus)

Ctrl-a Ctrl-a

Toggle to previously displayed window. (other)

Ctrl-a a

Send the command character (Ctrl-a) to the window. (meta)

Ctrl-a A

Prompt user to enter a name for the current window. (title)

Ctrl-a b

Send a break to the window. (break)

Ctrl-a B

Reopen the terminal line and send a break. (pow-break)

Ctrl-a c

Create a new window with a shell and switch to it. (screen)

Ctrl-a C

Clear the screen. (clear)

Ctrl-a d

Detach screen from this terminal. (detach)

Ctrl-a D D

Detach and log out. (pow-detach)

Ctrl-a f

Toggle flow control between on, off, and auto. (flow)

Ctrl-a F

Resize window to current region size. (fit)

Ctrl-a Ctrl-g

Toggle visual bell mode. (vbell)

Ctrl-a h

Write contents of the current window to the file hardcopy.n. (hardcopy)

Ctrl-a H

Begin/end logging of the current window to the file screenlog.n. (log)

Ctrl-a i

Show information about this window. (info)

Ctrl-a k

Kill current window. (kill)

Ctrl-a l

Refresh current window. (redisplay)

Ctrl-a L

Toggle window’s login slot. Requires that screen be configured to update the utmp database. (login)

Ctrl-a m

Redisplay last message. (lastmsg)

Ctrl-a M

Toggle monitoring of the current window. (monitor)

Ctrl-a Space
Ctrl-a n

Switch to next window. (next)

Ctrl-a N

Show number and title of current window. (number)

Ctrl-a Backspace
Ctrl-a h
Ctrl-a p

Switch to previous window. (prev)

Ctrl-a q

Send a start signal (associated with Ctrl-q by terminals) to current window. (xon)

Ctrl-a Q

Delete all regions except the current one. (only)

Ctrl-a r

Toggle current window’s line-wrap setting. (wrap)

Ctrl-a s

Send a stop signal (associated with Ctrl-s by terminals) to current window. (xoff)

Ctrl-a S

Split current region into two new regions. (split)

Ctrl-a t

Show system information, including time and date. (time)

Ctrl-a v

Display version information. (version)

Ctrl-a Ctrl-v

Enter digraph for entering characters that can’t normally be entered. (digraph)

Ctrl-a w

List all windows. (windows)

Ctrl-a W

Toggle 80/132 columns. (width)

Ctrl-a x

Lock terminal. (lockscreen)

Ctrl-a X

Kill the current region. (remove)

Ctrl-a z

Suspend screen. (suspend)

Ctrl-a Z

Reset virtual terminal to its “power-on” values. (reset)

Ctrl-a .

Write out a .termcap file. (dumptermcap)

Ctrl-a ?

Show all key bindings. (help)

Ctrl-a Ctrl-\

Kill all windows and terminate screen. (quit)

Ctrl-a :

Enter command-line mode. (colon)

Ctrl-a [
Ctrl-a Esc

Enter copy/scrollback mode. (copy)

Ctrl-a ]

Write contents of the paste buffer to the standard input queue of the current window. (paste)

Ctrl-a {
Ctrl-a }

Copy and paste a previous line. (history)

Ctrl-a >

Write paste buffer to a file. (writebuf)

Ctrl-a <

Read screen-exchange file into paste buffer. (readbuf)

Ctrl-a =

Remove file used by Ctrl-a < and Ctrl-a >. (removebuf)

Ctrl-a,

Show where screen comes from, where it went to, and why you can use it. (license)

Ctrl-a _

Start/stop monitoring the current window for inactivity. (silence)

Ctrl-a *

List all currently attached displays. (displays)

Name

script

Synopsis

script [option] [file]

Fork the current shell and make a typescript of a terminal session. The typescript is written to file. If no file is given, the typescript is saved in the file typescript. The script ends when the forked shell exits, usually with Ctrl-D or exit.

Options

-a

Append to file or typescript instead of overwriting the previous contents.

-c command

Run the specified command instead of an interactive shell.

-f

Flush output after each write. Useful if another person is monitoring the output file.

-q

Operate in quiet mode.

-t

Write timing data to standard error. Each entry has two fields: the first is the elapsed time since the last output, and the second is the number of characters in the current output.

Name

sdiff

Synopsis

sdiff -o outfile [options] from to

Find differences between the two files from and to and merge interactively, writing the results to outfile.

Options

--

Treat remaining options as filenames, even if they begin with -.

-a, --text

Treat all files as text and compare line by line.

-b, --ignore-space-change

Ignore differences in whitespace.

-B, --ignore-blank-lines

Ignore added or missing blank lines.

-d, --minimal

Use a different algorithm to find fewer changes. This option causes sdiff to run more slowly.

-H, --speed-large-files

Heuristically speed comparison of large files with many small scattered changes.

-i, --ignore-case

Ignore case changes.

-I regexp, --ignore-matching-lines=regexp

Ignore any changes that insert or delete lines matching the regular expression regexp.

--ignore-all-space

Ignore whitespace when comparing lines.

-l, --left-column

Print only the left column of common lines.

-o file, --output=file

Write merged output to the specified file.

-s, --suppress-common-lines

Suppress common lines.

-t, --expand-tabs

Convert tabs to spaces in the output to preserve alignment.

-v, --version

Print version information and exit.

-w cols, --width=cols

Set the output to cols columns wide.

-W

Ignore horizontal whitespace when comparing lines.

Name

sed

Synopsis

sed [options] [command] [files]

Stream editor. Edit one or more files without user interaction. See Chapter 10 for more information.

Name

sendmail

Synopsis

sendmail [flags] [address...]

System administration command. sendmail is a mail transfer agent (MTA) or, more simply, a mail router. It accepts mail from a user’s mail program, interprets the mail address, rewrites the address into the proper form for the delivery program, and routes the mail to the correct delivery program.

Command-line flags

--

End of options marker. Only addresses should follow this option.

-Ac

Use local submission configuration file /etc/mail/submit.cf, even when no mail is sent from the command line.

-Am

Use configuration file /etc/mail/sendmail.cf, even when mail is sent from the command line.

-Btype

Set message body type. Accepted values are 7BIT and 8BITMIME.

-bx

Set operation mode to x. Operation modes are:

a

Run in ARPAnet mode.

d

Run as a daemon.

D

Run as a daemon, but remain in the foreground.

h

Print persistent host status information.

H

Purge expired entries from persistent host status information.

i

Initialize the alias database.

m

Deliver mail (the default).

p

Print the mail queue.

s

Speak SMTP on input side.

t

Run in test mode.

v

Verify addresses; do not collect or deliver.

-C file

Use configuration file file.

-d level

Set debugging level.

-D file

Send debugging output to file instead of stdout.

-f name

Sender’s name is name.

-F name

Set full name of user to name.

-G

Relay message submission. Used by rmail.

-h cnt

Set hop count (number of times message has been processed by sendmail) to cnt.

-i

Do not interpret dots on a line by themselves as a message terminator.

-L identifier

Use the specified log identifier for messages sent to syslogd.

-N conditions

Specify conditions for delivery status notification (DSN) as a comma-separated list. Accepted values are never, delay, failure, and success.

-n

Do not alias or forward.

-oXvalue

Set an option specified by its short name X. Options are described in the next section.

-O option=value

Set an option specified by its long name. Options are described in the next section.

-pprotocol

Receive messages via the protocol protocol.

-q[time]

Process queued messages immediately, or at intervals indicated by time (for example, -q30m for every half hour).

-qf

Process saved messages in the queue using the foreground process.

-qG group

Process saved messages in the named queue group.

-q[!]Isubstring

Process jobs for named queues containing substring. Use ! to process mail for all queues not containing substring.

-qp[time]

Same as -q, but create a persistent process to handle the queue instead of initiating a new process at each time interval.

-q[!]Qsubstring

Process quarantined messages containing substring. Use ! to process mail for recipients not containing substring.

-q[!]Rsubstring

Process jobs with recipients containing substring. Use ! to process mail for recipients not containing substring.

-q[!]Ssubstring

Process jobs from senders containing substring. Use ! to process mail from senders not containing substring.

-Q[reason]

Quarantine messages for the given reason. Use query options above to specify the message to quarantine.

-R portion

When bouncing messages, return only the specified portion of the bounced message. portion may be hdrs for headers, or full for the full message.

-t

Read header for To:, Cc:, and Bcc: lines, and send to everyone on those lists.

-v

Verbose mode.

-V envid

Use envid as the original envelope ID.

-X file

Log all traffic to file. Not to be used for normal logging.

Configuration options

Command-line configuration options are the same options normally set with an O in the sendmail configuration file. On the command line, they are set using -O and the option’s long name. Many of these options have short-name variations that are used with the -o option. Here, we document items most likely to be useful on the command line, providing both their short- and long- name forms. Many of the commands call for timeout values. These should be given as a number followed by a letter indicating the interval: s for seconds, m for minutes, h for hours, or d for days. For example, 30s is 30 seconds, 10m is 10 minutes, and 3d is 3 days. The default is minutes when no letter is given.

Aliasfile=file, Afile

Use alternate alias file.

AliasWait=min, amin

If the D option is set, wait min minutes for the aliases file to be rebuilt before returning an alias database out-of-date warning.

BlankSub=char, Bchar

Set unquoted space replacement character.

CheckAliases, n

When running newaliases, validate the right side of aliases.

CheckpointInterval=num, Cnum

Checkpoint the queue when mailing to multiple recipients. sendmail will rewrite the list of recipients after each group of num recipients has been processed.

ClassFactor=factor, zfactor

Multiplier for priority increments. This determines how much weight to give to a message’s precedence header. sendmail’s default is 1800.

ConnectionCacheSize=num, knum

Specify the maximum number of open connections to cache.

ConnectionCacheTimeout=timeout, Ktimeout

Time out connections after timeout.

ConnectionRateThrottle=num

Restrict SMTP connections per second to num.

DefaultUser=uid[:gid], uuid[:gid]

Use user ID and group ID for mailers instead of 1:1. If no group ID is specified, the user’s default group is used.

DefaultCharSet=label

Use the specified label for 8-bit data.

DeliveryMode=x, dx

Set the delivery mode to x. Delivery modes are d for deferred delivery, i for interactive (synchronous) delivery, b for background (asynchronous) delivery, and q for queue only (i.e., deliver the next time the queue is run).

DialDelay=seconds

Specify the number of seconds to wait before redialing after a connection fails.

DontPruneRoutes, R

Don’t prune route addresses.

EightBitMode=mode, 8mode

Specify how to handle 8-bit input. Accepted values for mode are mimefy (convert to 7-bit), pass (send as is), or strict (bounce the message).

ErrorHeader=text, Etext

Set error-message header. text is either text to add to an error message, or the name of a file. A filename must include its full path and begin with a /.

ErrorMode=x, ex

Set error processing to mode x. Valid modes are m to mail back the error message, w to write back the error message, p to print the errors on the terminal (default), q to throw away error messages, and e to do special processing for the BerkNet.

FallbackMXhost=host, Vhost

Set fallback MX host. host should be the fully qualified domain name of the fallback host.

ForkEachJob, Y

Deliver each job that is run from the queue in a separate process. This helps limit the size of running processes on systems with very low amounts of memory.

ForwardPath=path, Jpath

Set an alternative .forward search path.

HelpFile=file, Hfile

Specify SMTP help file to use instead of /etc/mail/helpfile.

HoldExpensive, c

On mailers that are considered “expensive” to connect to, don’t initiate immediate connection.

IgnoreDots, i

Do not take dots on a line by themselves as a message terminator.

LogLevel=n, Ln

Specify log level. Default is 9.

MatchGECOS, G

Compare local mail names to the GECOS section in the password file.

MaxDaemonChildren=num

Restrict incoming SMTP daemon to no more than num child processes.

MaxHopCount=num, hnum

Allow a maximum of num hops per message.

MeToo, m

Also send to me (the sender) if I am in an alias expansion.

MinFreeBlocks=minblocks, bminblocks

Require at least minblocks on the filesystem to be free.

MinQueueAge=timeout

Wait the specified time before processing a new job in the queue.

NoRecipientAction=action

Specify what headers, if any, to add to a message without recipient headers. Accepted values are none, add-to, add-apparently-to, add-bcc, and add-to-undisclosed.

OldStyleHeaders, o

If set, this message may have old-style headers. If not set, this message is guaranteed to have new-style headers (i.e., commas instead of spaces between addresses).

PostmasterCopy=user, Puser

Send copies of all failed mail to user (usually postmaster).

PrivacyOptions=optionlist, poptionlist

Adjust the privacy of the SMTP daemon. The optionlist argument should be a comma-separated list of the following values:

public

Make SMTP fully public (the default).

needmailhelo

Require site to send HELO or ELHO before sending mail.

needexpnhelo

Require site to send HELO or ELHO before answering an address expansion request.

needvrfyhelo

Like preceding argument, but for verification requests.

noetrn

Deny requests to reverse the connection using extended TURN.

noexpn

Deny all expansion requests.

noverb

Deny requests for verbose mode.

novrfy

Deny all verification requests.

authwarnings

Insert special headers in mail messages advising recipients that the message may not be authentic.

goaway

Set all of the previous arguments (except public).

nobodyreturn

Don’t return message body with a delivery status notification.

noreceipts

Turn off delivery status notification on success.

restrictexpand

Deny untrusted users access to aliases, forwards, or include files. Restrict sendmail -bv and disallow -v.

restrictmailq

Allow only users of the same group as the owner of the queue directory to examine the mail queue.

restrictqrun

Limit queue processing to root and the owner of the queue directory.

QueueDirectory=dir, Qdir

Select the directory in which to queue messages.

QueueFactor=factor, qfactor

Multiplier (factor) for high-load queuing. Default is 600000.

QueueLA=load, xload

Queue messages when load level is higher than load.

QueueTimeout=timeout, Ttimeout

Set the timeout on undelivered messages in the queue to the specified time (overridden by Timeout.queuereturn).

RecipientFactor=factor, yfactor

Penalize large recipient lists by factor.

RefuseLA=load, Xload

Refuse SMTP connections when load is higher than load.

ResolverOptions=arg, I arg

Use DNS lookups and tune them. Queue messages on connection refused. The arg arguments are identical to resolver flags without the RES_ prefix. Each flag can be preceded by a plus or minus sign to enable or disable the corresponding nameserver option. There must be whitespace between the I and the first flag.

RetryFactor=inc, Zinc

Increment priority of items remaining in queue by inc after each job is processed. sendmail uses 90000 by default.

SaveFromLine, f

Save Unix-style From lines at the front of messages.

SendMimeErrors, j

Use MIME format for error messages.

SevenBitInput, 7

Format all incoming messages in 7 bits.

StatusFile=file, Sfile

Save statistics in the named file.

SuperSafe, s

Always instantiate the queue file, even when it is not strictly necessary.

TempFileMode=mode, Fmode

Set default file permissions for temporary files. If this option is missing, default permissions are 0600.

Timeout.queuereturn=timeout

Return undelivered mail that has been in the queue longer than the specified timeout. The default is 5d (five days).

TimeZoneSpec=timezone, ttimezone

Set name of the time zone.

UseErrorsTo, l

Do not ignore Errors-To header.

UserDatabaseSpec=database, Udatabase

Consult the user database for forwarding information.

Verbose, v

Run in verbose mode.

sendmail support files

/usr/lib/sendmail

Traditional location of sendmail binary.

/usr/bin/newaliases

Link to /usr/lib/sendmail; rebuilds the alias database from information in /etc/aliases.

/usr/bin/mailq

Prints a listing of the mail queue.

/etc/mail/sendmail.cf

Configuration file, in text form.

/etc/mail/submit.cf

Configuration file used for local message submissions.

/etc/mail/helpfile

SMTP help file.

/etc/mail/statistics

Statistics file.

/etc/aliases

Alias file, in text form.

/etc/aliases.db

Alias file in dbm format. Created by newaliases.

/var/spool/mqueue

Directory in which the mail queue and temporary files reside.

Name

sensors

Synopsis

sensors [options] [chips]

Display current readings of all sensor chips and set limits (with -s) as specified in the configuration file. The default configuration file is /etc/sensors.conf.

Options

-A

Omit adapter and algorithm for each chipset.

--bus-list

Generate bus statements for use in the configuration file. If multiple chips share an address on different buses of the same type, this lets you refer to each bus by name, not number.

-c config-file

Specify a configuration file to use in place of the default.

-f

Print temperatures in Fahrenheit, not Celsius.

-h

Display help information and exit.

-s

Evaluate all set statements in the configuration file. Requires superuser privileges.

-u

Produce raw output. Used for testing and debugging.

-v

Display version information and exit.

Name

seq

Synopsis

seq [options] [first [increment]] last

Print the numbers from first through last by increment. The default is to print one number per line to standard output. Both first and increment can be omitted and default to 1, but if first is omitted then increment must also be omitted. In other words, if only two numbers are specified, they are taken to be the first and last numbers. The numbers are treated as floating-point.

Options

-f format, --format=format

Write the output using the specified printf floating-point format, which can be one of %e, %f, or %g (the default).

--help

Print help message and exit.

-s string, --separator=string

Use string to separate numbers in the output. Default is newline.

-w, --equal-width

Equalize the width of the numbers by padding with leading zeros. (Use -f for other types of padding.)

--version

Print version information and exit.

Name

setkeycodes

Synopsis

setkeycodes scancode keycode

System administration command. Assign a keycode event to the specified keyboard scancode. The kernel matches these to its own keycodes. Scancodes in the range of 1–88 are hardwired in the kernel, but the remaining scancodes can be assigned to keycodes in the range of 1–127. Use getkeycodes to see current assignments. Use showkey to discover what scancode a key is sending.

Name

setleds

Synopsis

setleds [options]

Display or change the LED flag settings (NumLock, CapsLock, and ScrollLock) for the current virtual terminal. With no options, display the current settings for all three flags. Can be used in a startup script to set the initial state of the LEDs.

Options

+num, -num

Set or clear NumLock.

+caps, -caps

Set or clear CapsLock

+scroll, -scroll

Set or clear ScrollLock.

-D

Change both the current and the default flag settings. Useful for always having NumLock set, for example.

-F

Only change the flags (and their settings may be reflected by the keyboard LEDs). The default behavior.

-L

Change the LEDs but not the flags, so the leds no longer reflect the virtual terminal (VT) flags. Run setleds -L with no other options to restore the default behavior.

-v

Report the settings before and after the change.

Name

setmetamode

Synopsis

setmetamode [options]

Display or set Meta key handling for the current virtual terminal. With no option, print the current Meta key mode. Otherwise, set the mode and display the setting before and after the change.

Options

esc, prefix, escprefix

Set the Meta key to send an escape sequence.

meta, bit, metabit

Set the Meta key to set the high-order bit of the character.

Name

setquota

Synopsis

setquota [options] [name] [limits] filesystems

System administration command. Set quotas from the command line. Provide limits in the format soft-block-limit hard-block-limit soft-inode-limit hard-inode-limit. To disable a quota, set it to 0. See also edquota, a vi editor interface for editing and setting quotas.

Options

-a, --all

Apply settings to all filesystems listed in /etc/mtab that support quotas.

-b, --batch

Read new settings from standard input. Provide as a list, each line in the form of “name limits.”

-F format, --format=format

Specify filesystem quota format to use. See quota for a list of accepted values.

-g, --group

Set group quotas instead of users.

-p prototype, --prototype=prototype

Apply the same settings as used for the specified user or group: prototype.

-t blockgrace inodegrace, --edit_period blockgrace inodegrace

Specify overall grace times in seconds for block and inode quotas.

-T name blockgrace inodegrace, --edit-times name blockgrace inodegrace

Specify grace times in seconds for individual user or group name. Use the string unset to remove existing grace times.

-u, --user

Set user quotas. (This is the default.)

Name

setsid

Synopsis

setsid command [arguments]

System administration command. Execute the named command and optional command arguments in a new session.

Name

setterm

Synopsis

setterm [options]

Set terminal attributes by writing a character string to standard output to invoke the specified attributes.

Options

For Boolean options, the default value is on. Where 8-color is specified, the possible colors are black, red, green, yellow, blue, magenta, cyan, and white. Where 16-color is specified, the possible colors include the 8-color colors, plus grey, bright red, bright green, bright yellow, bright blue, bright magenta, bright cyan, and bright white.

-appcursorkeys [on|off]

Set cursor key application mode on or off. Virtual consoles only. Can cause problems with vi.

-append [num]

Write a snapshot of virtual console num to the file specified with the -file option, appending the snapshot to any existing contents. With no argument, write a snapshot of the current virtual terminal. Overridden by -dump.

-background 8-color|default

Set background color. Virtual consoles only.

-bfreq [freq]

Set the bell frequency in Hz (default 0).

-blank [min]

Set the delay before the screen blanks to the specified number of minutes. Virtual consoles only.

-blength [millisec]

Set the bell duration in milliseconds (default 0). Possible values are 0–2000.

-blink [on|off]

Turn blinking mode on or off. If the terminal is not a virtual console, -blink off also turns off bold, half-bright, and reverse modes.

-bold [on|off]

Turn bold on or off. If the terminal is not a virtual console, -bold off also turns off blink, half-bright, and reverse modes.

-clear [all]

Clear the screen.

-clear rest

Clear from the current cursor position to the end of the screen.

-clrtabs [tab1...tabn]

With no arguments, clear all tab stops. Otherwise, clear the specified tab stops. Virtual consoles only.

-cursor [on|off]

Turn the cursor on or off.

-default

Set rendering options to defaults.

-dump [num]

Write a snapshot of virtual console num to the file specified with the -file option, overwriting any existing contents. With no argument, dump the current virtual console. Overrides -append.

-file file

Write output from the -dump or -append option to the specified file. If no filename is specified, write to the file screen.dump in the current directory.

-foreground 8-color|default

Set foreground color. Virtual consoles only.

-half-bright [on|off]

Turn half-bright (dim) mode on or off. If the terminal is not a virtual console, -half-bright off also turns off bold, blink, and reverse modes.

-hbcolor 16-color

Set color for half-bright characters. Virtual consoles only.

-initialize

Display the terminal initialization string to reset the rendering options and other attributes to their defaults.

-inversescreen [on|off]

Invert the screen colors, swapping foreground and background, and underline and half-bright. Virtual consoles only.

-linewrap [on|off]

Turn line-wrapping on or off. Virtual consoles only.

-msg [on|off]

Enable or disable the sending of kernel printk( ) messages to the console. Virtual consoles only.

-msglevel [num]

Set the console logging level for kernel printk( ) messages. The value of num can be in the range 0–8. Messages more important than the specified number are printed, with 8 printing all kernel messages, and 0 equivalent to -msg on. Virtual consoles only.

-powerdown [min]

Set the VESA powerdown interval to the specified number of minutes, from 0–60. If no value is specified for min, defaults to 0, disabling powerdown.

-powersave [mode]

Put the monitor in the specified VESA powersave mode. Specifying no mode is equivalent to off. The possible values of mode are:

on, vsync

vsynch suspend mode.

hsync

hsync suspend mode.

powerdown

Powerdown mode.

off

Turn off VESA powersaving features.

-regtabs [num]

Clear all existing tab stops and set a regular tab stop pattern at every num number (default is 8). num is a number in the range 1–160. Virtual consoles only.

-repeat [on|off]

Turn keyboard repeat on or off. Virtual consoles only.

-reset

Display the terminal reset string to reset the terminal to its power-on state.

-reverse [on|off]

Turns reverse-video mode on or off. If the terminal is not a virtual console, -reverse off also turns off bold, half-bright, and blink modes.

-store

Store the current rendering options as the defaults. Virtual consoles only.

-tabs [tab1...tabn]

Set tab stops at the specified cursor positions, which can range from 1 to 160. Virtual consoles only.

-term term

Replace the value of the TERM environment variable with term.

-ulcolor 16-color

Set color for underlining. Virtual consoles only.

-underline [on|off]

Turn underlining on or off.

Name

sftp

Synopsis

sftp [options] host

An interactive file transfer program, similar to ftp except that it uses ssh to perform file transfers securely. sftp connects to host and logs in, prompting for a password if required. The host can be specified in the following ways:

Host
[user@]host[:file [file] ...]
[user@]host[:dir[/]]

If user is specified, that username is used for the login. If any files are specified, the sftp client automatically retrieves them after the user has been authenticated, and then exits. If a directory dir is specified, the client starts in that directory on the remote host. sftp is part of the OpenSSH suite of network tools.

Options

−1

Use SSH1. The default is to use SSH2, which offers stronger security.

-b file

Run in batch mode, taking commands from the specified file. Requires the use of a noninteractive authentication mechanism.

-B bytes

Specify the size of the buffer sftp uses for file transfers. Default is 32768 bytes.

-C

Enable compression (uses ssh -C).

-F file

Use file as the ssh configuration file instead of the default system configuration file. The systemwide file is usually /etc/ssh/ssh_config, and per-user files are $HOME/.ssh/config.

-o option

Pass an option to ssh. The passed option is in the format used by ssh_config(5) (e.g., -o PORT=nn, where nn is the port number). -o can appear more than once to pass multiple options to ssh. This option is useful for passing options that don’t have an equivalent sftp command-line option.

-P server_path

Connect directly to the local sftp server specified in server_path. Useful for debugging.

-R num

Specify the number of requests that may be outstanding at any time (default 64).

-s subsys|server_path

Specify the SSH2 subsystem or path to the sftp server on the remote system. Specifying the path is useful for using sftp via SSH1 or if the remote sshd does not have an sftp subsystem configured.

-S program

Specify the name of a program that understands ssh options and that you want to use for the encrypted connection.

-v

Raise the logging level.

Name

sh

Synopsis

sh [options] [file [arguments]]

The standard Unix shell, a command interpreter into which all other commands are entered. On modern versions of Linux, this is just another name for the bash shell. For more information, see Chapter 6. For legacy Linux versions and other Unix flavors, be careful not to rely on sh and bash being equivalent.

Name

sha1sum

Synopsis

sha1sum [option] [files]

Compute or check 160-bit SHA1 checksums to verify file integrity. If the file is not specified, or specified as -, read from standard input.

Options

-b, --binary

Read files in binary mode.

-c, --check

Read and check the SHA1 sums in the files (or standard input) and verify that they are consistent. The input must have been generated by an earlier sha1sum command.

--help

Print usage information and exit.

--status

Don’t generate output messages; the exit code indicates success or failure. Used only with --check.

-t, --text

Read files in text mode. The default.

--version

Print version information and exit.

-w, --warn

Warn about improperly formatted checksum lines. Used only with --check.

Name

showkey

Synopsis

showkey [options]

Print keycodes, scancodes, or ASCII codes of keys pressed on the keyboard. The default is to show keycodes. In keycode and scancode mode, the program terminates 10 seconds after the last key is pressed. In ASCII mode, press Ctrl-D to exit. This command may not function properly under the X Window System, which also reads from the console device.

Options

-a, --ascii

Print the ASCII character, decimal, octal, and hexadecimal values of keys pressed.

-h, --help

Print version number and help message, then exit.

-k, --keycodes

Print keycodes associated with key-press events. This is the default mode.

-s, --scancodes

Print the keyboard scancodes associated with key-press events.

Name

showmount

Synopsis

showmount [options] [host]

NFS/NIS command. Show information about an NFS server. This information is maintained by the mountd server on host. The default value for host is the value returned by hostname. With no options, show the clients that have mounted directories from the host. showmount is usually found in /usr/sbin, which is not in the default search path.

Options

-a, --all

Print all remote mounts in the format hostname:directory, where hostname is the name of the client and directory is the root of the filesystem that has been mounted.

-d, --directories

List directories that have been remotely mounted by clients.

-e, --exports

Print the list of exported filesystems.

-h, --help

Provide a short help summary.

--no-headers

Do not print headers.

-v, --version

Report the current version of the program.

Name

shred

Synopsis

shred [options] files

Overwrite a file to make the contents unrecoverable, and delete the file afterward if requested.

Options

-

Shred standard output.

-f, --force

Force permissions to allow writing to files.

--help

Print help message and exit.

-nnum, --iterations=num

Overwrite files num times (default is 25).

--random-source=file

Use file as the source of random bytes for overwriting. Default is /dev/urandom.

-snum, --size=num

Shred num bytes. num can be expressed with suffixes (e.g., K, M, or G).

-u, --remove

Remove file after overwriting. shred does not remove the file unless this option is specified.

-v, --verbose

Verbose mode.

--version

Print version information and exit.

-x, --exact

Shred the exact file size; do not round up to the next full block.

-z, --zero

On the final pass, overwrite with zeros to hide the shredding.

Name

shutdown

Synopsis

shutdown [options] when [message]

System administration command. Terminate all processing. when may be a specific time (in hh:mm format), a number of minutes to wait (in +m format), or now. A broadcast message notifies all users to log off the system. Processes are signaled with SIGTERM to allow them to exit gracefully. /etc/init is called to perform the actual shutdown, which consists of placing the system in runlevel 1. Only privileged users can execute the shutdown command, although init may call shutdown with root privileges when the Ctrl-Alt-Del key combination is pressed from the console keyboard. Broadcast messages, default or defined, are displayed at regular intervals during the grace period; the closer the shutdown time, the more frequent the message.

Options

-a

When called from init, shut down only if one of the users listed in the file /etc/shutdown.allow is currently logged in.

-c

Cancel a shutdown that is in progress.

-f

Reboot fast, by suppressing the normal call to fsck when rebooting.

-F

Force a filesystem check (fsck) on reboot.

-h

Halt or power off the system when shutdown is complete. Which it does depends on system hardware/BIOS.

-H

Halt the system when shutdown is complete.

-k

Print the warning message, but suppress actual shutdown.

-P

Power off the system when shutdown is complete.

-r

Reboot the system when shutdown is complete.

Name

size

Synopsis

size [options] [objfile...]

Print the number of bytes of each section of objfile and its total size. If objfile is not specified, a.out is used.

Options

-d

Display the size in decimal and hexadecimal.

--format=format

Imitate the size command from either System V (--format sysv) or BSD (--format berkeley).

--help

Print help message, then exit.

-o

Display the size in octal and hexadecimal.

--radix=num

Specify how to display the size: in hexadecimal and decimal (if num is 10 or 16) or hexadecimal and octal (if num is 8).

-t, --totals

Show object totals. Works only with Berkeley format listings.

--target=bfdname

Specify object format by binary file descriptor name. Use -h for a list of supported object formats.

-x

Display the size in hexadecimal and decimal.

-A

Imitate System V’s size command.

-B

Imitate BSD’s size command.

-V, --version

Print version, then exit.

Name

slabtop

Synopsis

slabtop [options]

Display kernel slab cache information in real time. slabtop displays a listing of the top caches as sorted by a given sort criteria.

Options

-d n, --delay=n

Refresh the display every n seconds. By default, the display is refreshed every three seconds.

-s S, --sort=S

Sort by S, where S is one of the following sort criteria:

a

Sort by the number of active objects in each cache.

b

Sort by the number of objects per slab.

c

Sort by cache size.

l

Sort by the number of slabs in each cache.

n

Sort by the name of each cache.

o

Sort by the number of objects in each cache (this is the default).

p

Sort by the number of pages per slab.

s

Sort by the size of objects in each cache.

u

Sort by cache utilization.

v

Sort by the number of active slabs.

-o, --once

Display once and then exit.

--help

Display usage information and then exit.

-V, --version

Display version information and then exit.

Name

slattach

Synopsis

slattach [options] [tty]

TCP/IP command. Attach serial lines as network interfaces, thereby preparing them for use as point-to-point connections. Only a privileged user may attach or detach a network interface.

Options

-c command

Run command when the connection is severed.

-d

Debugging mode.

-e

Exit immediately after initializing the line.

-h

Exit when the connection is severed.

-l

Create UUCP-style lockfile in /var/spool/uucp.

-L

Enable three-wire operation.

-m

Suppress initialization of the line to 8-bit raw mode.

-n

Similar to mesg -n.

-p protocol

Specify protocol, which may be slip, adaptive, ppp, or kiss.

-q

Quiet mode; suppress messages.

-s speed

Specify line speed.

Name

sleep

Synopsis

sleep amount [units]sleep option

Wait a specified amount of time before executing another command. units may be s (seconds), m (minutes), h (hours), or d (days). The default for units is s.

Options

--help

Print usage information and exit.

--version

Print version information and exit.

Name

sort

Synopsis

sort [options] [files]

Sort the lines of the named files. Compare specified fields for each pair of lines; if no fields are specified, compare them by byte, in machine-collating sequence. If no files are specified or if the file is -, the input is taken from standard input. See also uniq, comm, and join.

Options

-b, --ignore-leading-blanks

Ignore leading spaces and tabs.

-c, --check

Check whether files are already sorted and, if so, produce no output.

-C, --check=quiet, --check=silent

Like -c, but do not report the first bad line.

-d, --dictionary-order

Sort in dictionary order.

-f, --ignore-case

Fold; ignore uppercase/lowercase differences.

-g, --general-numeric-sort

Sort in general numeric order.

--help

Print a help message and then exit.

-i, --ignore-nonprinting

Ignore nonprinting characters (those outside ASCII range 040–176).

-k n[,m], --key=n[,m]

Skip n−1 fields and stop at m−1 fields (i.e., start sorting at the nth field, where the fields are numbered beginning with 1). If m is omitted, stop at the end of the line.

-m, --merge

Merge already sorted input files.

-M, --month-sort

Attempt to treat the first three characters as a month designation (JAN, FEB, etc.). In comparisons, treat JAN < FEB and any invalid name for a month as less than a valid month.

-n, --numeric-sort

Sort in arithmetic order.

-ofile, --output=file

Put output in file.

-r, --reverse

Reverse the order of the sort.

-s, --stable

Stabilize sort by disabling last-resort comparison.

-Ssize, --buffer-size=size

Set the size of the main memory buffer to size, which may include a suffix--e.g., K (1024, the default) or M.

-tc, --field-separator=c

Separate fields with c instead of nonblank to blank transition.

-Tdir, --temporary-directory=dir

Specify the directory pathname to be used for temporary files instead of $TMPDIR or /tmp. May be given more than once for multiple directories.

-u, --unique

Identical lines in input file appear only one time in output. With -c, check for strict ordering.

--version

Print version information and then exit.

-z, --zero-terminated

End lines with zero byte, not with newline.

Examples

List files by decreasing number of lines:

wc -l * | sort -r

Alphabetize a list of words, remove duplicates, and print the frequency of each word:

sort -fd wordlist | uniq -c

Sort the password file numerically by the third field (user ID):

sort -nk3,4 -t: /etc/passwd

Name

split

Synopsis

split [options] [infile [prefix]]

Split infile into equal-sized segments. infile remains unchanged, and the results are written to prefixaa, prefixab, and so on. The default prefix is x, giving the output files xaa, xab, etc. If infile is - or missing, standard input is read. See also csplit.

Options

-a n, --suffix-length=n

Use suffixes of length n (default is 2).

-b n[b|k|m], --bytes=n[b|k|m]

Split infile into n-byte segments. Alternate block sizes may be specified:

b

512 bytes.

k

1 kilobyte.

m

1 megabyte.

-C bytes[b|k|m], --line-bytes=bytes[b|k|m]

Put a maximum of bytes into file; insist on adding complete lines.

-d, --numeric-suffixes

Use numeric suffixes instead of alphabetic suffixes for the output filenames.

-n, -l n, --lines=n

Split infile into n-line segments (default is 1000).

--help

Print a help message and then exit.

--verbose

Print a message for each output file.

--version

Print version information and then exit.

Examples

Break bigfile into 1000-line segments:

split bigfile

Concatenate four files, then split them into 10-line files named new.aa, new.ab, and so on. Note that without the -, new. would be treated as a nonexistent input file:

cat list[1-4] | split −10 - new.

Name

ssh

Synopsis

ssh [options] hostname [command]

Securely log a user into a remote system and run commands on that system. The version of ssh described here is the OpenSSH client. ssh can use either version 1 (SSH1) or version 2 (SSH2) of the SSH protocol. SSH2 is preferable, as it provides stronger encryption methods and greater connection integrity. The hostname can be specified either as hostname or as user@hostname. If a command is specified, the user is authenticated, the command is executed, and the connection is closed. Otherwise, a terminal session is opened on the remote system. See Escape characters, later in this command, for functions that can be supported through an escape character. The default escape character is a tilde (˜). The exit status returned from ssh is the exit status from the remote system, or 255 if there was an error.

Commonly, authentication is handled with standard username/password credentials, but it can also be useful to authenticate with a key exchange. This is done by generating a key on the client with ssh-keygen and populating the authorized_keys file on the remote host.

Options

−1

Try only SSH1.

−2

Try only SSH2.

−4

Use only IPv4 addresses.

−6

Use only IPv6 addresses.

-a

Disable forwarding of the authentication agent connection.

-A

Allow forwarding of the authentication agent connection. Can also be specified on a per-host basis in a configuration file.

-b bind_address

Specify the interface to transmit from when there are multiple available interfaces or aliased addresses.

-c blowfish|3des|des|ciphers

Select the cipher for encrypting the session. The default is 3des. For SSH2, a comma-separated list of ciphers can also be specified, with the ciphers listed in order of preference. des is supported only for legacy SSH1 compatibility and otherwise should not be used.

-C

Enable compression. Useful mainly for slow connections. The default compression level can be set on a per-host basis in the configuration file with the CompressionLevel option.

-D [bind_address:]port

Enable dynamic application-level port forwarding using port on the local side. Can be specified in the configuration file. Only root can forward privileged ports. For IPv6, an alternative syntax is [bind_address/]port or the address can be enclosed in square brackets.

-e char|^char|none

Set the escape character (default ˜). The escape character must be the first character on a line. If none is specified, disable the use of an escape character.

-f

Run interactively for user authentication, then go into background mode for command execution. Implies -n.

-F configfile

Specify a per-user configuration file (default is $HOME/.ssh/config).

-g

Allow remote hosts to connect to local forwarded ports.

-i idfile

Use idfile to read identity (private key) for RSA or DSA authentication. Default is $HOME/.ssh/id_rsa or $HOME/.ssh/id_dsa for SSH2, or $HOME/.ssh/identity for SSH1. You can specify more than one -i option on the command line or in the configuration file.

-I device

Specify a smartcard device from which to get the user’s private RSA key.

-k

Disable forwarding of GSSAPI (Generic Security Service Application Programming Interface) credentials to the server. Can be set on a per-host basis in the configuration file.

-K

Enable forwarding of GSSAPI credentials to the server.

-l user

Log in as user on the remote system. Can be specified on a per-host basis in the configuration file.

-L [bind_address:]port:host:hostport

Forward port on the local host to the specified remote host and port. Can be specified in the configuration file. Only root can forward privileged ports. For IPv6, an alternative syntax is [bind_address/]port/host/hostport or the address can be enclosed in square brackets.

-m macspec

For SSH2, the contents of macspec specify message authentication code (MAC) algorithms to use. macspec is a comma-separated list of algorithms in order of preference.

-M

Put the ssh client into master mode for connection sharing.

-n

Get standard input as a redirection from /dev/null. Used to prevent reading from standard input, which is required when running ssh in the background. Useful for running X programs on a remote host.

-N

Do not execute a remote command. Useful with SSH2 for port forwarding.

-o option

Specify options in configuration-file format. Useful for specifying options that have no command-line equivalent. For details on the options, see the manpage for ssh_config(5).

-p port

Specify the port on the remote host to which ssh is to connect. Can be specified on a per-host basis in the configuration file.

-q

Run quietly, suppressing warnings and error messages.

-R [bind_address:]port:host:hostport

Forward port on the remote host to the local host:hostport. Can be specified in the configuration file. You can forward privileged ports only if you are logged in as root on the remote host. For IPv6, an alternative syntax is [bind_address/]port/host/hostport or the address can be enclosed in square brackets.

-s

For SSH2, request invocation of a subsystem on the remote host to be used for another application, such as sftp. The desired subsystem is specified as the remote command.

-S ctl

Specify the location of a control socket for connection sharing.

-t

Force pseudo-tty allocation. Multiple -t options can be specified to force tty allocation even when ssh has no local tty.

-T

Disable pseudo-tty allocation.

-v

Verbose mode. Useful for debugging. Specify multiple -v options to increase verbosity.

-V

Display version information and exit.

-w local[:remote]

Request tunnel device forwarding with the specified local (client) and remote (server) tunnel devices.

-x

Disable X11 forwarding.

-X

Enable X11 forwarding. Can be specified on a per-host basis in the configuration file.

-Y

Enable trusted X11 forwarding.

Escape characters

˜.

Disconnect.

˜˜

Send a single ˜.

˜#

List forwarded connections.

˜&

Run ssh in the background at logout, while waiting for a forwarded connection or X11 sessions to terminate.

˜?

Display the available escape characters.

˜B

Send a BREAK to the remote system. Only for SSH2 and if the remote system supports it.

˜C

Open a command line. Useful for adding port forwardings when using the -L and -R options.

˜R

Request rekeying of the connection. Useful only for SSH2 and if the peer supports it.

˜^Z

Run in the background.

Name

ssh-add

Synopsis

ssh-add [options] [files]
ssh-add -e|-s reader

Add RSA or DSA identities to the authentication agent (see ssh-agent), which must be running and must be an ancestor of the current process. ssh-add reads the files created by ssh-keygen for private keys. It reads the information in these private keys to obtain RSA or DSA identities. With no arguments specified, ssh-add adds the files $HOME/.ssh/id_rsa, $HOME/.ssh/id_dsa, and $HOME/.ssh/identity. If any files are specified, it adds those instead, prompting for a passphrase if required.

Options

-c

Confirm identities being added, by running the program specified in the SSH_ASKPASS environment variable. A 0 exit status from the program indicates successful confirmation.

-d

Remove an identity from the agent instead of adding one.

-D

Delete all identities from the agent.

-e reader

Remove key in specified smartcard reader.

-l

List fingerprints of all identities known to the agent.

-L

List public key parameters of all identities known to the agent.

-s reader

Add key in smartcard reader.

-t life

Set maximum lifetime when adding identities to an agent. The value of life can be in seconds or another time format specified in sshd_config(5).

-x

Lock the agent with a password.

-X

Unlock the agent.

Name

ssh-agent

Synopsis

ssh-agent [options] [command [arguments]]

Hold private keys used for public key authentication. ssh-agent is usually executed at the beginning of an X or login session; then all other windows or programs given as command are run as clients of ssh-agent. When a command is specified, the command and any arguments are executed. The agent dies when the command completes. Use ssh-add to add keys (identities) to the agent. Operations that require a private key are performed by the agent, which returns the results to the requestor.

Options

-a bind_addr

Bind the agent to the socket bind_addr (default is /tmp/ssh-nnnnnnnn/agent, where nnnnnnnn is a generated number).

-c

Write csh commands to standard output. This is the default if the environment variable SHELL looks like a csh-type shell.

-d

Debug mode.

-k

Kill the current agent.

-s

Write Bourne shell commands to standard output. This is the default if the environment variable SHELL does not look like a csh-type shell.

-t life

Set a default value for maximum identity lifetime for added identities. May be specified in seconds or in a format specified in sshd(8). This value can be overridden by a lifetime specified for an identity with ssh-add. The default maximum lifetime is forever.

Name

ssh-keygen

Synopsis

ssh-keygen [options]

Generate, manage, and convert authentication keys for ssh. When using ssh-keygen to create a key, the -t option must be specified to identify the type of key to create.

Options

-b bits

Specify the number of bits in the key. For RSA keys, the minimum is 512, and the default is 2048. DSA keys must be exactly 1024 bits.

-B

Show the bubblebabble digest (a digest represented as a string that looks like real words) for the private or public keyfile specified with -f.

-c

Change the comment in the private and public keyfiles (for RSA1 keys only).

-C comment

Specify a new comment.

-D reader

Download the RSA public key from the smartcard in reader.

-e

Read an OpenSSH private or public keyfile and write it in SECSH Public Key File Format to standard output for exporting to a commercial SSH.

-f file

Specify the filename of the keyfile.

-F hostname

List occurrences of the specified hostname found in a known_hosts file. Useful with -H to print keys that were found in a hashed format.

-H

Hash a known_hosts file.

-i

Read an SSH2-compatible unencrypted private or public keyfile and write an OpenSSH-compatible key to standard output. Used to import keys from a commercial SSH.

-l

Show fingerprint of public or private RSA1 keyfile specified with -f. With -v, also displays an ASCII art representation of the key.

-N passphrase

Specify the new passphrase.

-p

Change the passphrase for a private keyfile. Prompt for the file, the old passphrase, and twice for the new passphrase.

-P passphrase

Specify the old passphrase.

-q

Operate in quiet mode.

-t type

Specify the type of key to create. Possible values of type are rsa1 for SSH1, and rsa or dsa for SSH2.

-U reader

Upload an existing RSA private key to the smartcard in reader.

-v

Verbose mode; print debugging messages. Use multiple -v options for greater verbosity.

-y

Read a private OpenSSH-format file and print a public key to standard output.

Name

ssh-keyscan

Synopsis

ssh-keyscan [options]

Gather public and private host keys from a number of hosts. Can be used in scripts.

Options

−4

Use IPv4 addresses only.

−6

Use IPv6 addresses only.

-f file

Read hostnames or addrlist namelist pairs from file. If - is specified instead of a filename, read hosts or addrlist namelist pairs from standard input.

-H

Hash hostnames and addresses in the output.

-p port

Specify the port to connect to on the remote host.

-t type

Specify the type of key to get from the scanned hosts. Possible values are rsa1 for SSH1 (default), or rsa or dsa for SSH2. Specify multiple values in a comma-separated list.

-T timeout

Specify the timeout for attempting a connection, in seconds. Default is 5 seconds.

-v

Verbose mode.

Name

sshd

Synopsis

sshd [options]

TCP/IP command. Server for the ssh program, providing a secure remote-login and remote-execution facility equivalent to rlogin and rsh. Normally started at boot, sshd listens for incoming connections, forking a new daemon when one is detected. The forked daemon handles authentication, command execution, and encryption. Most implementations of sshd support both SSH protocols 1 and 2. The following options are those used by OpenSSH, OpenBSD’s Secure Shell implementation.

Options

−4

Use only IPv4 addresses.

−6

Use only IPv6 addresses.

-b bits

Use the specified number of bits in the server key. Default is 768.

-d

Run sshd in the foreground and send verbose debug information to the system log. Process only one connection. Use the specified number of bits in the server key. This option may be specified from one to three times. Each additional -d increases the level of information sent to the system log.

-D

Do not detach from the foreground process.

-e

Send output to standard error instead of the system log.

-f file

Read configuration information from file instead of the default configuration file /etc/ssh/sshd_config.

-g seconds

Set the grace time a client has to authenticate itself before the server disconnects and exits. The default is 600 seconds. A value of 0 means there is no limit.

-h keyfile

Read the host’s cryptographic key from the specified keyfile instead of from the default file /etc/ssh/ssh_host_key for SSH protocol 1, and the default files /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for SSH protocol 2. The -h option may be given more than once to specify multiple keyfiles.

-i

Use when running sshd from inetd.

-k seconds

Set how often the version 1 server key should be regenerated. Default value is 3600 seconds. If set to 0 seconds, the key will never be regenerated.

-o setting

Pass a configuration file setting as an option.

-p port

Listen for connections on port. The default is 22. More than one -p option may be specified. This option overrides ports specified in a configuration file.

-q

Send no messages to the system log.

-t

Test configuration files and keys, then exit.

-u namelength

Specify the length of the remote hostname field in the UTMP structure as specifed in utmp.h. A namelength of 0 will cause sshd to write dotted decimal values instead of hostnames to the utmp file and prevent DNS requests unless required by the authentication mechanism.

Name

stat

Synopsis

stat [options] files

Print out the contents of an inode as they appear to the stat system call in a human-readable format. The error messages “Can’t stat file” and “Can’t lstat file” usually mean the file doesn’t exist. “Can’t readlink file” generally indicates that something is wrong with a symbolic link.

Options

-c format, --format=format

Display the output as specified by format.

-f, --filesystem

Display information about the filesystem where the file is located, not about the file itself.

--help

Display help information and exit.

-L, --dereference

Follow links and display information about the files found.

-t, --terse

Print the output tersely, in a form suitable for parsing by other programs.

--version

Print version information and exit.

Output

stat and stat -L display the following:

- Device number

- Inode number

- Access rights

- Number of hard links

- Owner’s user ID and name, if available

- Owner’s group ID and name, if available

- Device type for inode device

- Total size, in bytes

- Number of blocks allocated

- I/O block size

- Last access time

- Last modification time

- Last change time

- Security context for SELinux

If -f is specified, stat displays the following information about the filesystem:

- Filesystem type

- Filesystem block size

- Total blocks in the filesystem

- Number of free blocks

- Number of free blocks for nonroot users

- Total number of inodes

- Number of free inodes

- Maximum filename length

Format

The printf(3) flag characters #, 0, -, +, and space can be used in format. In addition, the field width and precision options can be used.

If -c format is specified, the following sequences can be used for format:

%a

Access rights in octal.

%A

Access rights in human-readable form.

%b

Number of blocks allocated.

%B

Size in bytes of each block reported by %b.

%d

Device number in decimal.

%D

Device number in hex.

%f

Raw mode in hex.

%F

File type.

%g

Owner’s group ID.

%G

Owner’s group name.

%h

Number of hard links.

%i

Inode number.

%n

Filename.

%N

Quoted filename. If file is a symbolic link, include path to original.

%o

I/O block size.

%s

Total size, in bytes.

%t

Major device type in hex.

%T

Minor device type in hex.

%u

Owner’s user ID.

%U

Owner’s username.

%x

Last access time.

%X

Last access time as seconds since the Epoch.

%y

Last modification time (modification of the file contents).

%Y

Last modification time as seconds since the Epoch.

%z

Time of last change (modification of the inode).

%Z

Time of last change as seconds since the Epoch.

If both -c format and -f are specified, the following sequences can be used for format:

%a

Free blocks available to nonroot user.

%b

Total data blocks in filesystem.

%c

Total file nodes in filesystem.

%d

Free file nodes in filesystem.

%f

Free blocks in filesystem.

%i

Filesystem ID, in hex.

%l

Maximum filename length.

%n

Filename.

%s

Optimal transfer block size.

%S

Fundamental block size (for block counts).

%t

Type in hex.

%T

Type in human-readable form.

Examples

Sample output from the command stat /:

stat /

File: "/"
Size: 4096             Blocks: 8          IO Block: 4096   Directory
Device: 303h/771d       Inode: 2           Links: 19
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2009-04-27 21:47:29.000000000 −0400
Modify: 2009-04-27 20:10:22.000000000 −0400
Change: 2009-04-27 20:10:22.000000000 −0400

Sample output with -f, displaying information about the filesystem:

stat -f /
File: "/"
ID: 0        0        Namelen: 255     Type: ext2/ext3
Blocks: Total: 2612475    Free: 1869472    Available: 1736735    Size: 4096
Inodes: Total: 1329696    Free: 1150253

Name

statd

Synopsis

rpc.statd [options]

System administration command. The NFS status server, statd, reports server status to clients like the rup command.

Options

-d

Debugging mode; log verbose information to standard error.

-F

Run statd in the foreground.

-n hostname, --name hostname

Specify a name to use for the local hostname. By default, this is read using the gethostname function.

-o port, --outgoing-port port

Specify the port that statd should use for its outgoing requests to other servers. When not specified, a port is assigned by portmap.

-p port, --port port

Specify the incoming port that statd should listen on. When not specified, a port is assigned by portmap.

-P directory, --state-directory-path directory

Store state information in directory instead of the default, /var/lib/nfs.

-V

Print version information, then exit.

-?

Print help message, then exit.

Name

strace

Synopsis

strace [options] command [arguments]

Trace the system calls and signals for command with optional arguments. strace shows you how data is passed between the program and the kernel. With no options, strace prints a line for each system call. It shows the call name, given arguments, return value, and any generated error messages. A signal is printed with both its signal symbol and a descriptive string. As it shows the data transfer between user and kernel-space, strace is very useful as both a diagnostic utility for system administrators and a debugging tool for programmers. By default, the output is written to standard error.

Options

-a n

Align the return values in column n. The default is 40.

-c

Count system calls, errors, signals, and time and provide a summary report when the program has ended.

-d

Debug mode. Print debugging information for strace on stderr.

-e [keyword=][!]values

Pass an expression to strace to limit the types of calls or signals that are traced or to change how they are displayed. If no keyword is given, trace is assumed. The values can be given as a comma-separated list. Preceding the list with an exclamation point (!) negates the list. The special values all and none are valid, as are the values listed with the following keywords:

abbrev=names

Abbreviate output from large structures for system calls listed in names.

read=descriptors

Print all data read from the given file descriptors.

signal=symbols

Trace the listed signal symbols (for example, signal=SIGIO,SIGHUP).

trace=sets

sets may be a list of system call names or one of the following:

desc

File descriptor related calls.

file

Calls that take a filename as an argument.

ipc

Interprocess communication.

network

Network-related.

process

Process management.

signal

Signal-related.

raw=names

Print arguments for the given system calls in hexadecimal.

verbose=names

Unabbreviate structures for the given system calls. Default is none.

write=descriptors

Print all data written to the given file descriptors.

-f

Trace forked processes.

-ff

Write system calls for forked processes to separate files named filename.pid when using the -o option.

-h

Print help and exit.

-i

Print the current instruction pointer with each system call.

-o filename

Write output to filename instead of stderr. If filename starts with the pipe symbol |, treat the rest of the name as a command to which output should be piped.

-O n

Override strace’s built-in timing estimates, and just subtract n microseconds from the timing of each system call to adjust for the time it takes to measure the call.

-p pid

Attach to the given process ID and begin tracking. strace can track more than one process if more than one option -p is given. Type Ctrl-C to end the trace.

-q

Quiet mode. Suppress attach and detach messages from strace.

-r

Relative timestamp. Print time in microseconds between system calls.

-s n

Print only the first n characters of a string. Default value is 32.

-S value

Sort output of -c option by the given value. value may be calls, name, time, or nothing. Default is time.

-t

Print time of day on each line of output.

-tt

Print time of day with microseconds on each line of output.

-ttt

Print timestamp on each line as the number of seconds and microseconds since the Epoch.

-T

Print time spent in each system call.

-u username

Run command as username. Needed when tracing setuid and setgid programs.

-V

Print version and exit.

-v

Verbose. Do not abbreviate structure information.

-x

Print all non-ASCII strings in hexadecimal.

-xx

Print all strings in hexadecimal.

Name

strings

Synopsis

strings [options] files

Search each file specified and print any printable character strings found that are at least four characters long and followed by an unprintable character. Often used to find human-readable content within binary files.

Options

@file

Read command-line options as a whitespace-separated list of options from file.

-, -a, --all

Scan entire object files; default is to scan only the initialized and loaded sections for object files.

-e encoding, --encoding=encoding

Specify the character encoding of the strings to be found. Possible values are:

b

16-bit big-endian

B

32-bit big-endian

I

16-bit little-endian

L

32-bit little-endian

s

Single-7-bit-byte characters, such as ASCII, ISO-8859, etc. (the default)

S

Single-8-bit-byte characters.

-f, --print-file-name

Print the name of the file before each string.

-min-len, -n min-len, --bytes=min-len

Print only strings that are at least min-len characters.

-o

The same as -t o.

-t base, --radix=base

Print the offset within the file before each string, in the format specified by base:

d

Decimal

o

Octal

x

Hexadecimal

-T format, --target=format

Specify an alternative object code format to the system default. See strings --help for a list of valid target formats.

--help

Print help message and then exit. The help message includes a list of valid targets.

-v, --version

Print version information and then exit.

Name

strip

Synopsis

strip [options] files

Remove symbols from object files, thereby reducing file sizes and freeing disk space.

Options

-F bfdname, --target=bfdname

Specify object format for both input and output by binary file descriptor name bfdname. Use option -h to see a list of supported formats.

-I bfdname, --input-target=bfdname

Expect object format bfdname for input.

--help

Print help message, then exit.

-K symbol, --keep-symbol=symbol

Delete all symbols except the specified symbol. This option may be used more than once.

-N symbol, --strip-symbol=symbol

Remove symbol from the source file.

-O bfdname, --output-target=bfdname

Use object format bfdname for output.

-o file

Write stripped object to file instead of replacing the original. Only one object file at a time may be stripped when using this option.

-p, --preserve-dates

Preserve access and modification times.

-R section, --remove-section=section

Delete section.

-S, -g, -d, --strip-debug

Strip debugging symbols.

-s, --strip-all

Strip all symbols.

--strip-unneeded

Remove symbols not needed for relocation processing.

-V, --version

Print version and exit.

-v, --verbose

Verbose mode.

-X, --discard-locals

Strip local symbols that were generated by the compiler.

-x, --discard-all

Strip nonglobal symbols.

Name

stty

Synopsis

stty [options] [modes]

Set terminal I/O options for the current standard input device. Without options, stty reports the terminal settings that differ from those set by running stty sane, where ^ indicates the Ctrl key and ^` indicates a null value. Most modes can be negated using an optional - (shown in brackets). The corresponding description is also shown in brackets. Some arguments use non-POSIX extensions; these are marked with *.

Options

-a, --all

Report all option settings.

-F dev, --device=dev

Open the specified device and use it instead of standard input.

-g, --save

Report settings in stty-readable form (i.e., hex).

--help

Print help message and exit.

--version

Print version information and exit.

Control modes

[-]clocal

[Enable] disable modem control.

[-]cread

[Disable] enable the receiver.

[-]crtscts*

[Disable] enable RTS/CTS handshaking.

csbits

Set character size to bits, which must be 5, 6, 7, or 8.

[-]cstopb

[1] 2 stop bits per character.

[-]hup, [-]hupcl

[Do not] hang up connection on last close.

[-]parenb

[Disable] enable parity generation and detection.

[-]parodd

Use [even] odd parity.

Input modes

[-]brkint

[Do not] signal INTR on break.

[-]icrnl

[Do not] map CR to NL on input.

[-]ignbrk

[Do not] ignore break on input.

[-]igncr

[Do not] ignore CR on input.

[-]ignpar

[Do not] ignore parity errors.

[-]imaxbel*

When input buffer is too full to accept a new character, [flush the input buffer] beep without flushing the input buffer.

[-]inlcr

[Do not] map NL to CR on input.

[-]inpck

[Disable] enable input parity checking.

[-]istrip

[Do not] strip input characters to 7 bits.

[-]iuclc*

[Do not] map uppercase to lowercase on input.

[-]iutf8*

[Do not] assume input characters are UTF-8 encoded.

[-]ixany*

Allow [only XON] any character to restart output.

[-]ixoff, [-]tandem

[Enable] disable sending of START/STOP characters.

[-]ixon

[Disable] enable XON/XOFF flow control.

[-]parmrk

[Do not] mark parity errors.

Output modes

bsn*

Select style of delay for backspaces (0 or 1).

crn*

Select style of delay for carriage returns (0–3).

ffn*

Select style of delay for formfeeds (0 or 1).

nln*

Select style of delay for linefeeds (0 or 1).

tabn, [-]tabs*

Select style of delay for horizontal tabs (0–3). tabs is the same as tab0 and -tabs is the same as tab3.

vtn*

Select style of delay for vertical tabs (0 or 1).

[-]ocrnl*

[Do not] map CR to NL on output.

[-]ofdel*

Set fill character to [NULL] DEL.

[-]ofill*

Delay output with [timing] fill characters.

[-]olcuc*

[Do not] map lowercase to uppercase on output.

[-]onlcr*

[Do not] map NL to CR-NL on output.

[-]onlret*

On the terminal, NL performs [does not perform] the CR function.

[-]onocr*

Do not [do] output CRs at column 0.

[-]opost

[Do not] postprocess output.

Local modes

[-]echo

[Do not] echo every character typed.

[-]echoe, [-]crterase

[Do not] echo ERASE character as BS-space-BS string.

[-]echok

[Do not] echo NL after KILL character.

[-]echonl

[Do not] echo NL.

[-]icanon

[Disable] enable canonical input (ERASE, KILL, WERASE, and RPRNT processing).

[-]iexten

[Disable] enable extended functions for input data.

[-]isig

[Disable] enable checking of characters against INTR, SUSPEND, and QUIT.

[-]noflsh

[Enable] disable flush after INTR or QUIT.

[-]tostop*

[Do not] send SIGTTOU when background processes write to the terminal.

[-]xcase*

[Do not] change case on local output.

[-]echoprt, [-]prterase*

When erasing characters, echo them backward, enclosed in \ and /.

[-]echoctl, [-]ctlecho*

Do not echo control characters literally. Use hat notation (e.g., ^Z).

[-]echoke, [-]crtkill*

Erase characters as specified by the echoprt and echoe settings (default is echoctl and echok settings).

Combination modes

[-]cooked

Same as [raw]-raw.

[-]evenp, [-]parity

Same as [-]parenb and cs[8]7.

ek

Reset ERASE and KILL characters to Ctrl-h and Ctrl-u, their defaults.

[-]lcase, [-]LCASE

[Unset] set xcase, iuclc, and olcuc.

[-]nl

[Unset] set icrnl and onlcr. -nl also unsets inlcr, igncr, ocrnl, and onlret.

[-]oddp

Same as [-]parenb, [-]parodd, and cs[8]7.

[-]raw

[Disable] enable raw input and output (no ERASE, KILL, INTR, QUIT, EOT, SWITCH, or output postprocessing).

sane

Reset all modes to reasonable values.

[-]cbreak

Same as [icanon]-icanon.

[-]pass8

Same as [parenb]-parenb [istrip]-istrip cs[7]8.

[-]litout

Same as [parenb]-parenb [istrip]-istrip [opost]-opost cs[7]8.

[-]decctlq*

Same as [-]ixany.

crt

Same as echoe echoctl echoke.

dec

Same as echoe echoctl echoke -ixany. Additionally, set INTERRUPT to Ctrl-C, ERASE to Del, and KILL to Ctrl-U.

Control assignments

ctrl-char c

Set control character to c. ctrl-char is dsusp (flush input and then send stop), eof, eol, eol2 (alternate end-of-line), erase, intr, lnext (treat next character literally), kill, rprnt (redraw line), quit, start, stop, susp, swtch, or werase (erase previous word). c can be a literal control character, a character in hat notation (e.g., ^Z), in hex (must begin with 0x), in octal (must begin with 0), or in decimal. Disable the control character with values of ^- or undef.

Special settings

n

Set terminal baud rate to n (e.g., 2400).

ispeed speed

Specify input speed.

line i*

Set line discipline to i (1–126).

min n

Set the minimum number of characters that will satisfy a read until the time value has expired when -icanon is set.

ospeed speed

Specify output speed.

rows rows*

Specify number of rows.

cols columns, columns columns*

Specify number of columns.

size*

Display current row and column settings.

speed

Display terminal speed.

time n

Set the number of tenths of a second before reads time out if the min number of characters has not been read when -icanon is set.

Name

su

Synopsis

su [option] [user] [shell_args]

Create a shell with the effective user ID user. If no user is specified, create a shell for a privileged user (i.e., become a superuser). Enter EOF to terminate. You can run the shell with particular options by passing them as shell_args (e.g., if the shell runs bash, you can specify -c command to execute command via bash, or -r to create a restricted shell).

Options

-, -l, --login

Go through the entire login sequence (i.e., change to user’s environment).

-c command, --command=command

Execute command in the new shell and then exit immediately. If command is more than one word, it should be enclosed in quotes. For example:

su -c 'find / -name \*.c -print' nobody

-f, --fast

Start the shell with the -f option, which suppresses the reading of the .cshrc or .tcshrc file. Applies to csh and tcsh.

-m, -p, --preserve-environment

Do not reset environment variables.

-s shell, --shell=shell

Execute shell, not the shell specified in /etc/passwd, unless shell is restricted.

--help

Print a help message and then exit.

--version

Print version information and then exit.

Examples

Become root and obtain all of root’s user environment:

$ su -

Become root long enough to restart the Apache httpd web server, then revert to the current user:

$ su -c /etc/rc.d/init.d/httpd restart

Name

sudo

Synopsis

sudo [options] [command]
sudoedit [options] files

If you are allowed, execute command as the superuser. Authorized users of sudo and the commands they are permitted to execute are listed in the sudo configuration file, /etc/sudoers. If an unauthorized user attempts to run a command, sudo informs an administrator via email. By default, it sends the message to the root account. Users attempting to run commands are prompted for their password. Once authenticated, sudo sets a timestamp for the user. For five minutes from the timestamp, the user may execute further commands without being prompted for her password. This grace period may be overridden by settings in the /etc/sudoers file. Also see /etc/sudoers for configuration examples. The sudoedit form of sudo is equivalent to running sudo -e.

Options

-b

Execute command in the background.

-e

Edit one or more files instead of running a command, running the editor specified by the VISUAL or EDITOR environment variable. If a specified file does not exist, it is created.

-h

Print help message, then exit.

-H

Set the HOME environment variable to the home directory of the target user (default is root).

-i

Run the shell specified in /etc/passwd for the user sudo is being run as.

-k

Revoke user’s sudo permissions. Similar to -K, but changes user’s timestamp to the Epoch instead of revoking it.

-K

Remove user’s timestamp.

-I

List all allowed and forbidden commands for the user on the current host, then exit.

-L

List parameters that may be set as defaults for a user in the /etc/sudoers file.

-p promptstring

Use the specified promptstring to prompt for a password. The string may contain the following escape codes, which are replaced with the current user’s login name and local hostname.

%h

Local hostname without the domain name.

%H

Local hostname with the domain name.

%u

Current user’s login name

%U

Login name of the user the command will run under. The default is root.

%%

A single percent (%) character.

-P

Preserve invoking user’s group membership.

-s

Run the shell specified in the SHELL environment variable, or the default shell specified in /etc/passwd. If a command is given, it should be a shell script and not a binary file.

-S

Read password from standard input instead of from the console.

-u user

Run command as the specified user instead of the root user. This may also be specified as a user ID number using #uid.

-v

Update timestamp for user to extend the timeout. Prompt for password if necessary. No command is run.

-V

Print version number, then exit. When run by the root user, print sudo’s defaults and the local network address as well.

--

Stop reading command-line arguments. Useful with -s.

Name

sum

Synopsis

sum [options] files

Calculate and print a checksum and the number of (1 KB) blocks for file. If no files are specified, or file is -, read from standard input. Useful for verifying data transmission.

Options

-r

The default setting. Use the BSD checksum algorithm.

-s, --sysv

Use alternate checksum algorithm as used on System V. The block size is 512 bytes.

--help

Print a help message and then exit.

--version

Print the version number and then exit.

Name

swapoff

Synopsis

swapoff [options] [devicelist]

System administration command. Stop making devices and files specified in devicelist available for swapping and paging.

Option

-a

Consult /etc/fstab for devices marked sw. Use those in place of the device argument.

-h

Print help message and then exit.

-V

Display version number and then exit.

Name

swapon

Synopsis

swapon [options] devices

System administration command. Make the listed devices available for swapping and paging.

Options

-a

Consult /etc/fstab for devices marked sw. Use those in place of the devices argument.

-e

Used with -a. Don’t complain about missing devices.

-h

Print help message, then exit.

-p priority

Specify a priority for the swap area. Higher priority areas will be used up before lower priority areas are used.

-s

Print swap usage summaries, then exit.

-V

Print version information, then exit.

Name

sync

Synopsis

sync

System administration command. Write filesystem buffers to disk. sync executes the sync( ) system call. If the system is to be stopped, sync must be called to ensure filesystem integrity. Note that shutdown automatically calls sync before shutting down the system. sync may take several seconds to complete, so the system should be told to sleep briefly if you are about to manually call halt or reboot. Note that shutdown is the preferred way to halt or reboot your system, as it takes care of sync-ing and other housekeeping for you.

Name

sysctl

Synopsis

sysctl [options] [key]

System administration command. Examine or modify kernel parameters at runtime using the /proc/sys filesystem. While many of these kernel keys can be altered by other utilities, sysctl provides a single interface to kernel settings.

Options

-a, -A

Display all available values.

-e

Ignore requests for unknown keys.

-n

Print values only, no keynames.

-N

Print keynames only.

-p [file]

Reset keys from information specified in /etc/sysctl.conf, or the specified file.

-q

When setting values, don’t print the values to stdout.

-w key=value

Write a new value to the specified key.

Name

sysklogd

Synopsis

syslogd [options]

System administration command. sysklogd provides both syslogd and klogd functionality. By default, it is meant to behave exactly like the BSD version of syslogd. While the difference should be completely transparent to the user, sysklogd supports an extended syntax. It is invoked as syslogd.

sysklogd logs system messages into a set of files described by the configuration file /etc/syslog.conf. Each message is one line. A message can contain a priority code, marked by a number in angle brackets at the beginning of the line. Priorities are defined in <sys/syslog.h>. syslogd reads from an Internet domain socket specified in /etc/services. To bring syslogd down, send it a terminate signal. See also klogd. On some newer systems sysklogd is replaced by rsyslogd.

Options

-a socket

Add socket to the list of sockets syslogd listens to.

-d

Turn on debugging.

-f configfile

Specify alternate configuration file.

-h

Forward messages from remote hosts to forwarding hosts.

-l hostlist

Specify hostnames that should be logged with just the hostname, not the fully qualified domain name. Multiple hosts should be separated by a colon (:).

-m markinterval

Select number of minutes between mark messages.

-n

Avoid auto-backgrounding. This is needed when starting syslogd from init.

-p socket

Send log to socket instead of /dev/log.

-r

Receive messages from the network using an internet domain socket with the syslog service.

-s domainlist

Strip off domain names specified in domainlist before logging. Multiple domain names should be separated by a colon (:).

-u user

Drop root privileges and run with the privileges of user while logging. While it will initially open logfiles as root, upon receiving a SIGHUP it will reopen them as user. This will fail if the logfiles are not writable by user.

-v

Print version number, then exit.

Name

syslogd

Synopsis

syslogd

System administration command. See sysklogd.

Name

tac

Synopsis

tac [options] [file]

Named for the common command cat, tac prints files in reverse to standard output. Without a filename or with -, it reads from standard input. By default, tac reverses the order of the lines, printing the last line first.

Options

-b, --before

Print separator (by default a newline) before the string it delimits.

-r, --regex

Expect separator to be a regular expression.

-s string, --separator=string

Specify alternate separator (default is newline).

--help

Print a help message and then exit.

--version

Print version information and then exit.

Name

tail

Synopsis

tail [options] [files]

Print the last 10 lines of each named file on standard output. Print from standard input with no filename or with -. If more than one file is specified, the output includes a header at the beginning of each file:

==> filename <==

For options that take the number of bytes or lines as an argument, you can prepend a plus sign (+) to num to begin printing with the numth item. These options can also specify a block size:

b

512 bytes

K

1 kilobyte

M

1 megabyte

G

1 gigabyte

Options

-c num, --bytes num

Print the last num bytes.

-f, --follow[=name|descriptor]

Don’t quit at the end of file; “follow” file as it grows and end when the user presses Ctrl-C. Following by file descriptor is the default, so -f, --follow, and --follow=descriptor are equivalent. Use --follow=name to track the actual name of a file even if the file is renamed, as with a rotated logfile.

-F

Identical to --follow=name --retry.

--help

Print a help message and exit.

-n num, --lines=num

Print the last num lines.

--max-unchanged-stats=num

Used with --follow=name to reopen a file whose size hasn’t changed after num iterations (default 5), to see if it has been unlinked or renamed (as with rotated logfiles).

--pid=pid

Used with -f to end when process ID pid dies.

-q, --quiet, --silent

Suppress filename headers.

--retry

Keep trying to open a file even if it isn’t accessible when tail starts or if it becomes inaccessible later. Useful with --follow=name.

-s sec, --sleep-interval=sec

With -f, sleep approximately sec seconds between iterations. Default is 1 second.

-v, --verbose

With multiple files, always output the filename headers.

--version

Print version information and then exit.

Examples

Show the last 20 lines containing instances of .Ah:

grep '\.Ah'  file | tail −20

Show the last 10 characters of variable name:

echo "$name" | tail -c

Print the last two blocks of bigfile:

tail −2b bigfile

Name

tailf

Synopsis

tailf file

Print the last 10 lines of a file, then wait for the file to grow. tailf is similar to tail -f, but it does nothing when the file is not growing. Useful for following a logfile, particularly on a laptop when you want to conserve the battery power.

Name

talk

Synopsis

talk person [ttyname]

Talk to another user. person is either the login name of someone on your own machine or user@host on another host. To talk to a user who is logged in more than once, use ttyname to indicate the appropriate terminal name. Once communication has been established, the two parties may type simultaneously, with their output appearing in separate windows. To redraw the screen, type Ctrl-L. To exit, type your interrupt character; talk then moves the cursor to the bottom of the screen and restores the terminal.

Name

tar

Synopsis

tar [options] [tarfile] [other-files]

Copy files to or restore files from an archive medium. If any files are directories, tar acts on the entire subtree. tar was originally used to create tape archives and still has options related to that use. However, here we document the options commonly used today. Options need not be preceded by - (though they may be). The exception to this rule is when you are using a long-style option (such as --touch). In that case, the exact syntax is:

tar -- long-option - function-options files

For example:

tar --touch -xvf tarfile.tar

Function options

You must use exactly one of these, and it must come before any other options:

-A, --catenate, --concatenate

Concatenate a second tar file to the end of the first.

-c, --create

Create a new archive.

-d, --diff, --compare

Compare the files stored in tarfile with other-files. Report any differences: missing files, different sizes, different file attributes (such as permissions or modification time).

--delete

Delete from the archive. This option cannot be used with magnetic tape.

-r, --append

Append other-files to the end of an existing archive.

-t, --list

Print the names of other-files if they are stored in the archive (if other-files are not specified, print names of all archived files).

-u, --update

Add files if not in the archive or if modified.

-x, --extract, --get

Extract other-files from an archive (if other-files are not specified, extract all files).

Options

--anchored

Exclude patterns must match the start of the filename (the default).

--atime-preserve

Preserve original access time on extracted files.

-b n, --blocking-factor=n

Set block size to n × 512 bytes. By default, n=20.

-B, --read-full-records

Reblock while reading; used for reading from 4.2BSD pipes.

--backup[=type]

Back up files rather than deleting them. If no backup type is specified, a simple backup is made with ˜ as the suffix. (See also --suffix.) The possible values of type are:

t, numbered

Make numbered backups.

nil, existing

Make numbered backups if there are already numbered backups; otherwise, make simple backups.

never, simple

Always make simple backups.

-C directory, --directory=directory

cd to directory before beginning tar operation.

--checkpoint

List directory names encountered.

--exclude=pattern

Remove files matching pattern from any list of files.

-f file, --file=file

Store files in or extract files from archive file. Note that file may take the form hostname:filename.

-F script, --info-script=script, --new-volume-script=script

Implies -M (multiple archive files). Run script at the end of each file.

--force-local

Interpret filenames in the form hostname:filename as local files.

-g file, --listed-incremental=file

Create, list, or extract new-style incremental backup.

-G, --incremental

Create, list, or extract old-style incremental backup.

--group=group

Use group as the group for files added to the archive.

-h, --dereference

Dereference symbolic links, and archive the files they point to rather than the symbolic link.

--help

Print help message and exit.

-i, --ignore-zeros

Ignore blocks of zeros (i.e., EOFs).

--ignore-case

Ignore case when excluding files.

--ignore-failed-read

Ignore unreadable files to be archived. Default behavior is to exit when encountering these.

--index-file=file

With -v, send output to file.

-j, --bzip2

Compress files with bzip2 before archiving them, or uncompress them with bunzip2 before extracting them.

-k, --keep-old-files

When extracting files, do not overwrite files with similar names. Instead, print an error message.

-K file, --starting-file=file

Begin tar operation at file in archive.

--keep-newer-files

When extracting files, do not overwrite files that are newer than the archive files.

-m, --touch

Do not restore file modification times; update them to the time of extraction.

-M, --multivolume

Expect archive to be multivolume. With -c, create such an archive.

--mode=permissions

Use permissions when adding files to an archive. The permissions are specified the same way as for the chmod command.

-N date, --newer=date, --after-date=date

Ignore files older than date.

--newer-mtime=date

Add only files whose contents have changed since date to the archive.

--no-anchored

Exclude patterns may match anything following a slash.

--no-ignore-case

Do not ignore case when excluding files.

--no-same-permissions

Do not extract permissions information when extracting files from the archive. This is the default for users, and therefore affects only the superuser.

--no-recursion

Do not move recursively through directories.

--no-wildcards

Don’t use wildcards when excluding files; treat patterns as strings.

--no-wildcards-match-slash

Wildcards do not match / when excluding files.

--null

Allow filenames to be null-terminated with -T. Override -C.

--numeric-owner

Use the numeric owner and group IDs rather than the names.

-o, --no-same-owner

When extracting, create files with yourself as owner.

-O, --to-stdout

Print extracted files to standard output.

--occurrence[=n]

Process only the nth occurrence of each file (default is 1). Use with --delete, --diff, --extract, or --list.

--one-file-system

Do not archive files from other filesystems.

--overwrite

Overwrite existing files and directory metadata when extracting from archive.

--overwrite-dir

Overwrite existing directory metadata when extracting from archive.

--owner=owner

Set owner as the owner of extracted files instead of the original owner. owner is first assumed to be a username, then, if there is no match, a numeric user ID.

-p, --same-permissions, --preserve-permissions

Keep permissions of extracted files the same as the originals.

-P, --absolute-names

Do not remove initial slashes (/) from input filenames.

--posix

Create a POSIX-compliant archive.

--preserve

Equivalent to invoking both the -p and -s options.

-R, --block-number

Display archive’s block number in messages.

--record-size=size

Treat each record as having size bytes, where size is a multiple of 512.

--recursion

Move recursively through directories.

--recursive-unlink

Remove existing directory hierarchies before extracting directories with the same name.

--remove-files

Remove originals after inclusion in archive.

--rsh-command=command

Do not connect to remote host with rsh; instead, use command.

-s, --same-order, --preserve-order

When extracting, sort filenames to correspond to the order in the archive.

-S, --sparse

Treat sparse files more efficiently when adding to archive.

--same-owner

When extracting, create files with the same ownership as the originals.

--show-defaults

Display the default tar options.

--show-omitted-dirs

List directories being omitted when operating on an archive.

--strip-components=num, --strip-path=num

Strip the specified number of leading components from filenames before extracting. Use --strip-components for tar versions beginning with tar-1.14.90. Earlier versions of tar-1.14 use --strip-path.

--suffix=suffix

Use suffix instead of the default ˜ when creating a backup file.

-T file, --files-from=file

Consult file for files to extract or create.

--totals

Print byte totals.

-U, --unlink-first

Remove each existing file from the filesystem before extracting from the archive.

--use-compress-program=program

Compress archived files with program, or uncompress extracted files with program.

--utc

Display file modification dates in UTC format.

-v, --verbose

Verbose. Print filenames as they are added or extracted.

-V name, --label=name

Name this volume name.

--version

Print version information and exit.

--volno-file=file

Use/update the volume number in file.

-w, --interactive, --confirmation

Wait for user confirmation (y) before taking any actions.

-W, --verify

Check archive for corruption after creation.

--wildcards

Use wildcards when excluding files.

--wildcards-match-slash

Wildcards match / when excluding files.

-X file, --exclude-from file

Consult file for list of files to exclude.

-z, --gzip, --gunzip, --ungzip

Compress files with gzip before archiving them, or uncompress them with gunzip before extracting them.

-Z, --compress, --uncompress

Compress files with compress before archiving them, or uncompress them with uncompress before extracting them.

Examples

Create an archive of book chapter files (c), show the command working (v), and store the results in Chapters.tar:

tar cvf Chapters.tar chapter*

List the archive’s contents in a format like ls -l:

tar tvf Chapters.tar

Extract Chapter 1:

tar xvf Chapters.tar chapter1

Create an archive of the current directory and store it in a file backup.tar:

tar cvf - `find . -print` > backup.tar

(The - tells tar to store the archive on standard output, which is then redirected.)

Create an archive and filter it through bzip2 to compress it:

tar cvfj Chapters.tar.bz2 chapter*

Filter an existing archive through gzip, extracting the contents but leaving the original file compressed:

tar xvfz chapters.tar.gz

Name

taskset

Synopsis

taskset [options] [mask | list] [pid | command [args]]

taskset is used to retrieve or set the processor affinity mask of either an existing process, given its PID, or to run a new a process, given its command name, with a specified affinity mask. The Linux scheduler will then honor the given affinity mask, ensuring that the process in question runs only on allowed processors.

Options

-c, --cpu-list

The affinity mask is provided in list form, for example, “0,2,5-6,” not as a bitmask.

-p, --pid

Set or retrieve the mask of the given PID. Do not start a new process.

-h, --help

Display usage information and then exit.

-V, --version

Display version information and then exit.

Name

tcpdump

Synopsis

tcpdump [options] [expression]

System administration command. Dump headers and packets of network traffic that match expression. The command continues to capture packets until it receives a SIGTERM or SIGINT signal (usually generated by typing the interrupt character control-C). When finished, it will generate a report on traffic captured, received, or dropped by the kernel.

Expressions

Create matching expressions using the following primitives followed by an ID or name.

direction

A qualifier indicating whether to match source or destination information. Accepted values are src, dst, src or dst, and src and dst. When not specified, the expression will match either source or destination traffic.

protocol

A qualifier restricting matches to a particular kind of packet. Accepted values are: ether, fddi, tr, wlan, ip, ip6, arp, rarp, decnet, tcp, and udp. If not specified, the match defaults to any appropriate protocol matching type.

type

A qualifier indicating what kind of thing the ID or name references, such as a part of a hostname (host), IP address (net) or port (port). When not specified, the match defaults to host.

Options

-A

Print packets in ASCII text.

-c n

Exit after receiving n packets.

-C n

When saving to a file, do not write files larger than n million bytes. Open a new file with the same basename appended by a number. Start with the number 1.

-d, -dd, -ddd

Compile and dump the packet-matching code for the given expression, then exit. Use the second form to dump it as a C programming fragment. Use the third form to dump the code in decimal.

-D

Print a list of the available interfaces, then exit.

-e

Print the link-level header on each line.

-F file

Read expression from the specified file.

-i interface

Listen on the specified interface. If not specified, tcpdump will listen on the lowest-numbered interface available, other than the loopback interface. Use any to listen to all available interfaces.

-l

Line buffer standard out.

-L

Print the data link types for an interface, then exit.

-n, -nn

Print IP addresses instead of converting them to hostnames. Use the second form to leave protocols and port numbers in numeric form, as well.

-N

Print hostnames instead of fully qualified domain names.

-p

Don’t put the interface into promiscuous mode.

-q

Abbreviate output, printing less protocol information.

-r file

Read packets from the specified file. (You can create such a file with the -w option.)

-s n

Read n bytes of data from each packet. (The default is 68.)

-S

Print absolute TCP sequence numbers.

-T n

Read n bytes of data from each packet. (The default is 68.)

-t, -tt, -ttt, -tttt

Change display of timestamp. Use the first form to omit the timestamp from each line. Use the second form to print an unformatted timestamp. Use the third form to print the time in seconds between the current and the previous dump line. The final form prints the date before the timestamp on each dump line.

-u

Print undecoded NFS handles.

-v, -vv, -vvv

Increase the verbosity of the printout. Each additional v increases the detail of the information printed.

-w file

Write the raw packet information to file without parsing or printing it. Specify - to write to standard output.

-W n

Wrap files creating a rotating buffer. Used with -C, this will set a limit on the number of files created. Upon reaching the limit, tcpdump will begin overwriting earlier files.

-x, -xx

Print packets in hex. Use the second form to print the packet’s link level header in hex as well.

-X, -XX

Print packets in hex and ASCII text. Use the second form to print the packet’s link level header in hex and ASCII as well.

-Z user

Drop root privileges and change to the specified user. Use the primary group of the specified user.

Examples

Place full packets into a file named tcpdump.cap for later analysis:

tcpdump -v -w tcpdump.cap -xX -s 0

Read all packet headers received on the eth0 interface, except for arp and SSH packets:

tcpdump -i eth0 not arp and not port ssh

Name

tcpslice

Synopsis

tcpslice [options] [start [end]] files

System administration command. Reads and manipulates packet capture files created by tcpdump -w. Based on timestamps, extract portions of or merge together files. Display all packets between the given start and end times. tcpslice understands most time and date formats. tcpslice also understands a relative time format specified as a unit of time--e.g., +1h10m to specify the first hour and ten minutes of packets in the specified files. This format is named ymdhmsu after the letters it uses to denote units of time: years, months, days, hours, minutes, seconds, and microseconds. If no constraining dates are specified, the command will print out all packets contained in files.

Options

-d

Print the start and end time of the specified range, then exit.

-D

When merging files, don’t discard duplicate packets.

-l

Merge packets based on the time relative to the start of the file. The default is to merge based on the absolute timestamp.

-r

Print the time and date of the first and last packet in each file, then exit.

-R

Print the raw timestamp of the first and last packet in each file, then exit.

-t

Print times associated with the first and last packet in each file in ymdhmsu format.

-w file

Write output to file instead of standard output.

Name

tee

Synopsis

tee [options] files

Accept output from another command and send it both to standard output and to files (like a T or fork in the road).

Options

-a, --append

Append to files; do not overwrite.

-i, --ignore-interrupts

Ignore interrupt signals.

--help

Print a help message and then exit.

--version

Print version information and then exit.

Example

ls -l | tee savefile    View listing and save for later

Name

telinit

Synopsis

telinit [option] [runlevel]

System administration command. Signal init to change the system’s runlevel. telinit is actually just a link to init, the ancestor of all processes.

Option

-t seconds

Send SIGKILL seconds after SIGTERM. Default is 20.

Runlevels

The default runlevels vary from distribution to distribution, but these are standard:

0

Halt the system.

1, s, S

Single user.

6

Reboot the system.

a, b, c

Process only entries in /etc/inittab that are marked with runlevel a, b, or c.

q, Q

Reread /etc/inittab.

Check the /etc/inittab file for runlevels on your system.

Name

telnet

Synopsis

telnet [options] [host [port]]

Access remote systems. telnet is the user interface that communicates with another host using the Telnet protocol. If telnet is invoked without host, it enters command mode, indicated by its prompt, telnet>, and accepts and executes commands. Type ? at the command prompt to see the available commands. If invoked with arguments, telnet performs an open command (shown in the following list) with those arguments. host indicates the host’s official name, alias, or Internet address. port indicates a port number (default is the Telnet port).

The Telnet protocol is often criticized because it uses no encryption and makes it easy for snoopers to pick up user passwords. Most sites now use ssh instead.

Options

−7

Request 7-bit operation.

−8

Request 8-bit operation.

-a

Automatic login to the remote system.

-b hostalias

Use bind to bind the local socket to an aliased address or the address of an interface other than the one that would be chosen by connect.

-c

Disable reading of the user’s .telnetrc file.

-d

Turn on socket-level debugging.

-e [escape_char]

Set initial telnet escape character to escape_char. If escape_char is omitted, no escape character is predefined.

-E

Disable the escape character functionality.

-f

With Kerberos V5 authentication, allow forwarding of the local credentials to the remote system.

-F

With Kerberos V5 authentication, allow local credentials to be forwarded to the remote system, including any that were already forwarded to the local environment.

-k realm

With Kerberos authentication, obtain tickets for the remote host in realm, instead of in the remote host’s realm.

-K

Do not allow automatic login to the remote system.

-l user

When connecting to remote system and if remote system understands ENVIRON, send user to the remote system as the value for variable USER. Implies the -a option.

-L

Specify an 8-bit data path on output.

-n tracefile

Open tracefile for recording the trace information.

-r

Emulate rlogin. The default escape character for this mode is a tilde (˜); an escape character followed by a dot causes telnet to disconnect from the remote host; a ^Z instead of a dot suspends telnet; and a ^] (the default telnet escape character) generates a normal telnet prompt. These codes are accepted only at the beginning of a line.

-x

Turn on data-stream encryption if possible.

-X atype

Disable the atype type of authentication.

Name

telnetd

Synopsis

telnetd [options]

TCP/IP command. Telnet protocol server. telnetd is invoked by the Internet server for requests to connect to the Telnet port (port 23 by default). telnetd allocates a pseudo-terminal device for a client, thereby creating a login process that has the slave side of the pseudo-terminal serving as stdin, stdout, and stderr. telnetd manipulates the master side of the pseudo-terminal by implementing the Telnet protocol and by passing characters between the remote client and the login process.

The Telnet protocol is often criticized because it uses no encryption and makes it easy for snoopers to pick up user passwords. Most sites now use ssh instead.

Options

-a type

When compiled with authentication support, this option sets the authentication type. Accepted values are:

debug

Debug authentication code.

none

No authentication required, but accept it if offered. Use login for any further verification needed to access an account.

off

Disable authentication.

user

Allow only authenticated remote users with permission to access their accounts without giving a password.

valid

Allow only authenticated remote users. Use login for any additional verification needed to access an account.

-debug [port]

Start telnetd manually instead of through inetd. port may be specified as an alternate TCP port number on which to run telnetd.

-D modifier(s)

Debugging mode. This allows telnet to print out debugging information to the connection, enabling the user to see what telnet is doing. Several modifiers are available for the debugging mode:

netdata

Display data stream received by telnetd.

options

Print information about the negotiation of the Telnet options.

ptydata

Display data written to the pseudo-terminal device.

report

Print options information, as well as some additional information about what processing is going on.

-edebug

When compiled with support for encryption, enable encryption debugging code.

-h

Don’t print host-specific information until after login is complete.

-L path

Specify path to alternative login program. By default telnetd uses /bin/login.

-n

Disable checking for lost connections with TCP keep-alives.

-U

Refuse connections from IP addresses with no reverse DNS information.

-X type

Disable authentication type.

Name

test

Synopsis

test expression
[expression]

Evaluate an expression and, if its value is true, return a zero exit status; otherwise, return a nonzero exit status. In shell scripts, you can use the alternate form [expression]. This command is generally used with conditional constructs in shell programs. Also exists as a built-in in most shells.

File testers

The syntax for all of these options is test option file. If the specified file does not exist, they return false. Otherwise, they test the file as specified in the option description.

-b

Is the file block special?

-c

Is the file character special?

-d

Is the file a directory?

-e

Does the file exist?

-f

Is the file a regular file?

-g

Does the file have the set-group-ID bit set?

-G

Is the file owned by the process’s effective group ID?

-k

Does the file have the sticky bit set?

-L, -h

Is the file a symbolic link?

-O

Is the file owned by the process’s effective user ID?

-p

Is the file a named pipe?

-r

Is the file readable by the current user?

-s

Is the file nonempty?

-S

Is the file a socket?

-t [file-descriptor]

Is the file associated with file-descriptor (or 1, standard output, by default) connected to a terminal?

-u

Does the file have the set-user-ID bit set?

-w

Is the file writable by the current user?

-x

Is the file executable?

File comparisons

The syntax for file comparisons is test file1 option file2. A string by itself, without options, returns true if it’s at least one character long.

-ef

Do the files have identical device and inode numbers?

-nt

Is file1 newer than file2? Check modification date, not creation date.

-ot

Is file1 older than file2? Check modification date, not creation date.

String tests

The syntax for string tests is test option string or test string1 [!]= string2.

-n

Is the string at least 1 character long?

-z

Is the string 0 characters long?

string1 = string2

Are the two strings equal?

string1 != string2

Are the strings unequal?

Expression tests

Note that an expression can consist of any of the previous tests.

(expression)

Is the expression true?

! expression

Is the expression false?

expression -a expression

Are the expressions both true?

expression -o expression

Is either expression true?

Integer tests

The syntax for integer tests is test integer1 option integer2. You may substitute -l string for an integer; this evaluates to string’s length.

-eq

Are the two integers equal?

-ge

Is integer1 greater than or equal to integer2?

-gt

Is integer1 greater than integer2?

-le

Is integer1 less than or equal to integer2?

-lt

Is integer1 less than integer2?

-ne

Are the two integers unequal?

Name

time

Synopsis

time [options] command [arguments]

Run the specified command, passing it any arguments, and time the execution. Note that there is also a shell time command, so you might need to specify the full path, usually /usr/bin/time, to run this version of time. time displays its results on standard error. The output includes elapsed time, user CPU time, system CPU time, and other information such as memory used and number of I/O operations. The output can be formatted using printf format strings specified with the -f option or the TIME environment variable.

Options

--

The end of the options. Anything after the -- is treated as the command or one of its arguments.

-a, --append

Used with -o to append the output to file instead of overwriting it.

-f format, --format=format

Specify the output format. Overrides any format specified in the TIME environment variable.

--help

Print help message and exit.

-o file, --output=file

Send the output from time to the specified file instead of to standard error. If file exists, it is overwritten.

-p, --portability

Use portable output format (POSIX).

-v, --verbose

Give verbose output, providing all available information.

-V, --version

Print version information and exit.

Resources

The following resources can be specified in format strings:

c

Number of involuntary context switches because of time slice expiring.

C

Name and arguments of command being timed.

D

Average size of unshared data area, in kilobytes.

e

Elapsed real time, in seconds.

E

Elapsed real time as hours:minutes:seconds.

F

Number of major (I/O-requiring) page faults.

I

Number of filesystem inputs.

k

Number of signals delivered to the process.

K

Average total (data+stack+text) memory use, in kilobytes.

M

Maximum resident set size, in kilobytes.

O

Number of filesystem outputs.

p

Average unshared stack size, in kilobytes.

P

Percent of CPU used.

r

Number of socket messages received.

R

Number of minor (recoverable) page faults.

s

Number of socket messages sent.

S

Total CPU seconds used by the system on behalf of the process.

t

Average resident set size, in kilobytes.

U

Total CPU seconds used directly by the process.

w

Number of voluntary context switches.

W

Number of times the process was swapped out of main memory.

x

Exit status of the command.

X

Average shared text size, in kilobytes.

Z

System page size, in bytes.

Example

Time the execution of the command ls -l and display the user time, system time, and exit status of the command:

/usr/bin/time -f "\t%U user,\t%S system,\t%x status" ls -Fs

Name

tload

Synopsis

tload [options] [tty]

Display system load average in graph format. If tty is specified, print it to that terminal.

Options

-d delay

Specify the delay, in seconds, between updates.

-s scale

Specify scale (number of characters between each graph tick). A smaller number results in a larger scale.

-V

Print version information and exit.

Name

tmpwatch

Synopsis

tmpwatch [options] hours directory

System administration command. Recursively remove regular files and directories in directory with access times older than hours. Specify the directory as an absolute path. This command is usually invoked by cron to remove old files in the /tmp directory.

Options

-a, --all

Remove all file types.

-c, --ctime

Make decision on last inode change time for files and modification time for directories instead of access time.

-d, --nodirs

Do not remove directories.

-f, --force

Force removal of read-only files (similar to rm -f).

-l, --nosymlinks

Don’t remove symbolic links.

-m, --mtime

Make decision on last modification time instead of access time.

-M, --dirmtime

Make directory deletion decisions based on modification time.

-q, --quiet

Report only fatal errors.

-s, --fuser

Before deleting, attempt to use fuser to see if a file is in use.

-t, --test

Verbosely test command, but don’t actually remove files.

-u, --atime

Make decision on access time. (This is the default.)

-U user, --exclude-user user

Don’t delete files owned by user, specified by name or user ID.

-v, --verbose

Print more details. Use two times to further increase the detail of the output.

-x, --exclude=path

Skip the specified path, the absolute path of a directory or file.

Name

top

Synopsis

top [options]

Provide information (frequently refreshed) about the most CPU-intensive processes currently running. You do not need to include a - before options. See ps for explanations of the field descriptors.

Options

-b

Run in batch mode; don’t accept command-line input. Useful for sending output to another command or to a file.

-c

Show command line or program name in display. -c is a toggle; top starts with the last remembered setting.

-d delay

Specify delay between refreshes. Specify as ss.tt (seconds and tenths).

-f

Add or remove fields or columns.

-h

Print a help message and exit.

-H

Display either all individual threads or a summary of all threads in process. -H is a toggle; top starts with the last remembered setting.

-i

Suppress display of idle and zombie processes. -i is a toggle; top starts with the last remembered setting.

-n num

Update display num times, then exit.

-p pids

Monitor only processes with the specified process IDs.

-s

Secure mode. Disable some (dangerous) interactive commands.

-S

Cumulative mode toggle. Print total CPU time of each process, including dead child processes when on. top starts with the last remembered setting.

-u user

Monitor only processes with the specified effective UID or username.

-U user

Monitor only processes with the specified UID or username, matching real, effective, saved, and filesystem ids.

-v

Print version information and exit.

Interactive commands

=

Remove restrictions on which tasks are shown. Reverses the effect of an active i or n command.

space, Enter

Update display immediately.

<, >

Move the sort field. Use < to move one column left and > to move one column to the right.

A

Toggle alternate display mode between a single window or multiple windows. See the following section, Alternate display mode commands, for the commands that work with A.

b

Toggle between bold and reverse display. Only works with x and/or y.

B

Globally toggle bold display.

c

Toggle display of program name or full command line.

d, s

Change delay between refreshes. Prompt for new delay time, which should be in seconds. Suppressed in secure mode.

f

Prompt to add fields to or remove fields from the display.

F, O

Select sort field.

G

Select another field group and make it current, or change by selecting a number from the following list:

1

Def

2

Job

3

Mem

4

Usr

h, ?

Display help about commands and the status of secure and cumulative modes.

H

Toggle between displaying all individual threads and a summary of all threads in process.

I, 1

Toggle SMP view. Use I to toggle IRIX/Solaris mode (divide CPU usage by number of CPUs), 1 to toggle single/separate states.

k

Prompt for process ID to kill, and signal to send (default is SIGTERM) to kill it.

i

Toggle suppression of idle and zombie processes.

l

Toggle display of load-average and uptime information.

m

Toggle display of memory information.

n, #

Prompt for maximum number of processes to show. If 0 is entered, show as many as will fit on the screen (default).

o

Prompt to change order of displayed fields.

q

Exit.

r

Apply renice to a process. Prompt for PID and renice value. Suppressed in secure mode.

R

Toggle normal or reverse sort.

S

Toggle cumulative mode. (See the -S option.)

t

Toggle display of processes and CPU states lines.

u

Prompt for user to show; matches on effective UID.

U

Prompt for user to show; matches on real, effective, saved, and filesystem UID.

W

Write current setup to ˜/.toprc. This is the recommended way to write a top configuration file.

x

Toggle highlighting for sort field.

y

Toggle highlights for running tasks.

z

Toggle between color and mono display.

Z

Globally change color mappings.

Alternate display mode commands

=

Rebalance tasks in the current window.

+

Rebalance tasks in every window.

-

Show or hide the current window.

_

Show all invisible windows or hide all visible windows.

a

Cycle forward through all four windows.

g

Change the name of the current window or group.

w

Cycle backward through all four windows.

Field descriptions

The first five entries in the following list describe the lines that appear at the top of the top display. The rest are the fields that can be displayed for each task (sizes are in kilobytes). Use the interactive f command to add or remove fields.

top

Display the time the system has been up, the number of users, and three load averages consisting of the average number of processes ready to run in the last 1, 5, and 15 minutes.

Tasks

The total number of processes running when the last update was taken, shown as the number of running, sleeping, stopped, or undead tasks.

Cpu(s)

The percentage of CPU time spent in user mode, in system mode, on tasks with a negative nice value, and idle.

Mem

Memory statistics, including total available memory, free memory, memory used, shared memory, and memory used for buffers.

Swap

Swapspace statistics, including total, available, used, and cached.

PID

Process ID.

PPID

Parent process ID.

UID

Effective user ID of task’s owner.

USER

Effective username of task’s owner.

RUSER

Real username of task’s owner.

GROUP

The effective group name of task’s owner.

PR

Priority.

NI

Nice value.

nFLT

Page fault count.

CODE

Code size.

DATA

Data plus stack size.

RES

Resident task size.

SWAP

Size of swapped-out portion of task.

VIRT

The total amount of virtual memory used by the task.

nDRT

Number of pages marked dirty.

#C

Last-used processor, for multiprocessor systems.

SHR

Amount of shared memory used.

S

State of the task. Values are S (sleeping), D (uninterruptible sleep), R (running), Z (zombies), or T (stopped or traced).

WCHAN

Address or name of the kernel function in which the task is currently sleeping.

TIME

Total CPU time used by task and any children.

TIME+

Like TIME, but shows the time down to hundredths of a second.

%CPU

Share of CPU time since last update, as percentage of total CPU time.

%MEM

Share of physical memory.

TTY

Controlling tty.

COMMAND

Command line (truncated if too long) or name of program depending on the state of the C toggle. Processes with no command line are shown in parentheses.

FLAGS

Task flags.

Name

touch

Synopsis

touch [options] files

For one or more files, update the access time and modification time (and dates) to the current time and date. touch is useful in forcing other commands to handle files a certain way; for example, the operation of make, and sometimes find, relies on a file’s access and modification time. If a file doesn’t exist, touch creates it with a file size of 0.

Options

-a, --time=atime, --time=access, --time=use

Update only the access time.

-c, --no-create

Do not create any file that doesn’t already exist.

-d time, --date=time

Change the time value to the specified time instead of the current time. time can use several formats and may contain month names, time zones, a.m. and p.m. strings, etc.

-m, --time=mtime, --time=modify

Update only the modification time.

-r file, --reference=file

Change times to be the same as those of the specified file, instead of the current time.

-t time

Use the time specified in time instead of the current time. This argument must be of the format [[cc]yy]mmddhhmm[.ss], indicating optional century and year, month, date, hours, minutes, and optional seconds.

--help

Print help message and then exit.

--version

Print the version number and then exit.

Name

tr

Synopsis

tr [options] [string1 [string2]]

Translate characters. Copy standard input to standard output, substituting characters from string1 to string2, or deleting characters in string1.

Options

-c, -C, --complement

Complement characters in string1 with respect to ASCII 001–377.

-d, --delete

Delete characters in string1 from output.

-s, --squeeze-repeats

Squeeze out repeated output characters in string2.

-t, --truncate-set1

Truncate string1 to the length of string2 before translating.

--help

Print help message and then exit.

--version

Print the version number and then exit.

Special characters

Include brackets ([ ]) where shown.

\a

Ctrl-G (bell)

\b

Ctrl-H (backspace)

\f

Ctrl-L (form feed)

\n

Ctrl-J (newline)

\r

Ctrl-M (carriage return)

\t

Ctrl-I (tab)

\v

Ctrl-K (vertical tab)

\nnn

Character with octal value nnn

\\

Literal backslash

char1-char2

All characters in the range char1 through char2. If char1 does not sort before char2, produce an error.

[char*]

In string2, expand char to the length of string1.

[char*number]

Expand char to number occurrences. [x*4] expands to xxxx, for instance.

[:class:]

Expand to all characters in class, where class can be:

alnum

Letters and digits

alpha

Letters

blank

Whitespace

cntrl

Control characters

digit

Digits

graph

Printable characters except space

lower

Lowercase letters

print

Printable characters

punct

Punctuation

space

Whitespace (horizontal or vertical)

upper

Uppercase letters

xdigit

Hexadecimal digits

[=char=]

The class of characters to which char belongs.

Examples

Change uppercase to lowercase in a file:

cat file | tr 'A-Z' 'a-z'

Turn spaces into newlines (ASCII code 012):

tr ' ' '\012' < file

Strip blank lines from file and save in new.file:

cat file | tr -s "" "\012" > new.file

Delete colons from file and save result in new.file:

tr -d : < file > new.file

Name

tracepath

Synopsis

tracepath [options] host [port]

TCP/IP command. Trace path to host and report the Maximum Transmission Unit (MTU). A simplified version of traceroute without options meant for use by unprivileged users. If specified, it will use port to send UDP probe packets. host is the destination hostname or the IP number of the host to reach.

Options

-l n

Use alternative packet length of n. The default is 65536 for IPv4 and 128000 for IPv6.

-n

Don’t look up host names, just print IP addresses.

Name

traceroute

Synopsis

traceroute [options] host [packetsize]

TCP/IP command. Trace route taken by packets to reach network host. traceroute attempts tracing by launching UDP probe packets with a small TTL (time-to-live), then listening for an ICMP “time exceeded” reply from a gateway. host is the destination hostname or the IP number of the host to reach. packetsize is the packet size in bytes of the probe datagram. Default is 40 bytes.

Options

−4, −6

Force IPv4 or IPv6 tracerouting.

-A

Perform AS path lookups.

-d

Turn on socket-level debugging.

-e

Show ICMP extensions.

-f n

Set the initial time-to-live to n hops.

-F

Set the “don’t fragment” bit.

-g addr

Enable the IP LSRR (Loose Source Record Route) option in addition to the TTL tests, to ask how someone at IP address addr can reach a particular target.

-i interface

Specify the network interface for getting the source IP address for outgoing probe packets. Useful with a multihomed host. Also see the -s option.

-I

Use ICMP ECHO requests instead of UDP datagrams.

-m max_ttl

Set maximum time-to-live used in outgoing probe packets to max-ttl hops. Default is 30.

-n

Show numerical addresses; do not look up hostnames. (Useful if DNS is not functioning properly.)

-N n

Send n probe packets simultaneously. The default is 16.

-p port

Set base UDP port number used for probe packets to port. Default is (decimal) 33434.

-q n

Set number of probe packets per hop to the value n. Default is 3.

-r

Bypass normal routing tables and send directly to a host on an attached network.

-s src_addr

Use src_addr as the IP address that will serve as the source address in outgoing probe packets.

-t tos

Set the type-of-service in probe packets to tos (default is 0). The value must be a decimal integer in the range 0 to 255.

-T

Use TCP SYN packets instead. This may help bypass some firewall rules.

-v

Verbose; received ICMP packets (other than TIME_EXCEEDED and PORT_UNREACHABLE) will be listed.

-w wait

Set time to wait for a response to an outgoing probe packet to wait seconds (default is 5).

-x

Toggle IP checksums, usually to turn them off. IP checksums are always calculated if -I is specified.

-z msecs

Set the delay between probes, in milliseconds. The default is 0.

Name

troff

Synopsis

troff

See groff.

Name

true

Synopsis

true

A null command that returns a successful (0) exit status. See also false.

Name

tset

Synopsis

tset [options] [terminal]
reset [options] [terminal]

Initialize a terminal. The terminal to be initialized is whichever is found first from the value of terminal, the value of the TERM environment variable, or the default terminal type. See also the reset command.

Options

-c

Set control characters.

-echar

Set the erase character to char.

-ichar

Set the interrupt character to char.

-I

Do not send terminal or tab initialization strings to the terminal.

-kchar

Set line-kill character to char.

-m arg

Specify a mapping from a port type to a terminal, where arg looks like this:

[port_type][operator][baud_rate][:]terminal_type

operator can be any combination of < (less than), > (greater than), @ (equal), and ! (not). The terminal type is a string (e.g., vt100 or xterm).

-q

Print the terminal type on standard output but do not initialize the terminal.

-Q

Don’t display values for the erase, interrupt, and line kill characters.

-r

Print the terminal type to standard error.

-s

Print the shell commands that initialize the TERM environment variable on standard output.

-V

Print the version of ncurses used for this program and exit.

Name

tsort

Synopsis

tsort [option] [file]

Perform a topological sort on partially ordered strings in the specified file. If no file is specified or is -, read standard input. Multiple strings on a line are separated by spaces, where each line indicates a partial ordering. The fully ordered results are written to standard output. See the tsort info page for an example of the use of tsort for sorting lists of functions into the order they are called.

Options

--help

Print help information and exit.

--version

Print version information and exit.

Name

tty

Synopsis

tty [options]

Print the filename of the terminal connected to standard input.

Options

--help

Print help message and exit.

-s, --silent, --quiet

Print nothing to standard output, but return an exit status.

--version

Display version information and exit.

Name

tune2fs

Synopsis

tune2fs [options] device

System administration command. Tune the parameters of a Linux Second Extended Filesystem by adjusting various parameters. You must specify the device on which the filesystem resides; it must not be mounted read/write when you change its parameters.

Options

-c max-mount-counts

Specify the maximum number of mount counts between two checks on the filesystem.

-e behavior

Specify the kernel’s behavior when encountering errors. behavior must be one of:

continue

Continue as usual.

remount-ro

Remount the offending filesystem in read-only mode.

panic

Cause a kernel panic.

-f

Force completion even if there are errors.

-g group

Allow group (a group ID or name) to use reserved blocks.

-j

Add an ext3 journal to the filesystem. If specified without -J, use the default journal parameters.

-J jrnl-options

Specify ext3 journal parameters as a comma-separated list of option=value pairs. The specified options override the default values. Only one size or device option can be specified for a filesystem. Possible options are:

device=ext-jrnl

Attach to the journal block device on ext-jrnl, which must exist and must have the same block size as the filesystem to be journaled. ext-jrnl can be specified by its device name, by the volume label (LABEL=label), or by the Universal Unique Identifier (UUID) stored in the journal’s ext2 superblock (UUID=uuid; see uuidgen). Create the external journal with:

mke2fs -O
jrnl-devext-jrnl

size=jrnl-size

The size of the journal in megabytes. The size must be at least equivalent to 1024 blocks and not more than 102,400 blocks.

-l

Display a list of the superblock’s contents.

-L label

Specify the volume label of filesystem. The label must be no more than 16 characters.

-m percentage

Specify the percentage of blocks that will be reserved for use by privileged users.

-M dir

Specify the filesystem’s last-mounted directory.

-o mount-options

Set or clear the specified default mount-options. Mount options specified in /etc/fstab or on the command line for mount will override these defaults. Specify multiple options as a comma-separated list. Prefixing an option with a caret (^) clears the option. No prefix or a plus sign (+) causes the option to be set. The following options can be cleared or set:

acl

Enable Posix Acess Control Lists.

bsdgroups

Assign new files the group-id of the directory in which they are created instead of the group-id of the process creating them.

debug

Enable debugging code.

journal_data

When journaling, commit all data to journal before writing to the filesystem.

journal_data_ordered

When journaling, force data to the filesystem before committing metadata to the journal.

journal_data_writeback

When journaling, force data to the filesystem after committing metadata to the journal.

-O option

Set or clear the specified filesystem options in the filesystem’s superblock. Specify multiple options as a comma-separated list. Prefixing an option with a caret (^) clears the option. No prefix or a plus sign (+) causes the option to be set. Run e2fsck after changing filetype or sparse_super. The following options can be cleared or set:

dir_index

Use B-trees to speed up lookups on large directories.

filetype

Save file type information in directory entries.

has_journal

Create an ext3 journal. Same as the -j option.

sparse_super

Save space on large filesystems by limiting the number of backup superblocks. Same as -s.

-r num

Specify the number of blocks that will be reserved for use by privileged users.

-s [0|1]

Turn the sparse superblock feature on or off. Run e2fsck after changing this feature.

-u user

Allow user (a user ID or name) to use reserved blocks.

-U uuid

Set the UUID of the filesystem to a UUID generated by uuidgen or to one of the following:

clear

Clear the existing UUID.

random

Randomly generate a new UUID.

time

Generate a new time-based UUID.

Name

tunelp

Synopsis

tunelp device [options]

System administration command. Control a line printer’s device parameters. Without options, print information about device(s).

Options

-a [on|off]

Specify whether or not to abort if the printer encounters an error. By default, do not abort.

-c n

Retry device n times if it refuses a character. (Default is 250.) After exhausting n, sleep before retrying.

-i irq

Use irq for specified parallel port. Ignore -t and -c. If 0, restore noninterrupt-driven (polling) action.

-o [on|off]

Specify whether to abort if device is not online or is out of paper.

-q [on|off]

Specify whether to print current IRQ setting.

-r

Reset port.

-s

Display printer’s current status.

-t time

Specify a delay of time in jiffies to sleep before resending a refused character to the device. A jiffy is defined as either one tick of the system clock or one AC cycle time; it should be approximately 1/100 of a second.

-w time

Specify a delay of time in jiffies to sleep before resending a strobe signal.

Name

ul

Synopsis

ul [options] [filenames]

Translate underscores to underlining. The process will vary by terminal type. Some terminals are unable to handle underlining.

Options

-i

When on a separate line, translate - to underline instead of translating underscores.

-t terminal-type

Specify terminal type. By default, TERM is consulted.

Name

umount

Synopsis

umount [options] [directory]

System administration command. Unmount filesystem specified by directory. You may also specify the filesystem by device name. umount announces to the system that the removable file structure previously mounted on the specified directory is to be removed. Any pending I/O for the filesystem is completed, and the file structure is flagged as clean. A busy filesystem cannot be unmounted.

Options

-a

Unmount all filesystems listed in /etc/mtab other than /proc.

-d

If the unmounted device was a loop device, free the loop device too. See also the losetup command.

-f

Force the unmount. This option requires kernel 2.1.116 or later.

-h

Print help message and exit.

-i

Don’t execute /sbin/umount.<filesystem> helper programs.

-l

Lazy unmount. Detach the filesystem from the hierarchy immediately, but don’t clean up references until it is no longer busy. Requires kernel 2.4.11 or later.

-n

Unmount, but do not record changes in /etc/mtab.

-O options

Unmount only filesystems with the specified options in /etc/fstab. Specify multiple options as a comma-separated list. Add no as a prefix to an option to indicate filesystems that should not be unmounted.

-r

If unmounting fails, try to remount read-only.

-t type

Unmount only filesystems of type type. Multiple types can be specified as a comma-separated list, and any type can be prefixed with no to specify that filesystems of that type should not be unmounted.

-v

Verbose mode.

-V

Print version information and exit.

Name

uname

Synopsis

uname [options]

Print information about the machine and operating system. Without options, print the name of the kernel (Linux).

Options

-a, --all

Combine all the system information from the other options.

-i, --hardware-platform

Print the system’s hardware platform.

-m, --machine

Print the name of the hardware that the system is running on.

-n, --nodename

Print the machine’s hostname.

-o, --operating-system

Print the operating system name.

-p, --processor

Print the type of processor.

-r, --kernel-release

Print the release number of the kernel.

-s, --kernel-name

Print the name of the kernel (Linux). This is the default action.

-v, --kernel-version

Print build information about the kernel.

--help

Display a help message and then exit.

--version

Print version information and then exit.

Name

unexpand

Synopsis

unexpand [options] [files]

Convert strings of initial whitespace, consisting of at least two spaces and/or tabs, to tabs. Read from standard input if given no file or a file named -.

Options

-a, --all

Convert all, not just leading, strings of spaces and tabs.

--first-only

Convert only leading spaces and tabs. Overrides -a.

-t nums, --tabs nums

nums is a comma-separated list of integers that specify the placement of tab stops. If a single integer is provided, the tab stops are set to every integer spaces. By default, tab stops are eight spaces apart. This option implies -a.

--help

Print help message and then exit.

--version

Print the version number and then exit.

Name

unicode_start

Synopsis

unicode_start [font [umap]]

Put keyboard and console in Unicode mode, setting the font to font and the Unicode map to umap if the font doesn’t have its own map. If no font is specified, use the default.

Name

unicode_stop

Synopsis

unicode_stop

Take keyboard and console out of Unicode mode.

Name

uniq

Synopsis

uniq [options] [file1 [file2]]

Remove duplicate adjacent lines from sorted file1 or from standard input, sending one copy of each line to file2 (or to standard output). Often used as a filter. Specify only one of -d or -u. See also comm and sort.

Options

-c, --count

Print each line once, prefixing number of instances.

-d, --repeated

Print duplicate lines once but no unique lines.

-D, --all-repeated[=method]

Print all duplicate lines. -D takes no delimiter method. The delimiter method method takes one of the following values: none (default), prepend, or separate. Blank lines are used as the delimiter.

-f n, --skip-fields=n

Ignore first n fields of a line. Fields are separated by spaces or by tabs.

-i, --ignore-case

Ignore case differences when checking for duplicates.

-s n, --skip-chars=n

Ignore first n characters of a field.

-u, --unique

Print only unique lines (no copy of duplicate entries is kept).

-w n, --check-chars=n

Compare only first n characters per line (beginning after skipped fields and characters).

--help

Print a help message and then exit.

--version

Print version information and then exit.

Examples

Send one copy of each line from list to output file list.new:

uniq list list.new

Show which names appear more than once:

sort names | uniq -d

Name

unlink

Synopsis

unlink filename
unlink option

Remove the specified file using the system unlink function.

Options

--help

Print help information and exit.

--version

Print version information and exit.

Name

uptime

Synopsis

uptime [option]

Print the current time, how long the system has been running, the number of users currently logged in (which may include the same user multiple times), and system load averages. This output is also produced by the first line of w command output.

Option

-V

Print version information and exit.

Name

useradd

Synopsis

useradd [options] [user]

System administration command. Create new user accounts or update default account information. Unless invoked with the -D option, user must be given. useradd will create new entries in system files. Home directories and initial files may also be created as needed.

Options

-b dir, --base-dir dir

Specify base dir for home directories. The default is /home.

-c comment, --comment comment

Comment field.

-d dir, --home dir

Home directory. The default is to use user as the directory name under the home directory specified with the -D option.

-D [options]

Set or display defaults. If options are specified, set them. If no options are specified, display current defaults. The options are:

-b dir, --base-dir dir

Home directory prefix to be used in creating home directories. If the -d option is not used when creating an account, the user name is appended to dir.

-e date, --expiredate date

Expire date. Requires the use of shadow passwords.

-f days, --inactive days

Number of days after a password expires to disable an account. Requires the use of shadow passwords.

-g group, --gid group

Initial group name or ID number.

-s shell, --shell shell

Default login shell.

-e date, --expiredate date

Account expiration date. Use the format MM/DD/YYYY. Two-digit year fields are also accepted. The value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords.

-f days, --inactive days

Permanently disable account this many days after the password has expired. A value of −1 disables this feature. This option requires the use of shadow passwords.

-g group, --gid group

Initial group name or ID number. If a different default group has not been specified using the -D option, the default group is 1.

-G groups, --groups groups

Supplementary groups given by name or number in a comma-separated list with no whitespace.

-k [dir], --skel [dir]

Copy default files to the user’s home directory. Meaningful only when used with the -m option. Default files are copied from /etc/skel/ unless an alternate dir is specified.

-K key=value, --key key=value

Override /etc/login.defs defaults. This option can be given multiple times.

-l

Keep old entries for user in lastlog and faillog databases. By default old user data in these are reset.

-m, --create-home

Make user’s home directory if it does not exist. The default is not to make the home directory.

-M

Do not create a home directory for the user, even if the system default in /etc/login.defs is to create one.

-o, --non-unique

Override. Accept a nonunique uid with the -u option. (Probably a bad idea.)

-p passwd, --password passwd

The encrypted password, as returned by crypt(3).

-r, --system

Red Hat-specific option. Create a system account with a non-expiring password and a UID lower than the minimum defined in /etc/login.defs. Do not create a home directory for the account unless -m is also specified.

-s shell, --shell shell

Login shell.

-u uid, --uid uid

Numerical user ID. The value must be unique unless the -o option is used. The default value is the smallest ID value greater than 99 and greater than every other uid.

Name

userdel

Synopsis

userdel [option] user

System administration command. Delete all entries for user in system account files.

Option

-f, --force

Remove the user even if they are currently logged in. Remove home directory and mail spool even if they are used by another user. Remove group too, if USERGROUPS_ENAB is set to yes in /etc/login.defs.

-r, --remove

Remove the home directory of user and any files contained in it.

Name

usermod

Synopsis

usermod [options] user

System administration command. Modify user account information.

Options

-a, --append

Used with the -G option. Add user to the specified groups, but don’t remove user from groups not in the current list.

-c comment, --comment comment

Comment field.

-d dir, --home dir

Home directory.

-e date, --expiredate date

Account expiration date. date is in the format MM/DD/YYYY; two-digit year fields are also accepted. The value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords.

-f days, --inactive days

Permanently disable account this many days after the password has expired. A value of −1 disables this feature. This option requires the use of shadow passwords.

-g group, --gid group

Initial group name or number.

-G groups, --groups groups

Supplementary groups given by name or number in a comma-separated list with no whitespace. user will be removed from any groups to which it currently belongs that are not included in groups.

-l name, --login name

Login name. This cannot be changed while the user is logged in.

-L, --lock

Lock user’s password by putting a ! in front of it. This option cannot be used with -p or -U.

-o, --non-unique

Override. Accept a nonunique uid with the -u option.

-p pw, -password pw

Encrypted password, as returned from crypt(3).

-s shell, --shell shell

Login shell.

-u uid, --uid uid

Numerical user ID. The value must be unique unless the -o option is used. Any files owned by user in the user’s home directory will have their user ID changed automatically. Files outside of the home directory will not be changed. user should not be executing any processes while this is changed.

-U, --unlock

Unlock the user’s password by removing the ! that -L put in front of it. This option cannot be used with -p or -L.

Name

users

Synopsis

users [file]
users option

Print a space-separated list of each login session on the host. Note that this may include the same user multiple times. Consult file or, by default, /var/log/utmp or /var/log/wtmp.

Options

--help

Print usage information and exit.

--version

Print version information and exit.

Name

usleep

Synopsis

usleep [microseconds]
usleep [option]

Sleep some number of microseconds (default is 1).

Options

-?, --help

Print help information and then exit.

--usage

Print brief usage message and then exit.

-v, --version

Print version information.

Name

uuidgen

Synopsis

uuidgen [option]

Create a new Universal Unique Identifier (UUID) and print it to standard output. The generated UUID consists of five hyphen-separated groups of hex digits (e.g., 3cdfc61d-87d3-41b5-ba50-32870b33dc67). The default is to generate a random-based UUID, but this requires that a high-quality random-number generator be available on the system.

Options

-r

Generate a random-based UUID.

-t

Generate a time-based UUID.

Name

vdir

Synopsis

vdir [options] [files]

Verbosely list directory contents. Equivalent to ls -lb. By default, list the current directory. Directory entries are sorted alphabetically unless overridden by an option. vdir takes the same options as ls.

Name

vi

Synopsis

vi [options] [files]

A screen-oriented text editor based on ex. vi is bi-modal, with a command mode and an insert mode. For more information on vi, see Chapter 9.

Name

vidmode

Synopsis

vidmode [option] image [mode [offset]]

System administration command. Set the video mode for a kernel image. If no arguments are specified, print current mode value. mode is a 1-byte value located at offset 506 in a kernel image. You may change the mode by specifying the kernel image to change, the new mode, and the byte offset at which to place the new information (the default is 506). Note that rdev -v is a synonym for vidmode. If LILO is used, vidmode is not needed. The video mode can be set from the LILO prompt during a boot.

Modes

−3

Prompt

−2

Extended VGA

−1

Normal VGA

0

Same as entering 0 at the prompt

1

Same as entering 1 at the prompt

2

Same as entering 2 at the prompt

3

Same as entering 3 at the prompt

n

Same as entering n at the prompt

Option

-o offset

Same as specifying an offset as an argument.

Name

vim

Synopsis

vim

An enhanced version of the vi screen editor. Both vi and vim are covered in Chapter 9.

Name

vmstat

Synopsis

vmstat [options] [interval [count]]

System administration command. Print report on virtual memory statistics, including information on processes, memory, paging block I/O, traps, system and CPU usage. vmstat initially reports average values since the last system reboot. If given a sampling period interval in seconds, it prints additional statistics for each interval. If specified, vmstat exits when it has completed count reports. Otherwise, it continues until it receives a Ctrl-C, printing a new header line each time it fills the screen.

Options

-a

Display active and inactive memory.

-d

Display disk statistics.

-f

Display the number of forks since the system was booted.

-m

Display the names and sizes of various kernel objects stored in a cache known as the slab layer. Also see the slabtop command.

-n

Don’t print new header lines when the screen is full.

-p partition

Display detailed statistics for the specified partition.

-s

Display various event counters and memory statistics.

-S units

Switch the output units. Possible values are k, K, m, or M.

-t

Add a timestamp to output.

-V

Print version number, then exit.

VM mode fields

procs

r

Processes waiting for runtime.

b

Uninterruptible sleeping processes.

memory

swpd

Virtual memory used, in kilobytes.

free

Idle memory, in kilobytes.

buff

Memory used as buffers, in kilobytes.

cache

Cache memory, in kilobytes.

inactive

Inactive memory, in kilobytes, displayed with -a.

active

Active memory, in kilobytes; displayed with -a.

swap

si

Memory swapped in from disk each second, in kilobytes.

so

Memory swapped out to disk each second, in kilobytes.

io

bi

Blocks received from block devices each second.

bo

Blocks sent to block devices each second.

system

in

Interrupts per second, including clock interrupts.

cs

Context switches per second.

cpu

us

Percentage of CPU time consumed by user processes.

sy

Percentage of CPU time consumed by system processes.

id

Percentage of CPU time spent idle.

wa

Percentage of CPU time spent waiting for I/O.

Disk mode fields

Reads and Writes

total

Total reads or writes completed successfully.

merged

Reads or writes grouped into one I/O.

sectors

Sectors read or written successfully.

ms

Milliseconds spent reading or writing.

IO

cur

I/O in progress

s

Seconds spent doing I/O.

Disk partition mode fields

reads

Total reads issued to this partition.

read sectors

Total sectors read for this partition.

writes

Total writes issued to this partition.

requested writes

Total write requests for this partition.

Slab mode fields

cache

Cache name.

num

Number of currently active objects.

total

Total number of available objects.

size

Size of each object.

pages

Number of pages with at least one active object.

totpages

Total number of allocated pages.

pslab

Number of pages per slab.

Name

volname

Synopsis

volname [devfile]

Return the volume name for a device such as a CD-ROM that was formatted with an ISO-9660 filesystem. The default device file devfile is /dev/cdrom.

Name

w

Synopsis

w [options] [user]

Print summaries of system usage, currently logged-in users, and what those users are doing. w is essentially a combination of uptime, who, and ps -a. Display output for one user by specifying user.

Options

-f

Toggle printing the from (remote hostname) field.

-h

Suppress heading and uptime information.

-s

Use the short format.

-u

Ignore the username while figuring out the current process and CPU times.

-V

Display version information.

File

/var/run/utmp

List of users currently logged in.

Name

wall

Synopsis

wall [file]
wall [-n] [message]

Write to all users. Depending on your Linux distribution, wall uses one of the two syntaxes shown. In both versions, the default is for wall to read a message from standard input and send the message to all users currently logged in, preceded by “Broadcast Message from . . . .” With the first syntax, which comes with Debian-based systems, for example, if file is specified, wall reads input from that file rather than from standard input, and only the super-user can write to a terminal if the user has disallowed messages. With the second syntax, distributed with Red Hat-based systems, for example, the text of the message can be included on the command line, and the message is limited to 20 lines. In this form, if -n is specified, the default banner message is replaced with “Remote broadcast message.” -n can only be specified by the super-user, and only if wall was installed set-group-id.

Example

Send the message contained in the file message.txt to all users:

$ wall < message.txt

Name

warnquota

Synopsis

warnquota [options] [filesystem]

System administration command. Mail warning messages to users that have exceeded their soft limit.

Options

-a file, --admins-file=file

Read group administrator information from file instead of /etc/quotagrpadmins.

-c file, --config=file

Read configuration information from file instead of /etc/-warnquota.conf.

-d, --no-details

Send messages without attaching quota reports.

-F format, -format=format

Read quota information of the specified format. (See quota for valid formats.)

-g, --group

Send messages for group quotas. Send the message to the user specified in /etc/quotagrpadmins.

-i, --no-autofs

Ignore automount mount points.

-q file, -quota-tab=file

Read device description strings from file instead of /etc/quotagrpadmins.

-s, --human-readable

Report sizes in more human-readable units.

-u, --user

Send messages for user quotas. (This is the default.)

Name

watch

Synopsis

watch [options] command [cmd_options]

Run the specified command repeatedly (by default, every two seconds) and display the output so you can watch it change over time. The command and any options are passed to sh -c, so you may need to use quotes to get correct results.

Options

-d, --differences[=cumulative]

Highlight changes between iterations. If cumulative is specified, the highlighting remains on the screen throughout, giving a cumulative picture of the changes.

-h, --help

Display help message and exit.

-n secs, --interval=secs

Run the command every secs seconds.

-t, --no-title

Do not display the header or the blank line following the header.

-v, --version

Print version information and exit.

Name

wc

Synopsis

wc [options] [files]

Print byte, word, and line counts for each file. Print a total line for multiple files. If files is omitted or is -, read standard input. See other examples under ls and sort.

Options

-c, --bytes

Print byte count only.

-l, --lines

Print line count only.

-L, --max-line-length

Print length of longest line.

-m, --chars

Print character count only.

-w, --words

Print word count only.

--help

Print help message and then exit.

--version

Print the version number and then exit.

Examples

Count the number of users logged in:

who | wc -l

Count the words in three essay files:

wc -w essay.[123]

Count lines in the file named by variable $file (don’t display filename):

wc -l < $file

Name

wget

Synopsis

wget [options] [urls]

Perform noninteractive file downloads from the Web. wget works in the background and can be used to set up and run a download without the user having to remain logged on. wget supports HTTP, HTTPS, and FTP, as well as downloads through HTTP proxies. wget uses a global startup file that you may find at /etc/wgetrc or /usr/local/etc/wgetrc. In addition, users can define their own $HOME/.wgetrc files.

Options

−4, --inet4-only

Force connection to IPv4 hosts only.

−6, --inet6-only

Force connection to IPv6 hosts only.

-a logfile, --append-output=logfile

Append output messages to logfile, instead of overwriting the contents as -o does. If logfile doesn’t exist, create it.

-A acclist, --accept=acclist

Specify a comma-separated list of filename suffixes or patterns to accept.

-b, --background

Go into the background immediately after startup, writing output to the file specified with -o or to wget-log.

-B url, --base=url

Used with -F to prepend the specified URL to relative links in the input file specified with -i.

--bind-address=address

When making client TCP/IP connections, bind( ) to the specified local address, which can be specified as a hostname or IP address. Useful if your system is bound to multiple IP addresses.

-c, --continue

Continue getting a partially downloaded file. Affects the restarting of downloads from an earlier invocation of wget. Works only with FTP servers and HTTP servers that support the Range header.

--connect-timeout=seconds

Set the timeout for a connection to be established in seconds. The default is never to time out, unless a timeout is implemented by system libraries.

--cut-dirs=num

Ignore the specified number of directory components when creating the local directory structure.

-d, --debug

Turn on debugging. wget must have been compiled with debug support.

-D domainlist, --domains=domainlist

Specify a comma-separated list of domains to be followed. Does not turn on -H.

--delete-after

Delete each retrieved file from the local machine after downloading it. Useful for prefetching pages through a proxy. -k is ignored if specified with --delete-after.

--dns-timeout=seconds

Set the DNS lookup timeout to seconds. The default is to never time out.

-e command, --execute=command

Execute the specified command after the commands in .wgetrc, overriding any .wgetrc commands. Can be included multiple times, once for each command to execute.

-E, --html-extension

Append the suffix .html to the filenames of downloaded files where the URL does not include it (for example, an .asp file).

--exclude-domains=domainlist

Specify a comma-separated list of names that are never to be followed.

-F, --force-html

When reading input from a file, force the file to be treated as an HTML file.

--follow-ftp

Follow FTP links from HTML documents. The default is to ignore FTP links.

--follow-tags=list

Specify a comma-separated list of tags to be considered, overriding the internal table that wget normally uses during a recursive retrieval.

--ftp-user, --ftp-password

Specify the user name and password on an FTP server.

-h, --help

Display usage information and exit.

-H, --span-hosts

Enable spanning across hosts when doing recursive retrieval.

--header=header

Add an additional header to be passed to the HTTP server. The header must include a colon (:) preceded by at least one nonblank character, and with no newline characters. Can be specified multiple times. If header is an empty string, all user-defined headers are cleared.

--http-user=user, --http-password=password

Specify the username and password on an HTTP server.

-i file, --input-file=file

Read URLs from the specified file. URLs specified on the command line are accessed before URLs in the file. If file is given as -, read from standard input.

-I list, --include-directories=list

Specify a comma-separated list of directories to follow when downloading. The list elements may contain wildcards.

--ignore-case

Ignore case when matching files and directories. Affects the behavior of -A, -I, -R, -X, and FTP globbing.

--ignore-length

Ignore the “Content-Length” header on the HTTP server.

--ignore-tags=list

Specify a comma-separated list of tags to be ignored for recursive retrievals.

-k, --convert-links

Convert document links after the download is complete so they work locally.

-K, --backup-converted

When converting a file, back up the original and add an .orig suffix. Affects the behavior of -N.

--keep-session-cookies

Causes --save-cookies to also save session cookies.

-l depth, --level=depth

For recursive retrievals, specify the maximum recursion depth. The default depth is 5.

-L, --relative

Follow relative links only.

--limit-rate=rate

Set the maximum download speed, The default is to specify the rate in bytes, or add a k suffix for kilobytes or m for megabytes.

--load-cookies=file

Load cookies from the specified file before the first HTTP retrieval.

-m, --mirror

Turn on options suitable for mirroring a remote site. Equivalent to -r -N -l inf --no-remove-listing.

--max-redirect=num

Set the maximum number of redirections to follow (default is 20).

-N, --timestamping

Turn on timestamping.

-nc, --no-clobber

Do not download a file if there is already a copy on the disk. The default is to preserve the original copy and rename successive downloads, adding .1, .2, etc. to their name. May not be specified with -N.

-nd, --no-directories

Do not create a directory hierarchy when doing recursive retrievals.

-nH, --no-host-directories

Disable creation of directories prefixed by the name of the host. The default is to include the hostname.

--no-cache

Disable server-side cache for an HTTP retrieval. The default is for caching to be on.

--no-cookies

Disable the use of cookies.

--no-dns-cache

Disable caching of DNS lookups; look up hostname again for each new connection.

--no-glob

Turn off FTP globbing to prevent the use of wildcards for multiple file retrievals.

--no-http-keep-alive

Turn off the keep-alive feature for HTTP retrievals.

--np, --no-parent

In recursive retrievals, do not ever go up to the parent directory.

--no-passive-ftp

Do not allow use of passive FTP transfer mode.

--no-proxy

Do not use proxies.

--no-remove-listing

Do not remove the temporary .listing files generated by FTP retrievals.

-nv, --non-verbose

Turn off verbose mode, but don’t run completely quietly. Displays error messages and basic information.

-o logfile, --output-file=logfile

Log output messages to logfile, instead of the default standard error.

-O file, --output-document=file

Concatenate all documents into the specified file. If the file exists, it is overwritten. Specify the file as - to write to standard output.

-p, --page-requisites

Download all files necessary to display an HTML page.

-P prefix, --directory-prefix=prefix

Set the directory prefix to the specified value.

--post-data=string, --post-file=file

Use POST as the method for HTTP requests and send the specified data in the request body. Use --post-data to send string as data and --post-file to send the file contents.

--prefer-family=family

Connect to the addresses of the specified family first when there is a choice. The possible values for family are IPv4 (the default), IPv6, and none.

--progress=type[:style]

Set the progress indicator to type. Valid types are dot and bar; the default is bar. With --progress=dot, you can also set a style. The default style is for each dot to represent 1 KB, with 10 dots in a cluster and 50 dots per line. Alternatives are binary, with each dot representing 8 KB, 16-dot clusters, and 48 dots per line; mega, for downloading very large files, with each dot representing 64 KB, 8 dots per cluster, and 48 dots per line; and giga, with each dot representing 1 MB, 8 dots per cluster, and 4 clusters per line.

--protocol-directories

Use the protocol name as part of the local filename.

--proxy-user=user, --proxy-passwd=password

Specify the username and password for authentication on a proxy server.

-q, --quiet

Run quietly; don’t produce output.

-Q quota, --quota=quota

Specify download quota for automatic retrievals. The default value is in bytes; add k suffix for kilobytes, or m for megabytes.

-r, --recursive

Turn on recursive retrieving.

-R rejlist, --reject=rejlist

Specify a comma-separated list of filename suffixes or patterns to reject.

--random-wait

Set a random wait time to prevent being identified by websites that look for patterns in time between requests so they can block access.

--read-timeout=seconds

Set the read (and write) timeout to the specified number of seconds. The default is 900 seconds.

--referer=url

Include a “Referer: url” header in an HTTP request.

--restrict-file-names=mode[,nocontrol]

Restrict the characters found in remote URLs from appearing in local filenames. The value of mode is the operating system--e.g., unix or windows (use unix for Linux). Such characters are escaped with a percent sign (%). The default is to escape characters not valid on your operating system. Appending ,nocontrol turns off escaping of control characters.

--retr-symlinks

When retrieving FTP directories recursively, follow symbolic links and retrieve the linked-to files.

--retry-connrefused

Retry after getting a “connection refused” error. Useful for mirroring unreliable sites whose servers are likely to go down briefly.

-S, --server-response

Print HTTP server headers and FTP server responses.

--save-cookies=file

Save cookies in the specified file before exiting. Does not save expired cookies, and only saves session cookies if --keep-session-cookies is also specified.

--save-headers

Save the headers sent by an HTTP server to the file, preceding the contents and separated by a blank line.

--spider

Behave like a web spider, checking that pages exist but not downloading them.

--strict-comments

Turn on strict parsing of HTML comments, instead of terminating comments at the first occurrence of -->.

-t num, --tries=num

Set the number of retries to the specified value of num. Set num to 0 or inf to keep trying forever (infinitely) (default is 20 retries), unless there is a fatal error such as “connection refused.”

-T seconds, --timeout=seconds

Set network timeout to the specified number of seconds. Equivalent to specifying all of --dns-timeout, --connect-timeout, and --read-timeout.

--user=user, --password=password

Specify the user name and password for both FTP and HTTP file retrieval.

-U agent, --user-agent=agent

Specify an agent string to the HTTP server to replace the default identification of Wget/version, where version is the current wget version. This string is used in the User-Agent header field.

-v, --verbose

Turn on verbose output, printing all available data. This is the default.

-V, --version

Display version information and exit.

-w seconds, --wait=seconds

Specify the wait in seconds between retrievals. Used to lighten server load. Use the suffix m to specify the wait in minutes, h for hours, or d for days.

--waitretry=seconds

Specify the number of seconds to wait between retries if the download fails. The default in the global configuration file is not to wait.

-x, --force-directories

Create a hierarchy of directories even if one wouldn’t otherwise be created.

-X list, --exclude-directories=list

Specify a comma-separated list of directories to exclude from download. List elements may contain wildcards.

Name

whatis

Synopsis

whatis keywords

Search the short manual page descriptions in the whatis database for each keyword and print a one-line description to standard output for each match. Like apropos, except that it searches only for complete words. Equivalent to man -f.

Name

whereis

Synopsis

whereis [options] files

Locate the binary, source, and manual page files for specified commands/files. The supplied filenames are first stripped of leading pathname components and any (single) trailing extension of the form .ext (for example, .c). Prefixes of s. resulting from use of source code control are also dealt with. whereis then attempts to locate the desired program in a list of standard Linux directories (/bin, /etc, /usr/bin, /usr/local/bin/, etc.).

Options

-b

Search only for binaries.

-B directories

Change or otherwise limit the directories to search for binaries.

-f

Terminate the last directory list and signal the start of filenames. Required when the -B, -M, or -S option is used.

-m

Search only for manual sections.

-M directory

Change or otherwise limit the directories to search for manual sections.

-s

Search only for sources.

-S directory

Change or otherwise limit the directories to search for sources.

-u

Search for unusual entries--that is, files that do not have one entry of each requested type. Thus, the command whereis -m -u * asks for those files in the current directory that have no documentation.

Example

Find all files in /usr/bin that are not documented in /usr/share/man/man1 but that have source in /usr/src:

$ cd /usr/bin
$ whereis -u -M /usr/share/man/man1 -S /usr/src -f *

Name

which

Synopsis

which [options] [--
] [commands]

List the full pathnames of the files that would be executed if the named commands had been run. which searches the user’s $PATH environment variable.

Options

-a, --all

Print all matches, not just the first.

-i, --read-alias

Read aliases from standard input and write matches to standard output. Useful for using an alias for which.

--read-functions

Read shell functions from standard input and report matches to standard output. Useful for also using a shell function for which itself.

--skip-alias

Ignore --read-alias if present. Useful for finding normal binaries while using --read-alias in an alias for which.

--show-dot

If a matching command is found in a directory that starts with a dot, print ./cmdname instead of the full pathname.

--show-tilde

Print a tilde (˜) to indicate the user’s home directory. Ignored if the user is root.

--skip-dot

Skip directories that start with a dot.

--skip-functions

Ignore --read-functions if present. Useful when searching for normal binaries while using --read-functions in an alias or function for which.

--skip-tilde

Skip directories that start with a tilde (˜) and executables in $HOME.

--tty-only

Stop processing options on the right if not on a terminal.

-v, -V, --version

Print version information and then exit.

--help

Print help information and then exit.

Example

$ which cc ls
/usr/bin/cc
ls:      aliased to ls -sFC

Name

who

Synopsis

who [options] [file]
who am i

Show who is logged into the system. With no options, list the names of users currently logged in, their terminal, the time they have been logged in, and the name of the host from which they have logged in. An optional system file (default is /etc/utmp) can be supplied to give additional information.

Options

-a, --all

Equivalent to -b -d --login -p -r -t -T -u.

am i

Print information for the invoking user.

-b, --boot

Print time of last system boot.

-d, --dead

Print a list of dead processes.

-H, --heading

Print column headings.

--help

Print a help message and then exit.

-l, --login

Print list of system login processes.

--lookup

Attempt to include canonical hostnames via DNS.

-m

Same as who am i.

-p, --process

Print active processes spawned by init.

-q, --count

“Quick.” Display all usernames and the total number of users.

-r, --runlevel

Print the current runlevel.

-s, --short

Print only name, line, and time. This is the default behavior.

-t, --time

Print the last system clock change.

-u, --users

Print a list of the users who are logged in.

--version

Print version information and then exit.

-w, -T, --mesg, --message, --writable

Include user’s message status in the output:

+

mesg y (write messages allowed)

-

mesg n (write messages refused)

?

Cannot find terminal device

Example

This sample output was produced at 8 a.m. on April 17:

$ who -uH
NAME    LINE   TIME         IDLE   PID  COMMENTS
Earvin  ttyp3  Apr 16 08:14 16:25  2240
Larry   ttyp0  Apr 17 07:33   .   15182

Since Earvin has been idle since yesterday afternoon (16 hours), it appears that he isn’t at work yet. He simply left himself logged in. Larry’s terminal is currently in use.

Name

whoami

Synopsis

whoami

Print current user ID. Equivalent to id -un.

Name

whois

Synopsis

whois[options] query[@server[:port]]
jwhois [options] query[@server[:port]]

Search a whois database for a domain name, IP address, or NIC name. The information returned varies, but usually contains administrative and technical contacts so that you can find a person to handle problems at that domain. By default, the command returns information on .com, .net, and .edu domains, but other hosts can be queried for other domains using host or the -h option.

Options

--

Indicate the end of whois options. A subsequent string that begins with a hyphen on the command line is taken as a query string.

-a, --raw

Do not rewrite query according to configuration before sending to server.

-c file, --config=file

Specify a configuration file to use instead of the default /etc/jwhois.conf.

-d, --disable-cache

Disable reading and writing to the cache.

-f, --force-lookup

Force the lookup query to go to the host, even if it is available from the cache.

-h host, --host=host

Query the whois server on the specified host. Same as host on the command line. By default, queries the server in the environment variable NICNAMESERVER or WHOISSERVER if either is set; otherwise queries whois.internic.net.

--help

Print help message and exit.

-i, --display-redirections

Display every step in a redirection. The default is to display only the last step.

-n, --no-redirect

Disable redirection from one server to the next.

-p port, --port=port

Connect to the specified port. Same as port on the command line. Default is 43.

-r, --rwhois

Force use of the rwhois protocol, instead of HTTP or whois.

--rwhois-display=display

Request receiving rwhois servers to display the results in the specified display instead of the default.

--rwhois-limit=limit

Request receiving rwhois servers to limit the number of matches to the specified limit.

-s, --no-whoisservers

Disable built-in support for whois-servers.net.

-v

Verbose. Print debugging information while running. Specify -vv to increase verbosity.

--version

Print version information and exit.

Name

wodim

Synopsis

wodim [options] track1,track2...

Record data or audio CD or DVD media. This program normally requires root access to the device file; run as root or install suid-root. It has a large number of options and settings; see the manpage for a complete list as well as a number of useful examples.

General options

General option flags go directly after the wodim command and before any track options or arguments. The general options are:

-atip

Display the ATIP (Absolute Time In Pregroove) information for a disc. Not all drives allow you to read this information.

blank=type

Erase data from a CD-RW in one of the following ways:

all

Erase all information on the disc. May take a long time.

fast

Perform a quick erase of the disc, erasing only the PMA, TOC, and pregap.

help

Display a possible list of blanking methods.

session

Blank the last session.

track

Blank a track.

trtail

Blank the tail of a track only.

unclose

Unclose the last session.

unreserve

Unreserve a track previously marked as reserved.

-checkdrive

Check to see if there are valid drivers for the current drive. Returns 0 if the drive is valid.

-d, debug=n

Set the debug level to an integer (greater numbers are more verbose), or use multiple -d flags as with the -v and -V flags.

-dao, -sao

Disk-at-once (session-at-once) mode. Works only with MMC drives that support nonraw session-at-once modes.

dev=target

Set the SCSI target for the CD/DVD recorder. May be specified as a device name or as three comma-separated integers representing bus, target, and logical unit. To check the options that are available, use the -scanbus option. By default wodim looks in the CDR_DEVICE environment variable.

driver=name

Lets you specify a driver for your system. Suggested for experts only. The special drivers cdr_simul and dvd_simul are used for simulation and profiling tests if your drive does not support the -dummy option.

driveropts=optlist

Specify a comma-separated list of driver options. To get a list of valid options, use driveropts=help together with -checkdrive.

-dummy

Perform a dry run, doing all the steps of recording with the laser turned off. This will let you know whether the process is going to work.

-eject

Eject disc after recording. Some hardware may need to eject a disc after a dummy recording and before the actual recording.

-fix

Close (“fixate”) the session, preventing future multisession recordings and allowing the disc to be played in standard audio CD players (some can also play a disc that has not been closed).

-force

Override errors if possible. May allow you to blank an otherwise broken CD-RW.

fs=n

Set the FIFO buffer size to n, in bytes. You may use k, m, s, or f to specify kilobytes, megabytes, or units of 2048 and 2352 bytes, respectively. The default is 4 MB.

gracetime=n

Set the number of seconds of grace time before writing. The value of n should be at least 2 (default is 4 seconds).

kdebug=n, kd=n

Set the kernel’s debug notification value to n during SCSI command execution. Works through the usal-driver.

mcn=n

Set the Media Catalog Number to n.

msifile=file

Like -msinfo, but also saves the information in the specified file.

-msinfo

Get multisession information from the CD. Used only with multisession discs onto which you can still record more sessions.

-multi

Set to record in multisession mode. Must be present on all sessions but the last one for a multisession disc.

-nofix

Do not close the disc after writing.

-reset

Attempt to reset the SCSI bus. Does not work on all systems.

-s, -silent

Silent mode. Do not print any SCSI command errors.

speed=n

Set the speed to n, a multiple of the audio speed. Normally, wodim gets the speed from /etc/wodim.conf or the CDR_SPEED environment variable. If your drive has trouble with higher numbers, try 0 as a value.

timeout=n

Set the SCSI command timeout to n seconds. Defaults to 40.

-tao

Track-at-once (TAO) write mode. Most drives require TAO mode for multisession recording.

-toc

Display the table of contents for the CD currently in the drive. Works for CD-ROM, as well as CD-R and CD-RW drives.

ts=n

Set the maximum transfer size for a single SCSI command to n. Defaults to 63 KB.

-scanbus

Scan SCSI devices. Useful for finding the SCSI address of the drive.

-useinfo

Use .inf files to override audio options set elsewhere.

-v

Verbose mode. Use one v for each level of verbosity. -vv would be very verbose, and -vvv would be even more so.

-V

A verbose mode counter that applies only to SCSI transport messages. This slows the application but can be useful for debugging.

-version

Print version information and exit.

-waiti

Wait for input on standard input before opening the SCSI driver. Useful for letting wodim read input from a pipe while writing additional sessions to a multisession disk.

Track options and arguments

Track options may be mixed with track arguments, and normally apply to the track immediately after them or to all tracks after them. The track arguments themselves should be the files that you will be writing to the CD. Options are:

-audio

Write all tracks after this track in digital audio format (playable by standard CD players). If you do not use this flag or the -data flag, wodim assumes that .au and .wav files are to be recorded as raw audio and that all other files are data.

-cdi

Write subsequent tracks in CDI format. Use with XA disks only.

-data

Record subsequent tracks as CD-ROM data. If you do not use this flag or the -audio flag, all files except for those that end in .wav or .au are assumed to be data.

-index=a,b,c

Set the index list for the next track. The values should be increasing comma-separated integers, starting with index 1 and counting in sectors (75ths of a second). For example, you could set three indices in a track with index=0,750,7500 and they would occur at the beginning of the track, after 10 seconds, and after 100 seconds.

-isosize

The size of the next track should match the size of the ISO-9660 filesystem. This is used when duplicating CDs or copying from raw-data filesystems.

isrc=n

Set the International Standard Recording Number for the track argument following this option.

-mode2

Write all subsequent tracks in CD-ROM mode 2 format.

-nopad

Do not insert blank data between data tracks following this flag. This is the default behavior.

-pad

Insert 15 sectors of blank data padding between data tracks. Applies to all subsequent tracks or until you use the -nopad argument, and is overridden by the padsize=n argument.

padsize=n

Insert n sectors of blank data padding after the next track. Applies only to the track immediately after it.

-swab

Declare that your data is in byte-swapped (little-endian) byte order. This is not normally necessary.

tsize=n

Set the size of the next track. Useful only if you are recording from a raw disk for which wodim cannot determine the file size. If you are recording from an ISO 9660 filesystem, use the -isosize flag instead.

-xa, -xa1, -xa2

Write subsequent tracks in CD-ROM XA mode 2 format. -xa1 writes in mode 2 form 1 format, and subheaders must be supplied by the application providing the data. -xa and -xa2 write in mode 2 form 1 and mode 2 form 2, respectively, and subheaders are created by the drive.

Name

write

Synopsis

write user [tty]
message

Initiate or respond to an interactive conversation with user. A write session is terminated with EOF. If the user is logged into more than one terminal, specify a tty number. See also talk; use mesg to keep other users from writing to your terminal.

Name

xargs

Synopsis

xargs [options] [command]

Execute command (with any initial arguments), but read remaining arguments from standard input instead of specifying them directly. xargs passes these arguments in several bundles to the command, allowing it to process more arguments than it could normally handle at once. The arguments are typically a long list of filenames (generated by ls or find, for example) that get passed to xargs via a pipe. The default command is /bin/echo.

Options

−0, --null

Expect filenames to be terminated by NULL instead of whitespace. Do not treat quotes or backslashes specially.

-a file, --arg-file=file

Read arguments from file, not standard input.

-E string

Set EOF to string. Default is no EOF string.

--help

Print usage information and then exit.

-I string

Replace all occurrences of string in the initial arguments with names read from standard input. Unquoted blanks are not considered argument terminators; newline character is used. Implies -x and -L 1.

-L lines

Allow no more than lines nonblank input lines on the command line (default is 1). Implies -x.

-n args, --max-args=args

Allow no more than args arguments on the command line. Overridden by the maximum number of characters set with -s.

-p, --interactive

Prompt for confirmation (y or Y) before running each command line. Implies -t.

-P max, --max-procs=max

Allow no more than max processes to run at once. The default is 1. A maximum of 0 allows as many as possible to run at once.

-r, --no-run-if-empty

Do not run command if standard input contains only blanks.

-s max, --max-chars=max

Allow no more than max characters per command line.

--show-limits

Display upper and lower limits on command-line length (based on system limits, xarg buffer size, and -s if specified) before running the command.

-t, --verbose

Verbose mode. Print command line on standard error before executing.

-x, --exit

If the maximum size (as specified by -s) is exceeded, exit.

--version

Print the version number of xargs and then exit.

Examples

grep for pattern in all files on the system:

find / | xargs grep pattern> out &

Run diff on file pairs (e.g., f1.a and f1.b, f2.a and f2.b, etc.):

echo $* | xargs -n2 diff

The previous line would be invoked as a shell script, specifying -filenames as arguments. Display file, one word per line (same as deroff -w):

cat file | xargs -n1

Move files in olddir to newdir, showing each command:

ls olddir | xargs -i -t mv olddir/{  } newdir/{  }

Name

xinetd

Synopsis

xinetd [options]

TCP/IP command. The extended Internet services daemon. xinetd saves system resources by listening to multiple sockets on the behalf of other server programs, invoking necessary programs as requests are made for their services. Beyond this, xinetd provides better logging facilities, including remote user ID, access times, and server-specific information. It also provides access-control facilities. Not limited to system administration use, it can launch services that are not listed in /etc/services. Unprivileged users can use this tool to start their own servers.

Options

-cc num

Perform an internal-state consistency check every num seconds.

-d

Turn on debugging support.

-dontfork

Execute in the foreground. This option automatically sets the -stayalive option.

-f file

Read configuration from the specified file instead of /etc/xinetd.conf.

-filelog file

Write log messages to the specified file. Cannot be combined with -syslog or -d.

-inetd_compat

Read the /etc/inetd.conf file after reading /etc/xinetd.conf.

-limit num

Start no more than num concurrent processes.

-logprocs num

Limit processes used to look up remote user IDs to num.

-pidfile file

Write xinetd’s process ID to file.

-stayalive

Keep running even when no services have been specified.

-syslog facility

Log messages to the specified syslogd facility. Accepted values are daemon, auth, user, and localn, where n can range from 0 to 7. Cannot be combined with -syslog or -d. The default behavior is to write messages to syslogd using the daemon facility.

-version

Print version information, then exit.

Configuration files

By default xinetd reads its configuration information from file /etc/xinetd.conf. Lines in this file beginning with # are treated as comments. The entries for each service differ completely from /etc/inetd entries. xinetd configuration entries for services follow the pattern:

service servicename
{
attribute1 = valueset1
attribute2 = valueset2
}

Some attributes allow assignment operators other than =. Other operators are +=, to add to a value set, and -=, to remove a value from a value set. There are many attributes available to control services. The following are the most common:

cps

Limit incoming connection rate. Accepts two numeric arguments: the number of connections per second to allow and the number of seconds to wait to accept a new connection when the rate is exceeded. The default is 50 incoming connections and a 10-second wait.

disable

Accept a Boolean yes or no. When disabled, xinetd will ignore the entry.

flags

Accept a set of the following values defining xinetd’s behavior:

IDONLY

Accept only connections when the remote user’s ID can be verified by an identification server. Cannot be used with USERID logging.

INTERCEPT

Intercept packets to ensure they are coming from allowed locations. Cannot be used with internal or multithreaded services.

IPv4

Service is an IPv4 service.

IPv6

Service is an IPv6 service.

KEEPALIVE

Set flag on socket, enabling periodic checks to determine if the line is still receiving data.

NAMEINARGS

Expect the first argument for the server_args attribute to be the command to run. This flag is necessary to wrap services with tcpd.

NODELAY

Set socket’s NODELAY flag.

NOLIBWRAP

Don’t use xinetd’s internal TCP wrapping facilities.

NORETRY

If service fails to fork, don’t try to fork again.

SENSOR

Instead of launching a service, add IP addresses that attempt to access this service to a list of denied addresses for a time specified by the deny_time attribute.

group

Specify a group ID for the server process. This may be used only when xinetd runs as root.

nice

Set service priority. This attribute accepts the same values as the renice command.

id

Specify a unique identifier for the service. Useful when creating multiple entries with the servicename. For example, two versions of the echo service, one supporting UDP and the other TCP, might be given the identifiers echo-stream and echo-dgram.

log_on_failure

Specify values to log when a server cannot be started. Accepted values are HOST, USERID, or just ATTEMPT.

log_on_success

Specify values to log when a server is started. Accepted values are PID, HOST, USERID, EXIT, and DURATION.

no_access

Specify hosts that should not be allowed access to a service. May be given as an IP address, a netmask, a hostname, a network name from /etc/networks, or a group of IP addresses like so: 192.168.1.{10,11,12,15,32}.

only_from

Restrict access to the service to the specified hosts. This attribute accepts the same values as no_access.

per_source

Specify the maximum number of instances allowed to a single source IP address. The default is “UNLIMITED”.

port

Specify the service port to listen to. This attribute is required for non-RPC services not listed in /etc/services. If the service is listed, the value of port cannot differ from what is listed.

protocol

Specify protocol to use, usually tcp or udp. The protocol must be listed in /etc/protocols. This attribute is required for RPC services, as well as services not found in /etc/services.

rpc_version

The RPC version used by the service. This can be a single number or a range of numbers from x-y. This attribute is required for RPC services.

rpc_number

Specify RPC ID number. This is required only for services not listed in /etc/rpc; otherwise it’s ignored.

server

The program to execute for the service. When using tcpd to wrap a service, also set the NAMEINARGS flag and use the server’s program name as the first argument for server_args. This attribute is required for all noninternal services.

server_args

Arguments to pass to the server program.

socket_type

Specify the socket type to create. Accepted values are stream, dgram, raw, and seqpacket.

type

Describe the type of service. Accepted values are RPC, INTERNAL, and UNLISTED.

user

Specify a user ID for the server process. This may be used only when xinetd runs as root.

wait

Determine whether services should be treated as single-threaded (yes) and xinetd should wait until the server exits to resume listening for new connections, or multithreaded (no) and xinetd should not wait to resume listening. This attribute is required for all serices.

Files

/etc/xinetd.conf

Default configuration file.

/etc/xinetd.d

Common directory containing configuration files included from /etc/xinetd.conf.

Name

yacc

Synopsis

yacc [options] file

Given a file containing context-free grammar, convert file into tables for subsequent parsing, and send output to y.tab.c. This command name stands for yet another compiler-compiler. See also flex, bison, and the book lex & yacc (O’Reilly).

Options

-b prefix

Prepend prefix, instead of y, to the output file.

-d

Generate y.tab.h, producing #define statements that relate yacc’s token codes to the token names declared by the user.

-g

Generate a VCG description.

-l

Exclude #line constructs from code produced in y.tab.c. (Use after debugging is complete.)

-o outfile

Write generated code to outfile instead of the default y.tab.c.

-p prefix

Change the symbol yacc uses for symbols it generates from the default yy to prefix.

-t

Compile runtime debugging code.

-v

Generate y.output, a file containing diagnostics and notes about the parsing tables.

Name

yes

Synopsis

yes [strings]
yes [option]

Print the command-line arguments, separated by spaces and followed by a newline, until killed. If no arguments are given, print y followed by a newline until killed. Useful in scripts and in the background; its output can be piped to a program that issues prompts.

Options

--help

Print a help message and then exit.

--version

Print version information and then exit.

Name

ypbind

Synopsis

ypbind [options]

NFS/NIS command. NIS binder process. ypbind is a daemon process typically activated at system startup time. Its function is to remember information that lets client processes on a single node communicate with some ypserv process. The information ypbind remembers is called a binding — the association of a domain name with the Internet address of the NIS server and the port on that host at which the ypserv process is listening for service requests. This information is cached in the file /var/yp/binding/domainname.version.

Options

-broadcast

Ignore configuration information in /etc/yp.conf and directly request configuration information from a remote system using ypset.

-broken-server

Allow connections to servers using normally illegal port numbers. Sometimes needed for compatibility with other versions of ypserv.

-c

Check configuration file for syntax errors, then exit.

-debug

Run in the foreground process instead of detaching and running as a daemon.

-f file

Read configuration information from file instead of /etc/yp.conf.

-no-ping

Don’t ping remote servers to make sure they are alive.

--version

Print version information, then exit.

-ypset

Allow remote machine to change the local server’s bindings. This option is very dangerous and should be used only for debugging the network from a remote machine.

-ypsetme

ypset requests may be issued from this machine only. Security is based on IP address checking, which can be defeated on networks on which untrusted individuals may inject packets. This option is not recommended.

Name

ypcat

Synopsis

ypcat [options] map

NFS/NIS command. Print values in an NIS database specified by map name or nickname.

Options

-d domain

Specify domain other than the default domain.

-h host

Specify a ypbind host other than the default.

-k

Display keys for maps in which values are null or key is not part of value.

-t

Do not translate mname to map name.

-x

Display map nickname table listing the nicknames (mnames) known and map name associated with each nickname. Do not require an mname argument.

Name

ypinit

Synopsis

ypinit [options]

NFS/NIS command. Build and install an NIS database on an NIS server. ypinit can be used to set up a master server, slave server, or slave copier. Only a privileged user can run ypinit.

Options

-m

Indicate that the local host is to be the NIS master server.

-s master_name

Set up a slave server database. master_name should be the hostname of an NIS server, either the master server for all the maps, or a server on which the database is up to date and stable.

Name

ypmatch

Synopsis

ypmatch [options] key... mname

NFS/NIS command. Print value of one or more keys from an NIS map specified by mname. mname may be either a map name or a map nickname.

Options

-d domain

Specify domain other than default domain.

-k

Before printing value of a key, print the key itself, followed by a colon (:).

-t

Do not translate nickname to map name.

-x

Display map nickname table listing the nicknames (mnames) known, and the map name associated with each nickname. Do not require an mname argument.

Name

yppasswd

Synopsis

yppasswd [options] [name]

NFS/NIS command. Change login password in Network Information Service. Create or change your password, and distribute the new password over NIS. The superuser can change the password for any user. This command may also be invoked as ypchfn and ypchsh.

Options

-f

Update the password information field (the GECOS field). Using this option is the same as ypchfn.

-l

Update the login shell. Using this option is the same as ypchsh.

-p

Update the password. This is the default behavior for yppasswd.

Name

yppasswdd

Synopsis

rpc.yppasswdd [options]

NFS/NIS command. Server for modifying the NIS password file. yppasswdd handles password-change requests from yppasswd. It changes a password entry only if the password represented by yppasswd matches the encrypted password of that entry and if the user ID and group ID match those in the server’s /etc/passwd file. Then it updates /etc/passwd and the password maps on the local server. If the server was compiled with the CHECKROOT=1 option, the password is also checked against the root password.

Options

-D dir

Specify a directory that contains the passwd and shadow files for rpc.yppasswdd to use instead of /etc/passwd and /etc/shadow. Useful to prevent all users in the NIS database from automatically gaining access to the NIS server.

-e [chsh|chfn]

Permit users to change the shell or user information in the GECOS field of their passwd entry. By default, rpc.yppasswdd does not permit users to change these fields.

-E program

Specify a program to edit the passwd and shadow files instead of rpc.yppasswdd. The program should return 0 for successful completion; 1 for successful completion, but the pwupdate program should not be run to update the NIS server’s maps; and anything else if the change failed.

-p pwfile

Specify an alternative passwd file to /etc/passwd, to prevent all users in the NIS database from automatically gaining access to the NIS server.

--port num

Specify a port that rpc.yppasswdd will try to register itself, allowing a router to filter packets to the NIS ports.

-s shadowfile

Use shadowfile instead of /etc/passwd for shadow password support.

-v

Print version information and whether the package was compiled with CHECKROOT.

-x program

Modify files using the specified program instead of using internal default functions. rpc.yppasswdd passes information to program in the following format:

username o:oldpassword p:password s:shell g:gcos

Any of the fields p, s, or g may be missing.

Name

yppoll

Synopsis

yppoll [options] map

NFS/NIS command. Determine version of NIS map at NIS server. yppoll asks a ypserv process for the order number and the hostname of the master NIS server for the map.

Options

-h host

Ask the ypserv process at host about the map parameters. If host is not specified, the hostname of the NIS server for the local host (the one returned by ypwhich) is used.

-d domain

Use domain instead of the default domain.

Name

yppush

Synopsis

yppush [options] mapnames

NFS/NIS command. Force propagation of changed NIS map. yppush copies a new version of an NIS map, mapname, from the master NIS server to the slave NIS servers. It first constructs a list of NIS server hosts by reading the NIS map ypservers with the -d option’s domain argument. Keys within this map are the ASCII names of the machines on which the NIS servers run. A map transfer request is sent to the NIS server at each host, along with the information needed by the transfer agent to call back to yppush. When the attempt has been completed and the transfer agent has sent yppush a status message, the results may be printed to standard error. Normally invoked by /var/yp/Makefile after commenting out the NOPUSH=true line.

Options

-d domain

Specify a domain.

-h host

Specify one or a group of systems to which a map should be transferred instead of using the list of servers in the ypservers map. Multiple -h options can be specified to create a list of hosts.

-p count, --parallel count

Send maps to count NIS slaves simultaneously (in parallel). By default, yppush sends maps to one server at a time (serially).

--port num

Specify a port to listen on for callbacks. This will not work when sending maps in parallel. By default, the command chooses a random port.

-t secs

Specify a timeout value in seconds. The timeout determines how long yppush will wait for a response from a slave server before sending a map transfer request to the next server. The default timeout is 90 seconds, but for big maps a longer timeout may be needed.

-v

Verbose; print message when each server is called and for each response. Specify twice to make yppush even more verbose.

Name

ypserv

Synopsis

ypserv [options]

NFS/NIS command. NIS server process. ypserv is a daemon process typically activated at system startup time. It runs only on NIS server machines with a complete NIS database. Its primary function is to look up information in its local database of NIS maps. The operations performed by ypserv are defined for the implementor by the NIS protocol specification, and for the programmer by the header file <rpcvc/yp_prot.h>. Communication to and from ypserv is by means of RPC calls. On startup or when receiving the signal SIGHUP, ypserv parses the file /etc/ypserv.conf. ypserv supports securenets, which can be used to restrict access to a given set of hosts.

Options

-d [path], --debug [path]

Run in debugging mode without going into background mode, and print extra status messages to standard error for each request. If path is specified, use it instead of /var/yp.

-i interface, --iface interface

Only provide service on the specified network interface.

-p port, --port port

Bind to the specified port. For use with a router to filter packets so that access from outside hosts can be restricted.

-v, --version

Print version information and exit.

Files and directories

/etc/yp.conf

Configuration file.

/var/yp/domainname

Location of NIS databases for domainname.

/var/yp/Makefile

Makefile that is responsible for creating NIS databases.

/var/yp/securenets

securenets information containing netmask/network pairs separated by whitespace.

Name

ypset

Synopsis

ypset [options] server

NFS/NIS command. Point ypbind at a particular server. ypset tells ypbind to get NIS services for the specified domain from the ypserv process running on server. server indicates the NIS server to bind to and can be specified as a name or an IP address.

Options

-d domain

Use domain instead of the default domain.

-h host

Set ypbind’s binding on host instead of the local host. host can be specified as a name or an IP address.

Name

yptest

Synopsis

yptest [options]

NFS/NIS command. Check configuration of NIS services by calling various NIS functions. Without arguments, yptest queries the NIS server for the local machine.

Options

-d domainname

Use domainname instead of the current host’s default domain. This option may cause some tests to fail.

-h host

Test ypserv on the specified host instead of the current host. This option may cause some tests to fail.

-m map

Use the specified map instead of the default map.

-q

Quiet mode. Print no messages.

-u user

Run tests as user instead of as nobody.

Name

ypwhich

Synopsis

ypwhich [options] [host]

NFS/NIS command. Return hostname of NIS server or map master. Without arguments, ypwhich cites the NIS server for the local machine. If host is specified, that machine is queried to find out which NIS master it is using.

Options

-d domain

Use domain instead of the default domain.

-m [map]

Find master NIS server for a map. No host can be specified with -m. map may be a map name or a nickname for a map. If no map is specified, display a list of available maps.

-t mapname

Inhibit nickname translation.

-Vn

Version of ypbind (default is v2).

-x

Display map nickname table. Do not allow any other options.

Name

ypxfr

Synopsis

ypxfr [options] mapname

NFS/NIS command. Transfer an NIS map from the server to the local host by making use of normal NIS services. ypxfr creates a temporary map in the directory /var/yp/domain (where domain is the default domain for the local host), fills it by enumerating the map’s entries, and fetches the map parameters and loads them. If run interactively, ypxfr writes its output to the terminal. However, if it is invoked without a controlling terminal, its output is sent to syslogd.

Options

-c

Do not send a “Clear current map” request to the local ypserv process.

-C tid prog ipadd port

This option is for use only by ypserv. When ypserv invokes ypxfr, it specifies that ypxfr should call back a yppush process at the host with IP address ipadd, registered as program number prog, listening on port port, and waiting for a response to transaction tid.

-d domain

Specify a domain other than the default domain.

-f

Force the transfer to occur even if the version on the master server is older than the local version.

-h host

Get the map from host instead of querying NIS for the map’s master server. host may be specified by name or IP address.

-p dir

Use dir as the path to the NIS map directory instead of /var/yp.

-s domain

Specify a source domain from which to transfer a map that should be the same across domains (such as the services.byname map).

Name

ypxfrd

Synopsis

rpc.ypxfrd [options]

NFS/NIS command. This server is used to copy a master’s NIS map using an RPC based file transfer program instead of building a local map the way ypxfr would. This will speed up the transfer of large maps.

Options

--debug

Debug mode. Do not fork.

-d dir

Use dir instead of /var/yp.

-p port

Bind to the specified port.

-v, --version

Print version information and exit.

Name

zcat

Synopsis

zcat [options] [files]

Read one or more files that have been compressed with gzip or compress and write them to standard output. Read standard input if no files are specified or if - is specified as one of the files; end input with EOF. zcat is identical to gunzip -c and takes the options described for gzip/gunzip.

Name

zcmp

Synopsis

zcmp [options] files

Read compressed files and pass them uncompressed to the cmp command, along with any command-line options. If a second file is not specified for comparison, look for a file called file.gz.

Name

zdiff

Synopsis

zdiff [options] files

Read compressed files and pass them, uncompressed, to the diff command, along with any command-line options. If a second file is not specified for comparison, look for a file called file.gz.

Name

zforce

Synopsis

zforce [names]

Rename all gzipped files to filename.gz, unless file already has a .gz extension.

Name

zgrep

Synopsis

zgrep [options] [files]

Uncompress files and pass to grep, along with any command-line arguments. If no files are provided, read from (and attempt to uncompress) standard input. May be invoked as zegrep or zfgrep and will in those cases invoke egrep or fgrep.

Name

zless

Synopsis

zless files

Uncompress files and allow paging through them. Equivalent to running zmore with the environment variable PAGER set to less. See zmore for the available commands.

Name

zmore

Synopsis

zmore [files]

Similar to more. Uncompress files and print them one screenful at a time. Works on files compressed with compress, gzip, or pack, and with uncompressed files. The argument i in the following zmore commands is an optional integer argument.

Commands

space

Print next screenful.

ispace

Print next i lines.

Return

Print one more line.

id, i^D

Print next i, or 11, lines.

iz

Print next i lines or a screenful. If i is specified, treat it as the new window size for the rest of the current file, then revert to the default.

is

Skip i lines, then print the next screenful.

if

Skip i screens, then print the next screenful.

q, Q, :q, :Q

Go to next file or, if current file is the last, exit zmore.

e, q

Exit zmore when the prompt “--More-- (Next file: file)” is displayed.

s

Skip next file and continue when the prompt “--More-- (Next file: file)” is displayed.

=

Print line number.

i/expr

Search forward for ith occurrence (in all files) of expr, which should be a regular expression. Display occurrence, including the two previous lines of context.

in

Search forward for the ith occurrence of the last regular expression searched for.

!command

Execute command in shell. If command is not specified, execute last shell command. To invoke a shell without passing it a command, enter \!.

.

Repeat the previous command.

Name

znew

Synopsis

znew [options] [files]

Uncompress .Z files and recompress them in .gz format.

Options

−9

Optimal (and slowest) compression method.

-f

Recompress even if filename.gz already exists.

-K

If the original .Z file is smaller than the .gz file, keep it.

-P

Pipe data to conversion program. This saves disk space.

-t

Test new .gz files before removing .Z files.

-v

Verbose mode.

Chapter 4. Boot Methods

This chapter describes techniques for booting your Linux system. Depending on your hardware and whether you want to run any other operating systems, you can configure the system to automatically boot Linux or to provide a choice between several operating systems. Choosing between operating systems is generally referred to as dual booting, although you can select between more than two. We talk more about dual booting in the section Dual-Booting Linux and Windows 2000/XP/Vista in Dual-Booting Linux and Windows 2000/XP/Vista.

An alternative to dual booting is virtualization, where you run one or more virtual operating systems inside a real operating system. The real system is known as the host, and the virtual systems are known as guests. Virtualization makes it easy to switch between systems without having to reboot. Two ways to run virtual systems are to make Linux the host system with another operating system running in a virtual machine. See Chapter 15 for an overview of virtualization concepts and for information on how to run guest systems under Linux. You can also run Linux as a guest with another operating system such as Windows as the host. Two ways to do this are with Microsoft’s Virtual PC and VMware server. Both are free downloads and are available at www.microsoft.com and www.vmware.com, respectively.

Once your Linux system is installed, rebooting the system is generally straightforward. There are several possibilities for configuring your boot process. The most common choices are:

- Boot Linux from a bootable disk, most likely a CD or an installation CD/DVD, leaving another operating system to boot from the hard drive.

- Use the Linux Loader, LILO. This used to be the traditional method of booting and lets you boot both Linux and other operating systems.

- Use GRUB (GRand Unified Bootloader), the GNU graphical boot loader and command shell. Like LILO, GRUB lets you boot both Linux and other operating systems. GRUB, which has additional functionality not found in LILO, is now the de facto Linux boot loader.

Whatever method you choose for booting, be sure to have a working boot disk available for emergency use. In particular, don’t experiment with the files and options in this chapter unless you have a boot disk, because any error could leave you unable to boot from the hard disk. Note, though, that one of the advantages of using GRUB is that if there is a problem booting from the menu, it drops you down to the command-line interface so you can enter commands directly and try to recover. In addition, your distribution CD or DVD undoubtedly has a recovery option on it. Or you can boot from a live Linux CD such as Knoppix.

The Boot Process

On an x86-based PC, the first sector of every hard disk is known as the boot sector and contains the partition table for that disk and possibly also code for booting an operating system. The boot sector of the first hard disk is known as the master boot record (MBR), because when you boot the system, the BIOS transfers control to a program that lives on that sector along with the partition table. That code is the boot loader, the code that initiates an operating system. When you add Linux to the system, you need to modify the boot loader, replace it, or boot from a floppy or CD to start Linux.

In Linux, each disk and each partition on the disk is treated as a device. For example, the entire first hard disk is known as /dev/hda, and the entire second hard disk is /dev/hdb. The first partition of the first hard drive is /dev/hda1, and the second partition is /dev/hda2. The first partition of the second hard drive is /dev/hdb1, and so on. If your drives are SCSI or SATA instead of IDE, the naming works the same way, except that the devices are /dev/sda, /dev/sda1, and so on. Thus, if you want to specify that the Linux partition is the second partition of the first hard drive (as in the examples in this chapter), you refer to it as /dev/hda2. Note that GRUB has its own disk naming convention, described later in this chapter in GRUB: The Grand Unified Bootloader in GRUB: The Grand Unified Bootloader.

Once you’ve made the decision to install LILO or GRUB, you still need to decide how it should be configured. Most Linux distributions will automatically set up the booting environment for you, whether you are installing Linux as the primary operating system or into a dual-booting environment (or in a virtual guest system where the real MBR is not modified). If for some reason your distribution doesn’t do it for you, or you want to do it manually, the rest of this chapter will help you. If your distribution does set up the boot environment for you, you might still want to read the sections on LILO or GRUB to find out how the customize your boot loader.

If you want your system to dual-boot Linux and Windows, you need to know that Windows has its own loader installed on the MBR, and it expects that loader to be in charge. The standard solution described in this chapter is to add Linux as an option in the Windows loader and install LILO or GRUB in the Linux partition as a secondary boot loader. The result is that the Windows loader transfers control to the secondary loader, which then boots Linux. See Dual-Booting Linux and Windows 2000/XP/Vista in Dual-Booting Linux and Windows 2000/XP/Vista for more information. You can also install one of the Linux boot loaders in the MBR and use it to boot Windows. (See the “Linux+WinNT” and the “Multiboot with GRUB” mini-HOWTOs at the Linux Documentation Project [www.tldp.org] if you’re interested in doing that.)

When you install the boot loader (either LILO or GRUB) on the MBR, it replaces the Windows boot loader. If you have problems with your installation or you simply want to restore the original boot loader, you can do one of the following:

- If you’re running LILO, you can boot Linux from a boot disk (CD or floppy) and restore the boot sector, which LILO automatically backs up:

$ /sbin/lilo -u

- For Windows 2000, XP, and Vista, boot your computer from the Windows CD. When you see “Welcome to Setup,” press R (for repair) and, in Windows 2000, then press C. Select your Windows installation from the numbered list that is displayed (there may be only one entry) and enter the administrator password at the prompt. Enter the command fixmbr at the command-line prompt and confirm it with y. After the MBR has been restored, type exit to reboot.

The common element in both methods is that they replace the boot loader on the MBR with the original Microsoft boot loader.

Whatever boot loader is on the MBR is the one that will be used to boot the system. This means that if you want to switch from LILO to GRUB, say, or from GRUB to LILO, you don’t need to uninstall the old loader; simply install the new one.

The rest of this chapter describes the various techniques for booting Linux and the options that you can specify to configure both the boot loader and the Linux kernel. Whether you use GRUB or LILO, you can pass options to the loader and specify options for the kernel.

LILO: The Linux Loader

In addition to booting Linux, LILO can boot other operating systems, such as Windows or any of the BSD systems. During installation, some Linux distributions provide the opportunity to install LILO (most now install GRUB by default). LILO can also be installed later if necessary. LILO can be installed on the MBR of your hard drive or as a secondary boot loader on the Linux partition. LILO consists of several pieces, including the boot loader itself, a configuration file (/etc/lilo.conf), a map file (/boot/map) containing the location of the kernel, and the lilo command (/sbin/lilo), which reads the configuration file and uses the information to create or update the map file and to install the files LILO needs.

One thing to remember about LILO is that it has two aspects: the boot loader and the lilo command. The lilo command configures and installs the boot loader and updates it as necessary. The boot loader is the code that executes at system boot time and boots Linux or another operating system.

You can make a rescue CD for LILO with the LILO command mkrescue --iso to make an image that can be burned to CD. Use mkrescue by itself or with other options to make a rescue floppy disk. See the mkrescue manpage for more information.

The LILO Configuration File

The lilo command reads the LILO configuration file, /etc/lilo.conf, to get the information it needs to install LILO. Among other things, it builds a map file containing the locations of all disk sectors needed for booting.

Note that any time you change /etc/lilo.conf or rebuild or move a kernel image, you need to rerun lilo to rebuild the map file and update LILO.

The configuration file starts with a section of global options, described in the next section. Global options are those that apply to every system boot, regardless of the operating system you are booting. Here is an example of a global section (a hash sign, #, begins a comment):

boot=/dev/hda           # The boot device is /dev/hda
map=/boot/map           # Save the map file as /boot/map
install=/boot/boot.b    # The file to install as the new boot sector
prompt                  # Always display the boot prompt
timeout=30              # Set a 3-second (30 tenths of a second) timeout

Following the global section, there is one section of options for each Linux kernel and for each non-Linux operating system that you want LILO to be able to boot. Each of these sections is referred to as an image section because each boots a different kernel image (shorthand for a binary file containing a kernel) or another operating system. Each Linux image section begins with an image= line.

image=/boot/vmlinuz     # Linux image file
label=linux          # Label that appears at the boot prompt
root=/dev/hda2       # Location of the root filesystem
vga=ask              # Always prompt the user for VGA mode
read-only            # Mount read-only to run fsck for a filesystem check

The equivalent section for a non-Linux operating system begins with other= instead of image=. For example:

other=/dev/hda1         # Location of the partition
label=winxp
table=/dev/hda       # Location of the partition table

Put LILO configuration options that apply to all images into the global section of /etc/lilo.conf, and options that apply to a particular image into the section for that image. If an option is specified in both the global section and an image section, the setting in the image section overrides the global setting for that image.

Here is an example of a complete /etc/lilo.conf file for a system that has the Linux partition on /dev/hda2:

## Global section
boot=/dev/hda2
map=/boot/map
delay=30
timeout=50
prompt
vga=ask

## Image section: For regular Linux
image=/boot/vmlinuz
label=linux
root=/dev/hda2
install=/boot/boot.b
map=/boot/map
read-only

## Image section: For testing a new Linux kernel
image=/testvmlinuz
label=testlinux
root=/dev/hda2
install=/boot/boot.b
map=/boot/map
read-only
optional               # Omit image if not available when map is built

## Image section: For booting Windows XP
other=/dev/hda1
label=winxp
loader=/boot/chain.b
table=/dev/hda         # The current partition table

Global options

In addition to the options listed here, the kernel options append, read-only, read-write, root, and vga (described later in Kernel options in Kernel options) can also be set as global options.

backup=backup-file

Copy the original boot sector to backup-file instead of to /boot/boot.nnnn, where nnnn is a number that depends on the disk device type.

boot=boot-device

Set the name of the device that contains the boot sector. boot defaults to the device currently mounted as root, such as /dev/hda2. Specifying a device such as /dev/hda (without a number) indicates that LILO should be installed in the master boot record; the alternative is to set it up on a particular partition, such as /dev/hda2.

change-rules

Begin a section that redefines partition types at boot time for hiding and unhiding partitions. See the LILO User’s Guide, which comes with the LILO distribution, for detailed information on using this option and creating a new rule set.

compact

Merge read requests for adjacent disk sectors to speed up booting. Use of compact is particularly recommended when booting from a floppy disk. Use of compact may conflict with linear.

default=name

Use the image name as the default boot image. If default is omitted, the first image specified in the configuration file is used.

delay=tsecs

Specify, in tenths of a second, how long the boot loader should wait before booting the default image. If serial is set, delay is set to a minimum of 20. The default is not to wait. See Boot-Time Kernel Options in Boot-Time Kernel Options for ways to get the boot prompt if no delay is set.

disk=device-name

Define parameters for the disk specified by device-name if LILO can’t figure them out. Normally, LILO can determine the disk parameters itself, and this option isn’t needed. When disk is specified, it is followed by one or more parameter lines, such as:

disk=/dev/sda
bios=0x80      # First disk is usually 0x80, second is usually 0x81
sectors=...
heads=...

Note that this option is not the same as the disk geometry parameters you can specify with the hd boot command-line option. With disk, the information is given to LILO; with hd, it is passed to the kernel. Note also that if either heads or sectors is specified, they must both be specified. The parameters that can be specified with disk are listed briefly here; they are described in detail in the LILO User’s Guide.

bios=bios-device-code

The number the BIOS uses to refer to the device. See the previous example.

cylinders=cylinders

The number of cylinders on the disk.

heads=heads

The number of heads on the disk.

inaccessible

Tell LILO that the BIOS can’t read the disk; used to prevent the system from becoming unbootable if LILO thinks the BIOS can read it. If this parameter is specified, it must be the only parameter.

partition=partition-device

Start a new section for a partition. The section contains one variable, start=partition-offset, which specifies the zero-based number of the first sector of the partition:

partition=/dev/sda1
start=2048

sectors=sectors

The number of sectors per track.

disktab=disktab-file

This option has been superseded by the disk= option.

fix-table

If set, allow lilo to adjust 3-D addresses (addresses specified as sector/head/cylinder) in partition tables. This is sometimes necessary if a partition isn’t track-aligned and another operating system is on the same disk. See the lilo.conf manpage for details.

force-backup=backup-file

Like backup, but overwrite an old backup copy if one exists.

ignore-table

Tell lilo to ignore corrupt partition tables.

install=boot-sector

Install the specified file as the new boot sector. If install is omitted, the boot sector defaults to /boot/boot.b.

lba32

Generate 32-bit Logical Block Addresses instead of sector/head/cylinder addresses, allowing booting from any partition on hard disks greater than 8.4 GB (i.e., remove the 1024-cylinder limit). Requires BIOS support for the EDD packet call interface[2] and at least LILO version 21–4.

linear

Generate linear sector addresses, which do not depend on disk geometry, instead of 3-D (sector/head/cylinder) addresses. If LILO can’t determine your disk’s geometry itself, you can try using linear; if that doesn’t work, then you need to specify the geometry with disk=. Note, however, that linear sometimes doesn’t work with floppy disks, and it may conflict with compact.

lock

Tell LILO to record the boot command line and use it as the default for future boots until it is overridden by a new boot command line. lock is useful if there are kernel options that you need to enter on the boot command line every time you boot the system.

map=map-file

Specify the location of the map file. Defaults to /boot/map. The map file records the location of the kernel(s) used on the system.

message=message-file

Specify a file containing a message to be displayed before the boot prompt. The message can include a formfeed character (Ctrl-L) to clear the screen. The map file must be rebuilt by rerunning the lilo command if the message file is changed or moved. The maximum length of the file is 65,535 bytes.

nowarn

Disable warning messages.

optional

Specify that any image that is not available when the map is created should be omitted and not offered as an option at the boot prompt. Like the per-image option optional, but applies to all images.

password=password

Specify a password that the user is prompted to enter when trying to load an image. The password is not encrypted in the configuration file, so if passwords are used, permissions should be set so that only the superuser is able to read the file. This option is like the per-image version, except that all images are password-protected and they all have the same password.

prompt

Automatically display the boot prompt without waiting for the user to press the Shift, Alt, or Scroll Lock key. Note that setting prompt without also setting timeout prevents unattended reboots.

restricted

Can be used with password to indicate that a password needs to be entered only if the user specifies parameters on the command line. Like the per-image restricted option, but applies to all images.

serial=parameters

Allow the boot loader to accept input from a serial line as well as from the keyboard. Sending a break on the serial line corresponds to pressing a Shift key on the console to get the boot loader’s attention. All boot images should be password-protected if serial access is insecure (e.g., if the line is connected to a modem). Setting serial automatically raises the value of delay to 20 (i.e., two seconds) if it is less than that. The parameter string parameters has the following syntax:

port[,bps[parity[bits]]]

For example, to initialize COM1 with the default parameters:

serial=0,2400n8

The parameters are:

port

The port number of the serial port. The default is 0, which corresponds to COM1 (/dev/ttys0). The value can be one of 0 through 3, for the four possible COM ports.

bps

The baud rate of the serial port. Possible values of bps are 110, 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200. The default is 2400 bps.

parity

The parity used on the serial line. Parity is specified as n or N for no parity, e or E for even parity, and o or O for odd parity. However, the boot loader ignores input parity and strips the 8th bit.

bits

Specify whether a character contains 7 or 8 bits. Default is 8 with no parity and 7 otherwise.

timeout=tsecs

Set a timeout (specified in tenths of a second) for keyboard input. If no key has been pressed after the specified time, the default image is booted automatically. timeout is also used to determine when to stop waiting for password input. The default timeout is infinite.

verbose=level

Turn on verbose output, where higher values of level produce more output. If -v is also specified on the lilo command line, the level is incremented by 1 for each occurrence of -v. The maximum verbosity level is 5.

Image options

The following options are specified in the image section for a particular boot image. The image can be a Linux kernel or a non-Linux operating system.

alias=name

Provide an alternate name for the image that can be used instead of the name specified with the label option.

image=pathname

Specify the file or device containing the boot image of a bootable Linux kernel. Each per-image section that specifies a bootable Linux kernel starts with an image option. See also the range option.

label=name

Specify the name that is used for the image at the boot prompt. Defaults to the filename of the image file (without the path).

loader=chainloader

For a non-Linux operating system, specify the chain loader to which LILO should pass control for booting that operating system. The default is /boot/chain.b. If the system will be booted from a drive that is neither the first hard disk nor a floppy or CD, the chainloader must be specified.

lock

Like lock, as described in the previous global options section; it can also be specified in an image section.

optional

Specify that the image should be omitted if it is not available when the map is created by the lilo command. Useful for specifying test kernels that are not always present.

other=pathname

Specify the path to a file that boots a non-Linux system. Each per-image section that specifies a bootable non-Linux system starts with an other option.

password=password

Specify that the image is password-protected and provide the password that the user is prompted for when booting. The password is not encrypted in the configuration file, so if passwords are used, permissions should be set so only the superuser can read the file.

range=sectors

Used with the image option, when the image is specified as a device (e.g., image=/dev/fd0), to indicate the range of sectors to be mapped into the map file. sectors can be given as the range start-end or as start+number, where start and end are zero-based sector numbers and number is the increment beyond start to include. If only start is specified, only that one sector is mapped. For example:

image=/dev/fd0
range=1+512   # take 512 sectors, starting with sector 1

restricted

Specify that a password is required for booting the image only if boot parameters are specified on the command line.

table=device

Specify, for a non-Linux operating system, the device that contains the partition table. If table is omitted, the boot loader does not pass partition information to the operating system being booted. Note that /sbin/lilo must be rerun if the partition table is modified. This option cannot be used with unsafe.

unsafe

Can be used in the per-image section for a non-Linux operating system to indicate that the boot sector should not be accessed when the map is created. If unsafe is specified, then some checking isn’t done, but the option can be useful for running the lilo command without having to insert a floppy disk when the boot sector is on a fixed-format floppy disk device. This option cannot be used with table.

Kernel options

The following kernel options can be specified in /etc/lilo.conf as well as on the boot command line:

append=string

Append the options specified in string to the parameter line passed to the kernel. This typically is used to specify certain hardware parameters. For example, while BIOSes on modern systems can recognize more than 64 MB of memory, BIOSes on older systems were limited to 64 MB. If you are running Linux on such a system, you can use append:

append="mem=128M"

initrd=filename

Specify the file to load into /dev/initrd when booting with a RAM disk. See also the options load_ramdisk (in Boot-Time Kernel Options in Boot-Time Kernel Options) and prompt_ramdisk, ramdisk_size, and ramdisk_start in this section.

literal=string

Like append, but replace all other kernel boot options.

noinitrd

Preserve the contents of /dev/initrd so they can be read after the kernel is booted.

prompt_ramdisk=n

Specify whether the kernel should prompt you to insert the floppy disk that contains the RAM disk image, for use during Linux installation. Values of n are:

0

Don’t prompt. Usually used for an installation in which the kernel and the RAM disk image both fit on one floppy.

1

Prompt. This is the default.

ramdisk_size=n

Specify the amount of memory, in kilobytes, to be allocated for the RAM disk. The default is 4096, which allocates 4 MB.

ramdisk_start=offset

Used for a Linux installation in which both the kernel and the RAM disk image are on the same floppy. offset indicates the offset on the floppy where the RAM disk image begins; it is specified in kilobytes.

read-only

Specify that the root filesystem should be mounted read-only for filesystem checking (fsck), after which it is typically remounted read/write.

read-write

Specify that the root filesystem should be mounted read/write.

root=root-device

Specify the device that should be mounted as root. If the special name current is used as the value, the root device is set to the device on which the root filesystem currently is mounted. Defaults to the root-device setting contained in the kernel image.

vga=mode

Specify the VGA text mode that should be selected when booting. The mode defaults to the VGA mode setting in the kernel image. The values are case-insensitive. They are:

ask

Prompt the user for the text mode. Pressing Enter in response to the prompt displays a list of the available modes.

extended (or ext)

Select 80 × 50 text mode.

normal

Select normal 80 × 25 text mode.

number

Use the text mode that corresponds to number. A list of available modes for your video card can be obtained by booting with vga=ask and pressing Enter.

[2] As long as your BIOS is dated after 1998, it should include EDD packet call interface support.

The lilo Command

You need to run the lilo command to install the LILO boot loader and to update it whenever the kernel changes or to reflect changes to /etc/lilo.conf. Note that if you replace your kernel image without rerunning lilo, your system may be unable to boot.

The path to the lilo command is usually /sbin/lilo. The syntax of the command is:

lilo [options]

Some of the options correspond to /etc/lilo.conf keywords:

Configuration keyword

Command option

boot=bootdev

-b bootdev

compact

-c

delay=tsecs

-d tsecs

default=label

-D label

disktab=file

-f file

install=bootsector

-i bootsector

lba32

-L

linear

-l

map=mapfile

-m mapfile

fix-table

-P fix

ignore-table

-P ignore

backup=file

-s file

force-backup=file

-S file

verbose=level

-v

These options should be put in the configuration file whenever possible; putting them on the lilo command line instead of in /etc/lilo.conf is deprecated. The next section describes those options that can be given only on the lilo command line; the others were described earlier.

lilo Command Options

The following list describes lilo command options that are available only on the command line. Multiple options are given separately; for example:

$ lilo -q -v

-C config-file

Specify an alternative to the default configuration file (/etc/lilo.conf). lilo uses the configuration file to determine which files to map when it installs LILO.

-I label

Print the path to the kernel specified by label to standard output, or an error message if no matching label is found. For example:

$ lilo -I linux
/boot/vmlinuz-2.0.34-0.6

-q

List the currently mapped files. lilo maintains a file (/boot/map by default) containing the name and location of the kernel(s) to boot. Running lilo with this option prints the names of the files in the map file to standard output, as in this example (the asterisk indicates that linux is the default):

$ lilo -q
linux     *
test

-r root-directory

Specify that before doing anything else, lilo should chroot to the indicated directory. Used for repairing a setup from a boot CD or floppy; you can boot from that disk but have lilo use the boot files from the hard drive. For example, if you issue the following commands, lilo will get the files it needs from the hard drive:

$ mount /dev/hda2 /mnt
$ lilo -r /mnt

-R command-line

Set the default command for the boot loader the next time it executes. The command executes once and then is removed by the boot loader. This option typically is used in reboot scripts, just before calling shutdown -r.

-t

Indicate that this is a test--do not really write a new boot sector or map file. Can be used with -v to find out what lilo would do during a normal run.

-u device-name

Uninstall lilo by restoring the saved boot sector from /boot/boot.nnnn, after validating it against a timestamp. device-name is the name of the device on which LILO is installed, such as /dev/hda2.

-U device-name

Like -u, but do not check the timestamp.

-V

Print the lilo version number.

LILO Boot Errors

As LILO loads itself, it displays the letters of the word LILO, one at a time as it proceeds. Once LILO is correctly loaded, you’ll see the full word printed on the screen. If nothing prints, then LILO has not been loaded at all; most likely LILO isn’t installed or it is installed, but on a partition that is not active. If LILO started loading, but there was a problem, you can see how far it got by how many letters printed:

L

The first stage boot loader is loaded and running, but it can’t load the second stage. There should be an error code indicating the type of problem; usually the problem is a media failure or bad disk parameters. See the LILO User’s Guide for the meaning of the error codes.

LI

The first stage boot loader loaded the second stage but was not able to run it. The problem is most likely bad disk parameters or the file /boot/boot.b (the boot sector) was moved but the lilo command wasn’t run.

LIL

The second stage boot loader was run, but it couldn’t load the descriptor table from the map file. This is usually caused by a media failure or bad disk parameters.

LIL?

The second stage boot loader was loaded at an incorrect address, probably because of bad disk parameters or by moving /boot/boot.b without running lilo.

LIL-

The descriptor table is corrupt. The problem is probably bad disk parameters or moving /boot/map without running lilo.

LILO

LILO was successfully loaded.

GRUB: The Grand Unified Bootloader

Like LILO, the GRUB boot loader can load other operating systems in addition to Linux. GRUB has become the default bootloader for most Linux variants. It was written by Erich Boleyn to boot operating systems on PC-based hardware and is now developed and maintained by the GNU project. GRUB was intended to boot operating systems that conform to the Multiboot Specification, which was designed to create one booting method that would work on any conforming PC-based operating system. In addition to multiboot-conforming systems, GRUB can boot directly into Linux, FreeBSD, OpenBSD, and NetBSD. It can also boot other operating systems such as Microsoft Windows indirectly, through the use of a chainloader. The chainloader loads an intermediate file, and that file loads the operating system’s boot loader.

GRUB provides a graphical menu interface. It also provides a command interface that is accessible both while the system is booting (the native command environment) and from the command line once Linux is running.

While LILO works perfectly well, especially if you usually boot the default image, GRUB has some advantages. The graphical menu interface shows you exactly what your choices are for booting, so you don’t have to remember them. It also lets you easily edit an entry on the fly, or drop down into the command interface. In addition, if you are using the menu interface and something goes wrong, GRUB automatically puts you into the command interface so you can attempt to recover and boot manually. Another advantage of GRUB is that if you install a new kernel or update the configuration file, that’s all you have to do; with LILO, you also have to remember to rerun the lilo command to reinstall the boot loader. On the other hand, if you are used to LILO, don’t need to see the prompts often, and have a stable system, LILO is quick and convenient.

A GRUB installation consists of at least two and sometimes three executables, known as stages. The stages are:

Stage 1

Stage 1 is the piece of GRUB that resides in the MBR or the boot sector of another partition or drive. Since the main portion of GRUB is too large to fit into the 512 bytes of a boot sector, Stage 1 is used to transfer control to the next stage, either Stage 1.5 or Stage 2.

Stage 1.5

Stage 1.5 is loaded by Stage 1 only if the hardware requires it. Stage 1.5 is filesystem-specific; that is, there is a different version for each filesystem that GRUB can load. The name of the filesystem is part of the filename (e2fs_stage1_5, fat_stage1_5, etc.). Stage 1.5 loads Stage 2.

Stage 2

Stage 2 runs the main body of the GRUB code. It displays the menu, lets you select the operating system to be run, and starts the system you’ve chosen.

If it was compiled with netboot support, GRUB can also be used to boot over a network. We don’t describe that process here; see the file netboot/README.netboot in the GRUB source directory for detailed information.

One of the first things to understand about GRUB is that it uses its own naming conventions. Drives are numbered starting from 0; thus, the first hard drive is hd0, the second hard drive is hd1, the first floppy drive is fd0, and so on. Partitions are also numbered from 0, and the entire name is put in parentheses. For example, the first partition of the first drive, /dev/hda1, is known as (hd0,0) to GRUB, and the third partition of the second drive is (hd1,2). GRUB makes no distinction between drive types; thus the first drive is hd0 regardless of whether it is IDE, SCSI, or SATA.

Files are specified either by the filename or by blocklist, which is used to specify files such as chainloaders that aren’t part of a filesystem. A filename looks like a standard Unix path specification with the GRUB device name prepended; for example:

(hd0,0)/grub/grub.conf

If the device name is omitted, the GRUB root device is assumed. The GRUB root device is the disk or partition where the kernel image is stored, set with the root command. See GRUB Commands in GRUB Commands for the command descriptions.

When you use blocklist notation, you tell GRUB which blocks on the disk contain the file you want. Each section of a file is specified as the offset on the partition where the block begins plus the number of blocks in the section. The offset starts at 0 for the first block on the partition. The syntax for blocklist notation is:

[device][offset+length[,offset]+length...

In this case, too, the device name is optional for a file on the root device. With blocklist notation, you can also omit the offset if it is 0. A typical use of blocklist notation is when using a chainloader to boot Windows. If GRUB is installed in the MBR, you can chainload Windows by setting the root device to the partition that has the Windows boot loader, making it the active partition, and then using the chainloader command to read the Windows boot sector:

rootnoverify (hd0,0)
makeactive
chainloader +1

In this example, the blocklist notation (+1) does not include either the device name or the offset because we set the root device to the Windows partition, and the Windows loader begins at offset 0 of that partition.

GRUB also includes a device map. The device map is an ASCII file, usually /boot/grub/device.map. Since the operating system isn’t loaded yet when you use GRUB to boot Linux (or any other operating system), GRUB knows only the BIOS drive names. The purpose of the device map is to map the BIOS drives to Linux devices. For example:

(fd0)   /dev/fd0
(hd0)   /dev/hda

Installing GRUB

Installing GRUB involves two stages. First, you install the GRUB files on your system, either by compiling and installing the source tarball or from a package. That puts the GRUB files in the correct locations on your system. The second step is to install the GRUB software as your boot manager. This is the step we describe in this section.

If you installed GRUB as part of your Linux installation, the distribution’s installation program took care of both stages of installing GRUB, and you’ll see the GRUB menu when you boot Linux. If you didn’t install GRUB as part of your Linux installation, you have two choices. The easiest way to install GRUB is with the grub-install shell script that comes with GRUB. If grub-install doesn’t work, or if you want to do the installation manually, you can run the grub command and issue the installation commands yourself.

The following sections describe how to create a GRUB boot CD, a GRUB boot floppy, and how to install GRUB. You can create a GRUB boot disk for everyday use or to have for an emergency.

Creating a GRUB boot CD

The following instructions make a CD that boots to GRUB:

1. Make a directory that will hold the GRUB iso image to be written to CD:

$ mkdir -p grubiso/boot/grub     # make parent dirs if needed

2. Copy the file stage2_eltorito[3] to the new directory from the directory where GRUB was installed (in this example /usr/lib/grub/x86_64-pc):

$ cp /usr/lib/grub/x86_64-pc grubiso/boot/grub

You can move other files to the directory as well, such as menu.lst to display the menu when you boot.

3. Run genisoimage to make an ISO9660 image file, grub.iso:

$ genisoimage -R -b boot/grub/stage2_eltorito -no-emul-boot \
-boot-load-size 4 -boot-info-table -o grub.iso grubiso

This command takes the contents of grubiso/boot/grub (only the top of the directory tree needs to be specified) and makes the image file grub.iso. See the genisoimage command in Chapter 3 for information on the options.

4. The image file can now be burned onto a CD (or DVD) with the burning software of your choice.

Creating a GRUB boot floppy

The following instructions make a floppy that boots to the GRUB command line:

1. From the directory where GRUB was installed (e.g., /usr/share/grub/i386-pc), use the dd command to write the file stage1 to the floppy:

$ dd if=stage1 of=/dev/fd0 bs=512 count=1

This command writes one block, with a block size of 512, from the input file stage1 to the floppy device /dev/fd0.

2. Now write the file stage2 to the floppy, skipping over the first block (seek=1) so you don’t overwrite stage1:

$ dd if=stage2 of=/dev/fd0 bs=512 seek=1

Put together, the process looks like this:

$ dd if=stage1 of=/dev/fd0 bs=512 count=1
1+0 records in
1+0 records out
$ dd if=stage2 of=/dev/fd0 bs=512 seek=1
254+1 records in
254+1 records out

The boot floppy is now ready to boot to the GRUB command line.

You can also make a boot floppy that boots to the GRUB menu:

1. Create a GRUB configuration file (/boot/grub/menu.lst) if you don’t already have one. The configuration file is described later in The GRUB Configuration File in The GRUB Configuration File.

2. Create a filesystem on your floppy disk. For example:

$ mke2fs /dev/fd0

3. Mount the floppy drive and create the directory /boot/grub:

$ mount /mnt
$ mkdir /mnt/boot
$ mkdir /mnt/boot/grub

4. Copy the stage1, stage2, and grub.conf GRUB images from /boot/grub on your Linux partition to /mnt/boot/grub.

5. Run the grub command. This example assumes the command is in /sbin/grub, but it might be in /usr/sbin/grub on your system:

$ /sbin/grub --batch <<EOT
root (fd0)
setup (fd0)
quit
EOT

You should now be able to boot to the GRUB menu from the floppy disk you just created.

Using grub-install

GRUB comes with a shell script, grub-install, which uses the GRUB shell to automate the installation. The command syntax is:

grub-install options install-device

where install-device is the name of the device on which you want to install GRUB, specified as either the GRUB device name (e.g., (hd0)) or the system device (e.g., /dev/hda). For example, you might issue the following command (as root):

$ grub-install /dev/hda

This command installs GRUB into the MBR of the first hard drive. The grub-install options are:

--force-lba

Force GRUB to use LBA mode, to allow booting from partitions beyond cylinder 1024.

--grub-shell=file

Specify that file is to be used as the GRUB shell. You might want to use this option to append options to grub. For example:

$ grub-install --grub-shell="grub --read-only" /dev/fd0

-h, --help

Print a help message on standard output and exit.

--recheck

Force probing of a device map. You should run grub-install with this option if you add or remove a disk from your system. The device map is found at /boot/grub/device.map.

--root-directory=dir

Install GRUB images in the directory dir instead of the GRUB root directory.

-v, --version

Print the GRUB version number to standard output and exit.

Installing from the GRUB command line

To install GRUB from the native command environment, make a GRUB boot disk as described previously. You will use that disk to boot to the GRUB command line to do the installation. If you know which partition holds the GRUB files, you’re all set. Otherwise, you can find the partition with the find command:

grub> find /boot/grub/stage1
(hd0,0)

Here, the files are on (hd0,0). Use that information to set the GRUB root device:

grub> root (hd0,0)

Run the setup command to install GRUB. To install GRUB on the MBR, run setup as follows:

grub> setup (hd0)

If you are going to chainload Linux and want to install GRUB on the boot sector of the Linux partition, run setup like this:

grub> setup (hd0,0)

[3] El Torito is a specification that lets you create a bootable CD.

The GRUB Configuration File

GRUB uses a configuration file that sets up the menu interface. The configuration file is called menu.lst and is found with the other GRUB files in the /boot/grub directory. In some distributions (e.g., Fedora and Red Hat) the configuration file is called grub.conf, which is a symbolic link to menu.lst.

The configuration file begins with a section containing global commands that apply to all boot entries, followed by an entry for each Linux image or other operating system that you want to be able to boot. Here is an example of a global section (a hash sign, #, begins a comment):

default=0                                  # default to the first entry
timeout=20                                 # set the timeout to 20 seconds
splashimage=(hd0,0)/grub/splash.xpm.gz     # the splash image displayed with
# the menu

Certain GRUB commands are available only in the global section of the configuration file, for use with the GRUB menu. These commands are described in the following list. All other commands can be used either in the configuration file or on the command line and are described later in GRUB Commands in GRUB Commands.

default num

Set the default menu entry to num. The default entry is started if the user does not make a selection before the timeout time. Menu entries are numbered from 0. If no default is specified, the first entry (0) is used as the default.

fallback num

Specify the entry to be used if for any reason the default entry has errors. If this command is specified and the default doesn’t work, GRUB boots the fallback entry automatically instead of waiting for user input.

hiddenmenu

Specify that the menu is not to be displayed. The user can press Esc before the end of the timeout period to have the menu displayed; otherwise, the default entry is booted at the end of the timeout.

timeout time

Specify the timeout period, in seconds. The timeout is the amount of time GRUB waits for user input before booting the default entry.

title name

Start a new boot entry with specified name.

Following the global section, the configuration file includes an entry for each boot image. An entry begins with a title command that specifies the text that will appear on the menu for that entry when the system boots. A typical boot entry might look like this:

title Linux 2.6.28
root (hd0,1)
kernel /vmlinuz-2.6.28 ro root=LABEL=/
initrd /initrd-2.6.28

This entry provides the information GRUB needs to boot to Linux. When the menu is displayed, it will include an entry that says:

Linux 2.6.28

The GRUB root is on the second partition of the first hard drive (hd0,1). The kernel command specifies which Linux kernel to run and passes some parameters to the kernel, and the initrd command sets up an initial RAM disk.

The configuration file also provides some security features, such as the ability to set passwords and to lock certain entries so only the root user can boot them. The configuration file can be set up so that a password is required to run interactively (i.e., for editing menu entries or using the command interface) or simply to protect certain menu entries while leaving other entries available to all users. See the explanation of the password and lock commands in GRUB Commands in GRUB Commands.

In addition to providing a password feature, GRUB provides the command md5crypt to encrypt passwords in MD5 format, and a corresponding Linux command, grub-md5-crypt. grub-md5-crypt is a shell script that acts as a frontend to the grub shell, calling md5crypt. Passwords encrypted either directly with md5crypt or with grub-md5-crypt can be used with the password command to set up a GRUB password. grub-md5-crypt has three possible options:

--help

Print help message and exit.

--grub-shell=file

Specify that file is to be used as the GRUB shell.

--version

Print version information and exit.

Using the Menu Interface

The most common way to use GRUB is with the menu interface. The Stage 2 loader reads the configuration file menu.lst and displays the menu. If a timeout is set in the configuration file, GRUB displays a countdown at the bottom of the window showing how much time is left before it boots to the default entry. Move the cursor to an entry and press Enter to boot; or, press e to edit the command line for that entry, a to modify the kernel arguments, or c to go to the command-line interface to issue commands manually.

If you go to the command line, you can return to the menu at any time by pressing Esc.

Selecting a and e are similar, except that a displays only the kernel command line and lets you append options to it, while e displays the entire boot entry for you to edit. In either case, the available editing commands are similar to those available on the shell command line. When you are through editing, press Esc to return to the main menu. Your changes take effect for this session only; the configuration file is not permanently changed.

One common use for editing a kernel command is to boot to single-user mode. To do that, select a from the menu and append the word “single” to the end of the kernel command. Then press Esc to return to the menu and select the entry.

The GRUB Shell

In addition to using the command line from within the GRUB menu interface (or booting directly to the command line), you can run a GRUB shell directly from the Linux command line with the grub command. For the most part, using the grub shell is the same as running in the native command-line environment. The major difference is that the shell uses operating system calls to emulate the BIOS calls that the native environment uses. That can lead to some differences in behavior.

The syntax of the grub command is:

grub [options]

For example:

$ grub --no-floppy

The grub command-line options are:

--batch

Turn on batch mode for noninteractive use. Equivalent to grub --no-config-file --no-curses --no-pager.

--boot-drive=drive

Use drive as the Stage 2 boot drive, specified as a decimal, hexadecimal, or octal integer. The default is hexadecimal 0x0.

--config-file=file

Use file as the GRUB configuration file. The default is /boot/grub/menu.lst.

--device-map=file

Use file for the device map. The value of file is usually /boot/grub/device.map.

--help

Display a help message to standard output and exit.

--hold

Wait for a debugger to attach before starting grub.

--install-partition=partition

Use partition as the Stage 2 installation partition, specified as a decimal, hexadecimal, or octal number. The default is hexadecimal 0x20000.

--no-config-file

Run without reading the configuration file.

--no-curses

Don’t use the curses interface for managing the cursor on the screen.

--no-floppy

Don’t probe for a floppy drive. This option is ignored if --device-map is also specified.

--no-pager

Don’t use the internal pager.

--preset-menu

Use a preset menu, for example if your system has no console and you need to get a serial terminal set up to see messages. To use this option, compile GRUB with the --enable-preset-menu=file option and create a menu file. See the GRUB documentation for more information.

--probe-second-floppy

Probe the second floppy drive (which is not probed by default). This option is ignored if --device-map is also specified.

--read-only

Do not write to any disk drives.

--verbose

Print verbose messages.

--version

Print version information and exit.

When you run grub, you will see something like this:

GRUB  version 0.94  (640K lower / 3072K upper memory)

[ Minimal BASH-like line editing is supported.  For the first word, TAB
lists possible command completions.  Anywhere else TAB lists the possible
completions of a device/filename. ]

grub>

You can now enter commands at the grub> prompt. Press Tab to get a brief help message, listing all the commands:

grub>
Possible commands are: blocklist boot cat chainloader cmp color configfile
debug device displayapm displaymem dump embed find fstest geometry halt help
hide impsprobe initrd install ioprobe kernel lock makeactive map md5crypt
module modulenounzip pager partnew parttype password pause quit read reboot
root rootnoverify savedefault serial setkey setup terminal testload testvbe
unhide uppermem vbeprobe

Using Tab is a quick way to remind yourself of the commands, but it can be confusing to see them all run together and wrapping across lines. You can also run the help command, which lists the most frequently used commands and their syntax:

grub> help
blocklist FILE                         boot
cat FILE                               chainloader [--force] FILE
color NORMAL [HIGHLIGHT]               configfile FILE
device DRIVE DEVICE                    displayapm
displaymem                             find FILENAME
geometry DRIVE [CYLINDER HEAD SECTOR [ halt [--no-apm]
help [--all] [PATTERN ...]             hide PARTITION
initrd FILE [ARG ...]                  kernel [--no-mem-option] [--type=TYPE]
makeactive                             map TO_DRIVE FROM_DRIVE
md5crypt                               module FILE [ARG ...]
modulenounzip FILE [ARG ...]           pager [FLAG]
partnew PART TYPE START LEN            parttype PART TYPE
quit                                   reboot
root [DEVICE [HDBIAS]]                 rootnoverify [DEVICE [HDBIAS]]
serial [--unit=UNIT] [--port=PORT] [-- setkey [TO_KEY FROM_KEY]
setup [--prefix=DIR] [--stage2=STAGE2_ terminal [--dumb] [--timeout=SECS] [--
testvbe MODE                           unhide PARTITION
uppermem KBYTES                        vbeprobe [MODE]

You can add the --all option to see all the commands.

To get help for a specific command, add the command name (e.g., help read). help treats the text you enter as a pattern; therefore, if you enter help find, you’ll get help for the find command, but if you enter help module, you’ll get help for both module and modulenounzip.

GRUB Commands

The following sections describe two sets of commands. Both can be used at the GRUB command line. In addition, the first set can be used in the global section of the menu, and the second can be used in individual menu entries. A few commands can be used only on the GRUB shell command line; this is noted in the command entry. The commands default, fallback, hiddenmenu, timeout, and title are available only in the configuration file, for use with the menu interface. They are described in The GRUB Configuration File in The GRUB Configuration File.

When running commands, if you find that you aren’t sure how to complete a pathname, you can use the Tab key to find the possible completions. For example:

grub> blocklist (hd0,1)/grub/[Tab]
Possible files are: grub.conf splash.xpm.gz menu.lst device.map stage1
stage2 e2fs_stage1_5 fat_stage1_5 ffs_stage1_5 jfs_stage1_5 minix_stage1_5
reiserfs_stage1_5 vstafs_stage1_5 xfs_stage1_5
grub> blocklist (hd0,1)/grub/stage2
(hd0,1)33306+24,33332+231

Command-Line and Global Menu Commands

The commands available at the command line and in the global section of the configuration file are as follows.

Name

bootp

Synopsis

bootp [--with-configfile]

Initialize a network device via the Bootstrap Protocol (BOOTP). This command is available only if GRUB was compiled with netboot support. If --with-configfile is specified, GRUB automatically loads a configuration file specified by your BOOTP server.

Name

color

Synopsis

color normal [highlight]

Specify colors for the menu. normal represents the color used for normal menu text, while highlight represents the color used to highlight the line the cursor is on. Both normal and highlight are specified as two symbolic color names, for foreground and background color, separated by a slash. For example:

color light-gray/blue cyan/black

You can prefix the foreground color with blink- (e.g., blink-cyan/red) to get a blinking foreground. The colors black, blue, green, cyan, red, magenta, brown, and light-gray can be specified for foreground or background. Additional colors that can be used only for the foreground are dark-gray, light-blue, light-green, light-cyan, light-red, light-magenta, yellow, and white.

Name

device

Synopsis

device drive file

Specify a file to be used as a BIOS drive. This command is useful for creating a disk image and/or for fixing the drives when GRUB fails to determine them correctly. The device command is available only from within the grub shell, not from the native command line. For example:

grub> device (fd0) /floppy-image
grub> device (hd0) /dev/sd0

Name

dhcp

Synopsis

dhcp [--with-configfile]

Initialize a network device via the DHCP protocol. Currently, this command is just an alias for bootp and is available only if GRUB was compiled with netboot support. If specified with --with-configfile, GRUB will fetch and load a configuration file specified by your DHCP server.

Name

hide

Synopsis

hide partition

Hide the specified partition. This is useful when you are booting Windows and there are multiple primary partitions on one disk. Hide all but the one you want to boot. Also see unhide.

Name

ifconfig

Synopsis

ifconfig [--server=server] [--gateway=gateway] [--mask=mask]
[--address=address]

Configure a network device manually. If no options are specified, displays the current network configuration. With the server address, gateway, netmask, and IP address specified, ifconfig configures the device. The addresses must be in dotted decimal format (e.g., 192.168.0.4), and the options can be specified in any order.

Name

pager

Synopsis

pager [flag]

Enable or disable the internal pager by setting flag to on (enable) or off (disable).

Name

partnew

Synopsis

partnew part type from to

Make a new primary partition, part, specified in GRUB syntax. type is the partition type, specified as a number in the range 0-0xff. from and to are the starting and ending sectors, specified as absolute numbers. Some of the common partition types are:

Type

Number

None

0

FAT 16, lt 32M

4

FAT 16, gt 32M

6

FAT 32

0xb

FAT 32, with LBA

0xc

WIN 95, extended

0xf

EXT2FS

0x83

Linux extended

0x85

Linux RAID

0xfd

FreeBSD

0xa5

OpenBSD

0xa6

NetBSD

0xfd

Name

parttype

Synopsis

parttype part type

Change the type of partition part to type. The type must be a number in the range 0-0xff. See partnew for a list of partition types.

Name

password

Synopsis

password [--md5] passwd [file]

Set a password for the menu interface. If used in the global section of the configuration file, outside the menu entries, GRUB prompts for a password before processing an a, e, or c entered by the user. Once the password passwd has been entered, if no file was specified, GRUB allows the user to proceed. Otherwise, GRUB loads the file as a new configuration file and restarts Stage 2. If password appears in an individual menu entry, GRUB prompts for the password before continuing. Specify --md5 to tell GRUB that the password was encrypted with the md5crypt command.

Name

rarp

Synopsis

rarp

Initialize a network device via the Reverse Address Resolution Protocol (RARP). This command is available only if GRUB was compiled with netboot support. The use of RARP is deprecated.

Name

serial

Synopsis

serial [options]

Initialize a serial device. The serial port is not used for communication unless terminal is also specified. This command is available only if GRUB was compiled with serial support.

Options

--device=device

Specify the tty device to be used in the host operating system. This option can be used only in the grub shell.

--parity=parity

Specify the parity. The possible values are no, odd, and even; the default is no.

--port=port

Specify the I/O port. The value of port overrides any value specified for --unit.

--speed=speed

Specify the transmission speed (default is 9600).

--stop=num

Specify the number of stop bits. The value of num is either 1 or 2 (default is 1).

--unit=num

Specify the serial port to use. The value of num is a number in the range 0–3; the default is 0, corresponding to COM1.

--word=num

Specify the number of data bits. The value of num is a number in the range 5–8 (default is 8).

Name

setkey

Synopsis

setkey [to-key from-key]

Configure the keyboard map for GRUB by mapping the key from-key to the key to-key. With no mappings specified, reset the keyboard map. setkey is useful for setting up international keyboards. Possible key values are letters; digits; one of the strings alt, backspace, capslock, control, delete, enter, escape, Fn (where n is one of the function key numbers), shift, tab; or one of the strings in the “Key value” columns of the following table.

Key value

Character

Key value

Character

ampersand

&

asterisk

*

at

@

backquote

`

backslash

\

bar

|

braceleft

{

braceright

}

bracketleft

[

bracketright

]

caret

^

colon

:

comma

,

dollar

$

doublequote

"

equal

=

exclam

!

greater

>

less

<

minus

-

numbersign

#

parenleft

(

parenright

)

percent

%

period

.

plus

+

question

?

quote

`

semicolon

;

slash

/

space

tilde

˜

underscore

_

Name

splashimage

Synopsis

splashimage file

Use the image in file as the background (splash) image. The file should be a gzipped .xpm (X pixmap) file, created with a 14-color palette at 640 × 480 resolution and specified with standard GRUB device syntax:

splashimage=(hd0,0)/grub/splash.xpm.gz

Programs that you can use to create .xpm files include the GIMP, xv, and xpaint.

Name

terminal

Synopsis

terminal [options] [console] [serial]

Specify a terminal for user interaction. This command is available only if GRUB was compiled with serial support. If both console and serial are specified, GRUB uses the first terminal where a key is pressed, or the first after the timeout has expired. If neither is specified, GRUB displays the current setting.

Options

--dumb

The terminal is a dumb terminal; if this option is not specified, the terminal is assumed to be VT100-compatible.

--lines=num

The terminal has num lines. The default is 24.

--silent

Suppress the prompt to hit any key (useful if your system does not have a terminal).

--timeout=secs

Specify the timeout in seconds.

Name

tftpserver

Synopsis

tftpserver ipaddress

Specify a TFTP server, overriding the address returned by a BOOTP, DHCP, or RARP server. The IP address must be specified in dotted decimal format. This command is available only if GRUB was compiled with netboot support. This command is deprecated; use ifconfig instead.

Name

unhide

Synopsis

unhide partition

Unhide the specified partition. This is useful when booting DOS or Windows when there are multiple primary partitions on one disk. You can unhide the partition you want to boot and hide the others.

Command-Line and Menu-Entry Commands

The commands available at the command line and in the individual menu entries of the configuration file are as follows.

Name

blocklist

Synopsis

blocklist file

Print the specified file in blocklist notation, where file is an absolute pathname or a blocklist. For example:

grub> blocklist (hd0,1)/grub/grub.conf
(hd0,1)33746+2

Name

boot

Synopsis

boot

Boot the operating system or chainloader that has been loaded. You need to run this command only if you are in the interactive command-line mode.

Name

cat

Synopsis

cat file

Display the contents of the specified file.

Name

chainloader

Synopsis

chainloader [--force] file

Load file as a chainloader. You can use blocklist notation to specify the first sector of the current partition with +1. If --force is specified, the file is loaded forcibly.

Name

cmp

Synopsis

cmp file1 file2

Compare the two files file1 and file2. Report differences by printing nothing if the files are identical, the sizes if they are different, or the bytes at an offset if they differ at that offset.

Name

configfile

Synopsis

configfile file

Load file as the configuration file.

Name

debug

Synopsis

debug

Toggle debug mode, which prints extra messages to show disk activity. The default debug mode is off.

Name

displayapm

Synopsis

displayapm

Display Advanced Power Management (APM) BIOS information.

Name

displaymem

Synopsis

displaymem

Display the system address space map of the machine, including all regions of physical RAM installed. For example:

grub> displaymem
displaymem
EISA Memory BIOS Interface is present
Address Map BIOS Interface is present
Lower memory: 640K, Upper memory (to first chipset hole):
3072K
[Address Range Descriptor entries immediately follow
(values are 64-bit)]
Usable RAM:  Base Address:  0x0 X 4GB + 0x0,
Length:   0x0 X 4GB + 0xa0000 bytes
Reserved:  Base Address:  0x0 X 4GB + 0xa0000,
Length:   0x0 X 4GB + 0x60000 bytes
Usable RAM:  Base Address:  0x0 X 4GB + 0x100000,
Length:   0x0 X 4GB + 0x300000 bytes

Name

dump

Synopsis

dump from to

Dump the contents of one file into another. The file you’re dumping from is a GRUB file, and the file you’re dumping to is an operating system file.

Name

embed

Synopsis

embed stage1.5 device

Embed the specified Stage 1.5 file in the sectors following the MBR if device is a drive, or in the boot loader area if it is an FFS (Berkeley Fast File System) partition (or, in the future, a ReiserFS partition). If successful, print the number of sectors the Stage 1.5 file occupies. You don’t usually need to run this command directly.

Name

find

Synopsis

find file

Search all partitions for the specified file and print the list of devices where it was found. The filename specified should be an absolute filename, such as /boot/grub/stage1, or a blocklist.

Name

fstest

Synopsis

fstest

Toggle the filesystem test mode, which prints data for device reads and the values being sent to the low-level routines. The install and testload commands turn off filesystem test mode. The test output is in the following format:

<partition-offset-sector, byte-offset, byte-length>

for high-level reads in a partition, and:

[disk-offset-sector]

for low-level sector requests from the disk.

Name

geometry

Synopsis

geometry drive [cylinder head sector [total_sector]]

Print geometry information for drive. From the GRUB shell, you can specify the number of cylinders, heads, sectors, and total sectors to set the drive’s geometry. If total_sector is omitted, it is calculated from the other values.

Name

halt

Synopsis

halt [--no-apm]

Shut down the computer. The computer is halted with an APM BIOS call unless the option --no-apm is specified.

Name

help

Synopsis

help [--all] [patterns]

Provide help for built-in commands. With no options, show the command and any options or parameters for the most common commands. With --all, show the same information for all possible commands. If you specify a pattern (i.e., a partial command name) or a full command name, a more complete description of the command or commands matching the pattern is displayed.

Name

impsprobe

Synopsis

impsprobe

Probe the Intel Multiprocessor Specification 1.1 or 1.4 configuration table and boot the CPUs that are found into a tight loop. This command can be used only in Stage 2.

Name

initrd

Synopsis

initrd file [args]

Load an initial ramdisk file and pass any arguments.

Name

install

Synopsis

install [options] stage1_file [d] dest_dev stage2_file [addr]
[p] [config_file] [real_config_file]

Perform a full GRUB install. See also the setup command, which acts as a frontend to install and is easier to use. The Stage 2 or Stage 1.5 file (both referred to as stage2_file here because they are loaded the same way) must be in its final install location (e.g., in the /boot/grub directory). install loads and validates stage1_file, installs a blocklist in the Stage 1 file for loading stage2_file as Stage 2 or Stage 1.5, and writes the completed Stage 1 file to the first block of the device dest_dev.

Options

--force-lba

If the BIOS has LBA support but might return the incorrect LBA bitmap (which sometimes happens), --force-lba forces install to ignore the incorrect bitmap.

--stage2=os_stage2_file

This option is required to specify the operating system name of the Stage 2 file if the filesystem where it is located cannot be unmounted.

Parameters

addr

Specify the address at which Stage 1 is to load Stage 2 or Stage 1.5. The possible values are 0x8000 for Stage 2 and 0x2000 for Stage 1.5. If omitted, GRUB determines the address automatically.

config_file

Specify the location of the configuration file for Stage 2.

d

Tell Stage 1 to look for the actual disk on which stage2_file was installed if it’s not on the boot drive.

dest_dev

Specify the destination device. The final Stage 1 file is written to this device.

p

If present, the partition where stage2_file is located is written into the first block of Stage 2.

real_config_file

If stage2_file is really a Stage 1.5 file, real_config_file specifies the real configuration filename and is written into the Stage 2 configuration file.

stage1_file

Specify the Stage 1 file to be written.

stage2_file

Specify the file that Stage 1 is to load for Stage 2.

Name

ioprobe

Synopsis

ioprobe drive

Probe the I/O ports used for drive and write the results to standard output.

Name

kernel

Synopsis

kernel [--non-mem-option] file [...]

Load the kernel image from file. Any text following file is passed on as the kernel command line. After running this command, you must reload any modules. The option --type specifies the kernel type and is required only for loading a NetBSD ELF kernel; GRUB automatically determines other types. The possible values of type are linux, biglinux, freebsd, multiboot, netbsd, and openbsd. For Linux, --no-mem-option tells GRUB not to pass the mem= option to the kernel.

Name

lock

Synopsis

lock

Lock the entry until a valid password is entered. This is used in a menu entry immediately after title to prevent nonroot users from executing the entry. This command is most useful in conjunction with the password command.

Name

makeactive

Synopsis

makeactive

Set the active partition on the root disk to GRUB’s root device. Use only on primary PC hard disk partitions.

Name

map

Synopsis

map to from

Map the from drive to the to drive. You need to do this when chainloading an operating system such as Windows, if it is not on the first drive. For example, if Windows is on (hd1):

grub> map (hd0) (hd1)
grub> map (hd1) (hd0)

This swaps the mappings of the first and second hard drives, tricking Windows into thinking it’s on the first drive so it can boot.

Name

md5crypt

Synopsis

md5crypt

Prompt for a password and encrypt it in MD5 format for use with the password command.

Name

module

Synopsis

module file [...]

Load the boot module file for a multiboot format boot image. Anything after the filename is passed as the module command line.

Name

modulenounzip

Synopsis

modulenounzip files

Like module, except that automatic decompression is disabled.

Name

pause

Synopsis

pause messages

Print the specified message and wait for a key to be pressed before continuing.

Name

quit

Synopsis

quit

Used only from within the grub shell to exit from the shell. In the native command environment, use reboot instead to reboot the computer.

Name

read

Synopsis

read addr

Read a 32-bit value from memory at the specified address and display it in hex.

Name

reboot

Synopsis

reboot

Reboot the system.

Name

root

Synopsis

root device [hdbias]

Set the root device to the specified device and attempt to mount it to get the partition size (and some additional information for booting BSD kernels). If you are booting a BSD kernel, you can specify hdbias to tell the kernel how many BIOS drive numbers are before the current one.

Name

rootnoverify

Synopsis

rootnoverify device [hdbias]

Similar to root, but don’t attempt to mount the partition. Used when you are booting a non-GRUB-readable partition such as Windows.

Name

savedefault

Synopsis

savedefault

Save the current menu entry as the default. GRUB will default to that entry the next time you boot the system.

Name

setup

Synopsis

setup [options] install_device [image_device]

Set up installation of GRUB and run the install command to actually install GRUB onto the device install_device. Find the GRUB images on image_device if it is specified; otherwise use the current root device as set by the root command. If install_device is a hard disk, embed a Stage 1.5 file in the disk if possible.

Options

--force-lba

Force install to use LBA mode. Specify this option if your BIOS supports LBA mode but you find that GRUB isn’t working in LBA mode without it.

--prefix=dir

Specify the directory where the GRUB images are located. If not specified, GRUB searches for them in /boot/grub and /grub.

--stage2=os_stage2_file

Passed to install to tell GRUB the operating system name of the Stage 2 file.

Name

testload

Synopsis

testload file

Read the contents of a file in different ways and compare the results to test the filesystem code. If no errors are reported and the final output reports an equal value for the reported variables i and filepos, then the filesystem is consistent and you can try loading a kernel.

Name

testvbe

Synopsis

testvbe mode

For a VBE (VESA BIOS Extension) BIOS, test the specified VESA BIOS extension mode. You should see an animation loop, which you can cancel by pressing any key.

Name

uppermem

Synopsis

uppermem kbytes

Tell GRUB to assume that only the specified number of kilobytes of upper memory are installed. You should need to use this command only for old systems, where not all the memory may be recognized.

Name

vbeprobe

Synopsis

vbeprobe [mode]

For a VBE BIOS, probe VESA BIOS extension information. If mode is specified, the output shows only information for that mode; otherwise, all available VBE modes are listed.

Dual-Booting Linux and Windows 2000/XP/Vista

As mentioned earlier, when you run Windows, its boot loader expects to be the one in charge; therefore, the standard way to dual-boot Windows and Linux is to add Linux as an option on the Windows boot menu. This section describes how to do that. The information provided here applies to Windows 2000 and Windows XP, which use the Windows NT loader ntldr (so called because it was developed for Windows NT). Windows Vista uses a different boot loader. If you want to set up Vista to dual-boot Linux, you can use the free download EasyBCD by Neosmart Technologies (neosmart.net).

Note again that you do not need the information in this section if your Linux installation software set up the dual-booting for you, which it probably did.

To set up dual booting with the NT loader manually, you need to provide the loader with a copy of the Linux boot sector. We’ll describe how to do that on a computer running Windows with an NTFS filesystem (note that Windows should be installed on your system already). See the “Linux+NT-loader” mini-HOWTO for more information and other alternatives.

You should have a Linux boot floppy or CD available so that if necessary you can boot Linux before the Windows boot loader has been modified. You should also have a DOS-formatted floppy to transfer the boot sector to the Windows partition. If you are running LILO and it is already installed, you may need to modify /etc/lilo.conf as described later. Otherwise, install LILO or GRUB to the boot sector of the Linux partition; once the Linux boot manager is installed and you have a configuration file, you can set up the system for dual booting.

The following instructions assume your Linux partition is on /dev/hda2. If Linux is on another partition in your system, be sure to replace /dev/hda2 in the following examples with the correct partition. The instructions also assume that you have a floppy drive to make a diskette for transferring the boot sector to your NTFS filesystem. If you don’t have a floppy drive, you will have to use some other means of doing the transfer. If you have a FAT partition, you can mount that on Linux and transfer the file there. Other possibilities include putting it on a CD, transferring it over a network to another system while you reboot to Windows, or even emailing it to yourself and reading it from the Windows side.

1. If you are running LILO, specify the Linux root partition as your boot device in /etc/lilo.conf. If you are editing /etc/lilo.conf manually, your entry will look like this:

boot=/dev/hda2

and will be the same as the root= entry.
If you are running GRUB, make sure your configuration file, /boot/grub/menu.lst, includes a menu entry for booting Linux. The exact values of the entries in the menu depend on the filename of the kernel image that you wish to boot. For example:

title Linux 2.6.28
root (hd0,1)
kernel /vmlinuz-2.6.28 ro root=LABEL=/
initrd /initrd-2.6.28

You can then skip to Step 3.

2. Run the lilo command to install LILO on the Linux root partition.

3. At this point, if you need to reboot Linux, you’ll have to use a boot floppy or CD because the NT loader hasn’t been set up yet to boot Linux.

4. From Linux, run the dd command to make a copy of the Linux boot sector:

$ dd if=/dev/hda2 of=/bootsect.lnx bs=512 count=1

This command copies one block, with a block size of 512 bytes, from the input file /dev/hda2 to the output file /bootsect.lnx. Note that if you are running GRUB, the boot sector is actually the stage1 file. (The output filename can be whatever makes sense to you; it doesn’t have to be bootsect.lnx.)

5. Copy bootsect.lnx to a DOS-formatted floppy disk if that is how you are going to transfer it to Windows:

$ mount -t msdos /dev/fd0 /mnt
$ cp /bootsect.lnx /mnt
$ umount /mnt

6. Reboot the system to Windows and copy the boot sector from the floppy disk to the hard disk. You can drag and drop the file to the hard drive, or use the command line to copy the file, as in the following example:

C:> copy a:\bootsect.lnx c:\bootsect.lnx

It doesn’t matter where on the hard drive you put the file because you’ll tell the NT loader where to find it in step 8.

7. Modify the attributes of the file boot.ini[4] to remove the system and read-only attributes so you can edit it:

C:> attrib -s -r c:\boot.ini

8. Edit boot.ini with a text editor to add the line:

C:\bootsect.lnx="Linux"

This line adds Linux to the boot menu and tells the NT boot loader where to find the Linux boot sector. You can insert the line anywhere in the [operating systems] section of the file. Its position in the file determines where it will show up on the boot menu when you reboot your computer. Adding it at the end, for example, results in a boot.ini file that looks something like this (the second multi(0) entry is wrapped to fit the margins of this page):

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows NT Server Version 4.00"
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows NT Server Version
4.00 [VGA mode]" /basevideo /sos
C:\bootsect.lnx="Linux"

If you want Linux to be the default operating system, modify the default= line:

default=C:\bootsect.lnx

9. Rerun attrib to restore the system and read-only attributes:

C:> attrib +s +r c:\boot.ini

Now you can shut down Windows and reboot. Windows will prompt you with a menu that looks something like this:

OS Loader V4.00
Please select the operating system to start:
Windows NT Workstation Version 4.00
Windows NT Workstation Version 4.00 [VGA mode]
Linux

Select Linux, and the NT loader will read the Linux boot sector and transfer control to LILO or GRUB on the Linux partition.

If you are using LILO and you later modify /etc/lilo.conf or rebuild the kernel, you need to rerun the lilo command, create a new bootsect.lnx file, and replace the version of bootsect.lnx on the Windows partition with the new version. In other words, you need to rerun steps 2–6.

Tip

If you have any problems or you simply want to remove LILO or GRUB later, you can reverse the installation procedure: boot to Windows, change the system and read-only attributes on boot.ini, re-edit boot.ini to remove the Linux entry, save the file, restore the system and read-only attributes, and remove the Linux boot sector from the Windows partition.

[4] boot.ini is the Windows counterpart to /etc/lilo.conf. It defines which operating systems the -Windows loader can boot.

Boot-Time Kernel Options

The earlier sections of this chapter described some of the options you can specify when you boot Linux. There are many more options that can be specified. This section touches on the ways to pass options to the kernel and then describes some of the kinds of parameters you might want to use. The parameters in this section affect the kernel and therefore apply regardless of which boot loader you use.

If LILO is your boot loader, you can add to or override the parameters specified in /etc/lilo.conf during the boot process as follows:

- If prompt is set in /etc/lilo.conf, LILO always presents the boot prompt and waits for input. At the prompt, you can choose the operating system to be booted. If you choose Linux, you can also specify parameters.

- If prompt isn’t set, press Ctrl, Shift, or Alt when the word “LILO” appears. The boot prompt will then appear. You also can press the Scroll Lock key before LILO is printed and not have to wait poised over the keyboard for the right moment.

- At the boot prompt, specify the system you want to boot, or press Tab to get a list of the available choices. You then can enter the name of the image to boot. For example:

LILO boot: <press Tab>
linux   test   winxp
boot: linux

You also can add boot command options:

boot: linux single

- If you don’t provide any input, LILO waits the amount of time specified in the delay parameter and then boots the default operating system with the default parameters, as set in /etc/lilo.conf.

If you are using GRUB, you can pass parameters to the kernel on the kernel command line, either in the configuration file or from the command-line interface. If you are booting from the GRUB menu, you can edit or add parameters by entering e or a when the menu appears.

Some of the boot parameters have been mentioned earlier. Many of the others are hardware-specific and are too numerous to mention here. For a complete list of parameters and a discussion of the booting process, see the “BootPrompt HOWTO.” Some of the parameters not shown earlier that you might find useful are listed next; many more are covered in the HOWTO. Most of the following parameters are used to provide information or instructions to the kernel, rather than to LILO or GRUB:

acpi=off

Disable ACPI (Advanced Configuration and Power Interface) if it was to be enabled. This is useful for debugging possible hardware problems.

debug

Print all kernel messages to the console.

hd=cylinders,heads,sectors

Specify the hard drive geometry to the kernel. Useful if Linux has trouble recognizing the geometry of your drive, especially if it’s an IDE drive with more than 1024 cylinders.

load_ramdisk=n

Tell the kernel whether to load a RAM disk image for use during Linux installation. Values of n are:

0

Don’t try to load the image. This is the default.

1

Load the image from a floppy disk to the RAM disk.

mem=size

Specify the amount of system memory installed. Useful if your BIOS reports memory only up to 64 MB and your system has more memory installed. Specify as a number with M or k (case-insensitive) appended:

mem=128M

Because mem would have to be included on the command line for every boot, it often is specified on a command line saved with lock or with append to be added to the parameters passed to the kernel.

noinitrd

When set, disable the two-stage boot and preserve the contents of /dev/initrd so the data is available after the kernel has booted. /dev/initrd can be read only once, and then its contents are returned to the system.

number

Start Linux at the runlevel specified by number. A runlevel is an operating state that the system can be booted to, such as a multiuser system or a system configuration running the X Window System. A runlevel is generally one of the numbers from 1 to 6; the default is usually 3. On modern distributions using Upstart, the runlevels and their corresponding states are defined in the ttyN files in the directory /etc/event.d. On older systems using SysVinit, the runlevels are defined in the file /etc/inittab. See Chapter 2 for a discussion of the init process.

ro

Mount the root filesystem read-only. Used for doing system maintenance, such as checking the filesystem integrity, when you don’t want anything written to the filesystem.

rw

Mount the root filesystem read/write. If neither ro nor rw is specified, the default value (usually rw) stored in the kernel image is used.

single

Start Linux in single-user mode. This option is used for system administration and recovery. It gives you a root prompt as soon as the system boots, with minimal initialization. No other logins are allowed.

initrd: Using a RAM Disk

Modern Linux distributions use a modular kernel, which allows modules to be added without requiring that the kernel be rebuilt. If your root filesystem is on a device whose driver is a module (as is frequently true of SCSI disks), you can use the initrd facility, which provides a two-stage boot process, to first set up a temporary root filesystem in a RAM disk containing the modules you need to add (e.g., the SCSI driver) and then load the modules and mount the real root filesystem. The RAM disk containing the temporary filesystem is the special device file /dev/initrd.

Similarly, you need to use a RAM disk if your root partition uses the ext3 filesystem and ext3 was not compiled into the kernel image. In that case, the ext3 module must be loaded with initrd.

Before you can use initrd, both RAM disk support (CONFIG_BLK_DEV_RAM=y) and initial RAM disk support (CONFIG_BLK_DEV_INITRD=y) must be compiled into the Linux kernel. Then you need to prepare the normal root filesystem and create the RAM disk image. Your Linux distribution may have utilities to do some of the setup for you; for example, the Red Hat distribution comes with the mkinitrd command, which builds the initrd image. For detailed information, see the initrd manpage and the file initrd.txt (the path may vary, but it is usually something like /usr/src/linux/Documentation/initrd.txt).

Once your Linux system has been set up for initrd, you can do one of the following, depending on which boot loader you are using:

- If you are using LILO, add the initrd option to the appropriate image section:

image=/vmlinuz
initrd=/boot/initrd  # The file to load as the contents of /dev/initrd
...

- Run the /sbin/lilo command, and you can reboot with initrd.

- If you are using GRUB, add the initrd option to the kernel line of the -configuration-file boot entry, or to the kernel command if you are booting from the command-line interface:

kernel /vmlinuz-2.6.28 ro root=LABEL=/
initrd /initrd-2.6.28

Chapter 5. Package Management

This chapter describes the two major Linux packaging systems: the Red Hat Package Manager (RPM) and the Debian GNU/Linux Package Manager. It also describes the major frontend applications designed to simplify and automate package management: yum for RPM-based systems, and apt, aptitude, and synaptic for Debian-based systems (apt is now also available for RPM-based systems).

When you install applications on your Linux system, most often you’ll find a binary or a source package containing the application you want, instead of (or in addition to) a .tar.gz file. A package is a file containing the files necessary to install an application. However, while the package contains the files you need for installation, the application might require the presence of other files or packages that are not included, such as particular libraries (and even specific versions of the libraries), to actually be able to run. Such requirements are known as dependencies.

Package-management systems offer many benefits. As a user, you may want to query the package database to find out what packages are installed on the system and their versions. As a system administrator, you need tools to install and manage the packages on your system. And if you are a developer, you need to know how to build a package for distribution.

Among other things, package managers do the following:

- Provide tools for installing, updating, removing, and managing the software on your system.

- Allow you to install new or upgraded software directly across a network.

- Tell you what software package a particular file belongs to or what files a package contains.

- Maintain a database of packages on the system and their status, so you can determine what packages or versions are installed on your system.

- Provide dependency checking, so you don’t mess up your system with incompatible software.

- Provide GPG, PGP, MD5, or other signature-verification tools.

- Provide tools for building packages.

Any user can list or query packages. However, installing, upgrading, or removing packages generally requires root privileges. This is because the packages normally are installed in system-wide directories that are writable only by root. Sometimes you can specify an alternate directory to install a package into your home directory or into a project directory where you have write permission, if you aren’t running as root.

Signature verification is an important feature of package-management systems that helps maintain the security of your system. An MD5 checksum is used to check the integrity of a package, making sure, for example, that it was downloaded correctly and that it was not tampered with by a malicious user. GPG (and PGP) encrypt a digital signature into the package, which is used to verify the identity of the package creator.

Most often you’ll install a binary package, in which the source code has been compiled and the software is ready to run once it is installed. You may also want or need to install source packages, which provide the source code and instructions for compiling and installing it. Source code packages do not contain executable files. Packages follow certain naming conventions, and you can tell from the name whether it is a binary or source package. RPM and Debian package names contain the same information, but they are expressed slightly differently. An RPM package has the form:

package-version-release.architecture.rpm

A Debian package has the form:

package_version-revision_architecture.deb

In both cases, package is the name of the package, version is the version number of the software, release (RPM) and revision (Debian) indicate the revision number of the package for that version, and architecture shows what system architecture the software was packaged for (e.g., i386 or amd64). The value of architecture may also be noarch for a package that is not hardware-specific or src for an RPM source package (Debian source packages come as tarred, gzipped files).

All the package managers check for dependencies when you install a package. In the case of RPM, if there are missing dependencies, it prints an error and terminates without installing the package. To proceed, you need to first install the missing package (or packages). This can become an involved process if the missing package has its own dependencies. A major advantage of the high-level package managers described in this chapter (i.e., yum, apt, aptitude, and synaptic) is that they automatically resolve dependencies and install missing packages for you. Another advantage is that they locate and download the package automatically, based on information in configuration files specifying where to look for packages. With RPM, you first have to locate the package, then download it, and only then can you run RPM to do the install. On the other hand, if you already have the package file on your system or on a CD, RPM is quick and easy to run.

Both RPM and the apt system back up old files before installing an updated package. Not only does this let you go back if there is a problem, but it also ensures that you don’t lose your changes (to configuration files, for example).

The following list shows the package-management programs described in the rest of this chapter. Which program to use is very much a matter of personal preference, and you can use more than one at different times. However, it’s best to pick the program you prefer and use it consistently, so all your packages are maintained in a single database that you can query.

The Advanced Package Tool (APT)

APT is a modern, user-friendly package-management tool that consists of a number of commands. The most frequently used of these commands is apt-get, which is used to download and install a Debian package. apt-get can be run from the command line or selected as a method from dselect.

Note that there are versions of the apt commands that can be used on an RPM-based system. If you plan to do that, it’s best to install the version of apt that comes with your Linux distribution.

aptitude

High-level text-based interface to APT. Runs either from the command line or in a visual mode inside a terminal window such as an xterm.

dpkg

The original Debian packaging tool. Used to install or uninstall packages, or as a frontend to dpkg-deb. Getting and installing packages is usually done with apt-get, but dpkg is still commonly used to install a package that is already on your system. In fact, apt-get calls dpkg to do the installation once it’s gotten the package.

dpkg-deb

Lower-level packaging tool. Used to create and manage the Debian package archives. Accepts and executes commands from dpkg or can be called directly.

dselect

An interactive frontend to dpkg. With the advent of the newer tools and the increased number of packages, the use of dselect is deprecated.

synaptic

A graphical frontend to APT.

RPM

The original command-line system for installing and managing RPM packages. RPM has two commands: rpm for installing and managing packages, and rpmbuild for creating packages.

yum

A frontend to RPM that runs from the command line.

Another RPM-based package manager, up2date, used to be the default for Red Hat Enterprise Linux systems. Red Hat has since switched to yum as the default, but up2date is still available if you prefer it. up2date has both command line and graphical interfaces, and like yum, it resolves dependencies as needed.

If you want to update your system regularly, to keep it current and to be sure you have the latest security fixes, you can set up a command that you can reissue at some regular interval (say, every day or once a week), or you can set it up as a cron job to run overnight daily or weekly. (See the descriptions of the cron and crontab commands in Chapter 3 for more information on setting up a cron job.)

You can set up your cron job to automatically download and install updated packages, but a safer approach is to have your job download the updates and email you a summary, leaving it up to you when and how to do the installation. This is particularly true in a production environment where you want to test changes thoroughly before incorporating them into your system.

Yum: Yellowdog Updater Modified

Yum is a system for managing RPM packages, including installing, updating, removing, and maintaining packages; it automatically handles dependencies between packages. Yum is derived from yup, an updating system written for Yellow Dog Linux, an RPM-based PowerPC distribution. Yum downloads the information in the package headers to a directory on your system, which it then uses to make decisions about what it needs to do. Yum obtains both the headers and the RPMs themselves from a collection of packages on a server, known as a repository.

A repository consists of a set of RPM packages and the package headers, which are on a server that can be accessed via FTP or HTTP, from an NFS server, or from a local filesystem. A single server can contain one or multiple repositories; repositories are often mirrored on many servers, and you can configure yum to use multiple repositories. When they are downloaded to your system, the header and package files are maintained in /var/cache/yum.

The configuration file, /etc/yum.conf, is where you customize yum. It consists of two section types. The first section, [main], sets configuration defaults for yum operation. This section is followed by [server] sections, where each server is named according to the repository it specifies. For example, for Fedora, you might have [base] for the base Fedora repository and [development] for the development repository.

The server sections can also be stored, one to a file, in /etc/yum.repos.d. yum comes with a default yum.conf/ file, which you can use as is or as a starting point from which to add additional repositories.

The yum Command

The yum command is an automated system for updating rpm-based packages, particularly on Fedora and Red Hat Enterprise Linux. Yum can automatically install, upgrade, and remove packages. In addition to individual packages or a list of packages, yum can operate on an entire group of packages at a time.

When you run yum, it first updates the cache (unless you tell it not to with the -C option); then it proceeds to perform the requested operation.

The format of the yum command is:

yum [options] [command] [package ...]

Any general options are specified first, followed by a command telling yum what you want it to do, usually followed by a list of one or more packages. The command is always required, except with the --help, -h, and --version options.

Package names can be specified in various combinations of name, architecture, version, and release. For example, you could refer to the bash package as bash, bash.x86_64, bash-3.2, bash-3.2-30, or bash-3.2-30.fc10.x86_64.

General options

The following general options can be set on the command line. For those that can also be set in the [main] section of the yum.conf configuration file, the name of the configuration option is given.

-c [onfig-file]

Specify the location of the yum configuration file. The file can be specified as a path to a local file or as an HTTP or FTP URL. The default is /etc/yum.conf.

-C

Run entirely from the local cache. Don’t download or update headers unless required to complete the requested action.

-d [num]

Set the debug level to num, which is generally a number between 0 and 10, to specify how much debugging information to print. The configuration option is debuglevel.

--disableexcludes=option

Disable the excludes defined in yum.conf. The possible options are all to disable all excludes, main to disable only the excludes defined in [main] in yum.conf, or repoid to disable any excludes defined for the specified repository.

--disableplugin=plugin

Run with the specified plugins disabled, where plugin is a comma-separated list of plugins.

--disablerepo=repoid

Disable the repository specified by repoid so yum won’t use it for this operation. The configuration option is enabled.

-e [num]

Set the error level to num, where num is a number, generally between 0 and 10. If the value is 0, print only critical errors. If it is 1, print all errors. Values greater than 1 mean print more errors, if there are any. The configuration option is errorlevel.

--enablerepo=repoid

Enable the specified repository that is marked as disabled (enable=0) in the configuration file. This allows the repository to be used for this operation. The configuration option is enabled.

-h [command], --help [command]

Display a help message and exit. With a command, display help for that command.

--installroot=root

Specify an alternative root for package installation. All packages will be installed relative to root. The configuration option is installroot.

--nogpgcheck

Disable GPG signature checking. The configuration option is gpgcheck.

--noplugins

Disable all plugins. The configuration option is plugins.

--obsoletes

Enable obsoletes processing logic, taking into consideration packages that are obsoleted by other packages in the repository. Meaningful only with the yum update command. The configuration option is obsoletes.

-q, --quiet

Run without producing output. See also -y.

-R [minutes]

Set the maximum amount of time in minutes that yum will wait before performing a command.

--showduplicates

For the info, list, and search commands, show all matching packages, not just the latest versions.

--skipbroken

If yum finds dependency problems in a transaction, resolve them by removing the packages causing problems. The configuration option is skip_broken.

-t, --tolerant

Currently does nothing. This option was originally intended to allow yum to keep going (be tolerant) in spite of any package errors on the command line. The configuration option is tolerant.

-v, --verbose

Display debugging information.

--version

Display the version of yum and exit.

-x[package], --exclude=package

Exclude the specified package from updates on all repositories. package can be given as a name or a glob. The configuration option is exclude.

-y

Assume that the answer to any question is yes. The configuration option is assumeyes.

yum Command Summary

The individual yum commands are listed here.

Name

check-update

Synopsis

check-update

Determine if updates are available, without running yum interactively. If any package updates are available, returns an exit value of 100 and a list of packages. If there are no updates, returns 0. Returns 1 on error.

Name

clean

Synopsis

clean [options]

Clean up the yum cache directory.

Options

all

Clean everything: headers, packages, metadata, and the cache.

dbcache

Clean up the sqlite database cache, forcing yum to recreate it the next time it runs.

headers

Remove all header files, forcing yum to download new headers the next time it runs.

metadata

Remove the metadata files, which maintain information about the packages such as package name, file size, description, dependencies, etc. The metadata will be downloaded again the next time yum is run.

packages

Remove cached packages from the system.

Name

deplist

Synopsis

deplist packages

Generate a list of dependencies for the specified packages, including what packages satisfy the dependencies.

Name

groupinfo

Synopsis

groupinfo groups

Like info, but operates on package groups instead of individual packages.

Name

groupinstall

Synopsis

groupinstall groups
groupupdate groups

Like install, but operates on package groups instead of individual packages.

Name

grouplist

Synopsis

grouplist

Generate a list of installed and available groups to standard output. You can use these groups as input parameters to the other group commands, with their names in quotes (" ").

Name

groupremove

Synopsis

groupremove groups

Like remove, but operates on package groups instead of individual packages.

Name

help

Synopsis

help [command]

Display help information for the specified command, or if no command is given, for all commands.

Name

info

Synopsis

info [options] [packages]

Display version information, a summary, and a description for each package, or for all packages if none is specified. See the list command for a description of the options.

Name

install

Synopsis

install packages

Install the latest version of a package or packages, ensuring that all dependencies are met. If no package matches the name as specified, the name is treated as a shell glob and any matches are installed.

Name

list

Synopsis

list [options] [packages]

Display a list of packages that match the packages specification and that are installed or available for installation.

Options

all

List all installed or available packages.

available

List packages on the repository that are available for installation.

extras

List packages on the system that are not available on any repository specified in the configuration file.

installed

List installed packages.

obsoletes

List installed packages that are made obsolete by any packages in any repository in the configuration file.

recent

List packages that have been recently added to any repository in the configuration file.

updates

List packages that have updates available for installation.

Name

localinstall

Synopsis

localinstall packages

Install the specified packages, which reside on the local system, rather than downloading them from a repository.

Name

localupdate

Synopsis

localupdate packages

Update the specified packages, which reside on the local system, rather than downloading them from a repository.

Name

makecache

Synopsis

makecache

Download and cache the metadata files from the repository. Once the cache has been built, you can use the -C option to run the commands that use the metadata (check-update, info, list, provides, and search) directly from the cache.

Name

provides

Synopsis

provides feature1 [feature2 ...]
whatprovides feature1 [feature2 ...]

List packages that are available or installed that provide the specified features. The features can be specified as a name or as a wildcard in file-glob syntax format, and Perl or Python regular expressions can be used.

Name

reinstall

Synopsis

reinstall package1 [package2 ...]

Reinstall the specified packages. The packages must already exist on the system.

Name

remove

Synopsis

remove package1 [package2 ...]
erase package1 [package2 ...]

Remove the specified packages from the system. Also remove any packages that depend on the specified packages.

Name

repolist

Synopsis

repolist [option]

Generate a list of configured repositories. With no option or if the option is all, list all repositories. The other options are disabled to list disabled repositories, and enabled to list enabled repositories.

Name

resolvedep

Synopsis

resolvedep dep1 [dep2 ...]

List the packages that provide the specified dependencies.

Name

search

Synopsis

search string1 [string2 ...]

Find packages matching the specified string or strings in the description, summary, packager, or package name fields. Perl or Python regular expressions can be used for the strings. Useful for finding a package if you don’t know the name.

Name

shell

Synopsis

shell [filename]

Run an interactive yum shell, allowing multiple commands to be run within one yum execution. A filename can be specified that contains the commands to be run.

Name

update

Synopsis

update [packages]

With no packages specified, update all installed packages. Otherwise, update the specified packages. In either case, yum makes sure that all dependencies are satisfied. If no package matches, the names specified are assumed to be shell globs, and any matches are installed.

With the --obsoletes option, yum includes package obsoletes in its calculations.

Name

upgrade

Synopsis

upgrade [packages]

Equivalent to update --obsoletes.

Plugins and yum-utils

You can install plugins to extend the capabilities of yum. Plugins are Python programs that are installed in a directory specified with the pluginpath option in /etc/yum.conf. In addition, to enable plugins, set the plugins option in /etc/yum.conf to 1.

One set of such plugins is yum-utils, a collection of tools for managing packages and repositories. The following list briefly describes each tool. For more information on a tool, run it with the -h or --help option.

debuginfo-install

Install debuginfo packages, which contain debugging information for programs.

package-cleanup

Clean up packages, handling duplicates, orphaned packages, and dependency problems.

repoclosure

Read the metadata of one or more repositories, check dependencies, and display a list of any unresolved dependencies.

repodiff

Compare two or more repositories and display a list of added, removed, or changed packages.

repo-graph

Display a full package dependency list in dot format.

repomanage

Manage a directory of rpm packages, returning a list of the newest or oldest packages in a directory.

repoquery

Query yum repositories for additional information.

repo-rss

Generate an RSS feed from one or more repositories.

reposync

Synchronize a remote repository to a local directory, using yum to retrieve packages.

repotrack

Keep track of packages and their dependencies, and download them.

yum-builddep

Install missing dependencies to build specified packages.

yum-complete-transaction

Find incomplete or aborted transactions and try to complete them.

yumdownloader

Download binary and source packages from yum repositories for specified packages.

The Red Hat Package Manager

The Red Hat Package Manager (RPM) is a freely available packaging system for software distribution and installation. In addition to the Red Hat Enterprise Linux and Fedora distributions, both SUSE and Mandriva are among the Linux distributions that use RPM.

Using RPM is straightforward. A single command, rpm, has options to perform all package-management functions except building packages.[5] For example, to find out if the Emacs editor is installed on your system, you could enter:

$ rpm -q emacs
emacs-22.2-5.fc9.x86_64

This command prints the full package name, confirming its presence.

The rpmbuild command is used to build both binary and source packages.

[5] In older versions of RPM, the build options were part of the rpm command.

RPM Package Concepts

This section provides an overview of some of the parts of an RPM package. Much of the information is of primary use to developers, but because some of the terms are referenced in the RPM command descriptions, they are explained briefly here.

An RPM package has three primary components. The header contains all the information about the package, such as its name and version, a description, a list of included files, the copyright terms, and where the source file can be found. The signature contains information used to verify the integrity and authenticity of the package. The archive contains the actual files that make up the package.

When a package is being built, one of the requirements for its developers is to create a spec file. If you download the source rpm for a package, you can look at the spec file; it has a filename of package.spec (e.g., yum.spec for the yum spec file). The spec file contains all the information required to build a package, including a description of the software, instructions telling the rpmbuild command how to build the package, and a list of the files included and where they get installed. Some other features of spec files include the following:

Macros

Macros are sequences of commands stored together and executed by invoking the macro name. The RPM build process provides two standard macros: %setup to unpack the original sources and %patch to apply patches. Other macros appear later in this chapter in the command descriptions and are described there.

Scripts

Scripts are used to control the build process. Some of the scripts RPM uses include %prep to begin the build process, %build primarily to run make and perhaps do some configuration, %install to do a make install and %clean to clean up afterward. Four additional scripts may be created to run when a package is actually installed on a system. These scripts are %pre for scripts run before package installation, %post for scripts run after package installation, %preun for scripts run before a package is uninstalled, and %postun for scripts run after a package is uninstalled.

Trigger scriptlets

Trigger scriptlets are extensions of the normal install and uninstall scripts. They provide for interaction between packages. A trigger scriptlet provided with one package will be triggered to run by the installation or removal of some other package. For example, a newly installed RPM package may cause an existing application to run or restart once installation is complete. In many cases, a newly installed package requires services to be restarted.

The rpm Command

RPM packages are built, installed, and queried with the rpm command. RPM package filenames usually end with a .rpm extension. rpm has a set of modes, each with its own options. The format of the rpm command is:

rpm [options] [packages]

With a few exceptions, as noted in the lists of options that follow, the first option specifies the rpm mode (install, query, update, etc.), and any remaining options affect that mode.

Options that refer to packages are sometimes specified as package-name and sometimes as package-file. The package name is the name of the program or application, such as xpdf. The package file is the name of the RPM file, such as xpdf-3.00-10.1.i386.rpm.

RPM provides a configuration file for specifying frequently used options. The default global configuration file is usually /usr/lib/rpm/rpmrc, the local system configuration file is /etc/rpmrc, and users can set up their own $HOME/.rpmrc files. You can use the --showrc option to show the values RPM will use by default for all the options that may be set in an rpmrc file:

rpm --showrc

The rpm command includes FTP and HTTP clients, so you can specify an ftp:// or http:// URL to install or query a package across the Internet. You can use an FTP or HTTP URL wherever package-file is specified in the commands presented here. Be careful, however, when downloading packages from the Internet. Always verify package contents by checking MD5 hashes and signatures. Whenever possible, install from trusted sites.

Any user can query the RPM database. Most of the other functions, such as installing and removing packages, require superuser privileges.

General options

The following options can be used with all modes:

--dbpath path

Use path as the path to the RPM database instead of the default /var/lib/rpm.

-?, --help

Print a long usage message (run rpm with no options for a shorter usage message).

--pipe command

Pipe the query output to the specified command.

--quiet

Display only error messages.

--rcfile filelist

Get configuration from the files in the colon-separated filelist. If --rcfile is specified, the list must contain at least one file and that file must exist. filelist defaults to /usr/lib/rpm/rpmrc:/usr/lib/rpm/redhat/rpmrc:/etc/rpmrc:~/.rpmrc. Use with --showrc to see what options will be used if alternate configuration files are specified.

--root dir

Perform all operations within the directory tree rooted at dir.

-v

Verbose. Print progress messages.

--version

Print the rpm version number.

-vv

Print debugging information.

Install, upgrade, and freshen options

Use the install command to install or upgrade an RPM package. Upgrading with install leaves any existing versions on the system. The install syntax is:

rpm -i [install-options] package_file ...
rpm --install [install-options] package_file ...

To install a new version of a package and remove an existing version at the same time, use the upgrade command instead:

rpm -U [install-options] package_file ...
rpm --upgrade [install-options] package_file ...

If the package doesn’t already exist on the system, -U acts like -i and installs it. To prevent that behavior, you can freshen a package instead; in that case, rpm upgrades the package only if an earlier version is already installed. The freshen syntax is:

rpm -F [install-options] package_file ...
rpm --freshen [install-options] package_file ...

For all forms, package-file can be specified as an FTP or HTTP URL to download the file before installing it. See FTP/HTTP options in FTP/HTTP options.

The installation and upgrade options are:

--aid

If rpm suggests additional packages, add them to the list of package files.

--allfiles

Install or upgrade all files.

--badreloc

Used with --relocate to force relocation even if the package is not relocatable.

--excludedocs

Don’t install any documentation files.

--excludepath path

Don’t install any file whose filename begins with path.

--force

Force the installation. Equivalent to --replacepkgs --replacefiles --oldpackage.

-h, --hash

Print 50 hash marks as the package archive is unpacked. Use this option with -v or --verbose for a nicer display.

--ignorearch

Install even if the binary package is intended for a different architecture.

--ignoreos

Install binary package even if the operating systems don’t match.

--ignoresize

Don’t check disk space availability before installing.

--includedocs

Install documentation files. This is needed only if excludedocs: 1 is specified in an rpmrc file.

--justdb

Update the database only; don’t change any files.

--nodeps

Don’t check whether this package depends on the presence of other packages.

--nodigest

Don’t verify package or header digests.

--nomanifest

Don’t process nonpackage files as manifests.

--noorder

Don’t reorder packages to satisfy dependencies before installing.

--nopost

Don’t execute any post-install script.

--nopostun

Don’t execute any post-uninstall script.

--nopre

Don’t execute any pre-install script.

--nopreun

Don’t execute any pre-uninstall script.

--noscripts

Don’t execute any pre-install or post-install scripts. Equivalent to specifying --nopre --nopost --nopreun --nopostun.

--nosignature

Don’t verify package or header signatures.

--nosuggest

Don’t suggest packages that provide a missing dependency.

--notriggerin

Don’t execute any install trigger scriptlet.

--notriggerun

Don’t execute any uninstall trigger scriptlet.

--notriggerpostun

Don’t execute any post-uninstall trigger scriptlet.

--notriggers

Don’t execute any scripts triggered by package installation. Equivalent to specifying --notriggerin --notriggerun --notriggerpostun.

--oldpackage

Allow an upgrade to replace a newer package with an older one.

--percent

Print percent-completion messages as files are unpacked. Useful for running rpm from other tools.

--prefix path

Set the installation prefix to path for relocatable binary packages.

--relocate oldpath=newpath

For relocatable binary files, change all file paths from oldpath to newpath. Can be specified more than once to relocate multiple paths.

--replacefiles

Install the packages even if they replace files from other installed packages.

--replacepkgs

Install the packages even if some of them are already installed.

--test

Go through the installation to see what it would do, but don’t actually install the package. This option lets you test for problems before doing the installation.

Query options

The syntax for the query command is:

rpm -q [package-selection-options] [package-query-options]
rpm --query [package-selection-options] [package-query-options]

There are two subsets of query options. Package-selection options determine which packages to query, and package-query options determine which information to provide.

Package-selection options

package_name

Query the installed package package_name.

-a, --all

Query all installed packages.

-f file, --file file

Find out which package owns file.

--fileid md5

Query package with the specified MD5 digest.

-g group, --group group

Find out which packages have group group.

--hdrid sha1

Query package with the specified SHA1 digest in the package header.

-p package_file, --package package_file

Query the uninstalled package package_file, which can be a URL. If package_file is not a binary package, it is treated as a text file containing a package manifest, with each line of the manifest containing a path or one or more whitespace-separated glob expressions to be expanded to paths. These paths are then used instead of package_file as the query arguments. The manifest can contain comments that begin with a hash mark (#).

--pkgid md5

Query the package with a package identifier that is the given MD5 digest of the combined header and contents.

--querybynumber num

Query the numth database entry. Useful for debugging.

-qf, --queryformat string

Specify the format for displaying the query output, using tags to represent different types of data (e.g., NAME, FILENAME, DISTRIBUTION). The format specification is a variation of the standard printf formatting, with the type specifier omitted and replaced by the name of the header tag inclosed in brackets ({ }). For example:

%{NAME}

The tag names are case-insensitive. Use --querytags (see Miscellaneous options in Miscellaneous options) to view a list of available tags. The tag can be followed by :type to get a different output format type. The possible types are:

:armor

Wrap a public key in ASCII armor.

:arraysize

Display number of elements in array tags.

:base64

Encode binary data as base64.

:date

Use %c format as in strftime(3) to display the preferred date and time format for this locale.

:day

Use %a %b %d %Y format as in the function strftime(3). This format displays the day, the month, the month as a decimal number, and the four-digit year.

:depflags

Format dependency flags.

:fflags

Format file flags.

:hex

Use hexadecimal format.

:octal

Use octal format.

:perms

Format file permissions.

:pgpsig

Display the PGP signature and time.

:shescape

Escape single quotes for use in a script.

:triggertype

Display trigger suffix (i.e., in, un, or postun, indicating whether it’s an install, uninstall, or post-uninstall trigger).

:xml

Wrap data in simple XML markup.

--specfile specfile

Query specfile as if it were a package. Useful for extracting information from a spec file.

--tid tid

List packages with the specified transaction identifier (tid), which is a Unix timestamp. All packages installed or erased in a single transaction have the same tid.

--triggeredby pkg

List packages containing triggers that are run when the installation status of package pkg changes. For example:

$ rpm -q --triggeredby glibc
redhat-lsb-3.2-2.fc10.x86_64

In this example, the package redhat-lsb-3.2-2.fc10.x86_64 contains a -triggerpostun scriptlet that runs after glibc is uninstalled.

--whatrequires capability

List packages that require the given capability to function. For example:

$ rpm -q --whatrequires popt
popt-devel-1.13-4.fc10.x86_64
logrotate-3.7.7-1.fc10.x86_64
nash-6.0.71-2.fc10.x86_64
initscripts-8.86-1.x86_64
rpm-4.6.0-0.rc1.7.x86_6

--whatprovides capability

List packages that provide the given capability. For example:

$ rpm -q --whatprovides popt
popt-1.13-4.fc10.x86_64

Package-query options

-c, --configfiles

List configuration files in the package. Implies -l.

--changelog

Display the log of change information for the package.

-d, --docfiles

List documentation files in the package. Implies -l.

--dump

Dump information for each file in the package. The output includes the following information in this order:

path size mtime md5sum mode owner group isconfig isdoc rdev symlink

--filesbypkg

List all files in each package.

-i, --info

Display package information, including the name, version, and description. The results are formatted according to --queryformat if specified.

-l, --list

List all files in the package.

--last

List packages by install time, with the latest packages listed first.

--provides

List the capabilities this package provides.

-R, --requires

List any packages this package depends on.

-s, --state

List each file in the package and its state. The possible states are normal, not installed, or replaced. Implies -l.

--scripts

List any package-specific shell scripts used during installation and uninstallation of the package.

--triggers, --triggerscript

Display any trigger scripts in the package.

Uninstall options

The syntax for erase, the uninstall command, is:

rpm -e [uninstall-options] package_name ...
rpm --erase [uninstall-options] package_name ...

The uninstall options are:

--allmatches

Remove all versions of the package. Only one package should be specified; otherwise, an error results.

--nodeps

Don’t check dependencies before uninstalling the package.

--nopostun

Don’t run any post-uninstall scripts.

--nopreun

Don’t run any pre-uninstall scripts.

--noscripts

Don’t execute any pre-uninstall or post-uninstall scripts. This option is equivalent to --nopreun --nopostun.

--notriggerpostun

Don’t execute any post-uninstall scripts triggered by the removal of this package.

--notriggers

Don’t execute any scripts triggered by the removal of this package. Equivalent to --notriggerun --notriggerpostun.

--notriggerun

Don’t execute any uninstall scripts triggered by the removal of this package.

--test

Don’t really uninstall anything; just go through the motions. Use with -vv for debugging.

Verify options

The syntax for the verify command is:

rpm -V | --verify [package-selection-options] [verify-options]

Verify mode compares information about the installed files in a package with information about the files that came in the original package and displays any discrepancies. The information compared includes the size, MD5 sum, permissions, type, owner, and group of each file. Uninstalled files are ignored.

The package selection options include those available for query mode. In addition, the following verify options are available:

--nodeps

Ignore package dependencies.

--nodigest

Ignore package or header digests.

--nofiles

Ignore attributes of package files.

--nogroup

Ignore group ownership errors.

--nolinkto

Ignore symbolic-link errors.

--nomd5

Ignore MD5 checksum errors.

--nomode

Ignore file mode (permissions) errors.

--nordev

Ignore major and minor device number errors.

--nomtime

Ignore modification time errors.

--noscripts

Ignore any verify script.

--nosignature

Ignore package or header signatures.

--nosize

Ignore file size errors.

--nouser

Ignore user ownership errors.

The output is formatted as an eight-character string, possibly followed by an attribute marker, and then the filename. Each of the eight characters in the string represents the result of comparing one file attribute to the value of that attribute from the RPM database. A period (.) indicates that the file passed that test. The following characters indicate failure of the corresponding test:

5

MD5 sum

D

Device

G

Group

L

Symlink

M

Mode (includes permissions and file type)

S

File size

T

Mtime

U

User

The possible attribute markers are:

c

Configuration file

d

Documentation file

g

Ghost file (contents not included in package)

l

License file

r

Readme file

Database rebuild options

The syntax of the command to rebuild the RPM database is:

rpm --rebuilddb [options]

You also can build a new database:

rpm --initdb [options]

The options available with the database rebuild mode are the --dbpath, --root, and -v options described earlier under General options in General options.

Signature-check options

RPM packages may have a GPG signature built into them. There are three types of digital signature options: you can check signatures, add signatures to packages, and import signatures.

The syntax of the signature check mode is:

rpm --checksig [options] package_file...
rpm -K [options] package_file...

The signature-checking options -K and --checksig check the digests and signatures contained in the specified packages to insure the integrity and origin of the packages. Note that RPM now automatically checks the signature of any package when it is read; these options are still useful, however, for checking all headers and signatures associated with a package.

The --nosignature and --nodigest options described earlier, under Verify options in Verify options, are available for use with signature check mode.

The syntax for adding signatures to binary packages is:

rpm --addsign binary-pkgfile...
rpm --resign binary-pkgfile...

Both --addsign and --resign generate and insert new signatures, replacing any that already exist in the specified binary packages.[6]

The syntax for importing signatures is:

rpm --import public-key

The --import option is used to import an ASCII public key to the RPM database so that digital signatures for packages using that key can be verified. Imported public keys are carried in headers, and keys are kept in a ring, which can be queried and managed like any package file.

Miscellaneous options

Several additional rpm options are available:

--querytags

Print the tags available for use with the --queryformat option in query mode.

--setperms packages

Set file permissions of the specified packages to those in the database.

--setugids packages

Set file owner and group of the specified packages to those in the database.

--showrc

Show the values rpm will use for all options that can be set in an rpmrc file.

FTP/HTTP options

The following options are available for use with FTP and HTTP URLs in install, update, and query modes.

--ftpport port

Use port for making an FTP connection on the proxy FTP server instead of the default port. Same as specifying the macro %_ftpport.

--ftpproxy host

Use host as the proxy server for FTP transfers through a firewall that uses a proxy. Same as specifying the macro %_ftpproxy.

--httpport port

Use port for making an HTTP connection on the proxy HTTP server instead of the default port. Same as specifying the macro %_httpport.

--httpproxy host

Use host as the proxy server for HTTP transfers. Same as specifying the macro %_httpproxy.

[6] In older versions of RPM, --addsign was used to add new signatures without replacing existing ones, but currently both options work the same way and replace any existing signatures.

RPM Examples

Query the RPM database to find Emacs-related packages:

$ rpm -q -a | grep emacs

Query an uninstalled package, printing information about the package and listing the files it contains:

$ rpm -qpil ˜/downloads/bash-3.2-29.fc10.x86_64.rpm

Install a package (assumes superuser privileges):

$ rpm -i sudo-1.6.9p17-2.fc10.x86_64.rpm

Do the same thing, but report on the progress of the installation:

$ rpm -ivh sudo-1.6. 9p17-2.fc10.x86_64.rpm

The rpmbuild Command

The rpmbuild command is used to build RPM packages. The syntax for rpmbuild is:

rpmbuild -[b|t] stage [build-options] spec-file ...

Specify -b to build a package directly from a spec file, or -t to open a tarred, gzipped file and use its spec file.

Both forms take the following single-character stage arguments, which specify the stages, or steps, required to build a package. The stages are listed in the order they would be performed:

p

Perform the prep stage, unpacking source files and applying patches.

l

Do a list check, expanding macros in the files section of the spec file and -verifying that each file exists.

c

Perform the prep and build stages; generally equivalent to doing a make.

i

Perform the prep, build, and install stages; generally equivalent to doing a make install.

b

Perform the prep, build, and install stages, then build a binary package.

s

Build a source package.

a

Perform the prep, build, and install stages, then build both binary and source packages.

The difference between the build stage, which is one of the early steps, and building a binary package in b or ais the difference between building a working binary for the software and putting all the pieces together into a final rpm package.

rpmbuild options

The general rpm options described under General options in General options can be used with rpmbuild.

The following additional options can also be used when building an rpm file with rpmbuild:

--buildroot dir

Override the BuildRoot tag with dir when building the package.

--clean

Clean up (remove) the build files after the package has been made.

--nobuild

Go through the motions, but don’t execute any build stages. Used for testing spec files.

--rmsource

Remove the source files when the build is done. Can be used as a standalone option to clean up files separately from creating the packages.

--rmspec

Remove the spec file when the build is done. Can be used as a standalone option.

--short-circuit

Can be used with -bc and -bi to skip previous stages that already ran successfully. With --short-circuit, -bc starts directly at the build stage and -bi starts with the install stage.

--sign

Add a GPG signature to the package for verifying its integrity and origin.

--target platform

When building the package, set the macros %_target, %_target_arch, and %_target_os to the value indicated by platform.

Two other options can be used standalone with rpmbuild to recompile or rebuild a package:

--rebuild source-pkgfile...

Like --recompile, but also build a new binary package. Remove the build directory, the source files, and the spec file once the build is complete.

--recompile source-pkgfile...

Install the named source package, and prep, compile, and install the package.

Finally, the --showrc option is used to show the current rpmbuild configuration:

rpmbuild --showrc

This option shows the values that will be used for all options that can be set in rpmrc and macros files.

The Debian Package Manager

Debian GNU/Linux provides several package-management tools, primarily intended to facilitate the building, installation, and management of binary packages. In addition, the tools described here also work on other Debian-based systems such as Ubuntu, Xandros, Knoppix, and numerous others.

Debian package names generally end in .deb. The Debian package-management tools we describe include the apt commands, aptitude, dpkg, dpkg-deb, dselect, and synaptic. Each of these tools is described in detail in Debian Package Manager Command Summary in Debian Package Manager Command Summary.

Files

Some important files used by the Debian package-management tools are described briefly here:

control

Comes with each package. Documents dependencies; contains the name and version of the package, a description, maintainer, installed size, the package priority, etc.

conffiles

Comes with each package. Contains a list of the configuration files associated with the package.

preinst, postinst, prerm, postrm

Scripts developers can include in a package to be run before installation, after installation, before removal, or after removal of the package.

/var/lib/dpkg/available

Contains information about packages available on the system.

/var/lib/dpkg/status

Contains information about the status of packages available on the system.

/etc/apt/sources.list

A list for APT of package sources, used to locate packages. The sources are listed one per line, in order of preference.

/etc/apt/apt.conf

The main APT configuration file.

/etc/apt/preferences

A preferences file that controls various aspects of APT, such as letting a user select the version or release of a package to install.

/etc/dpkg/dpkg.cfg

A configuration file containing default options for dpkg.

For a user, the important file is /etc/apt/sources.list. This file is where you set up the paths to the package archives, telling apt where to go to find packages. apt is installed with a default file. You aren’t required to modify the sources in the file, but you’ll probably want to change some sources or add additional ones at some point. You might also want to change some of the options in the configuration files apt.conf, preferences, and dpkg.config if you aren’t satisfied with the defaults. The control, conffiles, and the pre- and post-install and removal script files are created by the package developers and used internally by the package-management system.

Package Priorities

Every Debian package has a priority associated with it, indicating how important the package is to the system. The priorities are:

required

The package is essential to the proper functioning of the system.

important

The package provides important functionality that enables the system to run well.

standard

The package is included in a standard system installation.

optional

The package is one that you might want to install, but you can omit it if you are short on disk space, for example.

extra

The package either conflicts with other packages that have a higher priority, has specialized requirements, or is one that you would want to install only if you need it.

The control file for dpkg, for example, shows that dpkg itself has a priority of required; dpkg-dev (which provides tools for building Debian packages) has a priority of standard; and dpkg-doc is optional.

Package and Selection States

The possible states that a package can be in are:

config-files

Only the configuration files for the package are present on the system.

half-configured

The package is unpacked, and configuration was started but not completed.

half-installed

Installation was started but not completed.

installed

The package is unpacked and configured.

not-installed

The package is not installed.

unpacked

The package is unpacked but not configured.

The possible package selection states are:

deinstall

The package has been selected for deinstallation (i.e., for removal of everything but the configuration files).

install

The package has been selected for installation.

purge

The package has been selected to be purged (i.e., for removal of everything including the configuration files).

Package Flags

Two possible package flags can be set for a package:

hold

The package should not be handled by dpkg unless forced with the --force-hold option. Holding a package keeps it at the current version, preventing it from being updated. You might hold a package, for example, if the latest version is broken and you want to stay with the version you have until a newer one is released.

reinst-required

The package is broken and needs to be reinstalled. Such a package cannot be removed unless forced with the --force-reinstreq option.

Scripts

In addition to the commands described in the next section, a number of shell and Perl scripts are included with the package manager for use in managing and building packages:

apt-file

Search for packages, specifying an action and a pattern to search for. (Perl script)

apt-rdepends

Recursively list dependencies. (Perl script)

dpkg-architecture

Determine and set the build and host architecture for package building. (Perl script)

dpkg-checkbuilddeps

Check installed packages against the build dependencies and build conflicts listed in the control file. (Perl script)

dpkg-buildpackage

A control script to help automate package building. (Shell script)

dpkg-distaddfile

Add an entry for a file to debian/files. (Perl script)

dpkg-divert

Create and manage the list of diversions, used to override the default location for installing files. (Perl script)

dpkg-genchanges

Generate an upload control file from the information in an unpacked, built source tree and the files it has generated. (Perl script)

dpkg-gencontrol

Read information from an unpacked source tree, generate a binary package control file (by default, debian/tmp/DEBIAN/control), and add an entry for the binary file to debian/files. (Perl script)

dpkg-name

Rename Debian packages to their full package names. (Shell script)

dpkg-parsechangelog

Read and parse the changelog from an unpacked source tree and write the information to standard output in machine-readable form. (Perl script)

dpkg-preconfigure

Let packages ask questions prior to installation. (Perl script)

dpkg-reconfigure

Reconfigure a package that is already installed. (Perl script)

dpkg-scanpackages

Create a Packages file from a tree of binary packages. The Packages file is used by dselect to provide a list of packages available for installation. (Perl script)

dpkg-shlibdeps

Calculate shared library dependencies for named executables. (Perl script)

dpkg-source

Pack and unpack Debian source archives. (Perl script)

dpkg-statoverride

Manage the list of stat overrides, which let dpkg override file ownership and mode when a package is installed. (Perl script)

Debian Package Manager Command Summary

For the apt- commands, options can be specified on the command line or set in the configuration file. Boolean options set in the configuration file can be overridden on the command line in a number of different ways, such as --no-opt and -opt=no, where optis the single-character or full name of the option.

Name

apt-cache

Synopsis

apt-cache [options] command

Perform low-level operations on the APT binary cache, including the ability to perform searches and produce output reports from package metadata.

Commands

add files

Add the specified package index files to the source cache. Useful for debugging.

depends pkgs

For each specified package, show a list of dependencies and packages that can fulfill them.

dotty pkgs

Graph the relationships between the specified packages. The default is to trace out all dependent packages; turn this behavior off by setting the APT::Cache::GivenOnly configuration option.

dump

List every package in the cache. Used for debugging.

dumpavail

Print a list of available packages to standard output, suitable for use with dpkg.

gencaches

Build source and package caches from the sources in sources.list and from /var/lib/dpkg/status. Equivalent to running apt-get check.

madison [pkgs]

Display a table showing the available versions of each specified package. Similar to madison, a Debian tool that checks for package versions and reports their status. This option works locally and doesn’t require access to the Debian project’s internal archive.

pkgnames [prefix]

Print a list of packages in the system. If prefix is specified, print only packages whose names begin with that prefix. Most useful with the --generate option.

policy [pkgs]

Print detailed information about the priority selection of each specified package. With no arguments, print the priorities of all sources. Useful for debugging issues related to the preferences file.

rdepends [pkgs]

Show a list of reverse dependencies for each specified package--i.e., list any packages that depend on the specified packages.

search regex

Search package names and descriptions of all available package files for the specified regular expression and print the name and short description of each matching package. With --full, the output is identical to that from the show command. With --names-only, only the package name is searched. Multiple regular expressions can be specified. Useful for finding packages when you don’t know the actual package name.

show pkgs

Display the package records for each specified package. See the -a option for more details.

showpkg pkgs

Display information about the specified packages. For each package, the output includes the available versions, packages that depend on this package, and packages that this package depends on.

showsrc pkgs

Display source package records for each specified package.

stats

Display statistics about the cache.

unmet

Display the unmet dependencies in the package cache.

Options

-a, --all-versions

Print full records for all available versions. For use with the show command. The default is to show all versions; use with --no-all-versions to display only the version that would be installed. The configuration option is APT::Cache::AllVersions.

--all-names

Cause pkgnames to print all names, including virtual packages and missing dependencies. The configuration option is APT::Cache::AllNames.

-c file, --config-file=file

Specify a configuration file to be read after the default configuration file.

-f, --full

Print full package records when searching. The configuration option is APT::Cache::ShowFull.

-g, --generate

Automatically regenerate the package cache rather than using the current cache. Default is to regenerate; turn it off with --no-generate. The configuration option is APT::Cache::Generate.

-h, --help

Print usage information and exit.

-i, --important

Print only important dependencies (Depends and Pre-Depends relations). For use with unmet. The configuration option is APT::Cache::Important.

--installed

Only produce output for currently installed packages. For use with depends and rdepends. The configuration option is APT::Cache::Installed.

-n, --names-only

Search only on package names, not long descriptions. The configuration option is APT::Cache::NamesOnly.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

-p file, --pkg-cache=file

Use the specified file for the package cache, the primary cache used by all operations. The configuration option is Dir::Cache::pkgcache.

-q, --quiet

Operate quietly, producing output for logging but no progress indicators. Use -qq for even quieter operation. The configuration option is quiet.

--recurse

Run depends or rdepends recursively, so all specified packages are printed once. The configuration option is APT::Cache::RecurseDepends.

-s file, --src-cache=file

Specify the source cache file used by gencaches. The configuration option is Dir::Cache::srcpkgcache.

-v, --version

Print version information and exit.

Name

apt-cdrom

Synopsis

apt-cdrom [options] command

Add a new CD or DVD to apt’s list of available sources. The database of CD-ROM IDs that apt maintains is /var/lib/apt/cdroms.list.

Commands

add

Add a disk to the source list.

ident

Print the identity of the current disk and the stored filename. Used for debugging.

Options

-a, --thorough

Do a thorough package scan. May be needed with some old Debian CDs to find all package locations.

-c file, --config-file=file

Specify a configuration file to be read after the default configuration file.

-d mount-point, --cdrom=mount-point

Specify the CD-ROM mount point, which must be listed in /etc/fstab. The configuration option is Acquire::cdrom::mount.

-f, --fast

Do a fast copy, assuming the files are valid and don’t all need checking. Specify this only if the disk has been run before without error. The configuration option is APT::CDROM::Fast.

-h, --help

Print help message and exit.

-m, --no-mount

Don’t mount or unmount the mount point. The configuration option is APT::CDROM::NoMount.

-n, --just-print, --recon, --no-act

Check everything, but don’t actually make any changes. The configuration option is APT::CDROM::NoAct.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

-r, --rename

Prompt for a new label and rename the disk to the new value. The configuration option is APT::CDROM::Rename.

-v, --version

Print the version information and exit.

Name

apt-config

Synopsis

apt-config [options] shell args
apt-config [options] dump

An internal program for querying configuration information, accessing the main configuration file /etc/apt/apt.conf.

Commands

dump

Display the contents of the configuration space.

shell

Access the configuration information from a shell script. The arguments are in pairs, specifying the name of a shell variable and a configuration value to query. The value may be postfixed with /x, where x is one of the following letters:

b

Return true or false.

d

Return directories.

f

Return filenames.

i

Return an integer.

Options

-c file, --config-file=file

Specify a configuration file to be read after the default configuration file.

-h, --help

Print help message and exit.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

-v, --version

Print the version information and exit.

Name

apt-extracttemplates

Synopsis

apt-extracttemplates [options] files

Extract configuration scripts and templates from the specified Debian package files. For each specified file, a line of output is generated with the following information:

package version template-file config-script

and the template files and configuration scripts are written to the directory specified with -t or --temp-dir, or by the configuration option APT::ExtractTemplates::TempDir. The filenames are in the form package.template.xxxx and package.config.xxxx.

Options

-c file, --config-file=file

Specify a configuration file to be read after the default configuration file.

-h, --help

Print help message and exit.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

-t dir, --tempdir=dir

Write the extracted template files and configuration scripts to the specified directory. The configuration option is APT::ExtractTemplates::TempDir.

-v, --version

Print the version information and exit.

Name

apt-ftparchive

Synopsis

apt-ftparchive [options] command

Generate package and other index files used to access a distribution source. The files should be generated on the source’s origin site.

Commands

clean config-file

Clean the databases used by the specified configuration file by removing obsolete records.

contents path

Search the specified directory tree recursively to generate a contents file. For each .deb file found, read the file list, sort the files by package, and write the results to standard output. Use with --db to specify a binary caching database.

generate config-file sections

Build indexes according to the specified configuration file.

packages path [override [pathprefix]]

Generate a package file from the specified directory tree. The optional override file contains information describing how the package fits into the distribution, and the optional path prefix is a string prepended to the filename fields. Similar to dpkg-scanpackages. Use with --db to specify a binary caching database.

release path

Generate a release file from the specified directory tree.

sources paths [override [pathprefix]]

Generate a source index file from the specified directory tree. The optional override file contains information used to set priorities in the index file and to modify maintainer information. The optional path prefix is a string prepended to the directory field in the generated source index. Use --source-override to specify a different source override file. Similar to dpkg-scansources.

Options

-c file, --config-file=file

Specify a configuration file to be read after the default configuration file.

--contents

Perform contents generation. If set and if package indexes are being generated with a cache database, the file listing is extracted and stored in the database. If used with generate, allows the creation of any contents files. The default is on. The configuration option is APT::FTPArchive::Contents.

-d, --db

Use a binary caching database. This option has no effect on generate. The configuration option is APT::FTPArchive::DB.

--delink

Enable delinking of files when used with the External-Links setting. The default is on; turn off with --no-delink. The configuration option is APT::FTPArchive::DeLinkAct.

-h, --help

Print help message and exit.

--md5

Generate MD5 sums for the index files. The default is on. The configuration option is APT::FTPArchive::MD5.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

-q, --quiet

Run quietly, producing logging information but no progress indicators. Use -qq for quieter operation. The configuration option is quiet.

--read-only

Make the caching databases read-only. The configuration option is APT::FTPArchive::ReadOnlyDB.

-s file, --source-override=file

Specify a source override file. Use with the sources command. See the sources command description for more information. The configuration option is APT::FTPArchive::SourceOverride.

-v, --version

Print the version information and exit.

Name

apt-get

Synopsis

apt-get [options] command [package...]

A command-line tool for handling packages. Also serves as a backend to other APT tools such as dselect, synaptic, and aptitude (all described later in this section).

Commands

autoclean

Like clean, but remove only package files that can no longer be downloaded. Set the configuration option APT::Clean-Installed to off to prevent installed packages from being erased.

autoremove

Remove packages that were automatically installed to satisfy a dependency and are no longer needed.

build-dep

Install or remove packages to satisfy the build dependencies for a source package.

clean

Clear the local repository of retrieved package files. Useful for freeing up disk space.

check

Update the package cache and check for broken dependencies.

dist-upgrade

Like upgrade, but also handle changing dependencies for new package versions intelligently. See the -f option for more information.

dselect-upgrade

Used with dselect. Track the changes made by dselect to the Status field of available packages and take actions necessary to realize that status.

install packages

Install one or more packages. Specify the package name, not the full filename. Other required packages are also retrieved and installed. With a hyphen appended to the package name, the package is removed if it is already installed. Select a version to install by appending an equals sign and the version. Select a distribution to install by appending a slash and the distribution.

purge packages

Like remove, but also purge the specified packages from the system.

remove packages

Remove one or more packages. Specify the package name, not the full filename. With a plus sign appended to the name, the package is installed.

source packages

Find source packages and download them into the current directory. If specified with --compile, the source packages are compiled into binary packages. With --download-only, the source packages are not unpacked. Select a specific version by appending an equals sign and the version.

update

Resynchronize the package overview files from their sources. Must be done before an upgrade or dist-upgrade.

upgrade

Install the latest versions of all packages currently installed. Run update first.

Options

--arch-only

Process only architecture-dependent build dependencies. Configuration option is APT::Get::Arch-Only.

--auto-remove

With install or remove, remove unused dependencies; like running the autoremove command. Configuration option is APT::Get::AutomaticRemove.

-b, --compile, --build

Compile source packages after download. The configuration option is APT::Get::Compile.

-c file, --config-file=file

Specify a configuration file to read after the default.

-d, --download-only

Retrieve package files, but don’t unpack or install them. The configuration option is APT::Get::Download-only.

--diff-only

Download only the diff file from a source archive. The configuration option is APT::Get::Diff-Only.

--dsc-only

Download only the dsc file from a source archive. The configuration option is APT::GET::Dsc-Only.

-f, --fix-broken

Try to fix a system with broken dependencies. Can be used alone or with a command. Run with the install command if you have problems installing packages. You can run the sequence:

apt-get -f install
apt-get dist-upgrade

several times to clean up interlocking dependency problems. The configuration option is APT::Get::Fix-Broken.

--force-yes

Force yes. Cause apt to continue without prompting even if it is doing something that could damage your system. Use with great caution and only if absolutely necessary. The configuration option is APT::Get::force-yes.

-h, --help

Display a help message and exit.

--ignore-hold

Ignore a hold placed on a package, which would normally prevent the package from being upgraded. Use with dist-upgrade to override many undesired holds. The configuration option is APT::Get::Ignore-Hold.

--list-cleanup

Erase obsolete files from /var/lib/apt/lists. The default is on; use --no-list-cleanup to turn it off, which you would normally do only if you frequently modify your list of sources. The configuration option is APT::Get::List-Cleanup.

-m, --ignore-missing, --fix-missing

Ignore missing or corrupted packages or packages that cannot be retrieved. Can cause problems when used with -f. The configuration option is APT::Get::Fix-Missing.

--no-download

Disable package downloading; use with --ignore-missing to force APT to use only the packages that have already been downloaded. The configuration option is APT::Get::Download.

--no-remove

Do not remove any packages; instead, abort without prompting. The configuration option is APT::Get::Remove.

--no-upgrade

Do not upgrade packages. Use with install to prevent upgrade of packages that are already installed. The configuration option is APT::Get::Upgrade.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

--only-source

Do not map the names specified with the source or build-dep commands through the binary table. With this option, only source package names can be specified. The configuration option is APT::Get::Only-Source.

--print-uris

Print Uniform Resource Indicators (URIs) of files instead of fetching them. Prints path, destination filename, size, and expected MD5 hash. The configuration option is APT::Get::Print-URIs.

--purge

Tell dpkg to do a purge instead of a remove for items that would be removed. Purging removes packages completely, including any configuration files. The configuration option is APT::Get::Purge.

-q, --quiet

Quiet mode. Omit progress indicators and produce only logging output. Use -qq to make even quieter. The configuration option is quiet.

--reinstall

Reinstall packages that are already installed, upgrading them to the latest version. The configuration option is APT::Get::ReInstall.

-s, --simulate, --just-print, --dry-run, --recon, --no-act

Go through the motions, but don’t actually make any changes to the system. The configuration option is APT::Get::Simulate.

-t rel, --target-release=rel, --default-release=rel

Retrieve packages only from the specified release. The value of rel can be a release number or a value such as “unstable.” The configuration option is APT::Default-Release.

--tar-only

Download only the tar file from a source archive. The configuration option is APT::Get::Tar-Only.

--trivial-only

Perform only operations that are considered trivial--i.e., ones that won’t harm your system, by, say, removing needed files. Unlike --assume-yes, which always answers “yes” to any prompts, --trivial-only always answers “no.” The configuration option is APT::Get::Trivial-Only.

-u, --show-upgraded

Print a list of all packages to be upgraded. The configuration option is APT::Get::Show-Upgraded.

-v, --version

Display the version and exit.

-V, --verbose-versions

Show full versions for upgraded and installed packages. The configuration option is APT::Get::Show-Versions.

-y, --yes, --assume-yes

Automatically reply “yes” to prompts and run noninteractively. Abort if there is an error. The configuration option is APT::Get::Assume-Yes.

Name

apt-sortpkgs

Synopsis

apt-sortpkgs [options] indexfiles

Sort the records in a source or package index file by package name and write the results to standard output. apt-sortpkgs also sorts the internal fields of each record.

Options

-c file, --config-file=file

Specify a configuration file to read after the default.

-h, --help

Display a help message and exit.

-o, --option

Set a configuration option. Syntax is -o group::tool=option.

-s, --source

Order by source index field. The configuration option is APT::SortPkgs::Source.

-v, --version

Display the version and exit.

Name

aptitude

Synopsis

aptitude [options] [action [arguments]]

A text-based frontend to apt, which can be run either directly from the command line or from a visual mode that runs in a terminal window.

Actions

The following actions are supported. Running aptitude with no action invokes the visual mode. Package names can be entered individually or as search patterns. A search pattern consists of terms starting with a tilde (~), followed by a character indicating the type of term, followed by the text to be searched for. The most common usage is to use ~n to search for a package name (e.g., ~nemacs, to search for packages that have emacs in their name). You can find the full list of term types in the Aptitude User’s Manual. The manual can be found in /usr/share/doc/aptitude/README on a Debian-based system. On an RPM-based system with aptitude installed, the README file may be in /usr/share/aptitude or /usr/share/doc/aptitude.

autoclean

Clean out the cache by removing only packages that can no longer be downloaded.

changelog package[=version | /archive] ...

Download and display the Debian changelog for each specified package.

clean

Clean out the cache by removing all previously downloaded .deb files.

download package[=version | /archive] ...

Download the .deb file for each specified package to the current directory. With a version, install that version; with an archive, install the version from that archive.

forbid-version package[=version] ...

Don’t allow aptitude to upgrade the package to a particular version. If no version is specified, it is assumed to be the version that would normally be used. To override later, use the install action.

forget-new

Remove internal information about what packages are “new.”

full-upgrade

Upgrade as many installed packages as possible, installing and removing packages as needed to satisfy dependencies. Formerly called dist-upgrade, which is now deprecated.

help

Display help information and exit.

hold packages

Place a hold on each specified package.

install [package[=version | /archive] ...]

Install the specified packages. With a version, install that version. With an archive, install the version in that archive. With no arguments, install any stored or pending actions. You can also use install to perform different actions on multiple packages with a single command. Append - to the package name to remove, + to install, _ to purge, = to hold a package, or : to leave the package at the current version.

keep packages

Cancel any scheduled action on the specified packages.

keep-all

Cancel all scheduled actions on all packages.

markauto packages

Mark the specified packages as automatically installed.

purge [package[=version] ...]

Remove the specified packages and their configuration files.

remove [package[=version] ...]

Remove the specified packages.

safe-upgrade

Upgrade as many packages as possible; if a package has dependency problems, avoid upgrading that package (but don’t remove it).

search patterns

Search for packages matching each of the specified patterns and display a list of matches. The full list of search terms can be found in the Aptitude User’s Manual.

show patterns

Search for packages matching each of the specified patterns and display detailed information for every match found.

unhold packages

Remove the hold on each specified package.

unmarkauto packages

Mark the specified packages as manually installed.

update

Update the list of available packages by downloading the names of new and upgradeable packages.

why, why-not packages

Display reasons why the specified packages can or cannot be installed.

Options

Most of the aptitude options have corresponding configuration options that can be set in the configuration file.

-d, --download-only

Download packages to the cache but do not install them. Configuration option is Aptitude::CmdLine::Download-Only.

-D, --show-deps

Show summaries of why packages will be automatically installed or removed. Configuration option is Aptitude::CmdLine::Show-Deps.

-f

Attempt to fix dependencies of broken packages. Configuration option is Aptitude::CmdLine::Fix-Broken.

-F format, --display-format format

Specify the output format for search. See the Aptitude User’s Manual for details on specifying the format. Configuration option is Aptitude::CmdLine::Package-Display-Format.

-h, --help

Print help message and exit.

-O order, --sort order

Specify the sort order for search output. See the Aptitude User’s Manual for details.

-P, --prompt

Always display a prompt even for actions that were explicitly requested. The corresponding configuration option is -Aptitude::CmdLine::Always-Prompt.

--purge-unused

Purge packages that are no longer required by any installed package.

-q[=n], --quiet[=n]

Run in quiet mode, suppressing progress indicators. Use multiple qs to run even quieter, or specify a number n to indicate directly the degree of quietness.

-r, --with-recommends

Treat recommendations as dependencies when installing new packages. The corresponding configuration option is Aptitude::CmdLine::Recommends-Important.

-R, --without-recommends

Do not treat recommendations as dependencies when installing new packages. The corresponding configuration option is Aptitude::CmdLine::Recommends-Important.

-s, --simulate

Go through the motions, but do not actually perform the actions. Print the actions that would be performed. Configuration option is Aptitude::Simulate.

--schedule-only

Schedule actions to be performed later, but don’t perform them now. Works with actions that modify package states; to run them later, use aptitude install with no arguments.

-t release, --target-release release

Specify the release to use for installing packages. Equivalent to adding /release to package names for the changelog, download, and show actions.The corresponding configuration option is Aptitude::CmdLine::Default-Release.

-v, --verbose

Operate verbosely, displaying additional information. Specify multiple times to get even more information displayed. The corresponding configuration option is Aptitude::CmdLine::Verbose.

-V, --show-versions

Display the version for packages being installed. Configuration option is Aptitude::CmdLine::Show-Versions.

--version

Display the version information for aptitude and exit.

--visual-preview

Start the visual interface and display the preview screen.

-w width, --width width

Specify the output display width for search. The default is the terminal width. The corresponding configuration option is Aptitude::CmdLine::Package-Display-Width.

-y, --assume-yes

Assume a yes response to a yes/no prompt and don’t display the prompt. Prompts for dangerous actions are still shown. This option overrides -P. The corresponding configuration option is Aptitude::CmdLine::Assume-Yes.

-Z

Display the disk space that will be used or freed by the packages being acted upon. The corresponding configuration option is Aptitude::CmdLine::Show-Size-Changes.

Internal options

The following options are used internally for aptitude’s visual mode. You shouldn’t need to issue them directly.

-i

Display a download preview when the program starts. Cannot be used with -u.

-S filename

Load extended state information from the specified file, not the default state file.

-u

Begin updating the package lists when the program starts. Cannot be used with -i.

Name

dpkg

Synopsis

dpkg [options] action

A tool for installing, managing, and building packages. Also serves as a frontend to dpkg-deb and dpkg-query.

dpkg actions

These actions are carried out by dpkg itself:

-A pkgfile, --record-avail pkgfile

Update the record of available files kept in /var/lib/dpkg/available with information from pkgfile. This information is used by dpkg and dselect to determine which packages are available. With -R or --recursive, pkgfile must be a directory.

-C, --audit

Search for partially installed packages and suggest how to get them working.

--clear-avail

Remove existing information about which packages are available.

--clear-selections

Set the state of every nonessential package to deinstall to deselect them before running dpkg --set-selections.

--command-fd n

Accept commands passed on the file descriptor given by n. Note that any additional options set through this file descriptor or on the command line are not reset, but remain for other commands issued during the same session.

--compare-versions ver1 op ver2

Perform a binary comparison of two version numbers. The operators lt le eq ne ge gt treat a missing version as earlier. The operators lt-nl le-nl ge-nl gt-nl treat a missing version as later (where nl is “not later”). A third set of operators (< << <= = >= >> >) is provided for compatibility with control-file syntax. dpkg returns zero for success (i.e., the condition is satisfied) and nonzero otherwise.

--configure [packages | -a | --pending]

Reconfigure one or more unpacked packages. If -a or --pending is given instead of packages, configure all packages that are unpacked but not configured. Configuring a package involves unpacking the configuration files, backing up the old configuration files, and running the postinst script if one is present.

-Dh, --debug=help

Print debugging help message and exit.

--force-help

Print help message about the --force-list options and exit. See the --force-list option description for the possible values of list.

--forget-old-unavail

Forget about uninstalled, unavailable packages.

--get-selections [pattern]

Get list of package selections and write to standard output. With pattern specified, write selections that match the pattern.

--help

Print help message and exit.

-i pkgfile, --install pkgfile

Install the package specified as pkgfile. With -R or --recursive, pkgfile must be a directory.

--license, --licence

Print dpkg license information and exit.

--print-architecture

Print the target architecture.

--print-installation-architecture

Print the host architecture for installation.

-r, --remove [packages | -a | --pending]
-P, --purge [packages | -a | --pending]

Remove or purge one or more installed packages. Removal gets rid of everything except the configuration files listed in debian/conffiles; purging also removes the configuration files. If -a or --pending is given instead of packages, dpkg removes or purges all packages that are unpacked and marked (in /var/lib/dpkg/status) for removing or purging.

--set-selections

Set package selections based on input file read from standard input.

--unpack pkgfile

Unpack the package, but don’t configure it. When used with -R or --recursive, pkgfile must be a directory.

--update-avail pkgs-file
--merge-avail pkgs-file

Update the record of available files kept in /var/lib/dpkg/available. This information is used by dpkg and dselect to determine what packages are available. Update replaces the information with the contents of the pkgs-file, distributed as Packages. Merge combines the information from Packages with the existing information. You can also use dselect update to do the same thing.

--version

Print dpkg version information and exit.

--yet-to-unpack

Search for uninstalled packages that have been selected for installation.

dpkg-deb actions

The following actions can be specified for dpkg and are passed to dpkg-deb for execution. Also see dpkg-deb.

-b dir [archive], --build dir [archive]

Build a package.

-c archive, --contents archive

List the contents of a package.

-e archive [dir], --control archive [dir]

Extract control information from a package.

-f archive [control-fields], --field archive [control-fields]

Display the control field or fields of a package.

-I archive [control-files], --info archive [control-files]

Show information about a package.

--fsys-tarfile archive

Write the filesystem tree contained in a package to standard output in tar format.

-x archive dir, --extract archive dir

Extract the files from a package.

-X archive dir, --vextract archive dir

Extract the files and display the filenames from a package.

dpkg-query actions

The following actions can be specified for dpkg and are passed to dpkg-query for execution. Also see dpkg-query.

-l, --list [pkg-name-pattern]

List all packages whose names match the specified pattern. With no pattern, list all packages in /var/lib/dpkg/available.

-L packages, --listfiles packages

List installed files that came from the specified package or packages.

-p, --print-avail package

Print the details about package from /var/lib/dpkg/available.

-s packages, --status packages

Report the status of one or more packages.

-S filename-pattern, --search filename-pattern

Search installed packages for a filename.

Options

dpkg options can be specified on the command line or set in the configuration file. Each line in the configuration file contains a single option, specified without the leading dash (-).

--abort-after=num

Abort processing after num errors. Default is 50.

--admindir= dir, --instdir= dir, --root=dir

Change default directories. admindir contains administrative files with status and other information about packages; it defaults to /var/lib/dpkg. instdiris the directory into which packages are installed; it defaults to /. Changing the root directory to dir automatically changes instdir to dir and admindir to /dir/var/lib/dpkg.

-B, --auto-deconfigure

When a package is removed, automatically deconfigure any other package that depended on it.

-Doctal, --debug=octal

Turn on debugging, with the octal value specifying the desired level of debugging information. Use -Dh or --debug=help to display the possible values. You can OR the values to get the desired output.

-E, --skip-same-version

Don’t install the package if this version is already installed.

--force-list, --no-force-list, --refuse-list

Force or refuse to force an operation. list is specified as a comma-separated list of options. With --force, a warning is printed, but processing continues. --refuse and --no-force cause processing to stop with an error. Use --force-help to display a message describing the options. The force/refuse options are:

all

Turn all force options on or off.

architecture

Process even if intended for a different architecture.

bad-path

Some programs are missing from the path.

bad-verify

Install package even if it fails to verify.

confdef

Always choose the default action for modified configuration files. If there is no default and confnew or confold is also specified, use that to decide; otherwise, ask the user.

configure-any

Configure any unpacked but unconfigured package that the package depends on.

conflicts

Permit installation of conflicting packages. Can result in problems from files being overwritten.

confmiss

Always install a missing configuration file. Be careful using this option, since it means overriding the removal of the file.

confnew

Always install the new version of a modified configuration file, unless confdef is also specified. In that case, use the default action if there is one.

confold

Keep the old version of a modified configuration file, unless confdef is also specified. In that case, use the default action if there is one.

depends

Turn dependency problems into warnings.

depends-version

Warn of version problems when checking dependencies, but otherwise ignore.

downgrade

Install even if a newer version is already installed. Forced by default. Note that no dependency checking is done, so use of this option can cause serious system problems.

hold

Process packages even if they are marked to be held.

not-root

Try to install or remove even when not logged on as root.

overwrite

Overwrite a file from one package with the same file from another package.

overwrite-dir

Overwrite one package’s directory with a file from another package.

overwrite-diverted

Overwrite a diverted file with an undiverted version.

remove-essential

Remove a package even if it is essential. Note that this can cause your system to stop working.

remove-reinstreq

Remove a package even if it is broken and is marked to require reinstallation.

-G, --refuse-downgrade

Don’t install a package if a newer version is already installed.

--ignore-depends=pkglist

Dependency problems result only in a warning for the packages in pkglist.

--log=filename

Log status updates and actions to the specified file instead of the default /var/log/dpkg.log.

--new

New binary package format. This is a dpkg-deb option.

--no-act, --dry-run, --simulate

Go through the motions, but don’t actually write any changes. Used for testing. Be sure to specify before the action; otherwise, changes might be written.

--nocheck

Ignore the contents of the control file when building a package. This is a dpkg-deb option.

--no-debsig

Do not verify package signatures.

-O, --selected-only

Process only packages that are marked as selected for installation.

--old

Old binary package format. This is a dpkg-deb option.

-R, --recursive

Recursively handle .deb files found in the directories and their subdirectories specified with -A, -i, --install, --unpack, and --avail.

--status-fd n

Send the package status information to the specified file descriptor. Can be given more than once.

Name

dpkg-deb

Synopsis

dpkg-deb action [options]

Backend command for building and managing Debian package archives. Also see dpkg; you’ll often want to use dpkg to pass commands through to dpkg-deb, rather than call dpkg-deb directly.

Actions

-b dir [archive], --build dir [archive]

Create an archive from the filesystem tree starting with directory dir. The directory must have a DEBIAN subdirectory containing the control file and any other control information. If archive is specified and is a filename, the package is written to that file; if no archive is specified, the package is written to dir.deb. If the archive already exists, it is replaced. If archiveis the name of a directory, dpkg-deb looks in the control file for the information it needs to generate the package name. (Note that for this reason, you cannot use --nocheck with a directory name.)

-c archive, --contents archive

List the filesystem-tree portion of archive.

-e archive [dir], --control archive [dir]

Extract control information from archive into the directory dir, which is created if it doesn’t exist. If dir is omitted, a DEBIAN subdirectory in the current directory is used.

-f archive [control-fields], --field archive [control-fields]

Extract information about one or more fields in the control file for archive. If no fields are provided, print the entire control file.

-h, --help

Print help information and exit.

-I archive [control-files], --info archive [control-files]

Write information about binary package archive to standard output. If no control files are provided, print a summary of the package contents; otherwise, print the control files in the order they were specified. An error message is printed to standard error for any missing components.

--fsys-tarfile archive

Extract the filesystem tree from archive, and send it to standard output in tar format. Can be used with tar to extract individual files from an archive.

--license, --licence

Print the license information and exit.

--version

Print the version number and exit.

-W archive, --show archive

Show information about the specified archive. Display package name and version on one line or customize with the --showformat option.

-x archive dir, --extract archive dir
-X archive dir, --vextract archive dir

Extract the filesystem tree from archive into the specified directory, creating dir if it doesn’t already exist. -x (--extract) works silently, while -X (--vextract) lists the files as it extracts them. Do not use this action to install packages; use dpkg instead.

Options

-D, --debug

Turn on debugging.

--new

Build a new-style archive format (this is the default).

--nocheck

Don’t check the control file before building an archive. This lets you build a broken archive.

--old

Build an old-style archive format; obsolete.

--showformat=format

Specify the output format for -W/--show. The format can include the standard escape sequences \n (newline), \r (carriage return), or \\ (backslash). Specify package fields with the syntax ${var[;width]}. Fields are right-aligned by default, or left-aligned if width is negative.

-z#

Set the compression level to the value specified by # when building an archive.

-Z type

Set the type of compression to use when building an archive. Possible values are gzip, bzip2, and none.

Name

dpkg-query

Synopsis

dpkg-query [option] command

Display information about packages listed in the dpkg database. You can also use dpkg-query as a backend for dpkg, instead of calling dpkg-query directly.

Commands

--help

Print help information and exit.

-l [patterns], --list [patterns]

List packages whose names match any of the specified patterns. With no pattern specified, list all packages in /var/lib/dpkg/status. The pattern may need to be in quotes to avoid expansion by the shell.

-L packages, --listfiles packages

List files installed on your system from each of the specified packages. This command does not list files created by package-specific installation scripts.

--license, --licence

Print the license information and exit.

-p package, --print-avail package

Display details for the specified package, as found in /var/lib/dpkg/available.

-s package, --status package

Report on the status of the specified package.

-S patterns, --search patterns

Search the installed packages for filenames matching one of the specified patterns. At least one pattern must be specified.

-W [patterns], --show [patterns]

Like -l, but the output can be customized with the --showformat option.

--version

Print version information and exit.

Options

--admindir=dir

Use dir as the location of the dpkg database. The default is /var/lib/dpkg.

-f format, --showformat=format

Specify the output format for -W/--show. The format can include the standard escape sequences \n (newline), \r (carriage return), or \\ (backslash). Specify package fields with the syntax ${var[;width]}. Fields are right-aligned by default, or left-aligned if width is negative.

Name

dpkg-split

Synopsis

dpkg-split [action] [options]

Split a binary package into smaller pieces and reassemble the pieces, either manually or in automatic mode. The automatic mode maintains a queue of parts for reassembling.

Actions

-a -o output part, --auto -o output part

Add part to the queue for automatic reassembly, and if all the parts are available, reassemble the package as output. Requires the use of the -o (or --output) option, as shown.

-d [packages], --discard [packages]

Discard parts from the automatic-assembly queue. If any packages are specified, discard only parts from those packages. Otherwise, empty the queue.

-I parts, --info parts

Print information about the specified part file or files to standard output.

-j parts, --join parts

Join the parts of a package file together from the parts specified. The default output file is package-version.deb.

-l, --listq

List the contents of the queue of parts waiting for reassembly, giving the package name, the parts that are on the queue, and the number of bytes.

-s full-package [prefix], --split full-package [prefix]

Split the package full-package into parts N of M, named prefixNofM.deb. The prefix defaults to the full-package name without the .deb extension.

-h, --help

Print help message and exit.

--license, --licence

Print license information and exit.

--version

Print version information and exit.

Options

--depotdir dir

Specify an alternate directory dir for the queue of parts waiting for reassembly. Default is /var/lib/dpkg.

--msdos

Force --split output filenames to be MS-DOS-compatible.

-Q, --npquiet

Do not print an error message for a part that doesn’t belong to a binary package when doing automatic queuing or reassembly.

-o output, --output output

Use output as the filename for a reassembled package.

-S num, --partsize num

When splitting, specify the maximum part size (num) in kilobytes. Default is 450 KB.

Name

dselect

Synopsis

dselect [options] [action]

A screen-oriented user frontend to dpkg, used to install and manage packages. See dpkg and dpkg-deb for information on building packages.

Actions

If dselect is run with no action specified on the command line, it displays the following menu:

* 0. [A]ccess   Choose the access method to use.
1. [U]pdate   Update list of available packages, if
possible.
2. [S]elect   Request which packages you want on your
system.
3. [I]nstall  Install and upgrade wanted packages.
4. [C]onfig   Configure any packages that are
unconfigured.
5. [R]emove   Remove unwanted software.
6. [Q]uit     Quit dselect.

The asterisk (on the first line) shows the currently selected option. Any of the menu items can be specified directly on the command line as an action (access, update, select, install, config, remove, quit) to go directly to the desired activity. For example:

$ dselect access

If you enter quit on the command line, dselect exits immediately without doing anything. An additional command-line action is menu, which displays the menu and is equivalent to running dselect with no action.

Options

Options can be specified both on the command line and in the dselect configuration file, /etc/dpkg/dselect.cfg.

--admindir dir

Change the directory that holds internal datafiles to dir. Default is /var/lib/dpkg.

--color colorspec, --colour colorspec

Set colors for different parts of the screen, as specified by colorspec as follows:

screenpart:[fgcolor],[bgcolor][:attr[+attr+...]]

This option can be specified multiple times, to override the default colors for different screenparts. Rather than having to specify the colors on the command line each time you run dselect, you might prefer to set them in the configuration file. The possible screen parts (going from the top of the screen to the bottom) are:

title

The screen title.

listhead

The header line above the package list.

list

The scrolling list of packages and some help text.

listsel

The selected item in the list.

pkgstate

The text showing the current state of each package.

pkgstatesel

The text showing the current state of the selected package.

infohead

The header line showing the state of the selected package.

infodesc

The short description of the package.

info

The text that displays information such as the package description.

infofoot

The last line of the screen when selecting packages.

query

Query lines.

helpscreen

The color of help screens.

Either the foreground color, the background color, or both can be specified for each screen part. The colors are given as the standard curses colors. After the color specification, you can specify a list of attributes separated by plus signs (+). The possible attributes are normal, standout, underline, reverse, blink, bright, dim, and bold. Not all attributes work on all terminals.

--expert

Run in expert mode; don’t print help messages.

-D [file], --debug [file]

Turn on debugging. Send output to file if specified.

--help

Print help message and exit.

--license, licence

Print license information and exit.

--version

Print version information and exit.

Name

synaptic

Synopsis

synaptic [options]

Graphical frontend for APT. Use in place of apt-get to install, upgrade, or remove packages from your system. With synaptic, you can view a list of all available packages, or you can break the list down in various ways to make it more manageable. From the synaptic window, you can select from a list of categories. The categories are section (e.g., view only development-related packages), package status, origin, search history, or filter.

If you choose to display by filter, there is a set of predefined filters, or you can define your own. The predefined filters include ones to display all packages, packages marked for a status change, packages that can be configured with debconf (Debian systems only), packages with broken dependencies, and packages that can be upgraded to a later version. You can edit the existing filters or define your own, by selecting Filters from the Settings menu.

Once you’ve used the selection criteria to find the list of packages, you can select a single package, or you can select multiple packages by holding down the Shift or Ctrl key. Like apt-get, first do an update to update the package lists, then you can do an install or upgrade.

To start synaptic from Gnome, select Administration → Synaptic Package Manager from the System menu. From the KDE menu, select System → Synaptic Package Manager. You can also start the graphical interface from the command line, with the command:

synaptic [options]

Options

In addition to the following options, synaptic accepts the standard GTK+ toolkit command-line options.

-f filename, --filter-file=filename

Use the specified file as an alternative filter settings file.

-h, --help

Print help message and exit.

-i num, --initial-filter=num

Start up with the filter numbered num as the initial filter.

--non-interactive

Run without prompting for user input.

-ooption, --option=option

Set an internal option. Don’t use this option unless you are sure you know what you are doing.

-r

Open with the file repository window displayed. This window lists the repositories and shows which are active.

Chapter 6. The Bash Shell

The shell is a program that acts as a buffer between you and the operating system. In its role as a command interpreter, it should (for the most part) act invisibly. There are three main uses for the shell: interactive use; customizing your Linux session by defining variables and startup files; and programming, by writing and executing shell scripts.

The original Bourne shell became the standard shell for writing shell scripts. The Bourne shell is still found in /bin/sh on Linux systems but is now usually a symbolic link to Bash. Because the Berkeley C shell (csh and later tcsh) offered better features for interactive use, such as command history and job control, for a long time the standard practice was to use the Bourne shell for programming and the C shell for daily use. David Korn at Bell Labs enhanced the Bourne shell by adding csh-like features; his shell is known as the Korn shell (ksh).

The Free Software Foundation developed a clone of the Bourne shell, written from scratch, named “Bash,” the Bourne-Again SHell. Over time, Bash has become a POSIX-compliant version of the shell, incorporating many popular features from other shells, such as csh, tcsh, and ksh. Bash is the primary shell for Linux.

Another popular shell is the Z Shell, zsh, which is similar to ksh but with many extensions. zsh differs from Bash both in being based on ksh and because it does not attempt to be POSIX-compliant the way Bash does.

This chapter covers Bash. All references are to Bash version 4, which among numerous other changes includes new features such as associative arrays and coprocesses. The following topics are presented:

- Overview of features

- Invoking the shell

- Syntax

- Functions

- Variables

- Arithmetic expressions

- Command history

- Job control

- Command execution

- Restricted shells

- Built-in commands

http://www.gnu.org/software/bash/bash.html provides information about the Bash shell, as does http://tiswww.case.edu/php/chet/bash/bashtop.html. See also Classic Shell Scripting and Learning the bash Shell (both from O’Reilly).

Overview of Features

The Bash shell provides the following features:

- Input/output redirection

- Wildcard characters (metacharacters) for filename abbreviation

- Shell variables and options for customizing your environment

- A built-in command set for writing shell programs

- Shell functions, for modularizing tasks within a shell program

- Job control

- Command-line editing (using the command syntax of either vi or emacs)

- Access to previous commands (command history)

- Integer arithmetic

- Arrays and arithmetic expressions

- Command-name abbreviation (aliasing)

- Upward compliance with POSIX

- Internationalization facilities

- An arithmetic for loop

- More ways to substitute variables

Invoking the Shell

The command interpreter for the Bash shell (bash) can be invoked as follows:

bash [options] [arguments]

Bash can execute commands from a terminal, from a file (when the first argument is an executable script), or from standard input (if no arguments remain or if -s is specified). Bash automatically prints prompts if standard input is a terminal, or if -i is given on the command line.

On Linux systems, /bin/sh is generally a link to Bash. When invoked as sh, Bash acts more like the traditional Bourne shell: Login shells read /etc/profile and ~/.profile, and regular shells read $ENV, if it’s set. Full details are available on the bash manpage.

Options

If both single- and multi-character options appear on the command line, the multi-character options must appear first.

-, --

End option processing.

-c str

Read commands from string str.

-D, --dump-strings

Print all $”...” strings in the program.

--debugger

Read the debugging profile at startup, turn on the extdebug option to shopt, and enable function tracing. For use by the Bash debugger.

--dump-po-strings

Same as -D, but output in GNU gettext po (portable object) format.

--help

Print a usage message and exit successfully

-i

Create an interactive shell (prompt for input).

--init-file file, --rcfile file

Use file as the startup file instead of ~/.bashrc for interactive shells.

--login

Shell is a login shell.

--noediting

Do not use the readline library for input, even in an interactive shell.

--noprofile

Do not read /etc/profile or any of the personal startup files.

--norc

Do not read ~/.bashrc. Enabled automatically when invoked as sh.

-O option

Enable the shopt built-in command option option.

-p

Start up as a privileged user. Don’t read $ENV or $BASH_ENV, don’t import functions from the environment, and ignore the value of $SHELLOPTS.

--posix

Turn on POSIX mode.

-r, --restricted

Create a restricted shell.

-s

Read commands from standard input; output from built-in commands goes to file descriptor 1 (standard output); all other shell output goes to file descriptor 2 (standard error).

--verbose

Same as set -v; the shell prints lines as it reads them.

--version

Print a version message and exit.

The remaining options to Bash are listed under the set built-in command.

Arguments

Arguments are assigned in order to the positional parameters $1, $2, etc. If the first argument is an executable script, commands are read from it, and the remaining arguments are assigned to $1, $2, etc. The name of the script is available as $0.

Syntax

This section describes the many symbols peculiar to the Bash shell. The topics are arranged as follows:

- Special files

- Filename metacharacters

- Quoting

- Command forms

- Redirection forms

- Coprocesses

Special Files

Bash reads one or more startup files. Some of the files are read only when a shell is a login shell.

The startup files are, in the order they are read:

1. /etc/profile. Executed automatically at login.

2. The first file found from this list: ~/.bash_profile, ~/.bash_login, or ~/.profile. Executed automatically at login.

3. ~/.bashrc is read by every shell, after the login files. However, if invoked as sh, Bash instead reads $ENV.

The getpwnam ( ) and getpwuid ( ) functions are the sources of home directories for ~name abbreviations. (On single-user systems, the user database is stored in /etc/passwd. However on networked systems, this information may come from NIS, NIS+, or LDAP — not your workstation password file.)

Filename Metacharacters

Characters

Meaning

*

Match any string of zero or more characters.

?

Match any single character.

[ abc...]

Match any one of the enclosed characters; a hyphen can specify a range (e.g., a–z, A–Z, 0–9).

[! abc...], [^ abc...]

Match any character not enclosed as above.

~

Home directory of the current user.

~ name

Home directory of user name.

~+

Current working directory ($PWD).

~-

Previous working directory ($OLDPWD).

With the extglob option on:

Characters

Meaning

?( pattern)

Match zero or one instance of pattern.

*( pattern)

Match zero or more instances of pattern.

+( pattern)

Match one or more instances of pattern.

@( pattern)

Match exactly one instance of pattern.

!( pattern)

Match any strings that don’t match pattern.

This pattern can be a sequence of patterns separated by |, meaning that the match applies to any of the patterns. This extended syntax resembles that available in egrep and awk.

Bash supports the POSIX [[= c =]] notation for matching characters that have the same weight, and [[. c .]] for specifying collating sequences. In addition, character classes, of the form [[: class :]], allow you to match the following classes of characters.

Class

Characters matched

Class

Characters matched

alnum

Alphanumeric characters

graph

Nonspace characters

alpha

Alphabetic characters

print

Printable characters

blank

Space or tab

punct

Punctuation characters

cntrl

Control characters

space

Whitespace characters

digit

Decimal digits

upper

Uppercase characters

lower

Lowercase characters

xdigit

Hexadecimal digits

Bash also accepts the [:word:] character class, which is not in POSIX. [[:word:]] is equivalent to [[:alnum:]_].

Examples

$ ls new*                 List new and new.1
$ cat ch?                 Match ch9 but not ch10
$ vi [D-R]*               Match files that begin with uppercase D through R
$ pr !(*.o|core) | lp     Print files that are not object files or core dumps

Tip

On modern systems, ranges such as [D-R] are not portable; the system’s locale may include more than just the uppercase letters from D to R in the range.

Quoting

Quoting disables a character’s special meaning and allows it to be used literally, as itself. The following table displays characters that have special meaning to the Bash shell.

Character

Meaning

;

Command separator

&

Background execution

( )

Command grouping

|

Pipe

< > &

Redirection symbols

* ? [ ] ~ + - @ !

Filename metacharacters

" ' \

Used in quoting other characters

`

Command substitution

$

Variable substitution (or command or arithmetic substitution)

space tab newline

Word separators

These characters can be used for quoting:

" "

Everything between " and " is taken literally, except for the following characters that keep their special meaning:

$

Variable (or command and arithmetic) substitution will occur.

'

Command substitution will occur.

"

This marks the end of the double quote.

' '

Everything between ' and ' is taken literally except for another '. You cannot embed another ' within such a quoted string.

\

The character following a \ is taken literally. Use within " " to escape “, $, and '. Often used to escape itself, spaces, or newlines.

$” "

Just like " ", except that locale translation is done.

$' '

Similar to ' ', but the quoted text is processed for the following escape sequences.

Sequence

Value

Sequence

Value

\a

Alert

\t

Tab

\b

Backspace

\v

Vertical tab

\c X

Control character X

\ nnn

Octal value nnn

\e

Escape

\xnn

Hexadecimal value nn

\E

Escape

\'

Single quote

\f

Form feed

\”

Double quote

\n

Newline

\\

Backslash

\r

Carriage return

Examples

$ echo 'Single quotes "protect" double quotes'
Single quotes "protect" double quotes
$ echo "Well, isn't that \"special\"?"
Well, isn't that "special"?

$ echo "You have `ls | wc -l` files in `pwd`"
You have      43 files in /home/bob
$ echo "The value of \$x is $x"
The value of $x is 100

Command Forms

Syntax

Effect

cmd &

Execute cmd in background.

cmd1 ; cmd2

Command sequence; execute multiple cmds on the same line.

{ cmd1 ; cmd2 ; }

Execute commands as a group in the current shell.

( cmd1 ; cmd2)

Execute commands as a group in a subshell.

cmd1 | cmd2

Pipe; use output from cmd1 as input to cmd2.

cmd1 ' cmd2'

Command substitution; use cmd2 output as arguments to cmd1.

cmd1 $( cmd2)

POSIX shell command substitution; nesting is allowed.

cmd $(( expression))

POSIX shell arithmetic substitution. Use the result of expression as argument to cmd.

cmd1 && cmd2

AND; execute cmd1 and then (if cmd1 succeeds) cmd2. This is a “short-circuit” operation; cmd2 is never executed if cmd1 fails.

cmd1 || cmd2

OR; execute either cmd1 or (if cmd1 fails) cmd2. This is a “short-circuit” operation; cmd2 is never executed if cmd1 succeeds.

! cmd

NOT; execute cmd, and produce a zero exit status if cmd exits with a nonzero status. Otherwise, produce a nonzero status when cmd exits with a zero status.

Examples

$ nroff file > file.txt &                          Format in the background
$ cd; ls                          Execute sequentially
$ (date; who; pwd) > logfile                          All output is redirected
$ sort file | pr −3 | lp
Sort file, page output, then print
$ vi `grep -l ifdef *.c`                          Edit files found by grep
$ egrep '(yes|no)' `cat list`
Specify a list of files to search
$ egrep '(yes|no)' $(cat list)                          POSIX version of previous
$ egrep '(yes|no)' $(< list)                          Faster, not in POSIX
$ grep XX file && lp file
Print file if it contains the pattern;
$ grep XX file || echo "XX not found"
Otherwise, echo an error message

Redirection Forms

File descriptor

Name

Common abbreviation

Typical default

0

Standard input

stdin

Keyboard

1

Standard output

stdout

Screen

2

Standard error

stderr

Screen

The usual input source or output destination can be changed, as seen in the following sections.

Simple redirection

cmd > file

Send output of cmd to file (overwrite).

cmd >> file

Send output of cmd to file (append).

cmd < file

Take input for cmd from file.

cmd << text

The contents of the shell script up to a line identical to text become the standard input for cmd (text can be stored in a shell variable). This command form is sometimes called a Here document. Input is usually typed at the keyboard or in the shell program. Commands that typically use this syntax include cat, ex, and sed. (If <<- is used, leading tabs are stripped from the contents of the here document, and the tabs are ignored when comparing input with the end-of-input text marker.) If any part of text is quoted, the input is passed through verbatim. Otherwise, the contents are processed for variable, command, and arithmetic substitutions.

cmd <<< word

Supply text of word, with trailing newline, as input to cmd. (This is known as a here string, from the free version of the rc shell.)

cmd <> file

Open file for reading and writing on the standard input. The contents are not destroyed.[7]

cmd >| file

Send output of cmd to file (overwrite), even if the shell’s noclobber option is set.

Redirection using file descriptors

Syntax

Effect

cmd >& n

Send cmd output to file descriptor n.

cmd m>& n

Same, except that output that would normally go to file descriptor m is sent to file descriptor n instead.

cmd >&-

Close standard output.

cmd <& n

Take input for cmd from file descriptor n.

cmd m<& n

Same, except that input that would normally come from file descriptor m comes from file descriptor n instead.

cmd <&-

Close standard input.

cmd <& n-

Move input file descriptor n instead of duplicating it.

cmd >& n-

Move output file descriptor n instead of duplicating it.

Multiple redirection

Syntax

Effect

cmd 2> file

Send standard error to file; standard output remains the same (e.g., the screen).

cmd > file 2>&1

Send both standard error and standard output to file.

cmd &>>file

Append both standard error and standard output to file.

cmd &> file

Same. Preferred form.

cmd >& file

Same.

cmd > f1 2> f2

Send standard output to file f1, standard error to file f2.

cmd | tee files

Send output of cmd to standard output (usually the terminal) and to files. (See the example in Chapter 3 under tee.)

cmd 2>&1 | tee files

Send standard output and error output of cmd to standard output (usually the terminal) and to files.

cmd |&

Same as cmd 2>&1 | to send standard error through a pipe.

No space should appear between file descriptors and a redirection symbol; spacing is optional in the other cases.

Examples

$ cat part1 > book
$ cat part2 part3 >> book
$ mail tim < report
$ sed 's/^/XX /g' << END_ARCHIVE
> This is often how a shell archive is "wrapped",
> bundling text for distribution.  You would normally
> run sed from a shell program, not from the command line.
> END_ARCHIVE
XX This is often how a shell archive is "wrapped",
XX bundling text for distribution.  You would normally
XX run sed from a shell program, not from the command line.

To redirect standard output to standard error:

$ echo "Usage error:  see administrator" 1>&2

The following command sends output (files found) to filelist and error messages (inaccessible files) to file no_access:

$ find / -print > filelist 2>no_access

[7] With <, the file is opened read-only, and writes on the file descriptor will fail. With <>, the file is opened read-write; it is up to the application to actually take advantage of this.

Coprocesses

A coprocess is a shell command that runs asynchronously in a subshell, connected to the originating shell by a two-way pipe. Set up a coprocess with the coproc reserved word:

coproc [NAME] command [redirections]

The reserved word coproc sets up the pipe to communicate with command and runs command in the background. NAME is the name of the coprocess (COPROC by default). If command is a complex command, NAME is optional; with a simple command, NAME must not be given and the default is used. If any redirections are specified, they are set up after the pipe has been set up.

The coprocess establishes an array with two values: NAME[0] contains the file descriptor for command output and NAME[1] contains the file descriptor for command input. The variable NAME_PID contains the process id of the coprocess. The return status is the exit status of command. You can use the wait built-in command to wait for the output of command.

Functions

A shell function is a grouping of commands within a shell script. Shell functions let you modularize your program by dividing it up into separate tasks. This way the code for each task need not be repeated every time you need to perform the task. The POSIX shell syntax for defining a function follows the Bourne shell:

name (  ) {
function body's code come here
}

Functions are invoked just as are regular shell built-in commands or external commands. The command line parameters $1, $2, and so on receive the function’s arguments, temporarily hiding the global values of $1, etc. For example:

# fatal --- print an error message and die:

fatal (  ) {                                    # defining function fatal
echo "$0: fatal error:" "$@" >&2     # messages to standard error
exit 1
}
...
if [ $# = 0 ]                            # not enough arguments
then
fatal "not enough arguments"         # call function with message
fi

A function may use the return command to return an exit value to the calling shell program. Be careful not to use exit from within a function unless you really wish to terminate the entire program.

Bash allows you to define functions using an additional keyword, function, as follows:

function fatal {
echo "$0: fatal error:" "$@" >&2     # messages to standard error
exit 1
}

All functions share traps with the “parent” shell (except the DEBUG trap, if function tracing has been turned on). With the errtrace option enabled (either set -E or set -o errtrace), functions also inherit the ERR trap. If function tracing has been enabled, functions inherit the RETURN trap. Functions may have local variables, and they may be recursive. The syntax used to define a function is irrelevant.

Variables

This section describes the following:

- Variable substitution

- Built-in shell variables

- Other shell variables

- Arrays

- Special prompt strings

Variable Substitution

No spaces should be used in the following expressions. The colon (:) is optional; if it’s included, var must be nonnull, as well as set.

Variable expression

Description

var= value ...

Set each variable var to a value.

${ var}

Use value of var; braces are optional if var is separated from the following text. They are required for array variables.

${ var:- value}

Use var if set; otherwise, use value.

${ var:= value}

Use var if set; otherwise, use value and assign value to var.

${ var:? value}

Use var if set; otherwise, print value and exit (if not interactive). If value isn’t supplied, print the phrase “parameter null or not set.”

${ var:+ value}

Use value if var is set; otherwise, use nothing.

${# var}

Use the length of var.

${#*}, ${#@}

Use the number of positional parameters.

${ var# pattern}

Use value of var after removing pattern from the left. Remove the shortest matching piece.

${ var## pattern}

Same as # pattern, but remove the longest matching piece.

${ var% pattern}

Use value of var after removing pattern from the right. Remove the shortest matching piece.

${ var%% pattern}

Same as % pattern, but remove the longest matching piece.

${! prefix*}, ${! prefix@}

List of variables whose names begin with prefix.

${ var: pos}, ${ var: pos: len}

Starting at position pos (0-based) in variable var, extract len characters, or rest of string if no len. pos and len may be arithmetic expressions.

${ var/ pat/ repl}

Use value of var, with first match of pat replaced with repl.

${ var/ pat}

Use value of var, with first match of pat deleted.

${ var// pat/ repl}

Use value of var, with every match of pat replaced with repl.

${ var/# pat/ repl}

Use value of var, with match of pat replaced with repl. Match must occur at beginning of the value.

${ var/% pat/ repl}

Use value of var, with match of pat replaced with repl. Match must occur at end of the value.

You can indirectly reference a variable by “aliasing” one variable name to affect the value of the other:

$ greet="hello, world"                    Create initial variable
$ friendly_message=greet          Aliasing variable
$ echo ${!friendly_message}       Use the alias
hello, world

Examples

$ u=up d=down blank=             Assign values to three variables (last is null)
$ echo ${u}root                  Braces are needed here
uproot
$ echo ${u-$d}
Display value of u or d; since u is set, it's printed
up
$ echo ${tmp-`date`}             If tmp is not set, the date command is executed
Thu May 7 02:09:09 EDT 2009
$ echo ${blank="no data"}        blank is set, so it is printed (a blank line)

$ echo ${blank:="no data"}       blank is set but null, so the string is printed
no data
$ echo $blank                    blank now has a new value
no data
$ tail=${PWD##*/}                Take the current directory name and remove the
longest character string ending with /, which

removes the
leading pathname and leaves the tail

Built-in Shell Variables

Built-in variables are automatically set by the shell and are typically used inside shell scripts. Built-in variables can make use of the variable substitution patterns shown previously. Note that the $ is not actually part of the variable name, although the variable is always referenced this way.

Variable

Description

$#

Number of command-line arguments.

$-

Options currently in effect (arguments supplied on command line or to set).

$?

Exit value of last executed command.

$$

Process number of current process.

$!

Process number of last background command.

$0

First word; that is, command name. This will have the full pathname if it was found via a PATH search.

$ n

Individual arguments on command line (positional parameters). If n is greater than 9, it must be specified as ${ n}.

$*, $@

All arguments on command line ($1 $2 ...).

“$*”

All arguments on command line as one string (“$1 $2 ..."). The values are separated by the first character in the IFS special variable.

“$@”

All arguments on command line, individually quoted (“$1” “$2” ...).

$_

Temporary variable; initialized to pathname of script or program being executed. Later, stores the last argument of previous command. Also stores name of matching MAIL file during mail checks.

HISTCMD

The history number of the current command.

LINENO

Current line number within the script or function.

OLDPWD

Previous working directory (set by cd).

OPTARG

Name of last option processed by getopts.

OPTIND

Numerical index of OPTARG.

PPID

Process number of this shell’s parent.

PWD

Current working directory (set by cd).

RANDOM [= n]

Generate a new random number with each reference; start with integer n, if given.

REPLY

Default reply, used by select and read.

SECONDS [= n]

Number of seconds since the shell was started, or, if n is given, number of seconds + n since the shell started.

In addition, Bash sets the following variables. Many of these variables are for use by the Bash debugger (see http://bashdb.sourceforge.net) or for providing programmable completion (see the section Programmable Completion in Programmable Completion).

Variable

Description

BASH

The full pathname used to invoke this instance of Bash.

BASH_ARGC

Array variable. Each element holds the number of arguments for the corresponding function or dot-script invocation. Set only in extended debug mode, with shopt -s extdebug.

BASH_ARGV

An array variable similar to BASH_ARGC. Each element is one of the arguments passed to a function or dot-script. It functions as a stack, with values being pushed on at each call. Thus, the last element is the last argument to the most recent function or script invocation. Set only in extended debug mode, with shopt -s extdebug.

BASH_COMMAND

The command currently executing or about to be executed. Inside a trap handler, it is the command running when the trap was invoked.

BASH_EXECUTION_STRING

The string argument passed to the -c option.

BASH_LINENO

Array variable, corresponding to BASH_SOURCE and FUNCNAME. For any given function number i (starting at 0), ${ FUNCNAME[ i]} was invoked in file ${ BASH_SOURCE[ i]} on line ${ BASH_LINENO[ i]}. The information is stored with the most recent function invocation first.

BASH_REMATCH

Array variable, assigned by the =~ operator of the [[ ]] construct. Index 0 is the text that matched the entire pattern. The other indices are the text matched by parenthesized subexpressions. This variable is read-only.

BASH_SOURCE

Array variable, containing source filenames. Each element corresponds with those in FUNCNAME and BASH_LINENO.

BASH_SUBSHELL

This variable is incremented by one each time a subshell or subshell environment is created.

BASH_VERSINFO[0]

The major version number, or release, of Bash.

BASH_VERSINFO[1]

The minor version number, or version, of Bash.

BASH_VERSINFO[2]

The patch level.

BASH_VERSINFO[3]

The build version.

BASH_VERSINFO[4]

The release status.

BASH_VERSINFO[5]

The machine type; same value as in MACHTYPE.

BASH_VERSION

A string describing the version of Bash.

COMP_CWORD

For programmable completion. Index into COMP_WORDS, indicating the current cursor position.

COMP_LINE

For programmable completion. The current command line.

COMP_POINT

For programmable completion. The position of the cursor as a character index in COMP_LINE.

COMP_WORDBREAKS

For programmable completion. The characters that the readline library treats as word separators when doing word completion.

COMP_WORDS

For programmable completion. Array variable containing the individual words on the command line.

DIRSTACK

Array variable, containing the contents of the directory stack as displayed by dirs. Changing existing elements modifies the stack, but only pushd and popd can add or remove elements from the stack.

EUID

Read-only variable with the numeric effective UID of the current user.

FUNCNAME

Array variable, containing function names. Each element corresponds with those in BASH_SOURCE and BASH_LINENO.

GROUPS

Array variable containing the list of numeric group IDs in which the current user is a member.

HISTCMD

The history number of the current command.

HOSTNAME

The name of the current host.

HOSTTYPE

A string that describes the host system.

MACHTYPE

A string that describes the host system in the GNU cpu-company-system format.

OSTYPE

A string that describes the operating system.

PIPESTATUS

An array variable containing the exit statuses of the commands in the most recent foreground pipeline.

SHELLOPTS

A colon-separated list of shell options (for set -o). If set in the environment at startup, Bash enables each option present in the list.

SHLVL

Incremented by one every time a new Bash starts up.

UID

Read-only variable with the numeric real UID of the current user.

Other Shell Variables

The following variables are not automatically set by the shell, although many of them can influence the shell’s behavior. They are typically used in your .profile file, where you can define them to suit your needs. Variables can be assigned values by issuing commands of the form:

variable=value

This list includes the type of value expected when defining these variables.

Variable expression

Description

CDPATH= dirs

Directories searched by cd ; allows shortcuts in changing directories; unset by default.

COLUMNS= n

Screen’s column width; used in line edit modes and select lists.

COMPREPLY=( words ...)

Array variable from which Bash reads the possible completions generated by a completion function.

EDITOR= file

Pathname of line-edit mode to turn on (can end in emacs or vi); used when VISUAL is not set.

EMACS

If the value starts with t, Bash assumes it’s running in an Emacs buffer and disables line editing.

ENV= file

Name of script that gets executed at startup; useful for storing alias and function definitions. For example, ENV=$HOME/.bashrc.

FCEDIT= file

Editor used by fc command (default is /bin/ed).

FIGNORE= pattern

Colon-separated list of patterns describing filenames to ignore when doing filename completion.

GLOBIGNORE= patlist

Colon-separated list of patterns describing the set of filenames to ignore during pattern matching.

HISTCONTROL= list

Colon-separated list of values controlling how commands are saved in the history file. Recognized values are: ignoredups, ignorespace, ignoreboth, and erasedups.

HISTFILE= file

File in which to store command history. Default is ~/.bash_history.

HISTFILESIZE= n

Number of lines to be kept in the history file. This may be different than the number of commands.

HISTIGNORE= list

A colon-separated list of patterns that must match the entire command line. Matching lines are not saved in the history file. An unescaped & in a pattern matches the previous history line.

HISTSIZE= n

Number of history commands to be kept in the history file.

HISTTIMEFORMAT= string

A format string for strftime(3) to use for printing timestamps along with commands from the history command. If set (even if null), Bash saves timestamps in the history file along with the commands.

HOME= dir

Home directory; set by login (from /etc/passwd file).

HOSTFILE= file

Name of a file in the same format as /etc/hosts that Bash should use to find hostnames for hostname completion.

IFS=' chars'

Input field separators; default is space, tab, and newline.

IGNOREEOF= n

Numeric value indicating how many successive EOF characters must be typed before Bash exits. If null or nonnumeric value, default is 10.

INPUTRC= file

Initialization file for the readline library. This overrides the default value of ~/.inputrc.

LANG= dir

Default value for locale, used if no LC_* variables are set.

LC_ALL= locale

Current locale; overrides LANG and the other LC_* variables.

LC_COLLATE= locale

Locale to use for character collation (sorting order).

LC_CTYPE= locale

Locale to use for character class functions.

LC_MESSAGES= locale

Locale to use for translating $”...” strings.

LC_NUMERIC= locale

Locale to use for the decimal-point character.

LINES= n

Screen’s height; used for select lists.

MAIL= file

Default file to check for incoming mail; set by login.

MAILCHECK= n

Number of seconds between mail checks; default is 600 (10 minutes).

MAILPATH= files

One or more files, delimited by a colon, to check for incoming mail. Along with each file, you may supply an optional message that the shell prints when the file increases in size. Messages are separated from the filename by a ? character, and the default message is You have mail in $_. $_ is replaced with the name of the file. For example, you might have:

MAILPATH="$MAIL?Ring! Candygram!:/etc/motd?New Login Message"

OPTERR= n

When set to 1 (the default value), Bash prints error messages from the built-in getopts command.

PATH= dirlist

One or more pathnames, delimited by colons, in which to search for commands to execute.

POSIXLY_CORRECT= string

When set at startup or while running, Bash enters POSIX mode, disabling behavior and modifying features that conflict with the POSIX standard.

PROMPT_COMMAND= command

If set, Bash executes this command each time before printing the primary prompt.

PS1= string

Primary prompt string; default is $.

PS2= string

Secondary prompt (used in multiline commands); default is >.

PS3= string

Prompt string in select loops; default is #?.

PS4= string

Prompt string for execution trace (bash -x or set -x); default is +.

SHELL= file

Name of default shell (e.g., /bin/bash). Bash sets this if it’s not in the environment at startup.

TERM= string

Terminal type.

TIMEFORMAT= string

A format string for the output for the time keyword.

TMOUT= n

If no command is typed after n seconds, exit the shell. Also affects the read command and the select loop.

VISUAL= path

Same as EDITOR, but VISUAL is checked first.

auto_resume= list

Enables the use of simple strings for resuming stopped jobs. With a value of exact, the string must match a command name exactly. With a value of substring, it can match a substring of the command name.

histchars= chars

Two or three characters that control history expansion. The first character signals a history event. The second is the “quick substitution” character, and the third indicates the start of a comment. The default value is !^#.

Arrays

Bash supports one-dimensional arrays. Elements are referenced by an index; the first element is numbered 0 and there is no upper limit on the number of elements. Arrays are initialized with a special form of assignment:

message=(hi there how are you today)

where each value (in this example, each word) becomes an element of the array.

Elements may also be assigned individually:

message[0]=hi            This is the hard way
message[1]=there
message[2]=how
message[3]=are
message[4]=you
message[5]=today

Declaring arrays is not required. Any valid reference to a subscripted variable can create an array.

Bash also provides associative arrays, where the indices are strings instead of numbers. In this case, [ and ] act like double quotes. Associative arrays are created with declare -A arrayname. Unlike indexed arrays, when assigning a value to an associative array, a subscript is always required.

When referencing arrays, use the ${ ... } syntax. This isn’t needed when referencing arrays inside (( )) (the form of let that does automatic quoting). Note that [ and ] are typed literally (i.e., they don’t stand for optional syntax).

Syntax

Effect

${ name[ i]}

Use element i of array name. i can be any arithmetic expression as described under let.

${ name}

Use element 0 of indexed array name.

${ name[*]}, ${ name[@]}

Use all elements of array name.

${# name[*]}, ${# name[@]}

Use the number of elements in array name.

The built-in commands declare, local, and readonly accept the -a option for an indexed array and the -A option for an associative array. Use the unset built-in to remove arrays or array elements. The built-ins are described in detail later in this chapter.

Special Prompt Strings

Bash processes the values of the built-in shell variables PS1, PS2, and PS4 for the following special escape sequences:

Escape sequence

Description

\a

An ASCII BEL character (octal 07).

\A

The current time in 24-hour HH:MM format.

\d

The date in “weekday month day” format.

\D{ format}

The date as specified by the strftime(3) format format. The braces are required.

\e

An ASCII Escape character (octal 033).

\h

The hostname, up to the first period.

\H

The full hostname.

\j

The current number of jobs.

\l

The basename of the shell’s terminal device.

\n

A newline character.

\r

A carriage-return character.

\s

The name of the shell (basename of $0).

\t

The current time in 24-hour HH:MM:SS format.

\T

The current time in 12-hour HH:MM:SS format.

\u

The current user’s username.

\v

The version of Bash.

\V

The release (version plus patch level) of Bash.

\w

The current directory, with $HOME abbreviated as ~.

\W

The basename of the current directory, with $HOME abbreviated as ~.

\!

The history number of this command.

\#

The command number of this command.

\$

If the effective UID is 0, a # ; otherwise a $.

\@

The current time in 12-hour a.m./p.m. format.

\ nnn

The character represented by octal value nnn.

\\

A literal backslash.

\[

Start a sequence of nonprinting characters, such as for highlighting or changing colors on a terminal.

\]

End a sequence of nonprinting characters.

In Bash, the escape sequences are processed first. After that, variable, command, and arithmetic substitutions are performed if the promptvars shell option is enabled via the shopt command (the default).

Arithmetic Expressions

The let built-in command performs integer arithmetic. You can substitute arithmetic values (for use as command arguments or in variables); base conversion is also possible.

Expression

Meaning

$(( expr ))

Use the value of the enclosed arithmetic expression.

B# n

Interpret integer n in numeric base B. For example, 8#100 specifies the octal equivalent of decimal 64.

Operators

The shell uses arithmetic operators from the C programming language; the following table lists the operators in decreasing order of precedence.

Operator

Description

++ --

Auto-increment and auto-decrement, both prefix and postfix.

+ - ! ˜

Unary plus and minus, logical negation and binary inversion (one’s complement).

**

Exponentiation.

* / %

Multiplication; division; modulus (remainder).

+ -

Addition; subtraction.

<< >>

Bitwise left shift; bitwise right shift.

< <= > >=

Less than; less than or equal to; greater than; greater than or equal to.

== !=

Equality; inequality (both evaluated left to right).

&

Bitwise AND.

^

Bitwise exclusive OR.

|

Bitwise OR.

&&

Logical AND (short-circuit).

||

Logical OR (short-circuit).

?:

Inline conditional evaluation.

= += -=

Assignment.

*= /= %=

< <= > >=

&= ^= |=

'

Sequential expression evaluation.

Examples

See the let command for more information and examples:

let "count=0" "i = i + 1"              Assign i and count
let "num % 2"                          Test for an even number
(( percent >= 0 && percent <= 100 ))   Test the range of a value

Command History

Bash lets you display or modify previous commands. Commands in the history list can be modified using:

- Line-edit mode

- The fc and hist commands

Bash also supports a command-history mechanism very similar to that of the C shell. This mechanism uses a history expansion character (! by default) to select a line from the history. Portions of the line are then selected to be included in the current line. Because the interactive line-editing features are considerably superior we do not cover those features here. See the Bash manpage for more information.

Line-Edit Mode

Line-edit mode emulates many features of the vi and emacs editors. The history list is treated like a file. When the editor is invoked, you type editing keystrokes to move to the command line you want to execute. You can also change the line before executing it. When you’re ready to issue the command, press the Enter key.

Select an editor with either set -o vi or set -o emacs ; assignment to the VISUAL or EDITOR variables has no effect. Note that vi starts in input mode; to type a vi command, press the Escape key first.

Common editing keystrokes

vi

emacs

Result

k

Ctrl-P

Get previous command.

j

Ctrl-N

Get next command.

/ string

Ctrl-R string

Get previous command containing string.

h

Ctrl-B

Move back one character.

l

Ctrl-F

Move forward one character.

b

ESC-B

Move back one word.

w

ESC-F

Move forward one word.

X

DEL

Delete previous character.

x

Ctrl-D

Delete character under cursor.

dw

ESC-D

Delete word forward.

db

ESC-H

Delete word backward.

xp

Ctrl-R

Transpose two characters.

The fc Command

fc stands for either “find command” or “fix command,” since it does both jobs. Use fc -l to list history commands and fc -e to edit them. See the fc entry in the section Built-in Commands in Built-in Commands for more information.

Examples

$ history             List the last 16 commands
$ fc -l 20 30         List commands 20 through 30
$ fc −l −5            List the last five commands
$ fc -l cat           List all commands since the last command beginning with cat
$ fc -l 50            List all commands since command 50
$ fc -ln 5 > doit     Save command 5 to file doit
$ fc -e vi 5 20       Edit commands 5 through 20 using vi
$ fc -e emacs         Edit previous command using emacs

Interactive line editing is easier to use than fc, since you can move up and down in the saved command history using your favorite editor commands (as long as your favorite editor is either vi or Emacs!). You can also use the Up and Down arrow keys to traverse the command history and the right and left arrow keys to move around in the command line.

Programmable Completion

Bash and the readline library provide completion facilities, whereby you can type part of a command name, press the Tab key, and have Bash fill in part or all of the rest of the command or filename. Programmable completion lets you, as a shell programmer, write code to customize the list of possible completions that Bash will present for a particular, partially entered word. This is accomplished through the combination of several facilities:

- The complete command allows you provide a completion specification, or compspec, for individual commands. You specify, via various options, how to tailor the list of possible completions for the particular command. This is simple, but adequate for many needs. (See the complete entry in the section Built-in Commands in Built-in Commands.)

- For more flexibility, you may use complete -F funcname command. This tells Bash to call funcname to provide the list of completions for command. You write the funcname function.

- Within the code for a -F function, the COMP* shell variables provide information about the current command line. COMPREPLY is an array into which the function places the final list of completion results.

- Also within the code for a -F function, you may use the compgen command to generate is a list of results, such as “usernames that begin with a " or “all set variables.” The intent is that such results would be used with an array assignment:

...
COMPREPLY=( $( compgen options arguments ) )
...

Compspecs may be associated with either a full pathname for a command or, more commonly, with an unadorned command name (/usr/bin/man versus plain man). In the list that follows, completions are attempted based on the options provided to the complete command.

1. Bash first identifies the command. If a pathname is used, Bash looks to see if a compspec exists for the full pathname. Otherwise, it sets the command name to the last component of the pathname, and searches for a compspec for the command name.

2. If a compspec exists, Bash uses it. If not, Bash falls back to the default built-in completions.

3. Bash performs the action indicated by the compspec to generate a list of possible matches. Of this list, only those that have the word being completed as a prefix are used for the list of possible completions. For the -d and -f options, the variable FIGNORE is used to filter out undesirable matches.

4. Bash generates filenames as specified by the -G option. GLOBIGNORE is not used to filter the results, but FIGNORE is.

5. Bash processes the argument string provided to -W. The string is split using the characters in $IFS. The resulting list provides the candidates for completion. This is often used to provide a list of options that a command accepts.

6. Bash runs functions and commands as specified by the -F and -C options. For both, Bash sets COMP_LINE and COMP_POINT as described previously. For a shell function, COMP_WORDS and COMP_CWORD are also set.
Also for both, $1 is the name of the command whose arguments are being completed, $2 is the word being completed, and $3 is the word in front of the word being completed. Bash does not filter the results of the command or function.

a. Functions named with -F are run first. The function should set the COMPREPLY array to the list of possible completions. Bash retrieves the list from there.

b. Commands provided with -C are run next, in an environment equivalent to command substitution. The command should print the list of possible completions, one per line. An embedded newline should be escaped with a backslash.

7. Once the list is generated, Bash filters the results according to the -X option. The argument to -X is a pattern specifying files to exclude. By prefixing the pattern with a !, the sense is reversed, and the pattern instead specifies that only matching files should be retained in the list.
An & in the pattern is replaced with the text of the word being completed. Use \& to produce a literal &.

8. Finally, Bash prepends or appends any prefixes or suffixes supplied with -P or -S options.

9. In the case that no matches were generated, if -o dirnames was used, Bash attempts directory name completion.

10. On the other hand, if -o plusdirs was provided, Bash adds the result of directory completion to the previously generated list.

11. Normally, when a compspec is provided, Bash’s default completions are not attempted, nor are the readline library’s default filename completions.

a. If the compspec produces no results and -o bashdefault was provided, then Bash attempts its default completions.

b. If neither the compspec, nor the Bash default completions with -o bashdefault produced any results, and -o default was provided, then Bash has the readline library attempt its filename completions.

Ian Macdonald has collected a large set of useful compspecs, often distributed as the file /etc/bash_completion.

Examples

Restrict files for the C compiler to C, C++ and assembler source files, and relocatable object files:

complete -f -X '!*.[Ccos]' gcc cc

For the man command, restrict expansions to things that have manpages:

# Simple example of programmable completion for manual pages.
# A more elaborate example appears in the bash_completion file.
# Assumes   man [num] command   command syntax.

shopt -s extglob                                    Enable extended pattern matching
_man (  ) {
local dir mandir=/usr/share/man                         Local variables

COMPREPLY=(  )                                   Clear reply list
if [[ ${COMP_WORDS[1]} = +([0-9]) ]]
Section number provided
then
# section provided: man 3 foo
dir=$mandir/man${COMP_WORDS[COMP_CWORD-1]}  Look in that directory
else
# no section, default to commands
dir=$mandir/'man[18]'                       Look in command directories
fi
COMPREPLY=( $( find $dir -type f |              Generate raw file list
sed 's;..*/;;' |                        Remove leading directories
sed 's/\.[0-9].*$//' |                 Remove trailing suffixes
grep "^${COMP_WORDS[$COMP_CWORD]}" |    Keep those that match

given prefix
sort                                    Sort final list
) )
}
complete -F _man man
Associate function with command

Job Control

Job control lets you place foreground jobs in the background, bring background jobs to the foreground, or suspend (temporarily stop) running jobs. Many job-control commands take a jobID as an argument. This argument can be specified as follows:

% n

Job number n.

% s

Job whose command line starts with string s.

%? s

Job whose command line contains string s.

%%

Current job.

%+

Current job (same as above).

%-

Previous job.

The following job-control commands are described more completely in the section Built-in Commands in Built-in Commands.

bg

Put a job in the background.

fg

Put a job in the foreground.

jobs

List active jobs.

kill

Terminate a job.

stty tostop

Stop background jobs if they try to send output to the terminal. (Note that stty is not a built-in command.)

suspend

Suspend a job-control shell (such as one created by su).

wait

Wait for background jobs to finish.

Ctrl-Z

Suspend a foreground job. Then use bg or fg. (Your terminal may use something other than Ctrl-Z as the suspend character.)

Command Execution

When you type a command to Bash, it looks in the following places until it finds a match:

1. Keywords such as if and for.

2. Aliases. You can’t define an alias whose name is a shell keyword, but you can define an alias that expands to a keyword, e.g., alias aslongas=while.(In non-POSIX mode, Bash does allow you to define an alias for a shell keyword.)

3. Special built-ins like break and continue. The list of POSIX special built-ins is . (dot), :, break, continue, eval, exec, exit, export, readonly, return, set, shift, source, times, trap, and unset.

4. Functions. When in non-POSIX mode, Bash finds functions before built-in commands.

5. Nonspecial built-ins like cd and test.

6. Scripts and executable programs, for which the shell searches in the directories listed in the PATH environment variable.

The distinction between “special” built-in commands and nonspecial ones comes from POSIX. This distinction, combined with the command command, makes it possible to write functions that override shell built-ins, such as cd. For example:

cd (  ) {                      Shell function, found before built-in cd
command cd "$@"                        Use real cd to change directory
echo now in $PWD                        Other stuff we want to do
}

Restricted Shells

A restricted shell is one that disallows certain actions, such as changing directory, setting PATH, or running commands whose names contain a / character. See the Bash manpage for the full list of restrictions.

To run a restricted shell, enter the command bash -r. Depending on your Linux distribution, you may also be able to enter the command as rbash.

You can still run shell scripts, since in that case the restricted shell calls the unrestricted version of the shell to run the script after it reads /etc/profile, $HOME/.profile, and other startup files.

Restricted shells are not used much in practice, as they are difficult to set up correctly.

Built-in Commands

Examples to be entered as a command line are shown with the $ prompt. Otherwise, examples should be treated as code fragments that might be included in a shell script. For convenience, some of the reserved words used by multiline commands are also included.

Name

!

Synopsis

! pipeline

Negate the sense of a pipeline. Returns an exit status of 0 if the pipeline exited nonzero, and an exit status of 1 if the pipeline exited zero. Typically used in if and while statements.

Example

This code prints a message if user jane is not logged on:

if ! who | grep jane > /dev/null
then
echo jane is not currently logged on
fi

Name

#

Synopsis

#

Ignore all text that follows on the same line. # is used in shell scripts as the comment character and is not really a command.

Name

#!shell

Synopsis

#!shell [option]

Used as the first line of a script to invoke the named shell. Anything given on the rest of the line is passed as a single argument to the named shell. This feature is typically implemented by the kernel, but may not be supported on some older systems. Some systems have a limit of approximately 32 characters on the maximum length of shell. For example:

#!/bin/sh

Name

:

Synopsis

:

Null command. Returns an exit status of 0. The line is still processed for side effects, such as variable and command substitutions, or I/O redirection. See the following Example and the Example under case.

Example

Check whether someone is logged in:

if who | grep $1 > /dev/null
then :   # Do nothing if user is found
else echo "User $1 is not logged in"
fi

Name

.

Synopsis

. file [arguments]

Read and execute lines in file. file does not have to be executable, but must reside in a directory searched by PATH. The arguments are stored in the positional parameters. If Bash is not in POSIX mode and file is not found in PATH, Bash looks in the current directory for the file.

Name

[[ ]]

Synopsis

[[ expression ]]

Same as test expression or [ expression ], except that [[ ]] allows additional operators. Word splitting and filename expansion are disabled. Note that the brackets ([ ]) are typed literally and that they must be surrounded by whitespace.

Additional operators

&&

Logical AND of test expressions (short circuit).

||

Logical OR of test expressions (short circuit).

<

First string is lexically “less than” the second.

>

First string is lexically “greater than” the second.

Name

alias

Synopsis

alias [option] [name[='cmd']...]

Assign a shorthand name as a synonym for cmd. If ='cmd' is omitted, print the alias for name; if name is also omitted, print all aliases. By itself or with -p, alias prints one alias per line on standard output as alias name=value. If the value contains a trailing space, the next word on the command line also becomes a candidate for alias expansion. See also unalias.

Option

-p

Print the word alias before each alias.

Example

alias dir='echo ${PWD##*/}'

Name

bg

Synopsis

bg [jobIDs]

Put current job or jobIDs in the background. See the section Job Control in Job Control.

Name

bind

Synopsis

bind [-m map] [options]
bind [-m map] [-q function] [-r sequence] [-u function]
bind [-m map] -f file
bind [-m map] -x sequence:command
bind [-m map] sequence:function
bind readline-command

Manage the readline library. Nonoption arguments have the same form as in an .inputrc file.

Options

-f file

Read key bindings from file.

-l

List the names of all the readline functions.

-m map

Use map as the keymap. Available keymaps are: emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is the same as vi-command, and emacs is the same emacs-standard.

-p

Print the current readline bindings such that they can be reread from a .inputrc file.

-P

Print the current readline bindings.

-q function

Query which keys invoke the readline function function.

-r sequence

Remove the binding for key sequence sequence.

-s

Print the current readline key sequence and macro bindings such that they can be reread from a .inputrc file.

-S

Print the current readline key sequence and macro bindings.

-u function

Unbind all keys that invoke the readline function function.

-v

Print the current readline variables such that they can be reread from a .inputrc file.

-V

Print the current readline variables.

-x sequence:command

Execute the shell command command whenever sequence is entered.

Name

break

Synopsis

break [n]

Exit from a for, while, select, or until loop (or break out of n loops).

Name

builtin

Synopsis

builtin command [ arguments ... ]

Run the shell built-in command command with the given arguments. This allows you to bypass any functions that redefine a built-in command’s name. The command command is more portable.

Example

This function lets you do your own tasks when you change directory:

cd (  ) {
builtin cd "$@"    Actually change directory
pwd           Report location
}

Name

caller

Synopsis

caller [expression]

Print the line number and source filename of the current function call or dot file. With nonzero expression, prints that element from the call stack. The most recent is zero. This command is for use by the Bash debugger.

Name

case

Synopsis

case value in
pattern1) cmds1;;
pattern2) cmds2;;
.
.
.
esac

Execute the first set of commands (cmds1) if value matches pattern1, execute the second set of commands (cmds2) if value matches pattern2, etc. The last command in each set ends with ;; and no further matches are attempted. If the set ends in ;& instead, execution continues with the commands for the next set of patterns; if it ends in ;;&, the next pattern in the list is tested. value is typically a positional parameter or other shell variable. cmds are typically Linux commands, shell programming commands, or variable assignments. Patterns can use file-generation metacharacters. Multiple patterns (separated by |) can be specified on the same line; in this case, the associated cmds are executed whenever value matches any of these patterns. See the Examples here and under eval.

A pattern may be preceded by an optional open parenthesis, as in (pattern, necessary for balancing parentheses inside a $( ) construct.

Examples

Check first command-line argument and take appropriate action:

case $1 in     # Match the first arg
no|yes) response=1;;
-[tT])  table=TRUE;;
*)      echo "unknown option"; exit 1;;
esac

Read user-supplied lines until user exits:

while :        # Null command; always true
do
printf "Type . to finish ==> "
read line
case "$line" in
.) echo "Message done"
break ;;
*) echo "$line" >> $message ;;
esac
done

Name

cd

Synopsis

cd [-LP] [dir]
cd [-LP] [-]

With no arguments, change to the user’s home directory. Otherwise, change the working directory to dir. If dir is a relative pathname but is not in the current directory, the CDPATH variable is searched. A directory of - stands for the previous directory.

Options

-L

Use the logical path (what the user typed, including any symbolic links) for cd .. and the value of PWD. This is the default.

-P

Use the actual filesystem physical path for cd .. and the value of PWD.

Name

command

Synopsis

command [-pvV] name [arg ...]

Without -v or -V, execute name with given arguments. This command bypasses any aliases or functions that may be defined for name. When used with a special built-in, it prevents the built-in from exiting the script if it fails.

Options

-p

Use a predefined, default search path, not the current value of PATH.

-v

Print a description of how the shell interprets name.

-V

Print a more verbose description of how the shell interprets name.

Example

Create an alias for rm that gets the system’s version, and runs it with the -i option:

$ alias 'rm=command -p rm -i'

Name

compgen

Synopsis

compgen [options] [string]

Generate possible completions for string according to the options and write to standard output. Options are those accepted by complete, except for -p and -r. For more information, see the entry for complete.

Name

complete

Synopsis

complete [options] command ...

Specify the way to complete arguments for each command. See Programmable Completion in Programmable Completion for more discussion.

Options

-A type

Use type to specify a list of possible completions. The type may be one of the following. Options in parentheses are alternative specifications for -A type.

alias (-a)

Alias names.

arrayvar

Array variable names.

binding

Bindings from the readline library.

builtin (-b)

Shell built-in command names.

command (-c)

Command names.

directory (-d)

Directory names.

disabled

Names of disabled shell built-in commands.

enabled

Names of enabled shell built-in commands.

export (-e)

Names of exported shell variables.

file (-f)

Filenames.

function

Names of shell functions.

group (-g)

Group names.

helptopic

Help topics as allowed by the help built-in command.

hostname

Hostnames, as found in the file named by $HOSTFILE.

job (-j)

Job names.

keyword (-k)

Shell reserved keywords.

running

Names of running jobs.

service (-s)

Service names (from /etc/services).

setopt

Valid arguments for set -o.

shopt

Valid option names for the shopt built-in command.

signal

Signal names.

stopped

Names of stopped jobs.

user (-u)

Usernames.

variable (-v)

Shell variable names.

-C command

Run command in a subshell and use its output as the list of completions.

-E

Remaining options and actions apply to completion attempts on a blank line.

-F function

Run shell function function in the current shell. Upon its return, retrieve the list of completions from the COMPREPLY array.

-G pattern

Expand pattern to generate completions.

-o option

Control the behavior of the completion specification. The value for option is one of the following:

bashdefault

Fall back to the normal Bash completions if no matches are produced.

default

Use the default readline completions if no matches are produced.

dirnames

Do directory name completion if no matches are produced.

filenames

Inform the readline library that the intended output is filenames, so that the library can do any filename-specific processing, such as adding a trailing slash for directories or removing trailing spaces.

nospace

Inform the readline library that it should not append a space to words completed at the end of a line.

plusdirs

Attempt directory completion and add any results to the list of completions already generated.

-p

With no commands, print all completion settings in a way that can be reread.

-P prefix

The prefix is added to each resulting string as a prefix after all the other options have been applied.

-r

Remove the completion settings for the given commands, or all settings if no commands.

-S suffix

The suffix is added to each resulting string as a suffix after all the other options have been applied.

-W wordlist

Split wordlist (a single shell word) using $IFS. The generated list contains the members of the split list that matched the word being completed. Each member is expanded using brace expansion, tilde expansion, parameter and variable expansion, command substitution, and arithmetic expansion. Shell quoting is respected.

-X pattern

Exclude filenames matching pattern from the filename completion list. With a leading ! in the pattern, the sense is reversed, and only filenames matching pattern are retained.

Name

continue

Synopsis

continue [n]

Skip remaining commands in a for, while, select, or until loop, resuming with the next iteration of the loop (or skipping n loops).

Name

declare

Synopsis

declare [options] [name[=value]]
typeset [options] [name[=value]]

Declare variables and manage their attributes. In function bodies, variables are local, as if declared with the local command.

Options

-a

Each name is an indexed array variable.

-A

Each name is an associative array variable.

-f

Each name is a function.

-F

For functions, print just the function name and attributes, not the function definition (body). Implies -f.

-i

Each variable is an integer; in an assignment, the value is evaluated as an arithmetic expression.

-l

Assign all values as lowercase only; convert uppercase to lowercase.

-p

With no names, print all variables and their values. With names, print the names, attributes, and values of the given variables. Used with -f, print all function names and attributes. This option causes all other options to be ignored.

-r

Mark names as read-only. Subsequent assignments will fail.

-t

Apply the trace attribute to each name. Traced functions inherit the DEBUG and RETURN traps from the shell. This attribute has no meaning for variables.

-u

Assign all values as uppercase only; convert lowercase to uppercase.

-x

Mark names for export into the environment of child processes.

With a + instead of a -, the given attribute is disabled. With no variable names, all variables having the given attribute(s) are printed in a form that can be reread as input to the shell.

Examples

$ declare -i val              Make val an integer
$ val=4+7                     Evaluate value
$ echo $val                     Show result
11

$ declare -r z=42             Make z read-only
$ z=31                        Try to assign to it
bash: z: readonly variable    Assignment fails
$ echo $z
42

$ declare -p val z            Show attributes and values
declare -i val="11"
declare -r z="42"

Name

dirs

Synopsis

dirs [-clpv] [+n] [-n]

Print the directory stack, which is managed with pushd and popd.

Options

+n

Print the nth entry from the left; first entry is zero.

-n

Print the nth entry from the right; first entry is zero.

-c

Remove all entries from (clear) the directory stack.

-l

Produce a longer listing, one that does not replace $HOME with ~.

-p

Print the directory stack, one entry per line.

-v

Print the directory stack, one entry per line, with each entry preceded by its index in the stack.

Name

disown

Synopsis

disown [-ahr] [job ...]

Remove job from the list of jobs managed by Bash.

Options

-a

Remove all jobs. With -h, mark all jobs.

-h

Instead of removing jobs from the list of known jobs, mark them to not receive SIGHUP when Bash exits.

-r

With no jobs, remove (or mark) only running jobs.

Name

do

Synopsis

do

Reserved word that precedes the command sequence in a for, while, until, or select statement.

Name

done

Synopsis

done

Reserved word that ends a for, while, until, or select statement.

Name

echo

Synopsis

echo [-eEn] [string]

Write string to standard output. (See also echo in Chapter 3.)

Options

-e

Enable interpretation of the following escape sequences, which must be quoted (or escaped with a \) to prevent interpretation by the shell:

\a

Alert (ASCII BEL).

\b

Backspace.

\c

Suppress the terminating newline (same as -n).

\e

ASCII Escape character.

\f

Formfeed.

\n

Newline.

\r

Carriage return.

\t

Tab character.

\v

Vertical-tab character.

\\

Backslash.

\0nnn

ASCII character represented by octal number nnn, where nnn is zero, one, two, or three digits and is preceded by a 0.

\nnn

ASCII character represented by octal number nnn, where nnn is one, two, or three digits.

\xHH

ASCII character represented by hexadecimal number HH, where HH is one or two hexadecimal digits.

-E

Do not interpret escape sequences, even on systems where the default behavior of the built-in echo is to interpret them.

-n

Do not print the terminating newline.

Examples

$ echo "testing printer" | lp
$ echo "Warning: ringing bell \a"

Name

enable

Synopsis

enable [-adnps] [-f file] [command ...]

Enable or disable shell built-in commands. Disabling a built-in lets you use an external version of a command that would otherwise use a built-in version, such as echo or test.

Options

-a

For use with -p, print information about all built-in commands, disabled and enabled.

-d

Remove (delete) a built-in previously loaded with -f.

-f file

Load a new built-in command command from the shared library file file.

-n

Disable the named built-in commands.

-p

Print a list of enabled built-in commands.

-s

Print only the POSIX special built-in commands. When combined with -f, the new built-in command becomes a POSIX special built-in.

Name

esac

Synopsis

esac

Reserved word that ends a case statement.

Name

eval

Synopsis

eval args

Typically, eval is used in shell scripts, and args is a line of code that contains shell variables. eval forces variable expansion to happen first and then runs the resulting command. This “double--scanning” is useful any time shell variables contain input/output redirection symbols, aliases, or other shell variables. (For example, redirection normally happens before variable expansion, so a variable containing redirection symbols must be expanded first using eval; otherwise, the redirection symbols remain uninterpreted.)

Example

This fragment of a shell script shows how eval constructs a command that is interpreted in the right order:

for option
do
case "$option" in                   Define where output goes
save) out=' > $newfile' ;;
show) out=' | more' ;;
esac
done

eval sort $file $out

Name

exec

Synopsis

exec [-a name] [-cl] [command args ... ]

Execute command in place of the current process (instead of creating a new process). exec is also useful for opening, closing, or copying file descriptors.

Options

-a name

Use name for the value of argv[0].

-c

Clear the environment before executing the program.

-l

Place a minus sign at the front of argv[0], just as login(1) does.

Examples

trap 'exec 2>&-' 0        Close standard error when

shell script exits (signal 0)

$ exec /bin/csh           Replace shell with C shell
$ exec < infile           Reassign standard input to infile

Name

exit

Synopsis

exit [n]

Exit a shell script with status n (e.g., exit 1). n can be 0 (success) or nonzero (failure). If n is not given, exit status is that of the most recent command. exit can be issued at the command line to close a window (log out). Exit statuses can range in value from 0 to 255.

Example

if [ $# -eq 0 ]
then
echo "Usage: $0 [-c] [-d] file(s)" 1>&2
exit 1               # Error status
fi

Name

export

Synopsis

export [-fn] [name=[value] ...]
export -p

Pass (export) the value of one or more shell variables, specified by name, giving them global meaning (they are local by default). For example, a variable defined in one shell script must be exported if its value is used in other programs called by the script. If a value is specified, the variable is set to that value. If no names are given, or with -p, export lists the variables exported by the current shell.

Options

-f

Names refer to functions; the functions are exported in the environment.

-n

Remove the named variables or functions from the environment.

-p

Print names and values of exported variables.

Example

In the original Bourne shell, you would type:

TERM=vt100
export TERM

In Bash, type this instead:

export TERM=vt100

Name

false

Synopsis

false

Built-in command that exits with a false return value.

Name

fc

Synopsis

fc [-lnr] [-e editor] [first [last]]
fc -s [old=new] [command]

Display or edit commands in the history list. first and last are numbers or strings specifying the range of commands to display or edit. If last is omitted, fc applies to a single command (specified by first). If both first and last are omitted, fc edits the previous command or lists the last 16. The second form of fc takes a history command, replaces old with new, and executes the modified command. If no strings are specified, command is just reexecuted. If no command is given either, the previous command is reexecuted. command is a number or string like first. See the examples in the earlier section Command History in Command History.

Options

Use only one of -e, -l or -s.

-e editor

Invoke editor to edit the specified history commands. If no editor is specified, Bash defaults first to the value of FCEDIT, then to the value of EDITOR, then to vi.

-l

List the specified command or range of commands, or list the last 16.

-n

Suppress command numbering from the -l listing.

-r

Reverse the order of the -l listing.

-s [old=new]

Replace the string old with new in the specified command and execute the modified command.

Name

fg

Synopsis

fg [jobIDs]

Bring current job or jobIDs to the foreground. See the section Job Control in Job Control.

Name

fi

Synopsis

fi

Reserved word that ends an if statement. (Don’t forget to use it!)

Name

for

Synopsis

for x [in list]
do
commands
done

For variable x (in optional list of values) do commands. If in list is omitted, “$@” (the positional parameters) is assumed.

Examples

Paginate files specified on the command line; save each result:

for file; do
pr $file > $file.tmp
done

Search chapters for a list of words (like fgrep -f):

for item in `cat program_list`
do
echo "Checking chapters for"
echo "references to program $item..."
grep -c "$item.[co]" chap*
done

Extract a one-word title from each file and use as new filename:

for file
do
name=`sed -n 's/NAME: //p' $file`
mv $file $name
done

Name

for

Synopsis

for ((init; cond; incr))
do
commandsdone

Arithmetic for loop, similar to C’s. Evaluate init. While cond is true, execute the body of the loop. Evaluate incr before retesting cond. Any one of the expressions may be omitted; a missing cond is treated as being true.

Example

Search for a phrase in each odd chapter:

for ((x=1; x <= 20; x += 2))
do
grep $1 chap$x
done

Name

function

Synopsis

[function] name (  ) { commands; }
function name { commands; }

Define name as a shell function. See the description of semantic issues in the section Functions in Functions. If the reserved word function is given, the parentheses following name are optional.

Example

Define a function to count files:

$ function fcount {
>    ls | wc -l
>}

Name

getopts

Synopsis

getopts string name [args]

Process command-line arguments (or args, if specified) and check for legal options. getopts is used in shell-script loops and is intended to ensure standard syntax for command-line options. Standard syntax dictates that command-line options begin with -. Options can be stacked: i.e., consecutive letters can follow a single -. End processing of options by specifying -- on the command line. string contains the option letters to be recognized by getopts when running the shell script. Valid options are processed in turn and stored in the shell variable name. If an option is followed by a colon, the option must be followed by one or more arguments. (Multiple arguments must be given to the command as one shell word. This is done by quoting the arguments or separating them with commas. The application must be written to expect multiple arguments in this format.) getopts uses the shell variables OPTARG, OPTIND, and OPTERR.

Name

hash

Synopsis

hash [-dlrt] [-p file] [commands]

As the shell finds commands along the search path ($PATH), it remembers the found location in an internal hash table. The next time you enter a command, the shell uses the value stored in its hash table.

With no arguments, hash lists the current hashed commands. The display shows hits (the number of times the command is called by the shell) and the command name.

With commands, the shell adds those commands to the hash table.

Options

-d

Remove (delete) just the specified commands from the hash table.

-l

Produce output in a format that can be reread to rebuild the hash table.

-p file

Associate file, assumed to be the full pathname, with command in the hash table rather than searching $PATH.

-r

Remove all commands from the hash table.

-t

With one name, print the full pathname of the command. With more than one name, print the command name and the full path, in two columns.

Besides the -r option, the hash table is also cleared when PATH is assigned. Use PATH=$PATH to clear the hash table without affecting your search path. This is most useful if you have installed a new version of a command in a directory that is earlier in $PATH than the current version of the command.

Name

help

Synopsis

help [-s] [pattern]

Print usage information on standard output for each Bash command that matches pattern. The information includes descriptions of each command’s options. With the -s option, print only brief usage information.

Examples

$ help -s cd        Short help
cd: cd [-L|-P] [dir]

$ help true         Full help
true: true
Return a successful result.

Exit Status:
Always succeeds.

Name

history

Synopsis

history [count]
history [options]

Print commands in the history list or manage the history file. With no options or arguments, display the history list with command numbers. With a count argument, print only that number of the most recent commands.

Options

-a

Append new history lines (those executed since the beginning of the session) to the history file.

-c

Clear the history list (remove all entries).

-d position

Delete the history item at position position.

-n

Read unread history lines from the history file into the history list.

-p argument ...

Perform history substitution on each argument, printing the results to standard output. The results are not saved in the history list. Each argument must be quoted.

-r

Read the history file and replace the history list with its contents.

-s argument ...

Store the arguments in the history list as a single entry.

-w

Write the current history list to the history file, overwriting the file.

Name

if

Synopsis

if condition1
then commands1
[ elif condition2
then commands2 ]
.
.
.
[ else commands3 ]
fi

If condition1 is met, do commands1; otherwise, if condition2 is met, do commands2 ; if neither is met, do commands3. Conditions are often specified with the test and [[ ]] commands. See test and [[ ]] for a full list of conditions, and see additional Examples under : and exit.

Examples

Insert a 0 before numbers less than 10:

if [ $counter -lt 10 ]
then number=0$counter
else number=$counter
fi

Make a directory if it doesn’t exist:

if [ ! -d $dir ]; then
mkdir $dir
chmod 775 $dir
fi

Name

jobs

Synopsis

jobs [options] [jobIDs]

List all running or stopped jobs, or list those specified by jobIDs. For example, you can check whether a long compilation or text format is still running. Also useful before logging out. See the section Job Control in Job Control.

Options

-l

List job IDs and process group IDs.

-n

List only jobs whose status changed since last notification.

-p

List process group IDs only.

-r

List running jobs only.

-s

List stopped jobs only.

-x cmd

Replace each job ID found in cmd with the associated process ID and then execute cmd.

Name

kill

Synopsis

kill [options] IDs

Terminate each specified process ID or job ID. You must own the process or be a privileged user. This built-in command is similar to /usr/bin/kill, described in Chapter 3. See the section Job Control in Job Control.

Options

-l

List the signal names and numbers. (Used by itself.)

-n num

Send the given signal number.

-s name

Send the given signal name.

-signal

The signal number or name (from kill -l or /usr/include/sys/signal.h). With a signal number of 9, the kill is absolute.

Name

let

Synopsis

let expressions
or
((expressions))

Perform arithmetic as specified by one or more expressions. expressions consist of numbers, operators, and shell variables (which don’t need a preceding $). Expressions must be quoted if they contain spaces or other special characters. The (( )) form does the quoting for you. For more information and examples, see Arithmetic Expressions in Arithmetic Expressions. See also expr in Chapter 3.

Examples

Each of these examples adds 1 to variable i:

i=`expr $i + 1`
let i=i+1
let "i = i + 1"
(( i = i + 1 ))
(( i += 1 ))
(( i++ ))

Name

local

Synopsis

local [option] [name[=value]]

Declares local variables for use inside functions. The option can be any option accepted by declare; see declare for the full list. It is an error to use local outside a function body.

Name

logout

Synopsis

logout

Exit a login shell. The command fails if the current shell is not a login shell.

Name

mapfile

Synopsis

mapfile [options] [array]
readarray [options] [array]

Populate an array by reading lines from standard input and placing them into the specified array. The default array is MAPFILE. Without the -O option, mapfile clears the array before assigning entries to it.

Options

-c count

Used with -C to specify the number of lines read between callback calls.

-C callback

Evaluate the callback code every time count lines are read, where count is specified by -c (default is 5000).

-n num

Read in at most num lines, or all lines if num is 0.

-O origin

Begin assigning entries to the array at index origin (default index is 0).

-s count

Discard the first count lines read.

-t

Remove a trailing line from each input line.

-u fd

Read from the given file descriptor instead of standard input.

Name

name ( )

Synopsis

[function] name (  ) {commands; }

Define name as a function. POSIX syntax. The reserved word function is optional. The function definition can be written on one line or across many. See Functions in Functions for more detailed information.

Example

$ count (  ) {
> ls | wc -l
> }

When issued at the command line, count displays the number of files in the current directory.

Name

popd

Synopsis

popd [-n] [+count] [-count]

Pop the top directory off the directory stack (as shown by the dirs command), and change to the new top directory, or manage the directory stack.

Options

-n

Don’t change to the new top directory; just manipulate the stack.

+count

Remove the item count entries from the left, as shown by dirs. Counting starts at zero. No directory change occurs.

-count

Remove the item count entries from the right, as shown by dirs. Counting starts at zero. No directory change occurs.

Name

printf

Synopsis

printf [-v var] format [val ...]

Format the specified values according to the format format and write them to standard output. The possible format character strings are those of the ANSI C printf function plus several additional strings.

Option

-v var

Write output to the variable var instead of standard output.

Additional format strings

%b

Expand escape sequences in strings (e.g., \t to tab, and so on).

%q

Print a quoted string that can be reread later on.

Example

$ date             Reformat date/time
Fri May 15 15:39:42 EDT 2009
$ printf "%(It is now %m/%d/%Y %H:%M:%S)T\n" "$(date)"
It is now 05/15/2009 15:40:10

Name

pushd

Synopsis

pushd [-n] [directory]
pushd [-n] [+count] [-count]

Add directory to the directory stack, or rotate the directory stack. With no arguments, swap the top two entries on the stack, and change to the new top entry.

Options

-n

Don’t change to the new top directory, just manipulate the stack.

+count

Rotate the stack so that the count‘th item from the left, as shown by dirs, is the new top of the stack. Counting starts at zero. The new top becomes the current directory.

-count

Rotate the stack so that the count‘th item from the right, as shown by dirs, is the new top of the stack. Counting starts at zero. The new top becomes the current directory.

Name

pwd

Synopsis

pwd [-LP]

Print your present working directory on standard output.

Options

Options give control over the use of logical versus physical treatment of the printed path. See also the entry for cd, earlier in this section.

-L

Use logical path (what the user typed, including any symbolic links) and the value of PWD for the current directory. This is the default.

-P

Use the actual filesystem physical path for the current directory with no symbolic links.

Name

read

Synopsis

read [options] [variable1] [variable2 ...]

Read one line of standard input and assign each word to the corresponding variable, with all leftover words assigned to the last variable. If only one variable is specified, the entire line is assigned to that variable. See the examples here and under case. The return status is 0 unless EOF is reached. If no variables are given, input is stored in the REPLY variable.

Options

-a array

Read into indexed array array.

-d delim

Read up to first occurrence of delim, instead of newline.

-e

Use the readline library if reading from a terminal.

-i text

If readline is being used, put text into the editing buffer.

-n count

Read at most count bytes.

-p prompt

Print prompt before reading input.

-r

Raw mode; ignore \ as a line-continuation character.

-s

Read silently; do not echo characters.

-t timeout

When reading from a terminal or pipe, if no data is entered after timeout seconds, return 1. This prevents an application from hanging forever, waiting for user input.

-u [n]

Read input from file descriptor n (default is 0).

Example

Read three variables:

$ read first last address
Sarah Caldwell 123 Main Street

$ echo "$last, $first\n$address"
Caldwell, Sarah
123 Main Street

Name

readonly

Synopsis

readonly [-afp] [variable[=value] ...]

Prevent the specified shell variables from being assigned new values. An initial value may be supplied using the assignment syntax, but that value may not be changed subsequently. If no variables are specified, readonly displays a list of variables marked read-only.

Options

-a

Each variable must refer to an indexed array.

-A

Each variable must refer to an associative array.

-f

Each variable must refer to a function.

-p

Display the output in a format that allows the list of read-only variables to be saved for rereading later.

Name

return

Synopsis

return [n]

Use inside a function definition. Exit the function with status n or with the exit status of the previously executed command.

Name

select

Synopsis

select x [in list]
do
commands
done

Display a list of menu items on standard error, numbered in the order they are specified in list. If no in list is given, items are taken from the command line (via “$@”). Following the menu is a prompt string (set by the variable PS3). At the prompt, the user selects a menu item by typing its line number, or redisplays the menu by pressing the Enter key. User input is stored in the shell variable REPLY and the value selected is stored in x. If a valid item number is typed, the commands associated with the value in x are executed and the prompt is redisplayed for the user to select a new value. Typing EOF terminates the loop.

Example

PS3="Select the item number: "
select event in Format Page View Exit
do
case "$event" in
Format) nroff $file | lp;;
Page)   pr $file | lp;;
View)   more $file;;
Exit)   exit 0;;
*   )   echo "Invalid selection";;
esac
done

The output of this script looks like this:

1. Format
2. Page
3. View
4. Exit
Select the item number:

Name

set

Synopsis

set [options arg1 arg2 ...]

With no arguments, set prints the values of all variables known to the current shell. Options can be enabled (-option) or disabled (+option). Options can also be set when the shell is invoked. (See the section Invoking the Shell in Invoking the Shell.) Arguments are assigned in order to $1, $2, etc.

Options

-a

From now on, automatically mark variables for export after defining or changing them.

-b

Print job completion messages as soon as jobs terminate; don’t wait until the next prompt.

-B

Enable brace expansion. On by default.

-C

Prevent overwriting via > redirection; use >| to overwrite files.

-e

Exit if a command yields a nonzero exit status. The ERR trap executes before the shell exits.

-E

Cause shell functions, command substitutions, and subshells to inherit the ERR trap.

-f

Ignore filename metacharacters (e.g., * ? [ ]).

-h

Locate and remember commands as they are defined. On by default.

-H

Enable csh-style (!-style) history substitution. On by default.

-k

Assignment of environment variables (var=value) takes effect regardless of where they appear on the command line. Normally, assignments must precede the command name.

-m

Enable job control; background jobs execute in a separate process group. -m is usually on by default.

-n

Read commands but don’t execute; useful for checking syntax. Ignored if the shell is interactive.

+o [mode]

With mode, disable the given shell option. Plain set +o prints the settings of all the current options in a form that can be reread by the shell later.

-o [mode]

List shell modes, or turn on mode mode. Many modes can be set by other options. Modes are:

allexport

Same as -a.

braceexpand

Same as -B.

emacs

Set command-line editor to emacs.

errexit

Same as -e.

errtrace

Same as -E.

functrace

Same as -T.

hashall

Same as -h.

histexpand

Same as -H.

history

Enable command history. On by default.

ignoreeof

Don’t process EOF signals. To exit the shell, type exit.

keyword

Same as -k.

monitor

Same as -m.

noclobber

Same as -C.

noexec

Same as -n.

noglob

Same as -f.

notify

Same as -b.

nounset

Same as -u.

onecmd

Same as -t.

physical

Same as -P.

pipefail

Change pipeline exit status to be that of the rightmost command that failed, or zero if all exited successfully.

posix

Change to POSIX mode.

privileged

Same as -p.

verbose

Same as -v.

vi

Set command-line editor to vi.

xtrace

Same as -x.

+p

Reset effective UID to real UID.

-p

Start up as a privileged user. Don’t read $ENV or $BASH_ENV, don’t import functions from the environment, and ignore the value of $SHELLOPTS.

-P

Always use physical paths for cd and pwd; do not follow symbolic links.

-t

Exit after one command is executed.

-T

Cause shell functions, command substitutions, and subshells to inherit any DEBUG and RETURN traps.

-u

In substitutions, treat unset variables as errors.

-v

Show each shell command line when read.

-x

Show commands and arguments when executed, preceded by the value of PS4. This provides step-by-step tracing of shell scripts.

-

Turn off -v and -x, and turn off option processing. Included for compatibility with older versions of the Bourne shell.

--

Used as the last option; -- turns off option processing so that arguments beginning with - are not misinterpreted as options. (For example, you can set $1 to −1.) If no arguments are given after --, unset the positional parameters.

Examples

set -- "$num" −20 −30   Set $1 to $num, $2 to −20, $3 to −30
set -vx                 Read each command line; show it
;
execute it; show it again (with arguments)
set +x                  Stop command tracing
set -o noclobber        Prevent file overwriting
set +o noclobber        Allow file overwriting again

Name

shift

Synopsis

shift [n]

Shift positional arguments (e.g., $2 becomes $1). If n is given, shift to the left n places; otherwise n is assumed to be 1. Used in while loops to iterate through command-line arguments.

Name

shopt

Synopsis

shopt [-opqsu] [options]

Set or unset shell options. With no options or just -p, print the option names and whether they are set or not.

Options

-o

Each option must be one of the shell option names for set -o, instead of the options listed in the next section.

-p

Print the option settings as shopt commands that can be reread later.

-q

Quiet mode. The exit status is zero if the given option is set, nonzero otherwise. With multiple options, all of them must be set for a zero exit status.

-s

Set the given options. With no options, print only those that are set.

-u

Unset the given options. With no options, print only those that are unset.

Settable shell options

The following list describes the behavior when set. Options marked with an asterisk (*) are enabled by default.

autocd

Attempt to cd to a directory that is given as a command name. Allowed in interactive shells only.

cdable_vars

Treat a nondirectory argument to cd as a variable whose value is the directory to go to.

cdspell

Attempt spelling correction on each directory component of an argument to cd. Allowed in interactive shells only.

checkhash

Check that commands found in the hash table still exist before attempting to use them. If not, perform a normal PATH search.

checkjobs

Display the status of any running or stopped jobs before exiting an interactive shell.

checkwinsize

Check the window size after each command and update LINES and COLUMNS if the size has changed.

cmdhist *

Save all lines of a multiline command in one history entry. This permits easy reediting of multiline commands.

compat31

Behave like version 3.1 with respect to quoted arguments to the conditional command’s =~ operator.

dirspell

During filename completion, attempt to correct the spelling of directory names if the name as given is not found.

dotglob

Include filenames starting with a period in the results of filename expansion.

execfail

Do not exit a noninteractive shell if the command given to exec cannot be executed. Interactive shells do not exit in such a case, no matter the setting of this option.

expand_aliases *

Expand aliases created with alias. Disabled in noninteractive shells.

extdebug

Enable behavior needed for debuggers:

- declare -F displays the source filename and line number for each function name argument.

- When a command run by the DEBUG trap fails, the next command is skipped.

- When a command run by the DEBUG trap inside a shell function or script sourced with . (dot) or source returns with an exit status of 2, the shell simulates a call to return.

- BASH_ARGC and BASH_ARGV are set as described earlier.

- Function tracing is enabled. Command substitutions, shell functions, and subshells invoked via (...) inherit the DEBUG and RETURN traps.

- Error tracing is enabled. Command substitutions, shell functions, and subshells invoked via (...) inherit the ERROR trap.

extglob

Enable extended pattern-matching facilities such as +(...).

extquote *

Allow $'...’ and $”...” within ${variable} expansions inside double quotes.

failglob

Cause patterns that do not match filenames to produce an error.

force_fignore *

When doing completion, ignore words matching the list of suffixes in FIGNORE, even if such words are the only possible completions.

globstar

During filename expansion, the pattern ** matches all directories and subdirectories, and filenames in directories, recursively. Only directories and subdirectories match if the pattern ends in /.

gnu_errfmt

Print error messages in the standard GNU format.

histappend

Append the history list to the file named by HISTFILE upon exit, instead of overwriting the file.

histreedit

Allow a user to reedit a failed history substitution with the readline library.

histverify

Place the results of history substitution into the readline library’s editing buffer, in case the user wishes to modify it further, instead of executing it directly.

hostcomplete *

If using readline, attempt hostname completion when a word containing an @ is being completed.

huponexit

Send a SIGHUP to all running jobs upon exiting an interactive shell.

interactive_comments *

Allow words beginning with # to start a comment in an interactive shell.

lithist

If cmdhist is also set, save multiline commands to the history file with newlines instead of semicolons.

login_shell

Set by the shell when it is a login shell. This is a read-only option.

mailwarn

Print the message “The mail in mailfile has been read” when a file being checked for mail has been accessed since the last time Bash checked it.

no_empty_cmd_completion

If using readline, do not search $PATH when a completion is attempted on an empty line.

nocaseglob

Ignore letter case when doing filename matching.

nocasematch

Ignore case when pattern-matching in case or [[ ]] conditional commands.

nullglob

Expand patterns that do not match any files to the null string, instead of using the literal pattern as an argument.

progcomp *

Enable programmable completion.

promptvars *

Perform variable, command, and arithmetic substitution on the values of PS1, PS2 and PS4.

restricted_shell

Set by the shell when it is a restricted shell. This is a read-only option.

shift_verbose

Causes shift to print an error message when the shift count is greater than the number of positional parameters.

sourcepath *

Causes the . (dot) and source commands to search $PATH in order to find the file to read and execute.

xpg_echo

Causes echo to expand escape sequences, even without the -e or -E options.

Name

source

Synopsis

source file [arguments]

Identical to the . (dot) command; see that entry.

Name

suspend

Synopsis

suspend [-f]

Suspend the current shell. Often used to stop an su command.

Option

-f

Force the suspension, even if the shell is a login shell.

Name

test

Synopsis

test condition
or
[ condition ]
or
[[ condition ]]

Evaluate a condition and, if its value is true, return a zero exit status; otherwise, return a nonzero exit status. An alternate form of the command uses [ ] rather than the word test. An additional alternate form uses [[ ]], in which case word splitting and pathname expansion are not done. (See the [[ ]] entry.) condition is constructed using the following expressions. Conditions are true if the description holds true.

File conditions

-a file, -e file

file exists.

-b file

file exists and is a block special file.

-c file

file exists and is a character special file.

-d file

file exists and is a directory.

-f file

file exists and is a regular file.

-g file

file exists, and its set-group-id bit is set.

-G file

file exists, and its group is the effective group ID.

-h file, -L file

file exists and is a symbolic link.

-k file

file exists, and its sticky bit is set.

-N file

file exists and was modified after it was last read.

-O file

file exists, and its owner is the effective user ID.

-p file

file exists and is a named pipe (FIFO).

-r file

file exists and is readable.

-s file

file exists and has a size greater than zero.

-S file

file exists and is a socket.

-t [n]

The open file descriptor n is associated with a terminal device; default n is 1.

-u file

file exists, and its set-user-id bit is set.

-w file

file exists and is writable.

-x file

file exists and is executable.

f1 -ef f2

Files f1 and f2 are linked (refer to same file).

f1 -nt f2

File f1 is newer than f2.

f1 -ot f2

File f1 is older than f2.

String conditions

string

string is not null.

-n s1

String s1 has nonzero length.

-z s1

String s1 has zero length.

s1 = = s2

Strings s1 and s2 are identical. s2 can be a wildcard pattern. Quote s2 to treat it literally. Preferred over =.

s1 != s2

Strings s1 and s2 are not identical. s2 can be a wildcard pattern. Quote s2 to treat it literally.

s1 =~ s2

String s1 matches extended regular expression s2. Quote s2 to keep the shell from expanding embedded shell metacharacters. Strings matched by parenthesized subexpressions are placed into elements of the BASH_REMATCH array. See the description of BASH_REMATCH earlier in this chapter.

s1 < s2

ASCII value of s1 precedes that of s2. (Valid only within [[ ]] construct.)

s1 > s2

ASCII value of s1 follows that of s2. (Valid only within [[ ]] construct.)

Internal shell conditions

-o opt

Shell option opt for set -o is on.

Integer comparisons

n1 -eq n2

n1 equals n2.

n1 -ge n2

n1 is greater than or equal to n2.

n1 -gt n2

n1 is greater than n2.

n1 -le n2

n1 is less than or equal to n2.

n1 -lt n2

n1 is less than n2.

n1 -ne n2

n1 does not equal n2.

Combined forms

(condition)

True if condition is true (used for grouping). For test and [ ], the ( )s should be quoted by a \. The form using [[ ]] doesn’t require quoting the parentheses.

! condition

True if condition is false.

condition1 -a condition2

True if both conditions are true.

condition1 && condition2

True if both conditions are true. (Valid only within [[ ]] construct.)

condition1 -o condition2

True if either condition is true.

condition1 || condition2

True if either condition is true. (Valid only within [[ ]] construct.)

Examples

The following examples show the first line of various statements that might use a test condition:

while test $# -gt 0            While there are arguments...
while [ -n "$1" ]              While there are nonempty arguments..
if [ $count -lt 10 ]              If $count is less than 10...
if [ -d RCS ]                   If the RCS directory exists...
if [ "$answer" != "y" ]         If the answer is not y...
if [ ! -r "$1" -o ! -f "$1" ]   If the first argument is not a readable

file or a regular file...

Name

time

Synopsis

time command

Execute command and print the total elapsed time, user time, and system time (in seconds). Same as the Linux command time (see Chapter 3), except that the built-in version can also time other built-in commands as well as all commands in a pipeline.

Name

times

Synopsis

times

Print accumulated process times for user and system.

Name

trap

Synopsis

trap [options] [[commands] signals]

Execute commands if any signals are received. Common signals include EXIT (0), HUP (1), INT (2), and TERM (15). Multiple commands must be quoted as a group and separated by semi-colons internally. If the command is the null string (i.e., trap “” signals), the signals are ignored by the shell. If the commands are omitted entirely, processing of the specified signals is reset to the default action. If the command is -, the signals are reset to their initial defaults.

If both commands and signals are omitted, list current trap assignments. See the Examples here and in exec.

Options

-l

List all signals and their numbers, like kill -l.

-p

Print the current trap settings in a form suitable for rereading later.

Signals

A list of signal names, numbers, and meanings were given earlier in the kill entry; see the listing there. The shell allows you to use either the signal number or the signal name (without the SIG prefix). In addition, the shell supports “pseudo-signals,” signal names or numbers that aren’t real operating system signals but which direct the shell to perform a specific action. These signals are:

DEBUG

Execution of any command.

ERR

Nonzero exit status.

EXIT

Exit from shell (usually when shell script finishes).

0

Same as EXIT, for historical compatibility with the Bourne shell.

RETURN

A return is executed, or a script run with . (dot) or source finishes.

Examples

trap "" INT        Ignore interrupts (signal 2)

trap INT           Obey interrupts again

Remove a $tmp file when the shell program exits, or if the user logs out, presses Ctrl-C, or does a kill:

trap "rm -f $tmp; exit" EXIT HUP INT TERM    POSIX style

trap "rm -f $tmp; exit" 0 1 2 15    Pre-POSIX Bourne shell style

Print a “clean up” message when the shell program receives signals SIGHUP, SIGINT, or SIGTERM:

trap 'echo Interrupt!  Cleaning up...' HUP INT TERM

Name

true

Synopsis

true

Built-in command that exits with a true return value.

Name

type

Synopsis

type [-afpPt] commands

Show whether each command name is a Linux command, a built-in command, an alias, a shell keyword, or a defined shell function.

Options

-a

Print all locations in $PATH that include command, including aliases and functions. Use -p together with -a to suppress aliases and functions.

-f

Suppress function lookup, as with command.

-p

If type -t would print file for a given command, this option prints the full pathname for the executable files. Otherwise, it prints nothing.

-P

Like -p, but force a PATH search, even if type -t would not print file.

-t

Print a word describing each command. The word is one of alias, builtin, file, function, or keyword, depending upon the type of each command.

Example

$ type mv read if
mv is /bin/mv
read is a shell builtin
if is a shell keyword

Name

ulimit

Synopsis

ulimit [options] [n]

Print the value of one or more resource limits, or, if n is specified, set a resource limit to n. Resource limits can be either hard (-H) or soft (-S). By default, ulimit sets both limits or prints the soft limit. The options determine which resource is acted on.

Options

-H

Hard limit. Anyone can lower a hard limit; only privileged users can raise it.

-S

Soft limit. Anyone can raise a soft limit up to the value of the hard limit.

-a

Print all limits.

-b

Maximum socket buffer size.

-c

Maximum size of core files.

-d

Maximum kilobytes of data segment or heap.

-e

Maximum scheduling priority (“nice”).

-f

Maximum size of files (the default option).

-i

Maximum number of pending signals.

-l

Maximum size of address space that can be locked in memory.

-m

Maximum kilobytes of physical memory. (Not effective on all Linux systems.)

-n

Maximum number of file descriptors.

-p

Maximum size of pipe buffers in 512-byte blocks. (May not be set.)

-q

Maximum number of bytes in POSIX message queues.

-r

Maximum real-time scheduling priority.

-s

Maximum stack size.

-t

Maximum CPU seconds.

-T

Maximum number of threads.

-u

Maximum number of processes a single user can have.

-v

Maximum kilobytes of virtual memory.

-x

Maximum number of file locks

Name

umask

Synopsis

umask [-pS] [mask]

Display or set file creation mask. If mask begins with a digit, it is treated as an octal number; otherwise it is treated as a symbolic mask. The file creation mask determines which permission bits are turned off (e.g., umask 002 produces rw-rw-r--). The mask is similar to that accepted by the chmod command.

Options

-p

Output is in a form that can be reread later by the shell.

-S

Print the current mask using symbolic notation.

Name

unalias

Synopsis

unalias names
unalias -a

Remove names from the alias list. See also alias.

Option

-a

Remove all aliases.

Name

unset

Synopsis

unset [options] names

Erase definitions of functions or variables listed in names.

Options

-f

Unset functions names.

-v

Unset shell variables names (default).

Name

until

Synopsis

until condition
do
commands
done

Until condition is met, do commands. condition is often specified with the test command. See the Examples under case and test.

Name

wait

Synopsis

wait [ID]

Pause in execution until all background jobs complete (exit status 0 is returned), or pause until the specified background process ID or job ID completes (exit status of ID is returned). Note that the shell variable $! contains the process ID of the most recent background process.

Example

wait $!           Wait for most recent background process to finish

Name

while

Synopsis

while condition
do
commands
done

While condition is met, do commands. condition is often specified with the test command. See the Examples under case and test.

Chapter 7. Pattern Matching

A number of Linux text-processing utilities let you search for, and in some cases change, text patterns rather than fixed strings. These utilities include the editing programs ed, ex, vi, and sed; the gawk programming language; and the commands grep and egrep. Text patterns (called regular expressions in computer science literature) contain normal characters mixed with special characters (called metacharacters).

Perl’s regular expression support is so rich that it does not fit into this book; you can find a description in the O’Reilly books Mastering Regular Expressions by Jeffrey E.F. Friedl, Regular Expression Pocket Reference by Tony Stubblebine, Perl in a Nutshell by Nathan Patwardhan et al., or Perl 5 Pocket Reference by Johan Vromans. The Emacs editor also provides regular expressions similar to those shown in this chapter. See the O’Reilly books Learning GNU Emacs by Debra Cameron et al., or GNU Emacs Pocket Reference, also by Debra Cameron, for details.

This chapter presents the following topics:

- Filenames versus patterns

- Description of metacharacters

- List of metacharacters available to each program

- Examples

For more information on regular expressions, see the aforementioned O’Reilly book Mastering Regular Expressions.

Filenames Versus Patterns

Metacharacters used in pattern matching are different from metacharacters used for filename expansion (see Chapter 6). However, several metacharacters have meaning for both regular expressions and for filename expansion. This can lead to a problem: the shell sees the command line first, and can potentially interpret an unquoted regular expression metacharacter as a filename expansion. For example, the command:

$ grep [A-Z]* chap[12]

could be transformed by the shell into:

$ grep Array.c Bug.c Comp.c chap1 chap2

and grep would then try to find the pattern Array.c in files Bug.c, Comp.c, chap1, and chap2. To bypass the shell and pass the special characters to grep, use quotes as follows:

$ grep "[A-Z]*" chap[12]

Double quotes suffice in most cases, but single quotes are the safest bet, since the shell does absolutely no expansions on single-quoted text.

Note also that in pattern matching, ? matches zero or one instance of a regular expression; in filename expansion, ? matches a single character.

Metacharacters

Different metacharacters have different meanings, depending upon where they are used. In particular, regular expressions used for searching through text (matching) have one set of metacharacters, while the metacharacters used when processing replacement text (such as in a text editor) have a different set. These sets also vary somewhat per program. This section covers the metacharacters used for searching and replacing, with descriptions of the variants in the different utilities.

Search Patterns

The characters in the following table have special meaning only in search patterns.

Character

Pattern

.

Match any single character except newline. Can match newline in gawk.

*

Match any number (or none) of the single character that immediately precedes it. The preceding character can also be a regular expression. For example, since . (dot) means any character, .* means “match any number of any character.”

^

Match the following regular expression at the beginning of the line or string.

$

Match the preceding regular expression at the end of the line or string.

[ ]

Match any one of the enclosed characters. A hyphen (-) indicates a range of consecutive characters. A circumflex (^) as the first character in the brackets reverses the sense: it matches any one character not in the list. A hyphen or close bracket (]) as the first character is treated as a member of the list. All other metacharacters are treated as members of the list (i.e., literally).

{n,m}

Match a range of occurrences of the single character that immediately precedes it. The preceding character can also be a regular expression. {n} matches exactly n occurrences, {n,} matches at least n occurrences, and {n,m} matches any number of occurrences between n and m. n and m must be between 0 and 255, inclusive. (The GNU programs on Linux allow a range of 0 to 32767.)

\{n,m\}

Just like {n,m}, earlier, but with backslashes in front of the braces.

\

Turn off the special meaning of the following character.

\( \)

Save the subpattern enclosed between \( and \) into a special holding space. Up to nine subpatterns can be saved on a single line. The text matched by the subpatterns can be “replayed” in substitutions by the escape sequences \1 to \9.

\n

Replay the nth subpattern enclosed in \( and \) into the pattern at this point. n is a number from 1 to 9, with 1 starting on the left. See the following Examples.

\< \>

Match characters at beginning (\<) or end (\>) of a word.

+

Match one or more instances of preceding regular expression.

?

Match zero or one instances of preceding regular expression.

|

Match one or the other of the regular expressions specified before and after the vertical bar. (This is known as alternation.)

( )

Apply a match to the enclosed group of regular expressions.

Linux allows the use of POSIX “character classes” within the square brackets that enclose a group of characters. They are typed enclosed in [: and :]. For example, [[:alnum:]] matches a single alphanumeric character.

Class

Characters matched

Class

Characters matched

alnum

Alphanumeric characters

lower

Lowercase characters

alpha

Alphabetic characters

print

Printable characters

blank

Space or Tab

punct

Punctuation characters

cntrl

Control characters

space

Whitespace characters

digit

Decimal digits

upper

Uppercase characters

graph

Non-space characters

xdigit

Hexadecimal digits

Finally, the GNU utilities on Linux accept additional escape sequences that act like metacharacters. (Because \b can also be interpreted as the sequence for the ASCII Backspace character, different utilities treat it differently. Check each utility’s documentation.)

Sequence

Meaning

\b

Word boundary, either beginning or end of a word, as for the \< and \> metacharacters described earlier.

\B

Interword match; matches between two word-constituent characters.

\w

Matches any word-constituent character; equivalent to [[:alnum:]_].

\W

Matches any non-word-constituent character; equivalent to [^[:alnum:]_].

\`

Beginning of an Emacs buffer. Used by most other GNU utilities to mean unambiguously “beginning of string.”

\'

End of an Emacs buffer. Used by most other GNU utilities to mean unambiguously “end of string.”

Replacement Patterns

The characters in the following table have special meaning only in replacement patterns, used for example in editing, when searching for and replacing text.

Character

Pattern

\

Turn off the special meaning of the following character.

\n

Reuse the text matched by the nth subpattern previously saved by \( and \) as part of the replacement pattern. n is a number from 1 to 9, with 1 starting on the left.

&

Reuse the text matched by the search pattern as part of the replacement pattern.

~

Reuse the previous replacement pattern in the current replacement pattern. Must be the only character in the replacement pattern (ex and vi).

%

Reuse the previous replacement pattern in the current replacement pattern. Must be the only character in the replacement pattern (ed).

\u

Convert the first character of replacement pattern to uppercase.

\U

Convert the entire replacement pattern to uppercase.

\l

Convert the first character of replacement pattern to lowercase.

\L

Convert the entire replacement pattern to lowercase.

\e

Turn off previous \u or \l.

\E

Turn off previous \U or \L.

Metacharacters, Listed by Program

Some metacharacters are valid for one program but not for another. Those that are available are marked by a bullet (•) in the following table. Items marked with a “P” are specified by POSIX. Full descriptions were provided in the previous section.

Symbol

ed

ex

vi

sed

gawk

grep

egrep

Action

•

•

•

•

•

•

•

•

Match any character.

*

•

•

•

•

•

•

•

Match zero or more preceding characters.

^

•

•

•

•

•

•

•

Match beginning of line/string.

$

•

•

•

•

•

•

•

Match end of line/string.

\

•

•

•

•

•

•

•

Escape following character.

[ ]

•

•

•

•

•

•

•

Match one from a set.

\( \)

•

•

•

•

•

Store pattern for later replay.[a]

\n

•

•

•

•

•

Replay subpattern in match.

{ }

• P

• P

Match a range of instances.

\{ \}

•

•

•

Match a range of instances.

\< \>

•

•

•

Match word’s beginning or end.

+

•

•

Match one or more preceding characters.

?

•

•

Match zero or one preceding characters.

|

•

•

Separate choices to match.

( )

•

•

Group expressions to match.

[a] Stored subpatterns can be “replayed” during matching. See the following table.

Note that in ed, ex, vi, and sed, you specify both a search pattern (on the left) and a replacement pattern (on the right). The metacharacters listed above are meaningful only in a search pattern.

In ed, ex, vi, and sed, the metacharacters in the following table are valid only in a replacement pattern.

Symbol

ex

vi

sed

ed

Action

\

•

•

•

•

Escape following character.

\n

•

•

•

•

Text matching pattern stored in \( \).

&

•

•

•

•

Text matching search pattern.

~

•

•

Reuse previous replacement pattern.

%

•

Reuse previous replacement pattern.

\u \U

•

•

Change character(s) to uppercase.

\l \L

•

•

Change character(s) to lowercase.

\e

•

•

Turn off previous \u or \l.

\E

•

•

Turn off previous \U or \L.

Examples of Searching

When used with grep or egrep, regular expressions should be surrounded by quotes. (If the pattern contains a $, you must use single quotes; e.g., 'pattern'.) When used with ed, ex, sed, and gawk, regular expressions are usually surrounded by /, although (except for gawk) any delimiter works. The following tables show some sample patterns.

Pattern

What does it match?

bag

The string bag.

^bag

bag at the beginning of the line.

bag$

bag at the end of the line.

^bag$

bag as the only word on the line.

[Bb]ag

Bag or bag.

b[aeiou]g

Second letter is a vowel.

b[^aeiou]g

Second letter is a consonant (or uppercase or symbol).

b.g

Second letter is any character.

^...$

Any line containing exactly three characters.

^\.

Any line that begins with a dot.

^\.[a-z][a-z]

Same, followed by two lowercase letters (e.g., troff requests).

^\.[a-z]\{2\}

Same as previous; ed, grep, and sed only.

^[^.]

Any line that doesn’t begin with a dot.

bugs*

bug, bugs, bugss, etc.

“word”

A word in quotes.

“*word"*

A word, with or without quotes.

[A-Z][A-Z]*

One or more uppercase letters.

[A-Z]+

Same; egrep or gawk only.

[[:upper:]]+

Same as previous, egrep or gawk.

[A-Z].*

An uppercase letter, followed by zero or more characters.

[A-Z]*

Zero or more uppercase letters.

[a-zA-Z]

Any letter, either lower- or uppercase.

[^0-9A-Za-z]

Any symbol or space (not a letter or a number).

[^[:alnum:]]

Same, using POSIX character class.

egrep or gawk pattern

What does it match?

[567]

One of the numbers 5, 6, or 7.

five|six|seven

One of the words five, six, or seven.

80[2-4]?86

8086, 80286, 80386, or 80486.

80[2-4]?86|(Pentium(-III?)?)

8086, 80286, 80386, 80486, Pentium, Pentium-II, or Pentium-III.

compan(y|ies)

company or companies.

ex or vi pattern

What does it match?

\<the

Words like theater or the.

the\>

Words like breathe or the.

\<the\>

The word the.

ed, sed, or grep pattern

What does it match?

0\{5,\}

Five or more zeros in a row.

[0-9]\{3\}-[0-9]\{2\}-[0-9]\{4\}

U.S. Social Security number (nnn-nn-nnnn).

\(why\).*\1

A line with two occurrences of why.

\([[:alpha:]_][[:alnum:]_.]*\) = \1;

C/C++ simple assignment statements.

Examples of Searching and Replacing

The examples in the following table show the metacharacters available to sed or ex. Note that ex commands begin with a colon. A space is marked by a ❐; a tab is marked by a tab.

Command

Result

s/.*/( & )/

Redo the entire line, but add spaces and parentheses.

s/.*/mv & &.old/

Change a wordlist (one word per line) into mv commands.

/^$/d

Delete blank lines.

:g/^$/d

Same as previous, in ex editor.

/^[❐tab]*$/d

Delete blank lines, plus lines containing only spaces or tabs.

:g/^[❐tab]*$/d

Same as previous, in ex editor.

s/❐❐*/❐/g

Turn one or more spaces into one space.

:%s/❐❐*/❐/g

Same as previous, in ex editor.

:s/[0-9]/Item &:/

Turn a number into an item label (on the current line).

:s

Repeat the substitution on the first occurrence.

:&

Same as previous.

:sg

Same as previous, but for all occurrences on the line.

:&g

Same as previous.

:%&g

Repeat the substitution globally (i.e., on all lines).

:.,$s/Fortran/\U&/g

On current line to last line, change word to uppercase.

:.,$s/\(F\)\(ORTRAN\)/\1\L\2/g

On current line to last line, change spelling of “FORTRAN” to correct, modern usage.

:%s/.*/\L&/

Lowercase entire file.

:s/\<./\u&/g

Uppercase first letter of each word on current line. (Useful for titles.)

:%s/yes/No/g

Globally change a word to No.

:%s/Yes/˜/g

Globally change a different word to No (previous replacement).

Finally, some sed examples for transposing words. A simple transposition of two words might look like this:

s/die or do/do or die/                 Transpose words

The real trick is to use hold buffers to transpose variable patterns. For example:

s/\([Dd]ie\) or \([Dd]o\)/\2 or \1/    Transpose, using hold buffers

Chapter 8. The Emacs Editor

The Emacs editor is found on many Unix systems, including Linux, because it is a popular alternative to vi. Many versions are available, but this book documents the most popular one, GNU Emacs (version 22.3), which is available from the Free Software Foundation (http://www.gnu.org/software/emacs).

Emacs is much more than “just an editor” — in fact, it provides a fully integrated user environment. From within Emacs, you can issue individual shell commands or open a window where you can work in the shell, read and send mail, read news, access the Internet, write and test programs, and maintain a calendar. To fully describe Emacs would require more space than we have available. In this chapter, therefore, we focus on the editing capabilities of Emacs.

This chapter presents the following topics:

- Conceptual overview

- Command-line syntax

- Summary of emacs commands by group

- Summary of emacs commands by key

- Summary of emacs commands by name

For more information about Emacs, see Learning GNU Emacs, by Debra Cameron et al. (O’Reilly).

Conceptual Overview

This section describes some Emacs terminology that may be unfamiliar if you haven’t used Emacs before.

Modes

One of the features that makes Emacs popular is its editing modes. The modes set up an environment designed for the type of editing you are doing, with features such as having appropriate key bindings available and automatically indenting according to standard conventions for that type of document. There are two types of modes: major and minor. The major modes include modes for various programming languages such as C or Perl, for text processing (e.g., XML, or even straight text), and many more. One particularly useful major mode is Dired (Directory Editor), which has commands that let you manage directories. Minor modes set or unset features that are independent of the major mode, such as auto-fill (which controls word wrapping), insert versus overwrite, and auto-save. For a full discussion of modes, see Learning GNU Emacs (O’Reilly) or the Emacs Info documentation system (C-h i).

Buffer and Window

When you open a file in Emacs, the file is put into a buffer so you can edit it. If you open another file, that file goes into another buffer. The view of the buffer contents that you have at any point in time is called a window. For a small file, the window might show the entire file; for a large file, it shows only a portion of a file. Emacs allows multiple windows to be open at the same time, to display the contents of different buffers or different portions of a single buffer.

Point and Mark

When you are editing in Emacs, the position of the cursor is known as point. You can set a mark at another place in the text to operate on the region between point and mark. This is a very useful feature for such operations as deleting or moving an area of text.

Kill and Yank

Emacs uses the terms kill and yank for the concepts more commonly known today as cut and paste. You cut text in Emacs by killing it, and paste it by yanking it back. If you do multiple kills in a row, you can yank them back all at once.

Notes on the Tables

Emacs commands use the Ctrl key and the Meta key (Meta is usually the Alt key or the Escape key). In this chapter, the notation C- indicates that the Ctrl key is pressed at the same time as the character that follows. Similarly, M- indicates the use of the Meta key. When using Escape for Meta, press and release the Escape key, then type the next key. If you use Alt (or Option on the Mac) for Meta, it is just like Ctrl or Shift, and you should press it simultaneously with the other key(s).

In the command tables that follow, the first column lists the keystroke and the last column describes it. When there is a middle column, it lists the command name. If there are no keystrokes for a given command, you’ll see (none) in the first column. Access these commands by typing M-x followed by the command name. If you’re unsure of the name, you can type a tab or a carriage return, and Emacs lists possible completions of what you’ve typed so far.

Because Emacs is such a comprehensive editor, containing literally thousands of commands, some commands must be omitted for the sake of preserving a “quick” reference. You can browse the command set from within Emacs by typing C-h (for help) or M-x Tab (for command names).

Absolutely Essential Commands

If you’re just getting started with Emacs, here’s a short list of the most important commands.

Keystrokes

Description

C-h

Enter the online help system.

C-x C-s

Save the file.

C-x C-c

Exit Emacs.

C-x u

Undo last edit (can be repeated).

C-g

Get out of current command operation.

C-p

Move up to the previous line.

C-n

Move down to the next line.

C-f

Move forward one character.

C-b

Move backward one character.

C-v

Move forward by one screen.

M-v

Move backward by one screen

C-s

Search forward for characters.

C-r

Search backward for characters.

C-d

Delete the current character.

Del

Delete the previous character.

Command-Line Syntax

To start an Emacs editing session, type:

emacs [file]

Summary of Commands by Group

Reminder: C- indicates the Ctrl key; M- indicates the Meta key.

File-Handling Commands

Keystrokes

Command name

Description

C-x C-f

find-file

Find file and read it.

C-x C-v

find-alternate-file

Read another file; replace the one read with C-x C-f.

C-x i

insert-file

Insert file at cursor position.

C-x C-s

save-buffer

Save file (may hang terminal; use C-q to restart).

C-x C-w

write-file

Write buffer contents to file.

C-x C-c

save-buffers-kill-emacs

Exit Emacs.

C-z

suspend-emacs

Suspend Emacs (use exit or fg to restart).

Cursor-Movement Commands

Keystrokes

Command name

Description

C-f

forward-char

Move forward one character (right).

C-b

backward-char

Move backward one character (left).

C-p

previous-line

Move to previous line (up).

C-n

next-line

Move to next line (down).

M-f

forward-word

Move one word forward.

M-b

backward-word

Move one word backward.

C-a

beginning-of-line

Move to beginning of line.

C-e

end-of-line

Move to end of line.

M-a

backward-sentence

Move backward one sentence.

M-e

forward-sentence

Move forward one sentence.

M-{

backward-paragraph

Move backward one paragraph.

M-}

forward-paragraph

Move forward one paragraph.

C-v

scroll-up

Move forward one screen.

M-v

scroll-down

Move backward one screen.

C-x [

backward-page

Move backward one page.

C-x ]

forward-page

Move forward one page.

M->

end-of-buffer

Move to end of file.

M-<

beginning-of-buffer

Move to beginning of file.

M-g g or M-g M-g

goto-line

Go to line n of file.

(none)

goto-char

Go to character n of file.

C-l

recenter

Redraw screen with current line in the center.

M-n

digit-argument

Repeat the next command n times.

C-u n

universal-argument

Repeat the next command n times.

Deletion Commands

Keystrokes

Command name

Description

Del

backward-delete-char

Delete previous character.

C-d

delete-char

Delete character under cursor.

M-Del

backward-kill-word

Delete previous word.

M-d

kill-word

Delete the word the cursor is on.

C-k

kill-line

Delete from cursor to end of line.

M-k

kill-sentence

Delete sentence the cursor is on.

C-x Del

backward-kill-sentence

Delete previous sentence.

C-y

yank

Restore what you’ve deleted.

C-w

kill-region

Delete a marked region (see next section).

(none)

backward-kill-paragraph

Delete previous paragraph.

(none)

kill-paragraph

Delete from the cursor to the end of the paragraph.

Paragraphs and Regions

Keystrokes

Command name

Description

C-@

set-mark-command

Mark the beginning (or end) of a region.

C-Space

(same as above)

(same as above)

C-x C-p

mark-page

Mark page.

C-x C-x

exchange-point-and-mark

Exchange location of cursor and mark.

C-x h

mark-whole-buffer

Mark buffer.

M-q

fill-paragraph

Reformat paragraph.

(none)

fill-region

Reformat individual paragraphs within a region.

M-h

mark-paragraph

Mark paragraph.

Stopping and Undoing Commands

Keystrokes

Command name

Description

C-g

keyboard-quit

Abort current command.

C-x u

advertised-undo

Undo last edit (can be done repeatedly).

(none)

revert-buffer

Restore buffer to the state it was in when the file was last saved (or auto-saved).

Transposition Commands

Keystrokes

Command name

Description

C-t

transpose-chars

Transpose two letters.

M-t

transpose-words

Transpose two words.

C-x C-t

transpose-lines

Transpose two lines.

(none)

transpose-sentences

Transpose two sentences.

(none)

transpose-paragraphs

Transpose two paragraphs.

Search Commands

Keystrokes

Command name

Description

C-s

isearch-forward

Incremental search forward.

C-r

isearch-backward

Incremental search backward

M-%

query-replace

Search and replace.

C-M-s Enter

re-search-forward

Regular expression search forward.

C-M-r Enter

re-search-backward

Regular expression search backward

Capitalization Commands

Keystrokes

Command name

Description

M-c

capitalize-word

Capitalize first letter of word.

M-u

upcase-word

Uppercase word.

M-l

downcase-word

Lowercase word.

M- - M-c

negative-argument; capitalize-word

Capitalize previous word.

M- - M-u

negative-argument; upcase-word

Uppercase previous word.

M- - M-l

negative-argument; downcase-word

Lowercase previous word.

(none)

capitalize-region

Capitalize region.

C-x C-u

upcase-region

Uppercase region

C-x C-l

downcase-region

Lowercase region.

Word-Abbreviation Commands

Keystrokes

Command name

Description

(none)

abbrev-mode

Enter (or exit) word abbreviation mode.

C-x a i g

inverse-add-global-abbrev

Type global abbreviation, then definition.

C-x a i l

inverse-add-local-abbrev

Type local abbreviation, then definition.

(none)

unexpand-abbrev

Undo the last word abbreviation.

(none)

write-abbrev-file

Write the word abbreviation file.

(none)

edit-abbrevs

Edit the word abbreviations.

(none)

list-abbrevs

View the word abbreviations.

(none)

kill-all-abbrevs

Kill abbreviations for this session.

Buffer-Manipulation Commands

Keystrokes

Command name

Description

C-x b

switch-to-buffer

Move to specified buffer.

C-x C-b

list-buffers

Display buffer list.

C-x k

kill-buffer

Delete specified buffer.

(none)

kill-some-buffers

Ask about deleting each buffer.

(none)

rename-buffer

Change buffer name to specified name.

C-x s

save-some-buffers

Ask whether to save each modified buffer.

Window Commands

Keystrokes

Command name

Description

C-x 2

split-window-vertically

Divide the current window into two, one on top of the other.

C-x 3

split-window-horizontally

Divide the current window into two, side by side.

C-x >

scroll-right

Scroll the window right.

C-x <

scroll-left

Scroll the window left.

C-x o

other-window

Move to the other window.

C-x 0

delete-window

Delete current window.

C-x 1

delete-other-windows

Delete all windows but this one.

(none)

delete-windows-on

Delete all windows on a given buffer.

C-x ^

enlarge-window

Make window taller.

(none)

shrink-window

Make window shorter.

C-x }

enlarge-window-horizontally

Make window wider.

C-x {

shrink-window-horizontally

Make window narrower.

C-M-v

scroll-other-window

Scroll other window.

C-x 4 f

find-file-other-window

Find a file in the other window.

C-x 4 b

switch-to-buffer-other-window

Select a buffer in the other window.

C-x 5 f

find-file-other-frame

Find a file in a new frame.

C-x 5 b

switch-to-buffer-other-frame

Select a buffer in another frame.

(none)

compare-windows

Compare two buffers; show first difference.

Special Shell Characters

Keystrokes

Command Name

Description

M-!

shell-command

Run a shell command and display the results.

(none)

shell

Start a shell buffer.

C-c C-c

comint-interrupt-subjob

Terminate the current job.

C-c C-d

comint-send-eof

End of file character.

C-c C-u

comint-kill-input

Erase current line.

C-c C-w

backward-kill-word

Erase the previous word.

C-c C-z

comint-stop-subjob

Suspend the current job.

Indentation Commands

Keystrokes

Command name

Description

C-x .

set-fill-prefix

Use characters from the beginning of the line up to the cursor column as the “fill prefix.” This prefix is prepended to each line in the paragraph. Cancel the prefix by typing this command in column 1.

(none)

indented-text-mode

Major mode: each tab defines a new indent for subsequent lines.

(none)

text-mode

Exit indented text mode; return to text mode.

C-M-\

indent-region

Indent a region to match first line in region.

M-m

back-to-indentation

Move cursor to first nonblank character on line.

M-^

delete-indentation

Join this line to the previous one.

C-M-o

split-line

Split line at cursor; indent to column of cursor.

(none)

fill-individual-paragraphs

Reformat indented paragraphs, keeping indentation.

Centering Commands

Keystrokes

Command name

Description

M-s

center-line

Center line that cursor is on.

M-S

center-paragraph

Center paragraph that cursor is on.

(none)

center-region

Center currently defined region.

Macro Commands

Keystrokes

Command name

Description

C-x ( or F3 key

start-kbd-macro

Start macro definition.

C-x ) or F4 key

end-kbd-macro

End macro definition.

C-x e or F4 key

call-last-kbd-macro

Execute last macro defined.

M-n C-x e

digit-argument and call-last-kbd-macro

Execute last macro defined n times.

C-u C-x (

universal-argument and start-kbd-macro

Execute last macro defined, then add keystrokes.

(none)

name-last-kbd-macro

Name last macro you created (before saving it).

(none)

insert-kbd-macro

Insert the macro you named into a file.

(none)

load-file

Load macro files you’ve saved and loaded.

(none)

macroname

Execute a keyboard macro you’ve saved.

C-x q

kbd-macro-query

Insert a query in a macro definition.

C-u C-x q

(none)

Insert a recursive edit in a macro definition.

C-M-c

exit-recursive-edit

Exit a recursive edit.

Detail Information Help Commands

Keystrokes

Command name

Description

C-h a

command-apropos

What commands involve this concept?

C-h d

apropos

What functions and variables involve this concept?

C-h c

describe-key-briefly

What command does this keystroke sequence run?

C-h b

describe-bindings

What are all the key bindings for this buffer?

C-h k

describe-key

What command does this keystroke sequence run, and what does it do?

C-h l

view-lossage

What are the last 100 characters I typed?

C-h e

view-echo-area-messages

Display the *Messages* buffer.

C-h w

where-is

What is the key binding for this command?

C-h f

describe-function

What does this function do?

C-h v

describe-variable

What does this variable mean, and what is its value?

C-h m

describe-mode

Tell me about the mode the current buffer is in.

C-h s

describe-syntax

What is the syntax table for this buffer?

Help Commands

Keystrokes

Command name

Description

C-h t

help-with-tutorial

Run the Emacs tutorial.

C-h i

info

Start the Info documentation reader.

C-h r

info-emacs-command

View the Emacs documentation in the Info reader.

C-h n

view-emacs-news

View news about updates to Emacs.

C-h C-c

describe-copying

View the Emacs General Public License.

C-h C-d

describe-distribution

View information on ordering Emacs from the FSF.

C-h C-w

describe-no-warranty

View the (non)warranty for Emacs.

Summary of Commands by Key

Emacs commands are presented below in two alphabetical lists. Reminder: C- indicates the Ctrl key; M- indicates the Meta key.

Control-Key Sequences

Keystrokes

Command name

Description

C-@

set-mark-command

Mark the beginning (or end) of a region.

C-Space

(same as previous)

C-]

(none)

Exit recursive edit and exit query-replace.

C-a

beginning-of-line

Move to beginning of line.

C-b

backward-char

Move backward one character (left).

C-c C-c

comint-interrupt-subjob

Terminate the current job.

C-c C-d

comint-send-eof

End-of-file character.

C-c C-u

comint-kill-input

Erase current line.

C-c C-w

backward-kill-word

Erase the previous word.

C-c C-z

comint-stop-subjob

Suspend the current job.

C-d

delete-char

Delete character under cursor.

C-e

end-of-line

Move to end of line.

C-f

forward-char

Move forward one character (right).

C-g

keyboard-quit

Abort current command.

C-h

help-command

Enter the online help system.

C-h a

command-apropos

What commands involve this concept?

C-h b

describe-bindings

What are all the key bindings for this buffer?

C-h C-c

describe-copying

View the Emacs General Public License.

C-h C-d

describe-distribution

View information on ordering Emacs from FSF.

C-h C-w

describe-no-warranty

View the (non)warranty for Emacs.

C-h c

describe-key-briefly

What command does this keystroke sequence run?

C-h d

apropos

What functions and variables involve this concept?

C-h e

view-echo-area-messages

Display the *Messages* buffer.

C-h f

describe-function

What does this function do?

C-h i

info

Start the Info documentation reader.

C-h k

describe-key

What command does this keystroke sequence run, and what does it do?

C-h l

view-lossage

What are the last 100 characters I typed?

C-h m

describe-mode

Tell me about the mode the current buffer is in.

C-h n

view-emacs-news

View news about updates to Emacs.

C-h r

info-emacs-manual

View the Emacs documentation in the Info reader.

C-h s

describe-syntax

What is the syntax table for this buffer?

C-h t

help-with-tutorial

Run the Emacs tutorial.

C-h v

describe-variable

What does this variable mean, and what is its value?

C-h w

where-is

What is the key binding for this command?

C-k

kill-line

Delete from cursor to end of line.

C-l

recenter

Redraw screen with current line in the center.

C-M-\

indent-region

Indent a region to match first line in region.

C-M-c

exit-recursive-edit

Exit a recursive edit.

C-M-o

split-line

Split line at cursor; indent to column of cursor.

C-M-v

scroll-other-window

Scroll other window.

C-n

next-line

Move to next line (down).

C-p

previous-line

Move to previous line (up).

C-r

isearch-backward

Start incremental search backward.

C-s

isearch-forward

Start incremental search forward.

C-t

transpose-chars

Transpose two letters.

C-u n

universal-argument

Repeat the next command n times.

C-u C-x (

universal-argument and start-kbd-macro

Execute last macro defined, then add keystrokes.

C-u C-x q

(none)

Insert recursive edit in a macro definition.

C-v

scroll-up

Move forward one screen.

C-w

kill-region

Delete a marked region.

C-x (

start-kbd-macro

Start macro definition.

C-x )

end-kbd-macro

End macro definition.

C-x [

backward-page

Move backward one page.

C-x ]

forward-page

Move forward one page.

C-x ^

enlarge-window

Make window taller.

C-x {

shrink-window-horizontally

Make window narrower.

C-x }

enlarge-window-horizontally

Make window wider.

C-x <

scroll-left

Scroll the window left.

C-x >

scroll-right

Scroll the window right.

C-x .

set-fill-prefix

Use characters from the beginning of the line up to the cursor column as the “fill prefix.” This prefix is prepended to each line in the paragraph. Cancel the prefix by typing this command in column 1.

C-x 0

delete-window

Delete current window.

C-x 1

delete-other-windows

Delete all windows but this one.

C-x 2

split-window-vertically

Divide the current window into two, one on top of the other.

C-x 3

split-window-horizontally

Divide the current window into two, side by side.

C-x 4 b

switch-to-buffer-other-window

Select a buffer in the other window.

C-x 4 f

find-file-other-window

Find a file in the other window.

C-x 5 b

switch-to-buffer-other-frame

Select a buffer in another frame.

C-x 5 f

find-file-other-frame

Find a file in a new frame.

C-x C-b

list-buffers

Display the buffer list.

C-x C-c

save-buffers-kill-emacs

Exit Emacs.

C-x C-f

find-file

Find file and read it.

C-x C-l

downcase-region

Lowercase region.

C-x C-p

mark-page

Mark page.

C-x C-q

(none)

Toggle read-only status of buffer.

C-x C-s

save-buffer

Save file (may hang terminal; use C-q to restart).

C-x C-t

transpose-lines

Transpose two lines.

C-x C-u

upcase-region

Uppercase region

C-x C-v

find-alternate-file

Read an alternate file, replacing the one read with C-x C-f.

C-x C-w

write-file

Write buffer contents to file.

C-x C-x

exchange-point-and-mark

Exchange location of cursor and mark.

C-x DEL

backward-kill-sentence

Delete previous sentence.

C-x a i g

inverse-add-global-abbrev

Type global abbreviation, then definition.

C-x a i l

inverse-add-local-abbrev

Type local abbreviation, then definition.

C-x b

switch-to-buffer

Move to the buffer specified.

C-x e

call-last-kbd-macro

Execute last macro defined.

C-x h

mark-whole-buffer

Mark buffer.

C-x i

insert-file

Insert file at cursor position.

C-x k

kill-buffer

Delete the buffer specified.

C-x o

other-window

Move to the other window.

C-x q

kbd-macro-query

Insert a query in a macro definition.

C-x s

save-some-buffers

Ask whether to save each modified buffer.

C-x u

advertised-undo

Undo last edit (can be done repeatedly).

C-y

yank

Restore what you’ve deleted.

C-z

suspend-emacs

Suspend Emacs (use exit or fg to restart).

Meta-Key Sequences

Keystrokes

Command name

Description

Meta

(none)

Exit a query-replace or successful search.

M- - M-c

negative-argument; capitalize-word

Capitalize previous word.

M- - M-l

negative-argument; downcase-word

Lowercase previous word.

M- - M-u

negative-argument; upcase-word

Uppercase previous word.

M-$

spell-word

Check spelling of word after cursor.

M-<

beginning-of-buffer

Move to beginning of file.

M->

end-of-buffer

Move to end of file.

M-{

backward-paragraph

Move backward one paragraph.

M-}

forward-paragraph

Move forward one paragraph.

M-^

delete-indentation

Join this line to the previous one.

M-n

digit-argument

Repeat the next command n times.

M-n C-x e

digit-argument and call-last-kbd-macro

Execute the last defined macro n times.

M-a

backward-sentence

Move backward one sentence.

M-b

backward-word

Move one word backward.

M-c

capitalize-word

Capitalize first letter of word.

M-d

kill-word

Delete word that cursor is on.

M-DEL

backward-kill-word

Delete previous word.

M-e

forward-sentence

Move forward one sentence.

M-f

forward-word

Move one word forward.

M-g g or M-g M-g

goto-line

Go to line n of file.

M-h

mark-paragraph

Mark paragraph.

M-k

kill-sentence

Delete sentence the cursor is on.

M-l

downcase-word

Lowercase word.

M-m

back-to-indentation

Move cursor to first nonblank character on line.

M-q

fill-paragraph

Reformat paragraph.

M-s

center-line

Center line that cursor is on.

M-S

cemter-paragraph

Center paragraph that cursor is on.

M-t

transpose-words

Transpose two words.

M-u

upcase-word

Uppercase word.

M-v

scroll-down

Move backward one screen.

M-x

(none)

Access command by command name.

Summary of Commands by Name

The Emacs commands below are presented alphabetically by command name. Use M-x to access the command name. Reminder: C- indicates the Ctrl key; M- indicates the Meta key.

Command name

Keystrokes

Description

macroname

(none)

Execute a keyboard macro you’ve saved.

abbrev-mode

(none)

Enter (or exit) word abbreviation mode.

advertised-undo

C-x u

Undo last edit (can be done repeatedly).

apropos

(none)

What functions and variables involve this concept?

back-to-indentation

M-m

Move cursor to first nonblank character on line.

backward-char

C-b

Move backward one character (left).

backward-delete-char

Del

Delete previous character.

backward-kill-paragraph

(none)

Delete previous paragraph.

backward-kill-sentence

C-x Del

Delete previous sentence.

backward-kill-word

C-c C-w

Erase previous word.

backward-kill-word

M-Del

Delete previous word.

backward-page

C-x [

Move backward one page.

backward-paragraph

M-{

Move backward one paragraph.

backward-sentence

M-a

Move backward one sentence.

backward-word

M-b

Move backward one word.

beginning-of-buffer

M-<

Move to beginning of file.

beginning-of-line

C-a

Move to beginning of line.

call-last-kbd-macro

C-x e

Execute last macro defined.

capitalize-region

(none)

Capitalize region.

capitalize-word

M-c

Capitalize first letter of word.

center-line

M-s

Center line that cursor is on.

center-paragraph

M-S

Center paragraph that cursor is on.

center-region

(none)

Center currently defined region.

comint-interrupt-subjob

C-c C-c

Terminate the current job.

comint-kill-input

C-c C-u

Erase current line.

comint-send-eof

C-c C-d

End of file character.

comint-stop-subjob

C-c C-z

Suspend current job.

command-apropos

C-h a

What commands involve this concept?

compare-windows

(none)

Compare two buffers; show first difference.

delete-char

C-d

Delete character under cursor.

delete-indentation

M-^

Join this line to previous one.

delete-other-windows

C-x 1

Delete all windows but this one.

delete-window

C-x 0

Delete current window.

delete-windows-on

(none)

Delete all windows on a given buffer.

describe-bindings

C-h b

What are all the key bindings for in this buffer?

describe-copying

C-h C-c

View the Emacs General Public License.

describe-distribution

C-h C-d

View information on ordering Emacs from the FSF.

describe-function

C-h f

What does this function do?

describe-key

C-h k

What command does this keystroke sequence run, and what does it do?

describe-key-briefly

C-h c

What command does this keystroke sequence run?

describe-mode

C-h m

Tell me about the mode the current buffer is in.

describe-no-warranty

C-h C-w

View the (non)warranty for Emacs.

describe-syntax

C-h s

What is the syntax table for this buffer?

describe-variable

C-h v

What does this variable mean, and what is its value?

digit-argument and call-last-kbd-macro

M-n C-x e

Execute the last defined macro n times.

digit-argument

M-n

Repeat next command n times.

downcase-region

C-x C-l

Lowercase region.

downcase-word

M-l

Lowercase word.

edit-abbrevs

(none)

Edit word abbreviations.

end-kbd-macro

C-x ) or F4 key

End macro definition.

end-of-buffer

M->

Move to end of file.

end-of-line

C-e

Move to end of line.

enlarge-window

C-x ^

Make window taller.

enlarge-window-horizontally

C-x }

Make window wider.

exchange-point-and-mark

C-x C-x

Exchange location of cursor and mark.

exit-recursive-edit

C-M-c

Exit a recursive edit.

fill-individual-paragraphs

(none)

Reformat indented paragraphs, keeping indentation.

fill-paragraph

M-q

Reformat paragraph.

fill-region

(none)

Reformat individual paragraphs within a region.

find-alternate-file

C-x C-v

Read an alternate file, replacing the one read with C-x C-f.

find-file

C-x C-f

Find file and read it.

find-file-other-frame

C-x 5 f

Find a file in a new frame.

find-file-other-window

C-x 4 f

Find a file in the other window.

forward-char

C-f

Move forward one character (right).

forward-page

C-x ]

Move forward one page.

forward-paragraph

M-}

Move forward one paragraph.

forward-sentence

M-e

Move forward one sentence.

forward-word

M-f

Move forward one word.

goto-char

(none)

Go to character n of file.

goto-line

M-g g or M-g M-g

Go to line n of file.

help-command

C-h

Enter the online help system.

help-with-tutorial

C-h t

Run the Emacs tutorial.

indent-region

C-M-\

Indent a region to match first line in region.

indented-text-mode

(none)

Major mode: each tab defines a new indent for subsequent lines.

info

C-h i

Start the Info documentation reader.

info-emacs-manual

C-h r

View the Emacs documentation in the Info reader.

insert-file

C-x i

Insert file at cursor position.

insert-kbd-macro

(none)

Insert the macro you named into a file.

inverse-add-global-abbrev

C-x a i g

Type global abbreviation, then definition.

inverse-add-local-abbrev

C-x a i l

Type local abbreviation, then definition.

isearch-backward

C-r

Start incremental search backward.

isearch-backward-regexp

C-r

Same, but search for regular expression.

isearch-forward

C-s

Start incremental search forward.

isearch-forward-regexp

C-r

Same, but search for regular expression.

kbd-macro-query

C-x q

Insert a query in a macro definition.

keyboard-quit

C-g

Abort current command.

kill-all-abbrevs

(none)

Kill abbreviations for this session.

kill-buffer

C-x k

Delete the buffer specified.

kill-line

C-k

Delete from cursor to end of line.

kill-paragraph

(none)

Delete from cursor to end of paragraph.

kill-region

C-w

Delete a marked region.

kill-sentence

M-k

Delete sentence the cursor is on.

kill-some-buffers

(none)

Ask about deleting each buffer.

kill-word

M-d

Delete word the cursor is on.

list-abbrevs

(none)

View word abbreviations.

list-buffers

C-x C-b

Display buffer list.

load-file

(none)

Load macro files you’ve saved.

mark-page

C-x C-p

Mark page.

mark-paragraph

M-h

Mark paragraph.

mark-whole-buffer

C-x h

Mark buffer.

name-last-kbd-macro

(none)

Name last macro you created (before saving it).

negative-argument; capitalize-word

M- - M-c

Capitalize previous word.

negative-argument; downcase-word

M- - M-l

Lowercase previous word.

negative-argument; upcase-word

M- - M-u

Uppercase previous word.

next-line

C-n

Move to next line (down).

other-window

C-x o

Move to the other window.

previous-line

C-p

Move to previous line (up).

query-replace

M-%

Search and replace.

query-replace-regexp

C-% Meta

Query-replace a regular expression.

recenter

C-l

Redraw screen, with current line in center.

rename-buffer

(none)

Change buffer name to specified name.

replace-regexp

(none)

Replace a regular expression unconditionally.

re-search-backward

(none)

Simple regular expression search backward.

re-search-forward

(none)

Simple regular expression search forward.

revert-buffer

(none)

Restore buffer to the state it was in when the file was last saved (or auto-saved).

save-buffer

C-x C-s

Save file (may hang terminal; use C-q to restart).

save-buffers-kill-emacs

C-x C-c

Exit Emacs.

save-some-buffers

C-x s

Ask whether to save each modified buffer.

scroll-down

M-v

Move backward one screen.

scroll-left

C-x <

Scroll the window left.

scroll-other-window

C-M-v

Scroll other window.

scroll-right

C-x >

Scroll the window right.

scroll-up

C-v

Move forward one screen.

set-fill-prefix

C-x .

Use characters from the beginning of the line up to the cursor column as the “fill prefix.” This prefix is prepended to each line in the paragraph. Cancel the prefix by typing this command in column 1.

set-mark-command

C-@ or C-Space

Mark the beginning (or end) of a region.

shell

(none)

Start a shell buffer.

shell-command

M-!

Run a shell command and display the results.

shrink-window

(none)

Make window shorter.

shrink-window-horizontally

C-x {

Make window narrower.

spell-buffer

(none)

Check spelling of current buffer.

spell-region

(none)

Check spelling of current region.

spell-string

(none)

Check spelling of string typed in minibuffer.

spell-word

M-$

Check spelling of word after cursor.

split-line

C-M-o

Split line at cursor; indent to column of cursor.

split-window-vertically

C-x 2

Divide the current window into two, one on top of the other.

split-window-horizontally

C-x 3

Divide the current window into two, side by side.

start-kbd-macro

C-x ( or F3 key

Start macro definition.

suspend-emacs

C-z

Suspend Emacs (use exit or fg to restart).

switch-to-buffer

C-x b

Move to the buffer specified.

switch-to-buffer-other-frame

C-x 5 b

Select a buffer in another frame.

switch-to-buffer-other-window

C-x 4 b

Select a buffer in the other window.

text-mode

(none)

Exit indented text mode; return to text mode.

transpose-chars

C-t

Transpose two letters.

transpose-lines

C-x C-t

Transpose two lines.

transpose-paragraphs

(none)

Transpose two paragraphs.

transpose-sentences

(none)

Transpose two sentences.

transpose-words

M-t

Transpose two words.

unexpand-abbrev

(none)

Undo the last word abbreviation.

universal-argument

C-u n

Repeat the next command n times.

universal-argument and start-kbd-macro

C-u C-x (

Execute last macro defined, then add keystrokes to it.

upcase-region

C-x C-u

Uppercase region.

upcase-word

M-u

Uppercase word.

view-emacs-news

C-h n

View news about updates to Emacs.

view-lossage

C-h l

What are the last 100 characters I typed?

where-is

C-h w

What is the key binding for this command?

write-abbrev-file

(none)

Write the word abbreviation file.

write-file

C-x C-w

Write buffer contents to file.

yank

C-y

Restore what you’ve deleted.

Chapter 9. The vi, ex, and vim Editors

The vi and ex editors are the “standard” editors on Unix systems. You can count on there being some version of them, no matter what Unix flavor you are using. The two editors are in fact the same program; based on how it was invoked, the editor enters full-screen mode or line mode.

vimis a popular extended version of vi. On some Linux distributions, the vi command invokes vim in a vi -compatible mode.

This chapter presents the following topics:

- Conceptual overview

- Command-line syntax

- Review of vi operations

- Alphabetical list of keys in command mode

- vi commands

- vi configuration

- ex basics

- Alphabetical summary of ex commands

vi is pronounced “vee eye.”

Besides the original Unix vi, there are a number of freely available vi clones (including vim). Both the original vi and the clones are covered in Learning the vi and Vim Editors by Arnold Robbins et al. (O’Reilly).

Conceptual Overview

vi is the classic screen-editing program for Unix. A number of enhanced versions exist, including nvi, vim, vile, and elvis. On GNU/Linux systems, the vi command is usually one of these programs (either a copy or a link). The Emacs editor, covered in Chapter 8, has several vi modes that allow you to use many of the same commands covered in this chapter.

The vi editor operates in two modes: command mode and insert mode. The dual modes make vi an attractive editor for users who separate text entry from editing. For users who edit as they type, the modeless editing of Emacs can be more comfortable. However, vim supports both ways of editing, through the insertmode option.

vi is based on an older line editor called ex. (ex, in turn, was developed by Bill Joy at the University of California, Berkeley, from the primordial Unix line editor, ed.) A user can invoke powerful editing capabilities within vi by typing a colon (:), entering an ex command, and pressing the Enter key. Furthermore, you can place ex commands in a startup file called ˜/.exrc, which vi reads at the beginning of your editing session. Because ex commands are such an important part of vi, they are also described in this chapter.

One of the most common versions of vi found on Linux systems is Bram Moolenaar’s Vi IMproved, or vim. On some Linux distributions, vim is the default version of vi and runs when you invoke vi. vim offers many extra features, and optionally changes some of the basic features of vi, most notoriously changing the undo key to support multiple levels of undo.

Fully documenting vim is beyond the scope of this chapter, but we do cover some of its most commonly used options and features. Beyond what we cover here, vim offers enhanced support to programmers through an integrated build and debugging process, syntax highlighting, extended ctags support, and support for Perl and Python, as well as GUI fonts and menus, function-key mapping, independent mapping for each mode, and more. Fortunately, vim comes with a powerful internal help system that you can use to learn more about the things we just couldn’t fit into this chapter. See http://www.vim.org for more information.

Command-Line Syntax

The three most common ways of starting a vi session are:

vi [options] file
vi [options] +num file
vi [options] +/pattern file

You can open file for editing, optionally at line num or at the first line matching pattern. If no file is specified, vi opens with an empty buffer.

Command-Line Options

Because vi and ex are the same program, they share the same options. However, some options only make sense for one version of the program. Options specific to vim are so marked.

+[num]

Start editing at line number num, or the last line of the file if num is omitted.

+/pattern

Start editing at the first line matching pattern. (For ex, fails if nowrapscan is set in your .exrc startup file, since ex starts editing at the last line of a file.)

-b

Edit the file in binary mode. {vim}

-c command

Run the given ex command upon startup. Only one -c option is permitted for vi; vim accepts up to 10. An older form of this option, + command, is still supported.

--cmd command

Like -c, but execute the command before any resource files are read. {vim}

-C

vim : Start the editor in vi-compatible mode.

-d

Run in diff mode. Can also be invoked by running the command vimdiff. {vim}

-D

Debugging mode for use with scripts. {vim}

-e

Run as ex (line editing rather than full-screen mode).

-h

Print help message, then exit. {vim}

-i file

Use the specified file instead of the default (˜/.viminfo) to save or restore vim ’s state. {vim}

-l

Enter Lisp mode for running Lisp programs (not supported in all versions).

-L

List files that were saved due to an aborted editor session or system crash (not supported in all versions). For vim, this option is the same as -r.

-m

Start the editor with the write option turned off so the user cannot write to files. {vim}

-M

Do not allow text in files to be modified. {vim}

-n

Do not use a swapfile; record changes in memory only. {vim}

--noplugin

Do not load any plug-ins. {vim}

-N

Run vim in a non-vi -compatible mode. {vim}

-o [num]

Start vim with num open windows. The default is to open one window for each file. {vim}

-O [num]

Start vim with num open windows arranged horizontally (split vertically) on the screen. {vim}

-r [file]

Recovery mode; recover and resume editing on file after an aborted editor session or system crash. Without file, list files available for recovery.

-R

Edit files read-only.

-s

Silent; do not display prompts. Useful when running a script. This behavior also can be set through the older - option. For vim, only applies when used together with -e.

-s scriptfile

Read and execute commands given in the specified scriptfile as if they were typed in from the keyboard. {vim}

-S commandfile

Read and execute commands given in commandfile after loading any files for editing specified on the command line. Shorthand for the option vim -c ’source commandfile‘. {vim}

-t tag

Edit the file containing tag and position the cursor at its definition. (See ctags in Chapter 3 for more information.)

-T type

Set the terminal type. This value overrides the $TERM environment variable. {vim}

-u file

Read configuration information from the specified resource file instead of default .vimrc resource file. If the file argument is NONE, vim will read no resource files, load no plug-ins, and run in compatible mode. If the argument is NORC, it will read no resource files, but it will load plug-ins. {vim}

-v

Run in full-screen mode (default for vi).

--version

Print version information, then exit. {vim}

-V[num]

Verbose mode; print messages about what options are being set and what files are being read or written. You can set a level of verbosity to increase or decrease the number of messages received. The default value is 10 for high verbosity. {vim}

-w rows

Set the window size so rows lines at a time are displayed; useful when editing over a slow dial-up line (or long distance Internet connection). Older versions of vi do not permit a space between the option and its argument. vim does not support this option.

-W scriptfile

Write all typed commands from the current session to the specified scriptfile. The file created can be used with the -s command. {vim}

-x

Prompt for a key that will be used to try to encrypt or decrypt a file using crypt (not supported in all versions).[8]

-y

Modeless vi; run vim in insert mode only, without a command mode. {vim}

-Z

Start vim in restricted mode. Do not allow shell commands or suspension of the editor. {vim}

While most people know ex commands only by their use within vi, the editor also exists as a separate program and can be invoked from the shell (for instance, to edit files as part of a script). Within ex, you can enter the vi or visual command to start vi. Similarly, within vi, you can enter Q to quit the vi editor and enter ex.

You can exit ex in several ways:

:x

Exit (save changes and quit).

:q!

Quit without saving changes.

:vi

Enter the vi editor.

[8] The crypt command’s encryption is weak. Don’t use it for serious secrets.

Review of vi Operations

This section provides a review of the following:

- vi modes

- Syntax of vi commands

- Status-line commands

Command Mode

Once the file is opened, you are in command mode. From command mode, you can:

- Invoke insert mode

- Issue editing commands

- Move the cursor to a different position in the file

- Invoke ex commands

- Invoke a Unix shell

- Save the current version of the file

- Exit vi

Insert Mode

In insert mode, you can enter new text in the file. You normally enter insert mode with the i command. Press the Escape key to exit insert mode and return to command mode. The full list of commands that enter insert mode is provided later, in the section Insert Commands in Insert Commands.

Syntax of vi Commands

In vi, editing commands have the following general form:

[n] operator [m] motion

The basic editing operators are:

c

Begin a change.

d

Begin a deletion.

y

Begin a yank (or copy).

If the current line is the object of the operation, the motion is the same as the operator: cc, dd, yy. Otherwise, the editing operators act on objects specified by cursor-movement commands or pattern-matching commands. (For example, cf. changes up to the next period.) n and m are the number of times the operation is performed, or the number of objects the operation is performed on. If both n and m are specified, the effect is n ×m.

An object of operation can be any of the following text blocks:

word

Includes characters up to a whitespace character (space or tab) or punctuation mark. A capitalized object is a variant form that recognizes only whitespace.

sentence

Is up to ., !, or ?, followed by two spaces.

paragraph

Is up to the next blank line or paragraph macro defined by the para= option.

section

Is up to the next nroff/troff section heading defined by the sect= option.

motion

Is up to the character or other text object as specified by a motion specifier, including pattern searches.

Examples

2cw

Change the next two words.

d}

Delete up to next paragraph.

d^

Delete back to beginning of line.

5yy

Copy the next five lines.

y]]

Copy up to the next section.

cG

Change to the end of the edit buffer.

More commands and examples may be found in the section Changing and deleting text in Changing and deleting text.

Visual mode (vim only)

vim provides an additional facility, “visual mode.” This allows you to highlight blocks of text which then become the object of edit commands such as deletion or saving (yanking). Graphical versions of vim allow you to use the mouse to highlight text in a similar fashion. See the vim help file visual.txt for the full story.

v

Select text in visual mode one character at a time.

V

Select text in visual mode one line at a time.

Ctrl-V

Select text in visual mode in blocks.

Status-Line Commands

Most commands are not echoed on the screen as you input them. However, the status line at the bottom of the screen is used to edit these commands:

/

Search forward for a pattern.

?

Search backward for a pattern.

:

Invoke an ex command.

!

Invoke a Unix command that takes as its input an object in the buffer and replaces it with output from the command. You type a motion command after the ! to describe what should be passed to the Unix command. The command itself is entered on the status line.

Commands that are entered on the status line must be entered by pressing the Enter key. In addition, error messages and output from the Ctrl-G command are displayed on the status line.

vi Commands

vi supplies a large set of single-key commands when in command mode. vim supplies additional multi-key commands.

Movement Commands

Some versions of vi do not recognize extended keyboard keys (e.g., arrow keys, Page Up, Page Down, Home, Insert, and Delete); some do. All, however, recognize the keys in this section. Many users of vi prefer to use these keys, as it helps them keep their fingers on the home row of the keyboard. A number preceding a command repeats the movement. Movement commands are also used after an operator. The operator works on the text that is moved.

Character

Command

Action

h, j, k, l

Left, down, up, right (←, ↓, ↑, →)

Space

Right

Backspace

Left

Ctrl-H

Left

Text

Command

Action

w, b

Forward, backward by “word” (letters, numbers, and underscore make up words).

W, B

Forward, backward by “WORD” (only whitespace separates items).

e

End of word.

E

End of WORD.

ge

End of previous word. {vim}

gE

End of previous WORD. {vim}

), (

Beginning of next, current sentence.

}, {

Beginning of next, current paragraph.

]], [[

Beginning of next, current section.

][, [ ]

End of next, current section. {vim}

Lines

Long lines in a file may show up on the screen as multiple lines. (They wrap around from one screen line to the next.) While most commands work on the lines as defined in the file, a few commands work on lines as they appear on the screen. The vim option wrap allows you to control how long lines are displayed.

Command

Action

0, $

First, last position of current line.

^, _

First nonblank character of current line.

+, -

First nonblank character of next, previous line.

Enter

First nonblank character of next line.

num|

Column num of current line.

g0, g$

First, last position of screen line. {vim}

g^

First nonblank character of screen line. {vim}

gm

Middle of screen line. {vim}

gk, gj

Move up, down one screen line. {vim}

H

Top line of screen (Home position).

M

Middle line of screen.

L

Last line of screen.

numH

num lines after top line.

numL

num lines before last line.

Screens

Command

Action

Ctrl-F, Ctrl-B

Scroll forward, backward one screen.

Ctrl-D, Ctrl-U

Scroll down, up one-half screen.

Ctrl-E, Ctrl-Y

Show one more line at bottom, top of screen.

z Enter

Reposition line with cursor to top of screen.

z.

Reposition line with cursor to middle of screen.

z-

Reposition line with cursor to bottom of screen.

Ctrl-L

Redraw screen (without scrolling).

Ctrl-R

vi: Redraw screen (without scrolling).

vim: Redo last undone change.

Searches

Command

Action

/pattern

Search forward for pattern. End with Enter.

/pattern/+num

Go to line num after pattern.

?pattern

Search backward for pattern. End with Enter.

?pattern?-num

Go to line num before pattern.

:noh

Suspend search highlighting until next search. {vim}.

n

Repeat previous search.

N

Repeat search in opposite direction.

/

Repeat previous search forward.

?

Repeat previous search backward.

*

Search forward for word under cursor. Matches only exact words. {vim}

#

Search backward for word under cursor. Matches only exact words. {vim}

g*

Search backward for word under cursor. Matches the characters of this word when embedded in a longer word. {vim}

g#

Search backward for word under cursor. Matches the characters of this word when embedded in a longer word. {vim}

%

Find match of current parenthesis, brace, or bracket.

fx

Move cursor forward to x on current line.

Fx

Move cursor backward to x on current line.

tx

Move cursor forward to character before x in current line.

Tx

Move cursor backward to character after x in current line.

,

Reverse search direction of last f, F, t, or T.

;

Repeat last f, F, t, or T.

Line numbering

Command

Action

Ctrl-G

Display current line number.

gg

Move to first line in file. {vim}

numG

Move to line number num.

G

Move to last line in file.

:num

Move to line number num.

Marks

Command

Action

mx

Place mark x at current position.

`x

(backquote) Move cursor to mark x.

'x

(apostrophe) Move to start of line containing x.

``

(backquotes) Return to position before most recent jump.

"

(apostrophes) Like preceding, but return to start of line.

’”

(apostrophe quote) Move to position when last editing the file. {vim}

`[, `]

(backquote bracket) Move to beginning/end of previous text operation. {vim}

'[, ' ]

(apostrophe bracket) Like preceding, but return to start of line where operation occurred. {vim}

`.

(backquote period) Move to last change in file. {vim}

‘.

(apostrophe period) Like preceding, but return to start of line. {vim}

`0

Position where you last exited vim. {vim}

:marks

List active marks. {vim}

Insert Commands

Command

Action

a

Append after cursor.

A

Append to end of line.

c

Begin change operation.

C

Change to end of line.

gI

Insert at beginning of line. {vim}

i

Insert before cursor.

I

Insert at beginning of line.

o

Open a line below cursor.

O

Open a line above cursor.

R

Begin overwriting text.

s

Substitute a character.

S

Substitute entire line.

ESC

Terminate insert mode.

The following commands work in insert mode.

Command

Action

Backspace

Delete previous character.

Delete

Delete current character.

Tab

Insert a tab.

Ctrl-A

Repeat last insertion. {vim}

Ctrl-D

Shift line left to previous shift width. {vim}

Ctrl-E

Insert character found just below cursor. {vim}

Ctrl-H

Delete previous character (same as Backspace).

Ctrl-I

Insert a tab.

Ctrl-K

Begin insertion of multi-keystroke character.

Ctrl-N

Insert next completion of the pattern to the left of the cursor. {vim}

Ctrl-P

Insert previous completion of the pattern to the left of the cursor. {vim}

Ctrl-T

Shift line right to next shift width. {vim}

Ctrl-U

Delete current line.

Ctrl-V

Insert next character verbatim.

Ctrl-W

Delete previous word.

Ctrl-Y

Insert character found just above cursor. {vim}

Ctrl-[

(Escape) Terminate insert mode.

Some of the control characters listed in the previous table are set by stty. Your terminal settings may differ.

Edit Commands

Recall that c, d, and y are the basic editing operators.

Changing and deleting text

The following table is not exhaustive, but it illustrates the most common operations.

Command

Action

cw

Change word.

cc

Change line.

c$

Change text from current position to end of line.

C

Same as c$.

dd

Delete current line.

numdd

Delete num lines.

d$

Delete text from current position to end of line.

D

Same as d$.

dw

Delete a word.

d}

Delete up to next paragraph.

d^

Delete back to beginning of line.

d/pat

Delete up to first occurrence of pattern.

dn

Delete up to next occurrence of pattern.

dfa

Delete up to and including a on current line.

dta

Delete up to (but not including) a on current line.

dL

Delete up to last line on screen.

dG

Delete to end of file.

gqap

Reformat current paragraph to textwidth. {vim}

g˜w

Switch case of word. {vim}

guw

Change word to lowercase. {vim}

gUw

Change word to uppercase. {vim}

p

Insert last deleted or yanked text after cursor.

gp

Same as p, but leave cursor at end of inserted text. {vim}

]p

Same as p, but match current indention. {vim}

[p

Same as P, but match current indention. {vim}

P

Insert last deleted or yanked text before cursor.

gP

Same as P, but leave cursor at end of inserted text. {vim}

rx

Replace character with x.

Rtext

Replace with new text (overwrite), beginning at cursor. Escape ends replace mode.

s

Substitute character.

4s

Substitute four characters.

S

Substitute entire line.

u

Undo last change.

Ctrl-R

Redo last change. {vim}

U

Restore current line.

x

Delete current cursor position.

X

Delete back one character.

5X

Delete previous five characters.

.

Repeat last change.

~

Reverse case and move cursor right.

Ctrl-A

Increment number under cursor. {vim}

Ctrl-X

Decrement number under cursor. {vim}

Copying and moving

Register names are the letters a-z. Uppercase names append text to the corresponding register.

Command

Action

Y

Copy current line.

yy

Copy current line.

"xyy

Copy current line to register x.

ye

Copy text to end of word.

yw

Like ye, but include the whitespace after the word.

y$

Copy rest of line.

"xdd

Delete current line into register x.

"xd

Delete into register x.

"xp

Put contents of register x.

y]]

Copy up to next section heading.

ye

Copy to end of word.

"xp

Put contents of register x.

J

Join current line to next line.

gJ

Same as J, but without inserting a space. {vim}

:j

Same as J.

:j!

Same as gJ.

Saving and Exiting

Writing a file means overwriting the file with the current text.

Command

Action

ZZ

Quit vi, writing the file only if changes were made.

:x

Same as ZZ.

:wq

Write file and quit.

:w

Write file.

:w file

Save copy to file.

:n,mw file

Write lines n to m to new file.

:n,mw >> file

Append lines n to m to existing file.

:w!

Write file (overriding protection).

:w! file

Overwrite file with current text.

:w %.new

Write current buffer named file as file.new.

:q

Quit vi (fails if changes were made).

:q!

Quit vi (discarding edits).

Q

Quit vi and invoke ex.

:vi

Return to vi after Q command.

%

Replaced with current filename in editing commands.

#

Replaced with alternate filename in editing commands.

Accessing Multiple Files

Command

Action

:e file

Edit another file; current file becomes alternate.

:e!

Return to version of current file at time of last write.

:e + file

Begin editing at end of file.

:e +num file

Open file at line num.

:e #

Open to previous position in alternate file.

:ta tag

Edit file at location tag.

:n

Edit next file in the list of files.

:n!

Force next file.

:n files

Specify new list of files.

:rewind

Edit first file in the list.

Ctrl-G

Show current file and line number.

:args

Display list of files to be edited.

:prev

Edit previous file in the list of files.

Window Commands

The following table lists common commands for controlling windows in vim. See also the split, vsplit, and resize commands in the Alphabetical Summary of ex Commands in Alphabetical Summary of ex Commands. For brevity, control characters are marked in the following list by ^.

Command

Action

:new

Open a new window.

:new file

Open file in a new window.

:sp [file]

Split the current window. With file, edit that file in the new window.

:sv [file]

Same as :sp, but make new window read-only.

:sn [file]

Edit next file in file list in new window.

:vsp [file]

Like :sp, but split vertically instead of horizontally.

:clo

Close current window.

:hid

Hide current window, unless it is the only visible window.

:on

Make current window the only visible one.

:res num

Resize window to num lines.

:wa

Write all changed buffers to file.

:qa

Close all buffers and exit.

^W s

Same as :sp.

^W n

Same as :new.

^W ^

Open new window with alternate (previously edited) file.

^W c

Same as :clo.

^W o

Same as :only.

^W j, ^W k

Move cursor to next/previous window.

^W p

Move cursor to previous window.

^W h, ^W l

Move cursor to window on left/right.

^W t, ^W b

Move cursor to window on top/bottom of screen.

^W K, ^W B

Move current window to top/bottom of screen.

^W H, ^W L

Move current window to far left/right of screen.

^W r, ^W R

Rotate windows down/up.

^W +, ^W -

Increase/decrease current window size.

^W =

Make all windows same height.

Interacting with the System

Command

Action

:r file

Read in contents of file after cursor.

:r !command

Read in output from command after current line.

:numr !command

Like above, but place after line num (0 for top of file).

:!command

Run command, then return.

!motion command

Send the text covered by motion to Unix command; replace with output.

:n,m! command

Send lines n-m to command; replace with output.

num!!command

Send num lines to Unix command; replace with output.

:!!

Repeat last system command.

:sh

Create subshell; return to file with EOF.

Ctrl-Z

Suspend editor, resume with fg.

:so file

Read and execute ex commands from file.

Macros

Command

Action

:ab in out

Use in as abbreviation for out in insert mode.

:unab in

Remove abbreviation for in.

:ab

List abbreviations.

:map string sequence

Map characters string as sequence of commands. Use #1, #2, etc., for the function keys.

:unmap string

Remove map for characters string.

:map

List character strings that are mapped.

:map! string sequence

Map characters string to input mode sequence.

:unmap! string

Remove input mode map (you may need to quote the character with Ctrl-V).

:map!

List character strings that are mapped for input mode.

qx

Record typed characters into register specified by letter x. If letter is uppercase, append to register. {vim}

q

Stop recording. {vim}

@x

Execute the register specified by letter x. Use @@ to repeat the last @ command.

In vi, the following characters are unused in command mode and can be mapped as user-defined commands:

Letters

g K q V v

Control keys

^A ^K ^O ^W ^X ^_ ^\

Symbols

_ * \ = #

Tip

The = is used by vi if Lisp mode is set. Different versions of vi may use some of these characters, so test them before using.

vim does not use ^K, ^_, _, or \.

Miscellaneous Commands

Command

Action

<

Shift text described by following motion command left by one shiftwidth. {vim}

>

Shift text described by following motion command right by one shiftwidth. {vim}

<<

Shift line left one shift width (default is eight spaces).

>>

Shift line right one shift width (default is eight spaces).

>}

Shift right to end of paragraph.

<%

Shift left until matching parenthesis, brace, or bracket. (Cursor must be on the matching symbol.)

= =

Indent line in C-style, or using program specified in equalprg option. {vim}

g

Start many multiple character commands in vim.

K

Look up word under cursor in manpages (or program defined in keywordprg). {vim}

^O

Return to previous jump. {vim}

q

Record keystrokes. {vim}

^Q

Same as ^V. {vim} (On some terminals, resume data flow.)

^T

Return to the previous location in the tag stack. (vim)

^]

Perform a tag lookup on the text under the cursor.

^\

Enter ex line-editing mode.

^^

(Caret key with Ctrl key pressed) Return to previously edited file.

vi Configuration

This section describes the following:

- The :set command

- Options available with :set

- Sample .exrc file

The :set Command

The :set command allows you to specify options that change characteristics of your editing environment. Options may be put in the ˜/.exrc file or set during a vi session.

The colon does not need to be typed if the command is put in .exrc:

Command

Action

:set x

Enable Boolean option x, show value of other options.

:set nox

Disable option x.

:set x=value

Give value to option x.

:set

Show changed options.

:set all

Show all options.

:set x?

Show value of option x.

Options Used by :set

Table 9-1 contains brief descriptions of the important set command options. In the first column, options are listed in alphabetical order; if the option can be abbreviated, that abbreviation is shown in parentheses. The second column shows the default setting. The last column describes what the option does, when enabled.

This table lists set options for vi, with the addition of important vim options. Other versions of vi may have more or fewer or different options. See your local documentation, or use :set all to see the full list. Options that receive a value are marked with an =.

Table 9-1. set options

Option

Default

Description

autoindent (ai)

noai

In insert mode, indent each line to the same level as the line above or below. Use with the shiftwidth option.

autoprint (ap)

ap

Display changes after each editor command. (For global replacement, display last replacement.)

autowrite (aw)

noaw

Automatically write (save) the file if changed before opening another file with a command such as :n, or before giving Unix command with :!.

background (bg)

Describe the background so the editor can choose appropriate highlighting colors. Default value of dark or light depends on the environment in which the editor is invoked. {vim}

backup (bk)

nobackup

Create a backup file when overwriting an existing file. {vim}

backupdir= (bdir)

.,~/tmp/,~/

Name directories in which to store backup files if possible. The list of directories is comma-separated and in order of preference. {vim}

beautify (bf)

nobf

Ignore all control characters during input (except tab, newline, or formfeed).

backupext= (bex)

~

String to append to filenames for backup files. {vim}

cindent (cin)

nocindent

In insert mode, indent each line relative to the one above it, as is appropriate for C or C++ code. {vim}

compatible (cp)

cp

Make vim behave more like vi. Default is nocp when a ˜/.vimrc file is found. {vim}

directory (dir)

/tmp

Name of directory in which ex/vi stores buffer files. (Directory must be writable.) This can be a comma--separated list for vim.

edcompatible

noedcompatible

Remember the flags used with the most recent substitute command (global, confirming) and use them for the next substitute command. Despite the name, no version of ed actually does this.

equalprg= (ep)

Use the specified program for the = command. When the option is blank (the default), the key invokes the internal C indention function or the value of the indentexpr option. {vim}

errorbells (eb)

errorbells

Sound bell when an error occurs.

exrc (ex)

noexrc

Allow the execution of .exrc files that reside outside the user’s home directory.

formatprg= (fp)

The gq command will invoke the named external program to format text. It will call internal formatting functions when this option is empty (the default). {vim}

gdefault (gd)

nogdefault

Set the g flag on for substitutions by default. {vim}

hardtabs= (ht)

8

Define boundaries for terminal hardware tabs.

hidden (hid)

nohidden

Hide buffers rather than unload them when they are abandoned. {vim}

hlsearch (hls)

hlsearch

Highlight all matches of most recent search pattern. Use :nohlsearch to remove highlighting. {vim}

history= (hi)

20

Number of ex commands to store in the history table. {vim}

ignorecase (ic)

noic

Disregard case during a search.

incsearch (is)

noincsearch

Highlight matches to a search pattern as it is typed. {vim}

lisp

nolisp

Insert indents in appropriate Lisp format. ( ), { }, [ [, and ] ] are modified to have meaning for Lisp.

list

nolist

Print tabs as ^I; mark ends of lines with $. (Use list to tell if end character is a tab or a space.)

magic

magic

Wildcard characters; . (dot), * (asterisk), and [ ] (brackets) have special meaning in patterns.

mesg

mesg

Permit system messages to display on terminal while editing in vi.

mousehide (mh)

mousehide

When characters are typed, hide the mouse pointer. {vim}

novice

nonovice

Require the use of long ex command names, such as copy or read.

number (nu)

nonu

Display line numbers on left of screen during editing session.

open

open

Allow entry to open or visual mode from ex. Although not in vim, this option has traditionally been in vi, and may be in your version of vi.

optimize (opt)

noopt

Abolish carriage returns at the end of lines when printing multiple lines; speed output on dumb terminals when printing lines with leading whitespace (spaces or tabs).

paragraphs (para)

IPLPPPQPP LIpplpipnpbp

Define paragraph delimiters for movement by { or }. The pairs of characters in the value are the names of troff macros that begin paragraphs.

paste

nopaste

Change the defaults of various options to make pasting text into a terminal window work better. All options are returned to their original value when the paste option is reset. {vim}

prompt

prompt

Display the ex prompt ( : ) when vi ’s Q command is given.

readonly (ro)

noro

Any writes (saves) of a file fail unless you use ! after the write (works with w, ZZ, or autowrite).

redraw (re)

vi redraws the screen whenever edits are made. noredraw is useful at slow speeds on a dumb terminal: the screen isn’t fully updated until you press Escape. Default depends on line speed and terminal type.

remap

remap

Allow nested map sequences.

report=

5

Display a message on the status line whenever you make an edit that affects at least a certain number of lines. For example, 6dd reports the message “6 lines deleted.”

ruler (ru)

ruler

Show line and column numbers for the current cursor position. {vim}

scroll=

[1/2 window]

Number of lines to scroll with ^D and ^U commands.

sections= (sect)

SHNHH HUnhsh+c

Define section delimiters for [ [ and ] ] movement. The pairs of characters in the value are the names of troff macros that begin sections.

shell= (sh)

/bin/sh

Pathname of shell used for shell escape (:!) and shell command (:sh). Default value is derived from shell environment, which varies on different systems.

shiftwidth= (sw)

8

Define number of spaces used when the indent in increased or decreased.

showmatch (sm)

nosm

In vi, when ) or } is entered, cursor moves briefly to matching ( or {. (If no match, rings the error message bell.) Very useful for programming.

showmode

noshowmode

In insert mode, display a message on the prompt line indicating the type of insert you are making. For example, “OPEN MODE” or “APPEND MODE.”

slowopen (slow)

Hold off display during insert. Default depends on line speed and terminal type.

smartcase (scs)

nosmartcase

Override the ignorecase option when a search pattern contains uppercase characters. {vim}

tabstop= (ts)

8

Define number of spaces a tab indents during editing session. (Printer still uses system tab of 8.)

taglength= (tl)

0

Define number of characters that are significant for tags. Default (zero) means that all characters are significant.

tags=

tags /usr/lib/tags

Define pathname of files containing tags. (See the Unix ctags command.) (By default, vi searches the file tags in the current directory and /usr/lib/tags.)

tagstack

tagstack

Enable stacking of tag locations on a stack. (Solaris vi and vim.)

term=

Set terminal type.

terse

noterse

Display shorter error messages.

textwidth= (tw)

0

The maximum width of text to be inserted; longer lines are broken after whitespace. Default (zero) disables this feature, in which case wrapmargin is used. {vim}

timeout (to)

timeout

Keyboard maps timeout after 1 second.[a]

timeoutlen= (tm)

1000

Number of milliseconds after which keyboard maps timeout. Default value of 1000 provides traditional vi behavior. {vim}

ttytype=

Set terminal type. This is just another name for term.

undolevels= (ul)

1000

Number of changes that can be undone. {vim}

warn

warn

Display the warning message, “No write since last change.”

window (w)

Show a certain number of lines of the file on the screen. Default depends on line speed and terminal type.

wrap

When on, long lines wrap on the screen. When off, only the first part of the line is displayed. {vim}

wrapmargin (wm)

0

Define right margin. If greater than zero, vi automatically inserts carriage returns to break lines.

wrapscan (ws)

ws

Searches wrap around either end of file.

writeany (wa)

nowa

Allow saving to any file.

writebackup (wb)

wb

Back up files before attempting to overwrite them. Remove the backup when the file has been successfully written, unless the backup option is set. {vim}

[a] When you have mappings of several keys (for example, :map zzz 3dw), you probably want to use notimeout. Otherwise, you need to type zzz within 1 second. When you have an insert mode mapping for a cursor key (for example, :map! ^[OB ^[ja), you should use timeout. Otherwise, vi won’t react to Escape until you type another key.

Sample .exrc File

The following lines of code are an example of a customized .exrc file:

set nowrapscan                   " Searches don't wrap at end of file
set wrapmargin=7                 " Wrap text at 7 columns from right margin
set sections=SeAhBhChDh nomesg   " Set troff macros, disallow message
map q :w^M:n^M                   " Alias to move to next file
map v dwElp                      " Move a word
ab ORA O'Reilly Media, Inc.      " Input shortcut

Tip

The q alias isn’t needed for vim, which has the :wn command. The v alias would hide the vim command v, which enters character-at-a-time visual-mode operation.

ex Basics

The ex line editor serves as the foundation for the screen editor vi. Commands in ex work on the current line or on a range of lines in a file. Most often, you use ex from within vi. In vi, ex commands are preceded by a colon and entered by pressing Enter.

You can also invoke ex on its own--from the command line--just as you would invoke vi. (You could execute an ex script this way.) You can also use the vi command Q to quit the vi editor and enter ex.

Syntax of ex Commands

To enter an ex command from vi, type:

:[address] command [options]

An initial : indicates an ex command. As you type the command, it is echoed on the status line. Execute the command by pressing the Enter key. address is the line number or range of lines that are the object of command. options and addresses are described below. ex commands are described in the next section Alphabetical Summary of ex Commands in Alphabetical Summary of ex Commands.

You can exit ex in several ways:

:x

Exit (save changes and quit).

:q!

Quit without saving changes.

:vi

Switch to the vi editor on the current file.

Addresses

If no address is given, the current line is the object of the command. If the address specifies a range of lines, the format is:

x,y

where x and y are the first and last addressed lines (x must precede y in the buffer). x and y may each be a line number or a symbol. Using ; instead of , sets the current line to x before interpreting y. The notation 1,$ addresses all lines in the file, as does %.

Address Symbols

Symbol

Meaning

1,$

All lines in the file.

x,y

Lines x through y.

x;y

Lines x through y, with current line reset to x.

0

Top of file.

.

Current line.

num

Absolute line number num.

$

Last line.

%

All lines; same as 1,$.

x-n

n lines before x.

x+n

n lines after x.

-[num]

One or num lines previous.

+[num]

One or num lines ahead.

'x

Line marked with x.

"

Previous mark.

/pattern/

Forward to line matching pattern.

?pattern?

Backward to line matching pattern.

See Chapter 7 for more information on using patterns.

Options

!

Indicates a variant form of the command, overriding the normal behavior. The ! must come immediately after the command.

count

The number of times the command is to be repeated. Unlike in vi commands, count cannot precede the command, because a number preceding an ex command is treated as a line address. For example, d3 deletes three lines beginning with the current line; 3d deletes line 3.

file

The name of a file that is affected by the command. % stands for the current file; # stands for the previous file.

Alphabetical Summary of ex Commands

ex commands can be entered by specifying any unique abbreviation. In this listing, the full name appears in the margin, and the shortest possible abbreviation is used in the syntax line. Examples are assumed to be typed from vi, so they include the : prompt.

Name

abbreviate

Synopsis

ab [string text]

Define string when typed to be translated into text. If string and text are not specified, list all current abbreviations.

Examples

Note: ^M appears when you type ^V followed by Enter.

:ab ora O'Reilly Media, Inc.
:ab id Name:^MRank:^MPhone:

Name

append

Synopsis

[address] a[!]
text
.

Append new text at specified address, or at present address if none is specified. Add a ! to toggle the autoindent setting that is used during input. That is, if autoindent was enabled, ! disables it. Enter new text after entering the command. Terminate input of new text by entering a line consisting of just a period.

Example

:a                    Begin appending to current line.
Append this line
and this line too.
.                     Terminate input of text to append.

Name

args

Synopsis

ar
args file ...

Print the members of the argument list (files named on the command line), with the current argument printed in brackets ([ ]).

The second syntax is for vim, which allows you to reset the list of files to be edited.

Name

bdelete

Synopsis

[num] bd[!] [num]

Unload buffer num and remove it from the buffer list. Add a ! to force removal of an unsaved buffer. The buffer may also be specified by filename. If no buffer is specified, remove the current buffer. {vim}

Name

buffer

Synopsis

[num] b[!] [num]

Begin editing buffer num in the buffer list. Add a ! to force a switch from an unsaved buffer. The buffer may also be specified by filename. If no buffer is specified, continue editing the current buffer. {vim}

Name

buffers

Synopsis

buffers[!]

Print the members of the buffer list. Some buffers (e.g., deleted buffers) will not be listed. Add ! to show unlisted buffers. ls is another abbreviation for this command. {vim}

Name

cd

Synopsis

cd dir
chdir dir

Change current directory within the editor to dir.

Name

center

Synopsis

[address] ce [width]

Center line within the specified width. If width is not specified, use textwidth. {vim}

Name

change

Synopsis

[address] c[!]
text
.

Replace the specified lines with text. Add a ! to switch the autoindent setting during input of text. Terminate input by entering a line consisting of just a period.

Name

close

Synopsis

clo[!]

Close current window unless it is the last window. If buffer in window is not open in another window, unload it from memory. This command will not close a buffer with unsaved changes, but you may add ! to hide it instead. {vim}

Name

copy

Synopsis

[address] co destination

Copy the lines included in address to the specified destination address. The command t (short for “to”) is a synonym for copy.

Example

:1,10 co 50    Copy first 10 lines to just after line 50

Name

delete

Synopsis

[address] d [register]

Delete the lines included in address. If register is specified, save or append the text to the named register. Register names are the lowercase letters a-z. Uppercase names append text to the corresponding register.

Examples

:/Part I/,/Part II/-1d   Delete to line above "Part II"

:/main/+d                Delete line below "main"
:.,$d x                  Delete from this line to last line into register x

Name

edit

Synopsis

e[!] [+num] [filename]

Begin editing on filename. If no filename is given, start over with a copy of the current file. Add a ! to edit the new file even if the current file has not been saved since the last change. With the +num argument, begin editing on line num. Or num may be a pattern, of the form /pattern.

Examples

:e file        Edit file in current editing buffer

:e +/^Index #  Edit alternate file at pattern match
:e!            Start over again on current file

Name

file

Synopsis

f [filename]

Change the filename for the current buffer to filename. The next time the buffer is written, it will be written to file filename. When the name is changed, the buffer’s “not edited” flag is set, to indicate you are not editing an existing file. If the new filename is the same as a file that already exists on the disk, you will need to use :w! to overwrite the existing file. When specifying a filename, the % character can be used to indicate the current filename. A # can be used to indicate the alternate filename. If no filename is specified, print the current name and status of the buffer.

Example

:f%.new

Name

fold

Synopsis

address fo

Fold the lines specified by address. A fold collapses several lines on the screen into one line, which later can be unfolded. It doesn’t affect the text of the file. {vim}

Name

foldclose

Synopsis

[address] foldc[!]

Close folds in specified address, or at present address if none is specified. Add a ! to close more than one level of folds. {vim}

Name

foldopen

Synopsis

[address] foldo[!]

Open folds in specified address, or at present address if none is specified. Add a ! to open more than one level of folds. {vim}

Name

global

Synopsis

[address] g[!]/pattern/[commands]

Execute commands on all lines which contain pattern or, if address is specified, on all lines within that range. If commands are not specified, print all such lines. Add a ! to execute commands on all lines not containing pattern. See also v.

Examples

:g/Unix/p            Print all lines containing "Unix"

:g/Name:/s/tom/Tom/  Change "tom" to "Tom" on all lines
containing "Name:"

Name

hide

Synopsis

hid

Close current window unless it is the last window, but do not remove the buffer from memory. This is a safe command to use on an unsaved buffer. {vim}

Name

insert

Synopsis

[address] i[!]
text
.

Insert text at line before the specified address, or at present address if none is specified. Add a ! to switch the autoindent setting during input of text. Terminate input of new text by entering a line consisting of just a period.

Name

join

Synopsis

[address] j[!] [count]

Place the text in the specified range on one line, with whitespace adjusted to provide two space characters after a period (.), no space characters before a ), and one space character otherwise. Add a ! to prevent whitespace adjustment.

Example

:1,5j!      Join first five lines, preserving whitespace

Name

jumps

Synopsis

ju

Print jump list used with Ctrl-I and Ctrl-O commands. The jump list is a record of most movement commands that skip over multiple lines. It records the position of the cursor before each jump. {vim}

Name

k

Synopsis

[address] k char

Same as mark; see mark, later in this list.

Name

left

Synopsis

[address] le [count]

Left-align lines specified by address, or current line if no address is specified. Indent lines by count spaces. {vim}

Name

list

Synopsis

[address] l [count]

Print the specified lines so that tabs display as ^I, and the ends of lines display as $. l is like a temporary version of :set list.

Name

map

Synopsis

map[!] [string commands]

Define a keyboard macro named string as the specified sequence of commands. string is usually a single character, or the sequence #num, representing a function key on the keyboard. Use a ! to create a macro for input mode. With no arguments, list the currently defined macros.

Examples

:map K dwwP            Transpose two words

:map q :w^M:n^M        Write current file; go to next
:map! + ^[bi(^[ea)    Enclose previous word in parentheses

Tip

vim has K and q commands, which the above aliases would hide.

Name

mark

Synopsis

[address] ma char

Mark the specified line with char, a single lowercase letter. Return later to the line with ‘x (where x is the same as char). vim also uses uppercase and numeric characters for marks. Lowercase letters work the same as in vi. Uppercase letters are associated with filenames and can be used between multiple files. Numbered marks, however, are maintained in a special viminfo file and cannot be set using this command. Same as k.

Name

marks

Synopsis

marks [chars]

Print list of marks specified by chars, or all current marks if no chars specified. {vim}

Example

:marks abc    Print marks a, b and c.

Name

mkexrc

Synopsis

mk[!] file

Create an .exrc file containing set commands for changed ex options and key mappings. This saves the current option settings, allowing you to restore them later.

Name

move

Synopsis

[address] m destination

Move the lines specified by address to the destination address.

Example

:.,/Note/m /END/     Move text block to after line containing "END"

Name

new

Synopsis

[count] new

Create a new window count lines high with an empty buffer. {vim}

Name

next

Synopsis

num[!] [[+num] filelist]

Edit the next file from the command-line argument list. Use args to list these files. If filelist is provided, replace the current argument list with filelist and begin editing on the first file. With the +num argument, begin editing on line num. Or num may be a pattern, of the form /pattern.

Example

:n chap*    Start editing all "chapter" files

Name

nohlsearch

Synopsis

noh

Temporarily stop highlighting all matches to a search when using the hlsearch option. Highlighting is resumed with the next search. {vim}

Name

number

Synopsis

[address] nu [count]

Print each line specified by address, preceded by its buffer line number. Use # as an alternate abbreviation for number. count specifies the number of lines to show, starting with address.

Name

only

Synopsis

on [!]

Make the current window be the only one on the screen. Windows open on modified buffers are not removed from the screen (hidden), unless you also use the ! character. {vim}

Name

open

Synopsis

[address] o [/pattern/]

Enter open mode (vi) at the lines specified by address, or at the lines matching pattern. Exit open mode with Q. Open mode lets you use the regular vi commands, but only one line at a time. It can be useful on slow dial-up lines (or on very distant Internet ssh connections).

Name

preserve

Synopsis

pre

Save the current editor buffer as though the system were about to crash.

Name

previous

Synopsis

prev[!]

Edit the previous file from the command-line argument list. {vim}

Name

print

Synopsis

[address] p [count]

Print the lines specified by address. count specifies the number of lines to print, starting with address. P is another abbreviation.

Example

:100;+5p    Show line 100 and the next five lines

Name

put

Synopsis

[address] pu [char]

Restore previously deleted or yanked lines from named register specified by char, to the line specified by address. If char is not specified, the last deleted or yanked text is restored.

Name

qall

Synopsis

qa[!]

Close all windows and terminate current editing session. Use ! to discard changes made since the last save. {vim}

Name

quit

Synopsis

q[!]

Terminate current editing session. Use ! to discard changes made since the last save. If the editing session includes additional files in the argument list that were never accessed, quit by typing q! or by typing q twice. vim only closes the editing window if there are still other windows open on the screen.

Name

read

Synopsis

[address] r filename

Copy the text of filename after the line specified by address. If filename is not specified, the current filename is used.

Example

:0r $HOME/data    Read file in at top of current file

Name

read

Synopsis

[address] r !command

Read the output of shell command into the text after the line specified by address.

Example

:$r !spell %    Place results of spell checking at end of file

Name

recover

Synopsis

rec [file]

Recover file from the system save area.

Name

redo

Synopsis

red

Restore last undone change. Same as Ctrl-R. {vim}

Name

resize

Synopsis

res [[±]num]

Resize current window to be num lines high. If + or - is specified, increase or decrease the current window height by num lines. {vim}

Name

rewind

Synopsis

rew[!]

Rewind argument list and begin editing the first file in the list. Add a ! to rewind even if the current file has not been saved since the last change.

Name

right

Synopsis

[address] ri [width]

Right-align lines specified by address, or current line if no address is specified, to column width. Use textwidth option if no width is specified. {vim}

Name

sbnext

Synopsis

[count] sbn [count]

Split the current window and begin editing the count‘th next buffer from the buffer list. If no count is specified, edit the next buffer in the buffer list. {vim}

Name

sbuffer

Synopsis

[num] sb [num]

Split the current window and begin editing buffer num from the buffer list in the new window. The buffer to be edited may also be specified by filename. If no buffer is specified, open the current buffer in the new window. {vim}

Name

set

Synopsis

se parameter1 parameter2 ...

Set a value to an option with each parameter, or, if no parameter is supplied, print all options that have been changed from their defaults. For Boolean options, each parameter can be phrased as option or nooption; other options can be assigned with the syntax option=value. Specify all to list current settings. The form set option? displays the value of option. See the list of set options in the section The :set Command in The :set Command.

Examples

:set nows wm=10
:set all

Name

shell

Synopsis

sh

Create a new shell. Resume editing when the shell terminates.

Name

snext

Synopsis

[count] sn [[+num] filelist]

Split the current window and begin editing the next file from the command-line argument list. If count is provided, edit the count’th next file. If filelist is provided, replace the current argument list with filelist and begin editing the first file. With the +n argument, begin editing on line num. Alternately, num may be a pattern of the form /pattern. {vim}

Name

source

Synopsis

so file

Read (source) and execute ex commands from file.

Example

:so $HOME/.exrc

Name

split

Synopsis

[count] sp [+num] [filename]

Split the current window and load filename in the new window, or the same buffer in both windows if no file is specified. Make the new window count lines high, or, if count is not specified, split the window into equal parts. With the +n argument, begin editing on line num. num may also be a pattern of the form /pattern. {vim}

Name

sprevious

Synopsis

[count] spr [+num]

Split the current window and begin editing the previous file from the command-line argument list in the new window. If count is specified, edit the count‘th previous file. With the +num argument, begin editing on line num. num may also be a pattern of the form /pattern. {vim}

Name

stop

Synopsis

st

Suspend the editing session. Same as Ctrl-Z. Use the shell fg command to resume the session.

Name

substitute

Synopsis

[address] s [/pattern/replacement/] [options] [count]

Replace the first instance of pattern on each of the specified lines with replacement. If pattern and replacement are omitted, repeat last substitution. count specifies the number of lines on which to substitute, starting with address. See additional examples in Chapter 7.

Options

c

Prompt for confirmation before each change.

g

Substitute all instances of pattern on each line (global).

p

Print the last line on which a substitution was made.

Examples

:1,10s/yes/no/g                         Substitute on first 10 lines

:%s/[Hh]ello/Hi/gc          Confirm global substitutions
:s/Fortran/\U&/ 3           Uppercase "Fortran" on next three lines
:g/^[0-9][0-9]*/s//Line &:/ For every line beginning with
one or more
digits, add "Line" and a colon

Name

suspend

Synopsis

su

Suspend the editing session. Same as Ctrl-Z. Use the shell fg command to resume the session.

Name

sview

Synopsis

[count] sv [+num] [filename]

Same as the split command, but set the readonly option for the new buffer. {vim}

Name

t

Synopsis

[address] t destination

Copy the lines included in address to the specified destination address. t is equivalent to copy.

Example

:%t$    Copy the file and add it to the end

Name

tag

Synopsis

[address] ta tag

In the tags file, locate the file and line matching tag, and start editing there.

Example

Run ctags, then switch to the file containing myfunction:

:!ctags *.c
:tag myfunction

Name

tags

Synopsis

tags

Print list of tags in the tag stack. {vim}

Name

unabbreviate

Synopsis

una word

Remove word from the list of abbreviations.

Name

undo

Synopsis

u

Reverse the changes made by the last editing command. In vi, the undo command will undo itself, redoing what you undid. vim supports multiple levels of undo. Use redo to redo an undone change in vim.

Name

unhide

Synopsis

[count] unh

Split screen to show one window for each active buffer in the buffer list. If specified, limit the number of windows to count. {vim}

Name

unmap

Synopsis

unm[!] string

Remove string from the list of keyboard macros. Use ! to remove a macro for input mode.

Name

v

Synopsis

[address] v/pattern/[command]

Execute command on all lines not containing pattern. If command is not specified, print all such lines. v is equivalent to g!. See global.

Example

:v/#include/d    Delete all lines except "#include" lines

Name

version

Synopsis

ve

Print the editor’s current version number and date of last change.

Name

view

Synopsis

vie[[+num] filename]

Same as edit, but set file to readonly. When executed in ex mode, return to normal or visual mode. {vim}

Name

visual

Synopsis

[address] vi [type] [count]

Enter visual mode (vi) at the line specified by address. Return to ex mode with Q. type can be one of -, ^, or . (see the z command). count specifies an initial window size.

Name

visual

Synopsis

vi [+num]file

Begin editing file in visual mode (vi), optionally at line num.

Name

vsplit

Synopsis

[count] vs [+num] [filename]

Same as the split command, but split the screen vertically. The count argument can be used to specify a width for the new window. {vim}

Name

wall

Synopsis

wa[!]

Write all changed buffers with filenames. Add ! to force writing of any buffers marked readonly. {vim}

Name

wnext

Synopsis

[count] wn[!] [[+num] filename]

Write current buffer and open next file in argument list, or the count’th next file if specified. If filename is specified, edit it next. With the +num argument, begin editing on line num. num may also be a pattern of the form /pattern. {vim}

Name

write

Synopsis

[address] w[!] [[>>] file]

Write lines specified by address to file, or write full contents of buffer if address is not specified. If file is also omitted, save the contents of the buffer to the current filename. If >> file is used, append lines to the end of the specified file. Add a ! to force the editor to write over any current contents of file.

Examples

:1,10w name_list    Copy first 10 lines to file name_list

:50w >> name_list   Now append line 50

Name

write

Synopsis

[address] w !command

Write lines specified by address to command.

Example

:1,66w !pr -h myfile | lp    Print first page of file

Name

wq

Synopsis

wq[!]

Write and quit the file in one movement. The file is always written. The ! flag forces the editor to write over any current contents of file.

Name

wqall

Synopsis

wqa[!]

Write all changed buffers and quit the editor. Add ! to force writing of any buffers marked readonly. xall is another alias for this command. {vim}

Name

X

Synopsis

X

Prompt for an encryption key. This command can be preferable to :set key, as typing the key is not echoed to the console. To remove an encryption key, just reset the key option to an empty value. {vim}

Name

xit

Synopsis

x

Write the file if it was changed since the last write, then quit.

Name

yank

Synopsis

[address] y [char] [count]

Place lines specified by address in named register char. Register names are the lowercase letters a-z. Uppercase names append text to the corresponding register. If no char is given, place lines in general register. count specifies the number of lines to yank, starting with address.

Example

:101,200 ya a    Copy lines 100-200 to register "a"

Name

z

Synopsis

[address] z [type] [count]

Print a window of text with the line specified by address at the top. count specifies the number of lines to be displayed.

Type

+

Place specified line at the top of the window (default).

-

Place specified line at the bottom of the window.

.

Place specified line in the center of the window.

^

Print the previous window.

=

Place specified line in the center of the window and leave the current line at this line.

Name

!

Synopsis

[address] !command

Execute Unix command in a shell. If address is specified, use the lines contained in address as standard input to command, and replace the lines with the output and error output. (This is called filtering the text through the command.)

Examples

:!ls              List files in the current directory
:11,20!sort -f    Sort lines 11-20 of current file

Name

=

Synopsis

[address] =

Print the line number of the line indicated by address. Default is line number of the last line.

Name

< >

Synopsis

[address] < [count]
[address] > [count]

Shift lines specified by address either left (<) or right (>). Only leading spaces and tabs are added or removed when shifting lines. count specifies the number of lines to shift, starting with address. The shiftwidth option controls the number of columns that are shifted. Repeating the < or > increases the shift amount. For example, :>>> shifts three times as much as :>.

Name

address

Synopsis

address

Print the lines specified in address.

Name

Enter

Print the next line in the file. (For ex only; not from the : prompt in vi.)

Name

@

Synopsis

[address] @ [char]

Execute contents of register specified by char. If address is given, move cursor to the specified address first. If char is @, repeat the last @ command.

Name

&

Synopsis

[address] & [options] [count]

Repeat the previous substitute (s) command. count specifies the number of lines on which to substitute, starting with address. options are the same as for the substitute command.

Examples

:s/Overdue/Paid/    Substitute once on current line

:g/Status/&         Redo substitution on all "Status" lines

Name

~

Synopsis

[address] ˜ [count]

Replace the last-used regular expression (even if from a search, and not from an s command) with the replacement pattern from the most recent s (substitute) command. This is rather obscure; see Chapter 6 of Learning the vi and Vim Editors by Arnold Robbins et al. (O’Reilly) for details.

Chapter 10. The sed Editor

The sed “stream editor” is one of the most prominent text-processing tools on Unix and Linux. It is most often used for performing simple substitutions on data streams going through pipelines, but sed scripts can be written to do much more.

This chapter presents the following topics:

- Conceptual overview of sed

- Command-line syntax

- Syntax of sed commands

- Group summary of sed commands

- Alphabetical summary of sed commands

The version of sed provided with Linux systems is the GNU version written by the Free Software Foundation; its home page is http://www.gnu.org/software/sed/sed.html. For more information on sed, see Dale Dougherty and Arnold Robbins’s sed & awk (O’Reilly).

Conceptual Overview

The stream editor, sed, is a noninteractive editor. It interprets a script and performs the actions in the script. sed is stream-oriented because, like many Unix programs, input flows through the program and is directed to standard output. For example, sort is stream-oriented; vi is not. sed’s input typically comes from a file or pipe, but it can also be taken from the keyboard. Output goes to the screen by default, but it can be captured in a file or sent through a pipe instead. GNU sed can edit files that use multibyte character sets.

Typical Uses of sed

- Editing one or more files automatically.

- Simplifying repetitive edits to multiple files.

- Writing conversion programs.

sed Operation

sed operates as follows:

- Each line of input is copied into a pattern space, an internal buffer where editing operations are performed.

- All editing commands in a sed script are applied, in order, to each line of input.

- Editing commands are applied to all lines (globally) unless line addressing restricts the lines affected.

- If a command changes the input, subsequent commands and address tests are applied to the current line in the pattern space, not the original input line.

- The original input file is unchanged because the editing commands modify an in-memory copy of each original input line. The copy is sent to standard output (but can be redirected to a file).

- sed also maintains the hold space, a separate buffer that can be used to save data for later retrieval.

Command-Line Syntax

The syntax for invoking sed has two forms:

sed [-n] [-e] 'command' file(s)
sed [-n]  -f  scriptfile file(s)

The first form allows you to specify an editing command on the command line, surrounded by single quotes. The second form allows you to specify a scriptfile, a file containing sed commands. Both forms may be used together, and they may be used multiple times. If no file (s) is specified, sed reads from standard input.

Standard Options

The following options are recognized:

-n

Suppress the default output; sed displays only those lines specified with the p command or with the p flag of the s command.

-e cmd

Next argument is an editing command. Necessary if multiple scripts or commands are specified.

-f file

Next argument is a file containing editing commands.

If the first line of the script is #n, sed behaves as if -n had been specified.

Multiple -e and -f options may be provided, and they may be mixed. The final script consists of the concatenation of all the script and file arguments.

GNU sed Options

GNU sed accepts a number of additional command-line options, as well as long-option equivalents for the standard options. The GNU sed options are:

-e cmd, --expression cmd

Use cmd as editing commands.

-f file, --file file

Obtain editing commands from file.

--help

Print a usage message and exit.

-i[suffix], --in-place[=suffix]

Edit files in place, overwriting the original file. If optional suffix is supplied, use it for renaming the original file as a backup file. See the GNU sed online Info documentation for the details.

-l len, --line-length len

Set the line length for the l command to len characters.

-n, --quiet, --silent

Suppress the default output; sed displays only those lines specified with the p command or with the p flag of the s command.

--posix

Disable all GNU extensions. Setting POSIXLY_CORRECT in the environment merely disables those extensions that are incompatible with the POSIX standard.

-r, --regexp-extended

Use Extended Regular Expressions instead of Basic Regular Expressions. See Chapter 7 for more information.

-s, --separate

Instead of considering the input to be one long stream consisting of the concatenation of all the input files, treat each file separately. Line numbers start over with each file, the address $ refers to the last line of each file, files read by the R command are rewound, and range addresses (/x/,/y/) may not cross file boundaries.

-u, --unbuffered

Buffer input and output as little as possible. Useful for editing the output of tail -f when you don’t want to wait for the output.

--version

Print the version of GNU sed and a copyright notice, and then exit.

Syntax of sed Commands

sed commands have the general form:

[address[,address]][!]command [arguments]

commands consist of a single letter or symbol; they are described later, by group and alphabetically. arguments include the label supplied to b or t, the filename supplied to r or w, and the substitution flags for s. addresses are described next.

Pattern Addressing

A sed command can specify zero, one, or two addresses. In POSIX sed, an address has one of the forms in the following table. Regular expressions are described in Chapter 7. Additionally, \n can be used to match any newline in the pattern space (resulting from the N command), but not the newline at the end of the pattern space.

Address

Meaning

/pattern/

Lines that match pattern.

\pattern;

Like previous, but use semicolon as the delimiter instead of slash. Any character may be used. This is useful if pattern contains multiple slash characters.

n

Line number n.

$

The last input line.

If the command specifies:

Then the command is applied to:

No address

Each input line.

One address

Any line matching the address. Some commands accept only one address: a, i, r, q, and =.

Two comma-separated addresses

First matching line and all succeeding lines up to and including a line matching the second address.

An address followed by !

All lines that do not match the address.

GNU sed allows additional address forms:

Address

Meaning

/pattern/i

Match pattern, ignoring case. I may be used instead of i.

/pattern/m

Match pattern, allowing ^ and $ to match around an embedded newline. M may be used instead of m.

0,/pattern/

Similar to 1,/pattern/, but if line 1 matches pattern, it will end the range.

address,+n

Matches line matching address, and the n following lines.

address~incr

Matches line matching address and every incr lines after it. For example, 42˜3 matches 42, 45, 48, and so on.

Pattern Addressing Examples

Command

Action performed

s/xx/yy/g

Substitute on all lines (all occurrences).

/BSD/d

Delete lines containing BSD.

/^BEGIN/,/^END/p

Print between BEGIN and END, inclusive.

/SAVE/!d

Delete any line that doesn’t contain SAVE.

/BEGIN/,/END/!s/xx/yy/g

Substitute on all lines, except between BEGIN and END.

Braces ({ }) are used in sed to nest one address inside another or to apply multiple commands at a single matched address:

[/pattern/[,/pattern/]]{
command1
command2
}

The opening curly brace must end its line, and the closing curly brace must be on a line by itself. Be sure there are no spaces after the braces.

GNU sed Regular Expression Extensions

With the -r option, GNU sed uses Extended Regular Expressions instead of Basic Regular expressions. (See Chapter 7 for more information.) However, even without -r, you can use additional escape sequences for more powerful text matching. The following escape sequences are valid only in regular expressions:

\b

Matches on a word boundary, where of the two surrounding characters (x\by), one is a word-constituent character and the other is not.

\B

Matches on a nonword boundary, where both of the two surrounding characters (x\by) are either word-constituent or not word-constituent.

\w

Matches any word-constituent character (i.e., a letter, digit, or underscore).

\W

Matches any nonword-constituent character (i.e., anything that is not a letter, digit, or underscore).

\'

Matches the beginning of the pattern space. This is different from ^ when the m modifier is used for a pattern or the s command.

\'

Matches the end of the pattern space. This is different from $ when the m modifier is used for a pattern or the s command.

The following escape sequences may be used anywhere.

\a

The ASCII BEL character.

\f

The ASCII formfeed character.

\n

The ASCII newline character.

\r

The ASCII carriage-return character.

\v

The ASCII vertical tab character.

\dnn

The character whose ASCII decimal value is nn.

\onn

The character whose ASCII octal value is nn.

\xnn

The character whose ASCII hexadecimal value is nn.

Group Summary of sed Commands

In the lists that follow, the sed commands are grouped by function and are described tersely. Full descriptions, including syntax and examples, can be found afterward in the Alphabetical Summary of sed Commands in Alphabetical Summary of sed Commands. Commands marked with a † are specific to GNU sed.

Basic Editing

Command

Action

a\

Append text after a line.

c\

Replace text (usually a text block).

i\

Insert text before a line.

d

Delete lines.

s

Make substitutions.

y

Translate characters (like Unix tr).

Line Information

Command

Action

=

Display line number of a line.

l

Display control characters in ASCII.

p

Display the line.

Input/Output Processing

Command

Action

e†

Execute commands.

n

Skip current line and go to the next line.

r

Read another file’s contents into the output stream.

R †

Read one line from a file into the output.

w

Write input lines to another file.

W †

Write first line in pattern space to another file.

q

Quit the sed script (no further output).

Q †

Quit without printing the pattern space.

v †

Require a specific version of GNU sed to run the script.

Yanking and Putting

Command

Action

h

Copy into hold space; wipe out what’s there.

H

Copy into hold space; append to what’s there.

g

Get the hold space back; wipe out the destination line.

G

Get the hold space back; append to the pattern space.

x

Exchange contents of the hold and pattern spaces.

Branching Commands

Command

Action

b

Branch to label or to end of script.

t

Same as b, but branch only after substitution.

T †

Same as t, but branch only if no successful substitutions.

:label

Label branched to by t or b.

Multiline Input Processing

Command

Action

N

Read another line of input (creates embedded newline).

D

Delete up to the embedded newline.

P

Print up to the embedded newline.

Alphabetical Summary of sed Commands

GNU sed lets you use the filenames /dev/stdin, /dev/stdout and /dev/stderr to refer to standard input, output, and error, respectively, for the r, R, w, and W commands and the w flag to the s command.

GNU-specific commands or extensions are noted with {G} in the command synopsis. When the GNU version allows a command to have two addresses, the command is performed for each input line within the range.

Name

#

Synopsis

#

Begin a comment in a sed script. Valid only as the first character of the first line. (Some versions, including GNU sed, allow comments anywhere, but it is better not to rely on this.) If the first line of the script is #n, sed behaves as if -n had been specified.

Name

:

Synopsis

:label

Label a line in the script for the transfer of control by b or t. According to POSIX, sed must support labels that are unique in the first eight characters. GNU sed has no limit, but some older versions support up to only seven characters.

Name

=

Synopsis

[/pattern/]=
[address1[,address2]]={G}

Write to standard output the line number of each line addressed by pattern.

Name

a

Synopsis

[address]a\
text
[address1[,address2]]a \ {G}
text

Append text following each line matched by address. If text goes over more than one line, newlines must be “hidden” by preceding them with a backslash. The text is terminated by the first newline that is not hidden in this way. The text is not available in the pattern space, and subsequent commands cannot be applied to it. The results of this command are sent to standard output when the list of editing commands is finished, regardless of what happens to the current line in the pattern space.

The GNU version accepts two addresses and allows you to put the first line of text on the same line as the a command.

Example

$ a\
This goes after the last line in the file\
(marked by $).  This text is escaped at the\
end of each line, except for the last one.

Name

b

Synopsis

[address1[,address2]]b[label]

Unconditionally transfer control to :label elsewhere in script. That is, the command following the label is the next command applied to the current line. If no label is specified, control falls through to the end of the script, so no more commands are applied to the current line.

Example

# Ignore HTML tables; resume script after </table>:
/<table/,/<\/table>/b

Name

c

Synopsis

[address1[,address2]]c\
text

Replace (change) the lines selected by the address(es) with text. (See a for details on text.) When a range of lines is specified, all lines are replaced as a group by a single copy of text. The contents of the pattern space are, in effect, deleted, and no subsequent editing commands can be applied to the pattern space (or to text).

Example

# Replace first 100 lines in a file:
1,100c\
\
<First 100 names to be supplied>

Name

d

Synopsis

[address1[,address2]]d

Delete the addressed line (or lines) from the pattern space. Thus, the line is not passed to standard output. A new line of input is read, and editing resumes with the first command in the script.

Example

# Delete all empty lines, including lines with just
whitespace:
/^[#tab]*$/d

Name

D

Synopsis

[address1[,address2]]D

Delete the first part (up to embedded newline) of a multiline pattern space created by the N command, and resume editing with the first command in the script. If this command empties the pattern space, then a new line of input is read, as if the d command had been executed.

Example

# Strip multiple blank lines, leaving only one:
/^$/{
N
/^\n$/D
}

Name

e

Synopsis

[address1[,address2]]e [command]{G}

With command, execute the command and send the result to standard output. Without command, execute the contents of the pattern space as a command, and replace the pattern space with the results.

Name

g

Synopsis

[address1[,address2]]g

Paste the contents of the hold space (see h and H) back into the pattern space, wiping out the previous contents of the pattern space. The Example shows a simple way to copy lines.

Example

This script collects all lines containing the word Item: and copies them to a place marker later in the file. The place marker is overwritten:

/Item:/H
/<Replace this line with the item list>/g

Name

G

Synopsis

[address1[,address2]]G

Same as g, except that a newline and the hold space are pasted to the end of the pattern space instead of overwriting it. The Example shows a simple way to “cut and paste” lines.

Example

This script collects all lines containing the word Item: and moves them after a place marker later in the file. The original Item: lines are deleted.

/Item:/{
H
d
}
/Summary of items:/G

Name

h

Synopsis

[address1[,address2]]h

Copy the pattern space into the hold space, a special temporary buffer. The previous contents of the hold space are obliterated. You can use h to save a line before editing it.

Example

# Edit a line; print the change; replay the original
/Linux/{
h
s/.* Linux \(.*\) .*/\1:/
p
x
}

Sample input:

This describes the Linux ls command.
This describes the Linux cp command.

Sample output:

ls:
This describes the Linux ls command.
cp:
This describes the Linux cp command.

Name

H

Synopsis

[address1[,address2]]H

Append a newline and then the contents of the pattern space to the contents of the hold space. Even if the hold space is empty, H still appends a newline. H is like an incremental copy. See Examples under g and G.

Name

i

Synopsis

[address]i\
text
[address1[,address2]]i \ {G}
text

Insert text before each line matched by address. (See a for details on text.)

The GNU version accepts two addresses and allows you to put the first line of text on the same line as the i command.

Example

/Item 1/i\
The five items are listed below:

Name

l

Synopsis

[address1[,address2]]l[
address1[,address2]]l [len]{G}

List the contents of the pattern space, showing nonprinting characters as ASCII codes. Long lines are wrapped. With GNU sed, len is the character position at which to wrap long lines. A value of 0 means to never break lines.

Name

n

Synopsis

[address1[,address2]]n

Read the next line of input into pattern space. The current line is sent to standard output, and the next line becomes the current line. Control passes to the command following n instead of resuming at the top of the script.

Example

In DocBook/XML, titles follow section tags. Suppose you are using a convention where each opening section tag is on a line by itself, with the title on the following line. To print all the section titles, invoke this script with sed -n:

/<sect[1-4]/{
n
p
}

Name

N

Synopsis

[address1[,address2]]N

Append the next input line to contents of pattern space; the new line is separated from the previous contents of the pattern space by a newline. (This command is designed to allow pattern matches across two lines.) By using \n to match the embedded newline, you can match patterns across multiple lines. See the Example under D.

Examples

Like the Example in n, but print the section tag line as well as header title:

/<sect[1-4]/{
N
p
}

Join two lines (replace newline with space):

/<sect[1-4]/{
N
s/\n/ /
p
}

Name

p

Synopsis

[address1[,address2]]p

Print the addressed line(s). Note that this can result in duplicate output unless default output is suppressed by using #n or the -n command-line option. Typically used before commands that change control flow (d, n, b), which might prevent the current line from being output. See the Examples under h, n, and N.

Name

P

Synopsis

[address1[,address2]]P

Print first part (up to embedded newline) of multiline pattern space created by N command. Same as p if N has not been applied to a line.

Example

Suppose you have function references in two formats:

function(arg1, arg2)
function(arg1,
arg2)

The following script changes argument arg2, regardless of whether it appears on the same line as the function name:

s/function(arg1, arg2)/function(arg1, XX)/
/function(/{
N
s/arg2/XX/
P
D
}

Name

q

Synopsis

[address]q
[address]q [value]{G}

Quit when address is encountered. The addressed line is first written to the output (if default output is not suppressed), along with any text appended to it by previous a or r commands. GNU sed allows you to provide value, which is used as the exit status.

Examples

Delete everything after the addressed line:

/Garbled text follows:/q

Print only the first 50 lines of a file:

50q

Name

Q

Synopsis

[address]Q [value]{G}

Quits processing, but without printing the pattern space. If value is provided, it is used as sed’s exit status.

Name

r

Synopsis

[address]r file
[address1[,address2]]r file{G}

Read contents of file and append to the output after the contents of the pattern space. There must be exactly one space between the r and the filename. The GNU version accepts two addresses.

Example

/The list of items follows:/r item_file

Name

R

Synopsis

[address1[,address2]]R file{G}

Read one line of file and append to the output after the contents of the pattern space. Successive R commands read successive lines from file.

Name

s

Synopsis

[address1[,address2]]s/pattern/replacement/[flags]

Substitute replacement for pattern on each addressed line. If pattern addresses are used, the pattern // represents the last pattern address specified. Any delimiter may be used. Use \ within pattern or replacement to escape the delimiter. The following flags can be specified (those marked with a † are specific to GNU sed):

n

Replace nth instance of pattern on each addressed line. n is any number in the range 1 to 512, and the default is 1.

e†

If the substitution was made, execute the contents of the pattern space as a shell command and replaces the pattern space with the results.

g

Replace all instances of pattern on each addressed line, not just the first instance.

i or I†

Do a case-insensitive regular expression match.

m or M†

Allow ^ and $ to match around a newline embedded in the pattern space.

p

Print the line if the substitution is successful. If several successful substitutions are successful, sed prints multiple copies of the line.

w file

Write the line to file if a replacement was done. In the traditional Unix sed, a maximum of 10 different files can be opened.

GNU sed allows you to use the special filenames /dev/stdout and /dev/stderr to write to standard output or standard error, respectively.

Within the replacement, GNU sed accepts special escape sequences, with the following meanings:

\L

Lowercase the replacement text until a terminating \E or \U.

\l

Lowercase the following character only.

\U

Uppercase the replacement text until a terminating \E or \L.

\u

Uppercase the following character only.

\E

Terminate case conversion from \L or \U.

Examples

Here are some short, commented scripts:

# Change third and fourth quote to ( and ):
/function/{
s/"/)/4
s/"/(/3
}

# Remove all quotes on a given line:
/Title/s/"//g

# Remove first colon and all quotes; print resulting lines:
s/://p
s/"//gp

# Change first "if" but leave "ifdef" alone:
/ifdef/!s/if/   if/

Name

t

Synopsis

[address1[,address2]]t [label]

Test if successful substitutions have been made on addressed lines, and if so, branch to the line marked by :label. (See b and :.) If label is not specified, control branches to the bottom of the script. The t command is like a case statement in the C programming language or the various shell programming languages. You test each case; when it’s true, you exit the construct.

Example

Suppose you want to fill empty fields of a database. You have this:

ID: 1   Name: greg   Rate: 45
ID: 2   Name: dale
ID: 3

You want this:

ID: 1   Name: greg   Rate: 45   Phone: ??
ID: 2   Name: dale   Rate: ??   Phone: ??
ID: 3   Name: ????   Rate: ??   Phone: ??

You need to test the number of fields already there. Here’s the script (fields are tab-separated):

#n
/ID/{
s/ID: .* Name: .* Rate: .*/&   Phone: ??/p
t
s/ID: .* Name: .*/&   Rate: ??   Phone: ??/p
t
s/ID: .*/&   Name: ????   Rate: ??   Phone: ??/p
}

Name

T

Synopsis

[address1[,address2]]T [label]{G}

Like t, but only branches to label if there not any successful substitutions. (see b, t, and :). If label is not specified, control branches to the bottom of the script.

Name

v

Synopsis

[address1[,address2]]v [version]{G}

This command doesn’t do anything. You use it to require GNU sed for your script. This works, because non-GNU versions of sed don’t implement the command at all, and will therefore fail. If you supply a specific version, GNU sed fails if the required version is newer than the one executing the script.

Name

w

Synopsis

[address1[,address2]]w file

Append contents of pattern space to file. This action occurs when the command is encountered rather than when the pattern space is output. Exactly one space must separate the w and the filename. This command will create the file if it does not exist; if the file exists, its contents will be overwritten each time the script is executed. Multiple write commands that direct output to the same file append to the end of the file.

GNU sed allows you to use the special filenames /dev/stdout and /dev/stderr to write to standard output or standard error, respectively.

Example

# Store HTML tables in  a file
/<table/,/<\/table>/w tables.html

Name

W

Synopsis

[address1[,address2]]W file

Like w, but only writes the contents of the first line in the pattern space to the file.

Name

x

Synopsis

[address1[,address2]]x

Exchange the contents of the pattern space with the contents of the hold space. See h for an example.

Name

y

Synopsis

[address1[,address2]]y/abc/xyz/

Translate characters. Change every instance of a to x, b to y, c to z, etc.

Example

# Change item 1, 2, 3 to Item A, B, C ...
/^item [1-9]/y/i123456789/IABCDEFGHI/

Chapter 11. The gawk Programming Language

gawk is the GNU version of awk, a powerful utility often used for text and string manipulation within shell scripts, particularly when input data may be viewed as records and fields. awk is also an elegant and capable programming language that allows you to accomplish a lot with very little work.

This chapter presents the following topics:

- Conceptual overview

- Command-line syntax

- Patterns and procedures

- Built-in variables

- Operators

- Variables and array assignment

- User-defined functions

- gawk-specific facilities

- Implementation limits

- Group listing of awk functions and commands

- Alphabetical summary of awk functions and commands

- Source code

Conceptual Overview

awk is a pattern-matching program for processing files, especially when each line has a simple field-oriented layout. Linux provides the GNU version of awk, called gawk, which provides a number of additional features. This utility can be invoked either through the standard name awk or through gawk.

This chapter describes functionality that is found in gawk. Most of this discussion applies to all versions of awk, but items marked “gawk-specific” or as an “extension” may not apply to versions of awk other than GNU’s. If portability to older, non-Linux systems is important, do not use gawk-specific features.

With gawk, you can:

- Think of a text file as made up of records and fields in a textual database.

- Perform arithmetic and string operations.

- Use programming constructs, such as loops and conditionals.

- Produce formatted reports.

- Define your own functions.

- Execute Unix commands from a script.

- Process the results of Unix commands.

- Process command-line arguments gracefully.

- Work easily with multiple input streams.

- Flush open output files and pipes.

- Sort arrays.

- Retrieve and format system time values.

- Do bit manipulation.

- Internationalize your gawk programs, allowing strings to be translated into a local language at runtime.

- Perform two-way I/O to a coprocess.

- Open a two-way TCP/IP connection to a socket.

- Dynamically add built-in functions.

- Profile your gawk programs.

Command-Line Syntax

The syntax for invoking awk has two forms:

awk  [options]  'script'  var=value  file(s)
awk  [options]  -f scriptfile  var=value  file(s)

You can specify a script directly on the command line, or you can store a script in a scriptfile and specify it with -f. gawk allows multiple -f scripts. Variables can be assigned a value on the command line. The value can be a string or numeric constant, a shell variable ($name), or a command substitution (`cmd`), but the value is available only after the BEGIN statement is executed.

awk operates on one or more files. If none are specified (or if - is specified), awk reads from standard input.

Standard Options

The standard options are:

-Ffs

Set the field separator to fs. This is the same as setting the built-in variable FS. gawk allows fs to be a regular expression. Each input line, or record, is divided into fields by whitespace (spaces or tabs) or by some other user-definable field separator. Fields are referred to by the variables $1, $2,..., $n. $0 refers to the entire record.

-v var=value

Assign a value to variable var. This allows assignment before the script begins execution.

For example, to print the first three (colon-separated) fields of each record on separate lines:

awk -F: '{ print $1; print $2; print $3 }' /etc/passwd

Numerous examples are shown in Simple Pattern-Procedure Examples in Simple Pattern-Procedure Examples.

Important gawk Options

Besides the standard command line options, gawk has a large number of additional options. This section lists those of most value in day-to-day use. Any unique abbreviation of these options is acceptable.

--dump-variables[=file]

When the program has finished running, print a sorted list of global variables, their types, and their final values to file. The default file is awkvars.out.

--gen-po

Read the awk program and print all strings marked as translatable to standard output in the form of a GNU gettext Portable Object file. See the section Internationalization in Internationalization for more information.

--help

Print a usage message to standard error and exit.

--lint[=fatal]

Enable checking of nonportable or dubious constructs, both when the program is read and as it runs. With an argument of fatal, lint warnings become fatal errors.

--non-decimal-data

Allow octal and hexadecimal data in the input to be recognized as such. This option is not recommended; use strtonum( ) in your program, instead.

--profile[=file]

With gawk, put a “prettyprinted” version of the program in file. Default is awkprof.out. With pgawk (see Profiling in Profiling), put the profiled listing of the program in file.

--posix

Turn on strict POSIX compatibility, in which all common and gawk-specific extensions are disabled.

--source='program text'

Use program text as the awk source code. Use this option with -f to mix command-line programs with awk library files.

--traditional

Disable all gawk-specific extensions, but allow common extensions (e.g., the ** operator for exponentiation).

--version

Print the version of gawk on standard error and exit.

Patterns and Procedures

awk scripts consist of patterns and procedures:

pattern  {procedure }

Both pattern and { procedure } are optional. If pattern is missing, { procedure } is applied to all lines. If { procedure } is missing, the matched line is printed.

Patterns

A pattern can be any of the following:

general expression
/regular expression/
relational expression
pattern-matching expression
BEGIN
END

- General expressions can be composed of quoted strings, numbers, operators, function calls, user-defined variables, or any of the predefined variables described in Built-in Variables in Built-in Variables.

- Regular expressions use the extended set of metacharacters, as described in Chapter 7.

- The ^ and $ metacharacters refer to the beginning and end of a string (such as the fields), respectively, rather than the beginning and end of a line. In particular, these metacharacters will not match at a newline embedded in the middle of a string.

- Relational expressions use the relational operators listed in Operators in Operators. For example, $2 > $1 selects lines for which the second field is greater than the first. Comparisons can be either string or numeric. Thus, depending upon the types of data in $1 and $2, awk will do either a numeric or a string comparison. This can change from one record to the next.

- Pattern-matching expressions use the operators ~ (match) and !~ (don’t match). See Operators in Operators.

- The BEGIN pattern lets you specify procedures that will take place before the first input line is processed. (Generally, you process the command line and set global variables here.)

- The END pattern lets you specify procedures that will take place after the last input record is read.

- BEGIN and END patterns may appear multiple times. The procedures are merged as if there had been one large procedure.

Except for BEGIN and END, patterns can be combined with the Boolean operators || (or), && (and), and ! (not). A range of lines can also be specified using comma-separated patterns:

pattern,pattern

Procedures

Procedures consist of one or more commands, function calls, or variable assignments, separated by newlines or semicolons, and are contained within curly braces. Commands fall into five groups:

- Variable or array assignments

- Input/Output commands

- Built-in functions

- Control-flow commands

- User-defined functions

Simple Pattern-Procedure Examples

Print first field of each line:

{ print $1 }

Print all lines that contain pattern:

/pattern/

Print first field of lines that contain pattern:

/pattern/ { print $1 }

Select records containing more than two fields:

NF > 2

Interpret input records as a group of lines up to a blank line. Each line is a single field:

BEGIN { FS = "\n"; RS = "" }

Print fields 2 and 3 in switched order, but only on lines whose first field matches the string URGENT:

$1 ˜ /URGENT/ { print $3, $2 }

Count and print the number of pattern found:

/pattern/ { ++x }
END { print x }

Add numbers in second column and print the total:

{ total += $2 }
END { print "column total is", total}

Print lines that contain less than 20 characters:

length($0) < 20

Print each line that begins with Name: and that contains exactly seven fields:

NF =  = 7 && /^Name:/

Print the fields of each record in reverse order, one per line:

{
for (i = NF; i >= 1; i--)
print $i
}

Built-in Variables

All awk variables are included in gawk.

Version

Variable

Description

awk

ARGC

Number of arguments on the command line.

ARGV

An array containing the command-line arguments, indexed from 0 to ARGC - 1.

ENVIRON

An associative array of environment variables.

FILENAME

Current filename.

FNR

Like NR, but relative to the current file.

FS

Field separator (a space).

NF

Number of fields in current record.

NR

Number of the current record.

OFMT

Output format for numbers (“%.6g”).

OFS

Output field separator (a space).

ORS

Output record separator (a newline).

RLENGTH

Length of the string matched by match( ) function.

RS

Record separator (a newline).

RSTART

First position in the string matched by match( ) function.

SUBSEP

Separator character for array subscripts (“\034”).

$0

Entire input record.

$n

nth field in current record; fields are separated by FS.

gawk

ARGIND

Index in ARGV of current input file.

BINMODE

Controls binary I/O for input and output files. Use values of 1, 2, or 3 for input, output, or both kinds of files, respectively. Set it on the command line to affect standard input, standard output, and standard error.

ERRNO

A string indicating the error when a redirection fails for getline or if close( ) fails.

FIELDWIDTHS

A space-separated list of field widths to use for splitting up the record, instead of FS.

IGNORECASE

When true, all regular expression matches, string comparisons, and index( ) ignore case.

LINT

Dynamically controls production of “lint” warnings. With a value of “fatal”, lint warnings become fatal errors.

PROCINFO

An array containing information about the process, such as real and effective UID numbers, process ID number, and so on.

RT

The text matched by RS, which can be a regular expression in gawk.

TEXTDOMAIN

The text domain (application name) for internationalized messages (“messages”).

Operators

The following table lists the operators, in order of increasing precedence, that are available in awk.

Symbol

Meaning

= += -= *= /= %= ^= **=

Assignment.

?:

C conditional expression.

||

Logical OR (short-circuit).

&&

Logical AND (short-circuit).

in

Array membership.

~ !~

Match regular expression and negation.

< <= > >= != ==

Relational operators.

(blank)

Concatenation.

+ -

Addition, subtraction.

* / %

Multiplication, division, and modulus (remainder).

+ - !

Unary plus and minus, and logical negation.

^ **

Exponentiation.

++ --

Increment and decrement, either prefix or postfix.

$

Field reference.

Tip

While ** and **= are common extensions, they are not part of POSIX awk.

Variable and Array Assignment

Variables can be assigned a value with an equals sign. For example:

FS = ","

Expressions using the operators +, -, /, and % (modulo) can be assigned to variables.

Arrays can be created with the split( ) function (described later), or they can simply be named in an assignment statement. Array elements can be subscripted with numbers (array[1], ..., array[n]) or with strings. Arrays subscripted by strings are called associative arrays.[9] For example, to count the number of widgets you have, you could use the following script:

/widget/ { count["widget"]++ }        Count widgets
ND      { print count["widget"] }    Print the count

You can use the special for loop to read all the elements of an associative array:

for (item in array)
process array[item]

The index of the array is available as item, while the value of an element of the array can be referenced as array[item].

You can use the operator in to test that an element exists by testing to see if its index exists. For example:

if (index in array)
...

tests that array[index] exists, but you cannot use it to test the value of the element referenced by array[index].

You can also delete individual elements of the array using the delete statement. (See also the delete entry in Alphabetical Summary of awk Functions and Commands in Alphabetical Summary of awk Functions and Commands.)

[9] In fact, all arrays in awk are associative; numeric subscripts are converted to strings before being used as array subscripts. Associative arrays are one of awk’s most powerful features.

Escape sequences

Within string and regular-expression constants, the following escape sequences may be used.

Sequence

Meaning

Sequence

Meaning

\a

Alert (bell)

\v

Vertical tab

\b

Backspace

\\

Literal backslash

\f

Form feed

\nnn

Octal value nnn

\n

Newline

\xnn

Hexadecimal value nn

\r

Carriage return

\”

Literal double quote (in strings)

\t

Tab

\/

Literal slash (in regular expressions)

Tip

The \x escape sequence is a common extension; it is not part of POSIX awk

Octal and Hexadecimal Constants in gawk

gawk allows you to use octal and hexadecimal constants in your program source code. The form is as in C: octal constants start with a leading 0, and hexadecimal constants with a leading 0x or 0X. The hexadecimal digits a–f may be in either uppercase or lowercase.

$ gawk 'BEGIN { print 042, 42, 0x42 }'
34 42 66

Use the strtonum( ) function to convert octal or hexadecimal input data into numerical values.

User-Defined Functions

gawk allows you to define your own functions. This makes it easy to encapsulate sequences of steps that need to be repeated into a single place and reuse the code from anywhere in your program.

The following function capitalizes each word in a string. It has one parameter, named input, and five local variables, which are written as extra parameters:

# capitalize each word in a string
function capitalize(input, result, words, n, i, w)
{
result = ""
n = split(input, words, " ")
for (i = 1; i <= n; i++) {
w = words[i]
w = toupper(substr(w, 1, 1)) substr(w, 2)
if (i > 1)
result = result " "
result = result w
}
return result
}

# main program, for testing
{ print capitalize($0) }

With this input data:

A test line with words and numbers like 12 on it.

This program produces:

A Test Line With Words And Numbers Like 12 On It.

Tip

For user-defined functions, no space is allowed between the function name and the left parenthesis when the function is called.

gawk-Specific Features

This section describes features unique to gawk.

Coprocesses and Sockets

gawk allows you to open a two-way pipe to another process, called a coprocess. This is done with the |& operator used with getline and print or printf.

print database command |& "db_server"
"db_server" |& getline response

If the command used with |& is a filename beginning with /inet/, gawk opens a TCP/IP connection. The filename should be of the following form:

/inet/protocol/lport/hostname/rport

The parts of the filename are:

protocol

One of tcp, udp or raw, for TCP, UDP, or raw IP sockets, respectively. Note: raw is currently reserved but unsupported.

lport

The local TCP or UPD port number to use. Use 0 to let the operating system pick a port.

hostname

The name or IP address of the remote host to connect to.

rport

The port (application) on the remote host to connect to. A service name (e.g., tftp) is looked up using the C getservbyname( ) function.

Profiling

When gawk is built and installed, a separate program named pgawk (profiling gawk) is built and installed with it. The two programs behave identically; however, pgawk runs more slowly because it keeps execution counts for each statement as it runs. When it is done, it automatically places an execution profile of your program in a file named awkprof.out. (You can change the filename with the --profile option.)

The execution profile is a “prettyprinted” version of your program, with execution counts listed in the left margin. For example, after running this program:

$ pgawk '/bash$/ { nusers++ }
> END { print nusers, "users use Bash." }' /etc/passwd
16 users use Bash.

the execution profile looks like this:

# gawk profile, created Mon Nov  1 14:34:38 2004

# Rule(s)
35  /bash$/ { # 16
16          nusers++
}

# END block(s)
END {
1          print nusers, "users use Bash."
}

If sent SIGUSR1, pgawk prints the profile and an awk function call stack trace, and then keeps going. Multiple SIGUSR1 signals may be sent; the profile and trace will be printed each time. This facility is useful if your awk program appears to be looping and you want to see if something unexpected is being executed.

If sent SIGHUP, pgawk prints the profile and stack trace, and then exits.

File Inclusion

The igawk program provides a file-inclusion facility for gawk. You invoke it the same way you do gawk: it passes all command line arguments on to gawk. However, igawk processes source files and command-line programs for special statements of the form:

@include file.awk

Such files are searched for along the list of directories specified by the AWKPATH environment variable. When found, the @include line is replaced with the text of the corresponding file. Included files may themselves include other files with @include.

The combination of the AWKPATH environment variable and igawk makes it easy to have and use libraries of awk functions.

Internationalization

You can internationalize your programs if you use gawk. This consists of choosing a text domain for your program, marking strings that are to be translated, and, if necessary, using the bindtextdomain( ), dcgettext( ), and dcngettext( ) functions.

Localizing your program consists of extracting the marked strings, creating translations, and compiling and installing the translations in the proper place. Full details are given in sed & awk by Dale Dougherty and Arnold Robbins (O’Reilly).

The internationalization features in gawk use GNU gettext. You may need to install the GNU gettext tools to create translations if your system doesn’t already have them. Here is a very brief outline of the steps involved:

1. Set TEXTDOMAIN to your text domain in a BEGIN block:

BEGIN { TEXTDOMAIN = "whizprog" }

2. Mark all strings to be translated by prepending a leading underscore:

printf(_"whizprog: can't open /dev/telepath (%s)\n",
dcgettext(ERRNO)) > "/dev/stderr"

3. Extract the strings with the --gen-po option:

$ gawk --gen-po -f whizprog.awk > whizprog.pot

4. Copy the file for translating, and make the translations:

$ cp whizprog.pot esperanto.po
$ ed esperanto.po

5. Use the msgfmt program from GNU gettext to compile the translations. The binary format allows fast lookup of the translations at runtime. The default output is a file named messages:

$ msgfmt esperanto.po
$ mv messages esperanto.mo

6. Install the file in the standard location. This is usually done at program installation. The location can vary from system to system.

That’s it! gawk will automatically find and use the translated messages, if they exist.

Implementation Limits

Many versions of awk have various implementation limits, on things such as:

- Number of fields per record

- Number of characters per input record

- Number of characters per output record

- Number of characters per field

- Number of characters per printf string

- Number of characters in literal string

- Number of characters in character class

- Number of files open

- Number of pipes open

- The ability to handle 8-bit characters and characters that are all zero (ASCII NUL)

gawk does not have limits on any of the above items, other than those imposed by the machine architecture and/or the operating system.

Group Listing of awk Functions and Commands

The following table classifies awk functions and commands.

Function type

Functions or commands

Arithmetic

atan2

cos

exp

int

log

rand

sin

sqrt

srand

String

asort[a]

asorti[a]

gensub[a]

gsub

index

length

match

split

sprintf

strtonum[a]

sub

substr

tolower

toupper

Control flow

break

continue

do/while

exit

for

if/else

return

while

I/O

close

fflush[b]

getline

next

nextfile[b]

print

printf

Programming

extension[a]

delete

function

system

[a] Available in gawk.

[b] Available in Bell Labs awk and gawk.

The following functions are specific to gawk.

Function type

Functions or commands

Bit manipulation

and

compl

lshift

or

rshift

xor

Time

mktime

strftime

systime

Translation

bindtext-domain

dcgettext

dcngettext

Alphabetical Summary of awk Functions and Commands

The following alphabetical list of keywords and functions includes all that are available in POSIX awk and gawk. Extensions that aren’t part of POSIX awk but that are in both gawk and the Bell Laboratories awk are marked as {E}. Cases where gawk has extensions are marked as {G}. Items that aren’t marked with a symbol are available in all versions.

Name

#

Synopsis

#

Ignore all text that follows on the same line. # is used in awk scripts as the comment character and is not really a command.

Name

and

Synopsis

and(expr1, expr2) {G}

Return the bitwise AND of expr1 and expr2, which should be values that fit in a C unsigned long.

Name

asort

Synopsis

asort(src [,dest]) {G}

Sort the array src based on the element values, destructively replacing the indices with values from one to the number of elements in the array. If dest is supplied, copy src to dest and sort dest, leaving src unchanged. Returns the number of elements in src.

Name

asorti

Synopsis

asorti(src [,dest]) {G}

Like asort( ), but the sorting is done based on the indices in the array, not based on the element values. For gawk 3.1.2 and later.

Name

atan2

Synopsis

atan2(y, x)

Return the arctangent of y/x in radians.

Name

bindtextdomain

Synopsis

bindtextdomain(dir [,domain]) {G}

Look in directory dir for message translation files for text domain domain (default: value of TEXTDOMAIN). Returns the directory where domain is bound.

Name

break

Synopsis

break

Exit from a while, for, or do loop.

Name

close

Synopsis

close(expr)
close(expr, how) {G}

In most implementations of awk, you can only have up to ten files and one pipe open simultaneously. Therefore, POSIX awk provides a close( ) function that allows you to close a file or a pipe. It takes the same expression that opened the pipe or file as an argument. This expression must be identical, character by character, to the one that opened the file or pipe — even whitespace is significant.

In the second form, close one end of either a TCP/IP socket or a two-way pipe to a coprocess. how is a string, either “from” or “to”. Case does not matter.

Name

compl

Synopsis

compl(expr) {G}

Return the bitwise complement of expr, which should be a value that fits in a C unsigned long.

Name

continue

Synopsis

continue

Begin next iteration of while, for, or do loop.

Name

cos

Synopsis

cos(x)

Return the cosine of x, an angle in radians.

Name

dcgettext

Synopsis

dcgettext(str [, dom [,cat]]) {G}

Return the translation of str for the text domain dom in message category cat. Default text domain is value of TEXTDOMAIN. Default category is "LC_MESSAGES".

Name

dcngettext

Synopsis

dcngettext(str1, str2, num [, dom [,cat]]) {G}

If num is one, return the translation of str1 for the text domain dom in message category cat. Otherwise, return the translation of str2. Default text domain is value of TEXTDOMAIN. Default category is "LC_MESSAGES". For gawk 3.1.1 and later.

Name

delete

Synopsis

delete array[element]
delete array {E}

Delete element from array. The brackets are typed literally. The second form is a common extension, which deletes all elements of the array in one shot.

Name

do

Synopsis

do
statement
while (expr)

Looping statement. Execute statement, then evaluate expr and if true, execute statement again. A series of statements must be put within braces.

Name

exit

Synopsis

exit [expr]

Exit from script, reading no new input. The END procedure, if it exists, will be executed. An optional expr becomes awk’s return value.

Name

exp

Synopsis

exp(x)

Return exponential of x (ex).

Name

extension

Synopsis

extension(lib, init) {G}

Dynamically load the shared object file lib, calling the function init to initialize it. Return the value returned by the init function. This function allows you to add new built-in functions to gawk. See Arnold Robbins’s Effective awk Programming (O’Reilly) for the details.

Name

fflush

Synopsis

fflush([output-expr]) {E}

Flush any buffers associated with open output file or pipe output-expr.

gawk extends this function. If no output-expr is supplied, it flushes standard output. If output-expr is the null string (“”), it flushes all open files and pipes.

Name

for

Synopsis

for (init-expr; test-expr; incr-expr)
statement

C-style looping construct. init-expr assigns the initial value of a counter variable. test-expr is a relational expression that is evaluated each time before executing the statement. When test-expr is false, the loop is exited. incr-expr is used to increment the counter variable after each pass. All of the expressions are optional. A missing test-expr is considered to be true. A series of statements must be put within braces.

Name

for

Synopsis

for (item in array)
statement

Special loop designed for reading associative arrays. For each element of the array, the statement is executed; the element can be referenced by array [item]. A series of statements must be put within braces.

Name

function

Synopsis

function name(parameter-list) {
statements
}

Create name as a user-defined function consisting of awk statements that apply to the specified list of parameters. No space is allowed between name and the left parenthesis when the function is called.

Name

gensub

Synopsis

gensub(regex, str, how [, target]) {G}

General substitution function. Substitute str for matches of the regular expression regex in the string target. If how is a number, replace the howth match. If it is “g” or “G”, substitute globally. If target is not supplied, $0 is used. Return the new string value. The original target is not modified. (Compare with gsub and sub.) Use & in the replacement string to stand for the text matched by the pattern.

Name

getline

Synopsis

getline
getline [var] [< file]
command | getline [var]
command |& getline [var] {G}

Read next line of input.

The second form reads input from file, and the third form reads the output of command. All forms read one record at a time, and each time the statement is executed, it gets the next record of input. The record is assigned to $0 and is parsed into fields, setting NF, NR and FNR. If var is specified, the result is assigned to var and $0 and NF are not changed. Thus, if the result is assigned to a variable, the current record does not change. getline is actually a function, and it returns 1 if it reads a record successfully, 0 if end-of-file is encountered, and −1 if for some reason it is otherwise unsuccessful.

The fourth form reads the output from coprocess command. See the section Coprocesses and Sockets in Coprocesses and Sockets for more information.

Name

gsub

Synopsis

gsub(regex, str [, target])

Globally substitute str for each match of the regular expression regex in the string target. If target is not supplied, defaults to $0. Return the number of substitutions. Use & in the replacement string to stand for the text matched by the pattern.

Name

if

Synopsis

if (condition)
statement1
[else
statement2]

If condition is true, do statement1; otherwise do statement2 in optional else clause. The condition can be an expression using any of the relational operators <, <=, = =, !=, >=, or >, as well as the array membership operator in, and the pattern-matching operators ~ and !~ (e.g., if ($1 ~ /[Aa].*/)). A series of statements must be put within braces. Another if can directly follow an else in order to produce a chain of tests or decisions.

Name

index

Synopsis

index(str, substr)

Return the position (starting at 1) of substr in str, or zero if substr is not present in str.

Name

int

Synopsis

int(x)

Return integer value of x by truncating any fractional part.

Name

length

Synopsis

length([arg])

Return length of arg, or the length of $0 if no argument.

Name

log

Synopsis

log(x)

Return the natural logarithm (base e) of x.

Name

lshift

Synopsis

lshift(expr, count) {G}

Return the result of shifting expr left by count bits. Both expr and count should be values that fit in a C unsigned long.

Name

match

Synopsis

match(str, regex)
match(str, regex [, array]) {G}

Function that matches the pattern, specified by the regular expression regex, in the string str and returns either the position in str where the match begins, or 0 if no occurrences are found. Sets the values of RSTART and RLENGTH to the start and length of the match, respectively.

If array is provided, gawk puts the text that matched the entire regular expression in array[0], the text that matched the first parenthesized subexpression in array[1], the second in array[2], and so on.

Name

mktime

Synopsis

mktime(timespec) {G}

Turns timespec (a string of the form YYYY MM DD HH MM SS[DST] representing a local time) into a time-of-day value in seconds since midnight, January 1, 1970, UTC.

Name

next

Synopsis

next

Read next input line and start new cycle through pattern/procedures statements.

Name

nextfile

Synopsis

nextfile {E}

Stop processing the current input file and start new cycle through pattern/procedures statements, beginning with the first record of the next file.

Name

or

Synopsis

or(expr1, expr2) {G}

Return the bitwise OR of expr1 and expr2, which should be values that fit in a C unsigned long.

Name

print

Synopsis

print [output-expr[ , ...]] [ dest-expr ]

Evaluate the output-expr and direct it to standard output followed by the value of ORS. Each comma-separated output-expr is separated in the output by the value of OFS. With no output-expr, print $0. The output may be redirected to a file or pipe via the dest-expr, which is described in Output Redirections in Output Redirections.

Name

printf

Synopsis

printf(format [, expr-list ]) [ dest-expr ]

An alternative output statement borrowed from the C language. It has the ability to produce formatted output. It can also be used to output data without automatically producing a newline. format is a string of format specifications and constants. expr-list is a list of arguments corresponding to format specifiers. As for print, output may be redirected to a file or pipe. See printf Formats in printf Formats for a description of allowed format specifiers.

Like any string, format can also contain embedded escape sequences: \n (newline) or \t (tab) being the most common. Spaces and literal text can be placed in the format argument by quoting the entire argument. If there are multiple expressions to be printed, there should be multiple formats specified.

Examples

Using the script:

{ printf("The sum on line %d is %.0f.\n", NR, $1+$2) }

The following input line:

5   5

produces this output, followed by a newline:

The sum on line 1 is 10.

Name

rand

Synopsis

rand(  )

Generate a random number between 0 and 1. This function returns the same series of numbers each time the script is executed, unless the random number generator is seeded using srand( ).

Name

return

Synopsis

return [expr]

Used within a user-defined function to exit the function, returning the value of expr. The return value of a function is undefined if expr is not provided.

Name

rshift

Synopsis

rshift(expr, count) {G}

Return the result of shifting expr right by count bits. Both expr and count should be values that fit in a C unsigned long.

Name

sin

Synopsis

sin(x)

Return the sine of x, an angle in radians.

Name

split

Synopsis

split(string, array [, sep])

Split string into elements of array array[1],...,array[n]. Return the number of array elements created. The string is split at each occurrence of separator sep. If sep is not specified, FS is used.

Name

sprintf

Synopsis

sprintf(format [, expressions])

Return the formatted value of one or more expressions, using the specified format. Data is formatted but not printed. See printf Formats in printf Formats for a description of allowed format specifiers.

Name

sqrt

Synopsis

sqrt(arg)

Return the square root of arg.

Name

srand

Synopsis

srand([expr])

Use optional expr to set a new seed for the random number generator. Default is the time of day. Return value is the old seed.

Name

strftime

Synopsis

strftime([format [,timestamp]]) {G}

Format timestamp according to format. Return the formatted string. The timestamp is a time-of-day value in seconds since midnight, January 1, 1970, UTC. The format string is similar to that of sprintf. If timestamp is omitted, it defaults to the current time. If format is omitted, it defaults to a value that produces output similar to that of the Unix date command. See the date entry in Chapter 3 for a list.

Name

strtonum

Synopsis

strtonum(expr) {G}

Return the numeric value of expr, which is a string representing an octal, decimal, or hexadecimal number in the usual C notations. Use this function for processing nondecimal input data.

Name

sub

Synopsis

sub(regex, str [, target])

Substitute str for first match of the regular expression regex in the string target. If target is not supplied, defaults to $0. Returns 1 if successful, 0 otherwise. Use & in the replacement string to stand for the text matched by the pattern.

Name

substr

Synopsis

substr(string, beg [, len])

Return substring of string at beginning position beg (counting from 1), and the characters that follow to maximum specified length len. If no length is given, use the rest of the string.

Name

system

Synopsis

system(command)

Function that executes the specified command and returns its exit status. The status of the executed command typically indicates success or failure. A value of 0 means that the command executed successfully. A nonzero value indicates a failure of some sort. The documentation for the command will give you the details.

awk does not make the output of the command available for processing within the awk script. Use command | getline to read the output of a command into the script.

Name

systime

Synopsis

systime(  ) {G}

Return a time-of-day value in seconds since midnight, January 1, 1970, UTC.

Examples

Log the start and end times of a data-processing program:

BEGIN {
now = systime(  )
mesg = strftime("Started at %m/%d/%Y %H:%M:%S", now)
print mesg
}
process data ...
END {
now = systime(  )
mesg = strftime("Ended at %m/%d/%Y %H:%M:%S", now)
print mesg
}

Name

tolower

Synopsis

tolower(str)

Translate all uppercase characters in str to lowercase and return the new string.[10]

[10] Very early versions of nawk don’t support tolower( ) and toupper( ). However, they are now part of the POSIX specification for awk.

Name

toupper

Synopsis

toupper(str)

Translate all lowercase characters in str to uppercase and return the new string.

Name

while

Synopsis

while (condition)
statement

Do statement while condition is true (see if for a description of allowable conditions). A series of statements must be put within braces.

Name

xor

Synopsis

xor(expr1, expr2) {G}

Return the bitwise XOR of expr1 and expr2, which should be values that fit in a C unsigned long.

Output Redirections

For print and printf, dest-expr is an optional expression that directs the output to a file or pipe.

> file

Direct the output to a file, overwriting its previous contents.

>> file

Append the output to a file, preserving its previous contents. In both this case and the > file case, the file will be created if it does not already exist.

| command

Direct the output as the input to a system command.

|& command

Direct the output as the input to a coprocess. gawk only.

Be careful not to mix > and >> for the same file. Once a file has been opened with >, subsequent output statements continue to append to the file until it is closed.

Remember to call close( ) when you have finished with a file, pipe, or coprocess. If you don’t, eventually you will hit the system limit on the number of simultaneously open files.

printf Formats

Format specifiers for printf and sprintf have the following form:

%[posn$][flag][width][.precision]letter

The control letter is required. The format-conversion control letters are given in the following table.

Character

Description

c

ASCII character.

d

Decimal integer.

i

Decimal integer (added in POSIX).

e

Floating-point format ([-]d.precisione[+−]dd).

E

Floating-point format ([-]d.precisionE[+−]dd).

f

Floating-point format ([-]ddd.precision).

g

e or f conversion, whichever is shortest, with trailing zeros removed.

G

E or f conversion, whichever is shortest, with trailing zeros removed.

o

Unsigned octal value.

s

String.

u

Unsigned decimal value.

x

Unsigned hexadecimal number. Uses a-f for 10 to 15.

X

Unsigned hexadecimal number. Uses A-F for 10 to 15.

%

Literal %.

gawk allows you to provide a positional specifier after the % (posn$). A positional specifier is an integer count followed by a $. The count indicates which argument to use at that point. Counts start at one and don’t include the format string. This feature is primarily for use in producing translations of format strings. For example:

$ gawk 'BEGIN { printf "%2$s, %1$s\n", "world", "hello" }'
hello, world

The optional flag is one of the following.

Character

Description

-

Left-justify the formatted value within the field.

space

Prefix positive values with a space and negative values with a minus.

+

Always prefix numeric values with a sign, even if the value is positive.

#

Use an alternate form: %o has a preceding 0; %x and %X are prefixed with 0x and 0X, respectively; %e, %E and %f always have a decimal point in the result; and %g and %G do not have trailing zeros removed.

0

Pad output with zeros, not spaces. This only happens when the field width is wider than the converted result. This flag applies to all output formats, even nonnumeric ones.

'

gawk 3.1.4 and later only. For numeric formats, in locales that support it, supply a thousands-separator charater.

The optional width is the minimum number of characters to output. The result will be padded to this size if it is smaller. The 0 flag causes padding with zeros; otherwise, padding is with spaces.

The precision is optional. Its meaning varies by control letter, as shown in the following table.

Conversion

Precision means

%d, %i, %o, %u, %x, %X

The minimum number of digits to print.

%e, %E, %f

The number of digits to the right of the decimal point.

%g, %G

The maximum number of significant digits.

%s

The maximum number of characters to print.

Chapter 12. Source Code Management: An Overview

Chapter 13 and Chapter 14 describe two popular source code management systems for Linux: Subversion (SVN) and Git. This chapter introduces the major concepts involved with using these systems for users who may never have used one. If you’re already familiar with source code management, feel free to skip ahead to the particular software suite that interests you.

This chapter covers the following topics:

- Introduction and terminology

- Usage models

- Source code management systems

- Other source code management systems

Introduction and Terminology

Source code management systems let you store and retrieve multiple versions of a file. While originally designed for program source code, they can be used for any kind of file: source code, documentation, configuration files, and so on. Modern systems allow you to store binary files as well, such as image or audio data.

Source code management systems let you compare different versions of a file, as well as do “parallel development.” In other words, you can work on two different versions of a file at the same time, with the source code management system storing both versions. You can then merge changes from two versions into a third version. This will become more clear shortly. We’ll start by defining some terms:

Repository

A repository is where the source code management system stores its copy of your file. Usually one file in the source code management system is used to hold all the different versions of a source file. Each source code management system uses its own format to allow it to retrieve different versions easily and to track who made what changes, and when.

Sandbox

A sandbox is your personal, so-called “working copy” of the program or set of documents under development. You edit your private copy of the file in your own sandbox, returning changes to the source code management system when you’re satisfied with the new version.

Check in, check out

You “check out” files from the repository, edit them, and then “check them in” when you’re satisfied with your changes. Other developers working against the same repository will not see your changes until after you check them back in. Another term used for check-in is commit.

Log message

Every time you check in a file, you are prompted for a message describing the changes you made. You should do so in a concise fashion. If your software development practices include the use of a bug tracking system, you might also wish to include the bug number or problem report (PR) number that your change resolves.

Keyword substitutions

When you check out a file, the source code management system can replace special keywords with values representing such things as the file’s version number, the name of the user who made the most recent change, the date and time the file was last changed, the file’s name, and so on. Each of the systems described in this book uses an overlapping set of keywords. Some systems always do keyword substitution, while others require that you explicitly enable the feature for each file.

Branch

A branch is a separate development path. For example, once you’ve released version 1.0 of whizprog, you will wish to proceed with the development for version 2.0. The main line of development is often called the trunk.

Now consider what happens when you wish to make a bug-fix release to whizprog 1.0, to be named version 1.1. You create a separate branch, based on the original 1.0 code, in a new sandbox. You perform all your development there, without disturbing the development being done for the 2.0 release.

Tag

A tag is a name you give to a whole group of files at once, at whatever version each individual file may be, in order to identify those files as being part of a particular group. For example, you might create tags WHIZPROG-1_0-ALPHA, WHIZPROG-1_0-BETA, WHIZPROG-1_0-RELEASE and so on. This is a powerful facility that should be used well, since it allows you to retrieve a “snapshot” of your entire development tree as it existed at different points in time.

Merging

Most typically, when development along a branch is completed, it becomes necessary to merge the changes from that branch back into the main line of development. In our hypothetical example, all the bugs fixed in whizprog 1.0 to create version 1.1 should also be fixed in the ongoing 2.0 development. Source code management systems can help you automate the process of merging.

Conflict

A conflict occurs when two developers make inconsistent changes to the same part of a source file. Modern source code management systems detect the conflict, usually marking the conflicting parts of the file in your working copy using special markers. You first discuss the conflict with the other developer, in order to arrive at a correct resolution of the conflict. Once that’s done, you then resolve the conflict manually (by making the appropriate changes) and check in the new version of the file.

Client/Server

As with other “client/server” networking models, the idea here is that the repository is stored on one machine, the server, and that different developers may access the repository from multiple client systems. This powerful feature facilitates distributed development, allowing developers to work easily on their local systems, with the repository kept in a central place where it can be easily accessed and administered.

Usage Models

Different systems have different conceptual “models” as to how they’re used.

Older systems such as SCCS and RCS use a “check out with locking” model. These systems were developed before client/server computing, when software development was done on centralized minicomputers and mainframes. In this model, the repository is a central directory on the same machine where the developers work, and each developer checks out a private copy into their own sandbox. In order to avoid two developers making conflicting changes to a file, the file must be locked when it’s checked out. Only one user may lock a particular version of a file at a time. When that user has checked in their changes, they unlock the file so that the next user can check in changes. If necessary, the second user may “break” the first user’s lock, in which case the first user is notified via electronic mail.

This model works well for small projects where developers are co-located and can communicate easily. As long as one developer locks a file when she checks it out, another developer wishing to work with the file will know that he can’t until the first one is done. The drawback is that such locking can slow down development significantly.

Newer systems, such as CVS and Subversion, use a “copy, modify, merge” model. In practice, when two developers wish to work on the same file, they usually end up changing different, unrelated parts of the file. Most of the time, each developer can make changes without adversely affecting the other. Thus, files are not locked upon checkout into a sandbox. Instead, the source code management system detects conflicts and disallows a check-in when conflicts exist.

For example, consider two developers, dangermouse and penfold, who are both working on whizprog.c. They each start with version 1.4 of the file. dangermouse commits his changes, creating version 1.5. Before penfold can commit his changes, the source code management system notices that the file has changed in the repository. penfold must first merge dangermouse’s changes into his working copy.

If there are no conflicts, he can then commit his changes, creating version 1.6. On the other hand, if there are conflicts, he must first resolve them (they’ll be marked in the working copy), and only then may he commit his version.

The combination of the “copy, modify, merge” model with a networked client/server facility creates a powerful environment for doing distributed development. Developers no longer have to worry about file locks. Because the source code management system enforces serialization (making sure that new changes are based on the latest version in the repository), development can move more smoothly, with little danger of miscommunication or that successive changes will be lost.

Source Code Management Systems

There are several source code management systems used in the Unix community:

SCCS

The Source Code Control System. SCCS is the original Unix source code management system. It was developed in the late 1970s for the Programmer’s Workbench (PWB) Unix systems within Bell Labs. It is still in use at a few large longtime Unix sites. However, for a long time it was not available as a standard part of most commercial or BSD Unix systems, and it did not achieve the widespread popularity of other, later systems. (It is still available with Solaris.) SCCS uses a file storage format that allows it to retrieve any version of a source file in constant time.

RCS

The Revision Control System. RCS was developed in the early 1980s at Purdue University by Walter F. Tichy. It became popular in the Unix world when it was shipped with 4.2 BSD in 1983. At the time, Berkeley Unix was the most widely used Unix variant, even though to get it, a site had to have a Unix license from AT&T.

RCS is easier to use than SCCS. Although it has a number of related commands, only three or four are needed for day-to-day use, and they are quickly mastered. A central repository is easy to use: you first create a directory for the sandbox. In the sandbox, you make a symbolic link to the repository named RCS, and then all the developers can share the repository. RCS uses a file format that is optimized for retrieving the most recent version of a file.

CVS

The Concurrent Versions System. CVS was initially built as a series of shell scripts sitting atop RCS. Later it was rewritten in C for robustness, although still using RCS commands to manage the storage of files. However, for quite some time, CVS has had the RCS functionality built into it, and it no longer requires that RCS be available. The file format continues to be the same. CVS was the first distributed source code management system and was until recently the standard one for Unix systems — in particular for collaborative, distributed, free and open source development projects.

The repository is named when you create a sandbox and is then stored in the files in the sandbox, so that it need not be provided every time you run a CVS command. Unlike SCCS and RCS, which provide multiple commands, CVS has one main command (named cvs), which you use for just about every operation.

Subversion

With increasing use, it became clear that CVS lacked some fundamental capabilities. The Subversion project was started by several longtime CVS users and developers with the explicit goal to “build a better CVS,” not necessarily to explore uncharted territory in source code management systems. Subversion is thus intentionally easy to learn for CVS users. Subversion uses its own format for data storage, based on the Berkeley DB in-process data library. Distributed use was designed in from day one, providing useful facilities that leverage the capabilities of the well-known Apache HTTP server.

Git

Git is a source control system originally developed by Linus Torvalds as the source control system to manage the Linux kernel. Today, it is maintained by a community of developers and used for many diverse projects. Unlike the previous source control systems, Git is distributed. A distributed system differs from a centralized one such as CVS in several ways. The most notable is that in distributed systems, individual check outs of the source tree, called clones in distributed systems, are themselves complete and fully functioning repositories. Instead of submitting changes to a centralized server, changes are pushed and pulled among repositories.

RCS, CVS, and Subversion represent a progression, each one building on the features of its predecessors. For example, all three share a large subset of the same keyword substitutions, and command names are similar or identical in all three. They also demonstrate the progression from locking-based development to conflict-resolution-based development. Git is a radical departure from the centralized model.

Other Source Code Management Systems

Besides the source code management systems covered in this book, several other systems are worth knowing about. The following list, though, is by no means exhaustive:

Arch

GNU Arch is a distributed source code management system similar to CVS and Subversion. One of its significant strengths is that you can do offline development with it, working on multiple versions even on systems that are not connected to the Internet and that cannot communicate with the central repository. For more information, see http://www.gnu.org/software/gnu-arch/.

Codeville

Codeville is a distributed version-control system in the early stages of development. It is written in Python, is easy to set up and use, and shows a lot of promise. For more information, see http://codeville.org/.

CSSC

CSSC is a free clone of SCCS. It intends to provide full compatibility with SCCS, including file format, command names and options, and “bug for bug” compatible behavior. If you have an existing SCCS repository, you should be able to drop CSSC into your environment, in place of SCCS. CSSC can be used to migrate from a commercial Unix system to a freely available clone, such as GNU/Linux or a BSD system. For more information, see http://directory.fsf.org/project/cssc.

Monotone

The web page for monotone describes it well:

monotone is a free distributed version control system. It provides a simple, single-file transactional version store, with fully disconnected operation and an efficient peer-to-peer synchronization protocol. It understands history-sensitive merging, lightweight branches, integrated code review, and third party testing. It uses cryptographic version naming and client-side RSA certificates. It has good internationalization support, has no external dependencies, runs on [Linux, Solaris, Mac OS X, NetBSD, and Windows], and is licensed under the GNU GPL.

For more information, see http://monotone.ca.

Chapter 13. The Subversion Version Control System

The Subversion version control system is a powerful, open source system for management of file and directory versions. Designed from the ground up to support distributed development, it offers many leading-edge features.

This chapter covers the following topics:

- Conceptual overview

- Using Subversion: a quick tour

- The Subversion command line client: svn

- Repository administration: svnadmin

- Examining the repository: svnlook

- Providing remote access: svnserve

Version control was introduced in Chapter 12, which contains a comparison of Subversion, GIT, and other popular systems. The material in the current chapter is adapted from Version Control with Subversion, Second Edition, by C. Michael Pilato et al. (O’Reilly). See that book for much more information on Subversion.

Conceptual Overview

Subversion is a version-control system. It lets you track changes to an entire project directory tree. Every change made to the tree is recorded and can be retrieved.

Basic Version-Control Operations

Project data is kept in a repository, a set of directories and files managed by Subversion. Users use the svn client program to access the repository and make changes to it.

Subversion uses the copy-modify-merge development model. You make a private copy of a given project in a sandbox. (This is often called checking out a copy.) This private copy is not locked in the repository. You then make all the changes you like to the copy within the sandbox, without having to worry about what other developers are doing. As you work, you can compare your changes to the version you started with, as well as the version currently in the repository. Once you’re satisfied with the changes, you commit them, sometimes referred to as a check-in.

In the event that another developer has modified part of a file that you were working on and checked it in, when you commit your changes, Subversion notices and indicates that a conflict exists. Conflicts are marked as such in the file, and Subversion creates pristine copies of the file as it exists in the repository and of the file as you modified it, so that you can do full comparisons. Once you have resolved the conflict, you tell Subversion about it, and then commit the final version.

Subversion lets you create a development branch, a separate stream of development versions. You can periodically merge changes from the main development stream (the trunk) into your branch, and also merge changes from your branch back into the trunk.

Finally, you can tag a particular copy of the project. For instance, when a project is ready for a release, you can create a snapshot of the project and give it a descriptive tag that allows you to re-create the project tree exactly as it was for the release. This is particularly valuable when you need to produce a bug fix for an older version of the project, or when you have to attempt to retrofit a fix or feature from current development into an older version.

Key Features

Directory versioning

Subversion implements a virtual versioned filesystem that tracks changes to whole directory trees over time. Files and directories are versioned. Because it tracks the history of the directory tree rather than just the files, you can add, delete, copy, and rename both files and directories. Every newly added file begins with a fresh, clean history all its own, even if the filename was previously used.

Atomic commits

A collection of modifications either goes into the repository completely, or not at all. This allows developers to construct and commit changes as logical chunks, and prevents problems that can occur when only a portion of a set of changes is successfully sent to the repository.

Versioned metadata

Each file and directory has a set of properties — keys and their values — associated with it. You can create and store any arbitrary key/value pairs. Properties are versioned over time, just like file contents.

Choice of network layers

Subversion has an abstracted notion of repository access, making it easy for people to implement new network mechanisms. Subversion can plug into the Apache HTTP Server as an extension module. A more lightweight, standalone Subversion server process is also available. This server speaks a custom protocol that can be easily tunneled over SSH.

Consistent data handling

Subversion expresses file differences using a binary differencing algorithm, which works identically on both text (human-readable) and binary (human-unreadable) files. Both types of files are stored equally compressed in the repository, and only the differences are transmitted in both directions across the network.

Efficient branching and tagging

The cost of branching and tagging need not be proportional to the project size. Subversion creates branches and tags by simply copying the project, using a mechanism similar to a hard link. Thus these operations take only a very small, constant amount of time.

Hackability

Subversion is implemented as a collection of shared C libraries with well-defined APIs. This makes Subversion extremely maintainable and usable by other applications and languages. Subversion is an open source project as well. You can contribute to its development.

Special File Properties

Subversion allows you to associate properties with files or directories. A property is just a keyword/value pair associated with the file. Subversion reserves property names starting with svn: for its own use. The special properties in Subversion 1.5.4 are:

svn:author

The username of the person who committed a particular revision.

svn:date

The server time when the transaction for a revision was created.

svn:eol-style

Different operating systems use different conventions to mark the end of lines in text files. It should be set to one of the following values:

CR

Clients should always use carriage return (CR) line terminators, no matter what the native format is.

CRLF

Clients should always use carriage return and line feed (CR-LF) line terminators, no matter what the native format is.

LF

Clients should always use linefeed (LF) line terminators, no matter what the native format is.

native

Clients should use the native format when checking out files.

Subversion always stores files in normalized, LF-only format in the repository.

svn:executable

Valid only for files. It indicates that the file should be made executable when it’s checked out or updated from the repository. It has no effect on filesystems, such as FAT-32 or NTFS, that don’t have the concept of an execute bit.

svn:externals

This property, when set on a directory under version control, allows you to specify other, external repositories to use for particular local subdirectories. You set this property with svn propset or svn propedit (see svn Subcommands in svn Subcommands). The value is a multiline table of directories and fully qualified Subversion URLs. For example:

$ svn propget svn:externals calc
third-party/sounds             http://sounds.red-bean.com/repos
third-party/skins              http://skins.red-bean.com/repositories/
skinproj
third-party/skins/toolkit -r21 http://svn.red-bean.com/repos/skin-maker

Once set, anyone else who checks out a working copy will also get the third party files checked out automatically.

svn:ignore

Used to tell Subversion to not place certain file types under version control. This property is set on a directory and should contain a list of file patterns that certain Subversion operations (like svn status, svn add, and svn import.) will ignore.

svn:keywords

A list of keywords for which Subversion should perform keyword expansion when checking out the file. The valid keywords are listed below.

svn:log

The log message associated with the commit of a particular revision.

svn:mime-type

An indication of the type of data stored in the file. This prevents an attempt to perform a “merge” on data that can’t be merged. This property also influences how the Subversion Apache module sets the HTTP Content-type: header. In general, if it does not begin with text/, Subversion assumes that the file contains binary data. For updates, this causes Subversion to rename a modified working copy of the file with a .orig extension and replace the file with the current version from the repository.

svn:realmstring

A specialized property that describes the “authentication realm” for a file in Subversion’s cached copy of the authentication credentials. See Chapter 6 of Version Control with Subversion for more information.

Valid subversion keywords

Subversion defines the list of keywords available for substitution. That list contains the following five keywords, some of which have shorter aliases that you can also use:

Date

This keyword describes the last time the file was changed in the repository and looks like $Date: 2009-02-23 21:42:37 −0700 (Mon, 23 Feb 2009) $. It may also be given as LastChangedDate.

Revision

This keyword describes the last revision in which this file changed in the repository and looks like $Revision$. It may also be given as LastChanged Revision or abbreviated as Rev.

Author

This keyword describes the last user to change this file in the repository, and looks like $Author$. It may be given as LastChangedBy.

HeadURL

This keyword describes the full URL to the latest version of the file in the repository. It looks like $HeadURL: http://svn.collab.net/repos/trunk/README $. It may be abbreviated as URL.

Id

This keyword is a compressed combination of the other keywords. Its substitution looks like $Id$: ch14.xml,v 1.5 2005/08/12 21:21:32 sally Exp sally $, and is interpreted to mean that the file calc.c was last changed in revision 148 on the evening of July 28, 2005 by the user sally.

Obtaining Subversion

The Subversion project website is http://subversion.tigris.org. It contains links to project documentation, Frequently Asked Questions (FAQs), and project source code.

Most GNU/Linux systems come with Subversion available on the installation CDs. Thus, you may be able to install a prebuilt binary for your system or use a package manager to download and install it.

Using Subversion: A Quick Tour

This section provides a very quick tour of using Subversion for version control. We start with the initial version of a project for importing into Subversion:

$ find /tmp/hello -print    Show directory layout
/tmp/hello
/tmp/hello/branches         Directory for branch development
/tmp/hello/tags             Directory for tagged releases
/tmp/hello/trunk
/tmp/hello/trunk/hello.c    Mainline development is done on the trunk
/tmp/hello/trunk/Makefile
/tmp/hello/trunk/README

The next steps are to create the repository and then to import the project into it:

$ svnadmin create /path/to/svnrepos
$ svn import /tmp/hello file:///path/to/svnrepos -m "initial import"
Adding         /tmp/hello/trunk
Adding         /tmp/hello/trunk/hello.c
Adding         /tmp/hello/trunk/Makefile
Adding         /tmp/hello/trunk/README
Adding         /tmp/hello/branches
Adding         /tmp/hello/tags

Committed revision 1.

Now that the project exists in Subversion, we check out a working copy into a sandbox underneath our home directory and start making changes:

$ cd                                           Move to home directory
$ svn checkout file:///path/to/svnrepos hello  Check out working copy
A  hello/trunk
A  hello/trunk/hello.c
A  hello/trunk/README
A  hello/trunk/Makefile
A  hello/branches
A  hello/tags
Checked out revision 1.

$ cd hello/trunk                               Change to sandbox
$ vi message.c hello.c Makefile                Make changes
3 files to edit

$ cat message.c                                Show newly created file
const char message[  ] = "hello, world!";
$ make                                         Compile program and test it
cc    -c -o hello.o hello.c
cc    -c -o message.o message.c
cc -O hello.o message.o -o hello
$ hello
hello, world!

One of the most common operations is to compare the changed copy with the original. The result is in unified diff format, the equivalent of the regular diff -u command:

$ svn diff hello.c
Index: hello.c
===============================================================
====
--- hello.c     (revision 1)
+++ hello.c     (working copy)
@@ −1,7 +1,9 @@
#include <stdio.h>

+extern const char message[  ];
+
int main(void)
{
−       printf("hello, world!\n");
+       printf("%s\n", message);
return 0;
}

Now that we’re comfortable with the changes, we schedule the new file, message.c, for addition to the repository, and then we actually commit our changes:

$ svn add message.c                            Schedule message.c for addition
A         message.c
$ svn commit                                   Commit all the changes
Sending        trunk/Makefile
Sending        trunk/hello.c
Adding         trunk/message.c
Transmitting file data ...
Committed revision 2.

Finally, we can view all our changes relative to the initial revision:

$ svn diff -r 1
Index: hello.c
===================================================================
--- hello.c     (revision 1)
+++ hello.c     (working copy)
@@ −1,7 +1,9 @@
#include <stdio.h>

+extern const char message[  ];
+
int main(void)
{
-       printf("hello, world!\n");
+       printf("%s\n", message);
return 0;
}
Index: Makefile
=================================================================
==
--- Makefile    (revision 1)
+++ Makefile    (working copy)
@@ −1,2 +1,2 @@
-hello: hello.c
-       $(CC) -O $< -o $@
+hello: hello.o message.o
+       $(CC) -O hello.o message.o -o $@
Index: message.c
=================================================================
==
--- message.c   (revision 0)
+++ message.c   (revision 2)
@@ −0,0 +1 @@
+const char message[  ] = "hello, world!";

The Subversion Command Line Client: svn

The syntax for the Subversion command line client, svn, consists of options and a subcommand. svn’s options and subcommand may be provided in any order.

Common svn Options

While Subversion subcommands have different valid options, all options mean the same thing regardless of the subcommand you use it with. For example, --verbose (-v) always means verbose output, regardless of the subcommand you use it with.

--accept arg

Specify action for automatic conflict resolution. Possible actions are postpone, base, mine-full, theirs-full, edit, and launch.

--auto-props

Automatically set properties an newly added or imported files, overriding the enable-auto-props directive in the config file. By default this is disabled.

--change arg, -c arg

Apply subcommand to specified change (a.k.a. revision.) This can be used as shorthand for “-r arg−1:arg“.

--changelist name, -cl name

Limit subcommand to files belonging to changelist name. You use the changelist subcommand to name the set of files to which you are making changes. A file can only belong to one changelist at a time. Changelists are local and are not saved in the repository. The name is usually discarded after committing. This option can be repeated to include more than one set of files.

--config-dir dir

Read configuration information from the specified directory instead of the default location (.subversion in the user’s home directory).

--depth arg

Control the tree-depth to which the subcommand should be recursively applied. When used with the checkout command this will set the depth property of the checked out files as well, affecting what you receive and what future commands will affect in the repository. To change this “ambient depth” use the --set-depth option. This option replaces the --recursive and --non-recursive options. argmay be one of the following:

empty

Apply to specified target only.

files

Apply to the immediate file children of the target.

immediates

Apply to the immediate file and directory children of target.

infinity

Apply recursively to all file and directory children of target.

--diff-cmd cmd

Use cmd as the external program to show differences between files instead of Subversion’s internal diff engine. (Use --extensions to pass options to the external diff program.)

--diff3-cmd cmd

Use cmd as the external program to merge files.

--dry-run

Run a command, but make no actual changes — either on disk or in the repository.

--editor-cmd cmd

Use cmd as the program for editing a log message or a property value. If not set, Subversion checks the environment variable SVN_EDITOR, the runtime configuration (usually ~/.subversion/config), then environment variables VISUAL and EDITOR for the name of the editor to use.

--encoding enc

Use enc as the encoding for the commit message. The default encoding is your operating system’s native locale, and you should specify the encoding if your commit message is in any other encoding.

--extensions args, -x args

Pass args to an external diff command when providing differences between files. To pass multiple arguments, enclose all of them in quotes (for example, svn diff --diff-cmd /usr/bin/diff -x “-b -E”). This option can be used only if you also pass the --diff-cmd option.

--file filename, -F filename

Use the contents of filename for the specified subcommand. How it’s used depends on the subcommand.

--force

Force a particular command or operation to run. There are some operations that Subversion prevents you from doing in normal usage, but you can pass this option to tell Subversion that you know what you’re doing, as well as the possible repercussions of doing it, so do it anyway. Use with caution.

--force-log

Force a suspicious parameter passed to the --message (-m) or --file (-F) options to be accepted as valid. This can be used to pass a versioned file as the source for the commit log message, something Subversion would usually consider a mistake and reject.

--help, -h, -?

If used with one or more subcommands, show the built-in help text for each subcommand. If used alone, display the general client help text.

--ignore-ancestry

Ignore ancestry when calculating differences (i.e., rely on path contents alone).

--ignore-externals

Ignore external definitions and external working copies managed by them.

--incremental

Print output in a format suitable for concatenation.

--keep-changelists

Don’t delete the changelist association after committing.

--keep-local

Keep the local copy of a file when using the delete subcommand to remove a file from the repository.

--limit num, -l num

Only show the first num log messages.

--message message, -m message

Use message as the commit message. For example:

$ svn commit -m "They don't make Sunday."

--native-eol format

Used with the export subcommand sets the end of line marker to use for all files with the svn:eol-style property set to native. You can specify LR, CR or CRLF for format.

--new arg

Use arg as the newer target when producing a diff.

--no-auth-cache

Do not cache authentication information (e.g., username and password) in the Subversion administrative directories.

--no-auto-props

Disable auto-props, overriding the enable-auto-props directive in the config file.

--no-diff-deleted

Do not print differences for deleted files. The default behavior when you remove a file is for svn diff to print the same differences that you would see if you had left the file but removed all the content.

--no-ignore

Show files in the status listing that would normally be omitted because they match a pattern in the svn:ignore property.

--no-unlock

Do not unlock files on commit.

--non-interactive

In the case of an authentication failure, or insufficient credentials, do not prompt for credentials (e.g., username or password). This is useful if you’re running Subversion inside of an automated script where it’s better to have Subversion fail instead of trying to prompt for more information.

--non-recursive, -N

Stop a subcommand from recursing into subdirectories. Most subcommands recurse by default, but some subcommands — usually those that have the potential to remove or undo your local modifications — do not. This command is deprecated. You should use --depth instead.

--notice-ancestry

Pay attention to ancestry when calculating differences.

--old arg

Use arg as the older target when producing a diff.

--parents

Create and add nonversioned parent directories to the working copy or the repository. Useful for creating directories on commit.

--password pass

Use pass as the password for authentication on the command line; otherwise, if it is needed, Subversion prompts you for it.

--quiet, -q

Print only essential information while performing an operation.

--record-only

Mark a revision as merged.

--reintegrate

Used with the svn merge subcommand, merges changes in a specified source URL into the working copy. This can be used to merge changes from a branch back into its original line.

--recursive, -R

Make a subcommand recurse into subdirectories. Most subcommands recurse by default. This option is deprecated. Use --depth instead.

--relocate from to [path ...]

Used with the svn switch subcommand to change the location of the repository that your working copy references. This is useful if the location of your repository changes and you have an existing working copy that you’d like to continue to use. See svn switch in svn Subcommands in svn Subcommands for an example.

--revision rev, -r rev

Use rev as the revision (or range of revisions) for a particular operation. You can provide revision numbers, revision keywords, or dates (in curly braces) as arguments to the revision option. To provide a range of revisions, provide two revisions separated by a colon. For example:

$ svn log -r 1729
$ svn log -r 1729:HEAD
$ svn log -r 1729:1744
$ svn log -r {2001-12-04}:{2002-02-17}
$ svn log -r 1729:{2002-02-17}

The acceptable revision keywords for --revision are:

BASE

The original, unmodified version of the working copy. This keyword cannot refer to a URL.

COMMITTED

The last revision, before or at BASE, at which an item actually changed. This keyword cannot refer to a URL.

HEAD

The most recent revision in the repository.

PREV

The revision just before that at which an item changed. Equivalent to COMMITED − 1. This keyword cannot refer to a URL.

Revision Date

A date specification enclosed in curly braces, { and }, such as {2002-02-17}, {15:30}, {"2002-02-17 15:30"}, {2002-02-17T15:30}, or {20020217T1530-0500}. See Version Control with Subversion for full details.

--revprop

Operate on a revision property instead of a Subversion property specific to a file or directory. This option requires that you also pass a revision with the --revision (-r) option.

--set-depth arg

Use arg as the new recursive depth for the target. This accepts the same values as the --depth command.

--show-revs arg

Used with svn mergeinfo, specifies which collection of merge information to display. arg may be either merged or eligible.

--show-updates, -u

Display information about which files in your working copy are out of date. This doesn’t actually update any of your files; it just shows you which files will be updated if you run svn update.

--stop-on-copy

Cause a Subversion subcommand that is traversing the history of a versioned resource to stop harvesting that historical information when it encounters a copy — that is, a location in history where that resource was copied from another location in the repository.

--strict

Use strict semantics. See Version Control with Subversion for more information.

--summarize

Use with diff to get a summary of changes without a list of the changes themselves.

--targets filename

Retrieve the list of files to operate on from filename instead of listing all the files on the command line.

--username name

Use name as the username for authentication; otherwise, if it is needed, Subversion prompts you for it.

--verbose, -v

Print out as much information as possible while running any subcommand. This may result in Subversion printing out additional fields, detailed information about every file, or additional information regarding its actions.

--version

Print the client version info. This information not only includes the version number of the client, but also a listing of all repository access modules that the client can use to access a Subversion repository.

--with-revprop property

Set a revision property when writing to the repository (specify in NAME=VALUE format). When used with svn log -xml, display the value of the specified property name in the log output.

--xml

Prints output in XML format.

svn Subcommands

The svn command is the main user interface to Subversion. It works by accepting subcommands with arguments. Five of the previous options are global in version 1.5. All subcommands will accept --config-dir, --no-auth-cache, --non-interactive, --password, and --username. Even commands for which these are meaningless will accept these options without fail. This is intended to make scripting easier. Because all subcommands accept these, we don’t list them in options the below.

The general form of a subcommand is:

svn subcommand [options] arguments

Name

add

Synopsis

svn add path ...

Add files and directories to your working copy and schedule them for addition to the repository. They will be uploaded and added to the repository on your next commit. If you add something and change your mind before committing, you can unschedule the addition using svn revert.

Alternate names: none

Changes: working copy

Accesses repository: no

Options

--auto-props

--depth arg

--no-auto-props

--no-ignore

--no-parents

--non-recursive (-N)

--quiet (-q)

--targets filename

Examples

To add a file to your working copy:

$ svn add foo.c
A         foo.c

You can add a directory without adding its contents:

$ svn add -depth empty otherdir
A         otherdir

Name

blame

Synopsis

svn blame target ...

Show author and revision information inline for the specified files or URLs. Each line of text is annotated at the beginning with the author (username) and the revision number for the last change to that line.

Alternate names: praise, annotate, ann

Changes: nothing

Accesses repository: yes

Options

--extensionsargs, -x args

--force

--incremental

--revision rev, -r rev

--use-merge-history, -g

--verbose, -v

--xml

Name

cat

Synopsis

svn cat target ...

Output the contents of the specified files or URLs. For listing the contents of directories, see svn list.

Alternate names: none

Changes: nothing

Accesses repository: yes

Options

--revision rev, -r rev

Examples

To view readme.txt in your repository without checking it out:

$ svn cat http://svn.red-bean.com/repos/test/readme.txt
This is a README file.
You should read this.

Tip

If your working copy is out of date (or if you have local modifications) and you want to see the HEAD revision of a file in your working copy, svn cat automatically fetches the HEAD revision when you give it a path.

$ cat foo.c
This file is in my local working copy
and has changes that I've made.

$ svn cat foo.c
Latest revision fresh from the repository!

Name

changelist

Synopsis

svn changelist name target...
svn changelist --remove name target...

Group files for operations into named collections. This makes it easier to work or multiple groups of files.

Alternate names: cl

Changes: working copy

Accesses repository: no

Options

--changelist name, -cl name

--depth arg

--quiet (-q)

--remove

--targets filename

Examples

Edit three files, add them to a changelist, then commit only files in that changelist.:

$ svn changelist issue1729 foo.c bar.c baz.c
Path "foo.c" is now a member of changelist 'issue1729'.
Path "bar.c" is now a member of changelist 'issue1729'.
Path "baz.c" is now a member of changelist 'issue1729'.

$ svn status
A  someotherfile.c
A  test/sometest.c

--Changelist 'issue1729':
A  foo.c
A  bar.c
A  baz.c

$ svn commit --changelist issue1729 -m "Fixing Issue 1729"
Adding        foo.c
Adding        bar.c
Adding        baz.c
Transmitting file data...
Committed revision 2

$ svn status
A  someotherfile.c
A  test/sometest.c

Name

checkout

Synopsis

svn checkout URL ... [path]

Check out a working copy from a repository. If path is omitted, the basename of the URL is used as the destination. If multiple URLs are given, each one is checked out into a subdirectory of path, with the name of the subdirectory being the basename of the URL.

Alternate names: co

Changes: creates a working copy

Accesses repository: yes

Options

--depth arg

--force

--ignore-externals

--quiet (-q)

--revision rev, -r rev

Examples

Check out a working copy into a directory called mine:

$ svn checkout file:///tmp/repos/test mine
A  mine/a
A  mine/b
Checked out revision 2.
$ ls
mine

If you interrupt a checkout (or something else interrupts your checkout, such as loss of connectivity, etc.), you can restart it either by issuing the identical checkout command again or by updating the incomplete working copy:

$ svn checkout file:///tmp/repos/test test
A  test/a
A  test/b
^C
svn: The operation was interrupted
svn: caught SIGINT

$ svn checkout file:///tmp/repos/test test
A  test/c
A  test/d
^C
svn: The operation was interrupted
svn: caught SIGINT

$ cd test
$ svn update
A  test/e
A  test/f
Updated to revision 3.

Name

cleanup

Synopsis

svn cleanup [path ...]

Recursively clean up the working copy, removing locks and resuming unfinished operations. If you ever get a working-copy-locked error, run this command to remove stale locks and get your working copy into a usable state again.

If, for some reason, an svn update fails due to a problem running an external diff program (e.g., user input or network failure), pass the --diff3-cmd option to allow cleanup to complete any merging with your external diff program. You can also specify any configuration directory with the --config-dir option, but you should need these options extremely infrequently.

Alternate names: none

Changes: working copy

Accesses repository: no

Options:

--diff3-cmd cmd

Name

commit

Synopsis

svn commit [path ...]

Send changes from your working copy to the repository. If you do not supply a log message with your commit by using either the --file or --message option, svn starts your editor for you to compose a commit message.

Tip

If you begin a commit and Subversion starts your editor to compose the commit message, you can still abort without committing your changes. To cancel your commit, just quit your editor without saving your commit message and Subversion prompts you to abort the commit, continue with no message, or edit the message again.

Alternate names: ci (short for check in--not co, which is short for checkout)

Changes: working copy, repository

Accesses repository: yes

Options

--changelist name, -cl name

--depth arg

--editor-cmd cmd

--encoding enc

--file file, -F file

--force-log

--keep-changelists

--message text, -m text

--no-unlock

--quiet (-q)

--targets filename

--with-revprop property

Examples

Commit a simple modification to a file with the commit message on the command line and an implicit target of your current directory (.):

$ svn commit -m "added howto section."
Sending        a
Transmitting file data.
Committed revision 3.

To commit a file scheduled for deletion:

$ svn commit -m "removed file 'c'."
Deleting       c
Committed revision 7.

Name

copy

Synopsis

svn copy src dst

Copy a file in a working copy or in the repository. src and dst can each be either a working-copy (WC) path or a URL:

WC→WC

Copy and schedule an item for addition (with history).

WC→URL

Immediately commit a copy of WC to URL.

URL→WC

Check out URL into WC, and schedule it for addition.

URL→URL

Complete server-side copy. This is usually used to branch and tag.

Tip

You can only copy files within a single repository. Subversion does not support cross-repository copying.

Alternate names: cp

Changes: repository if destination is a URL; working copy if destination is a WC path

Accesses repository: if source or destination is in the repository, or if needed to look up the source revision number

Options

--editor-cmd editor

--encoding enc

--file file, -F file

--force-log

--message text, -m text

--parents

--quiet (-q)

--revision rev, -r rev

--with-revprop property

Examples

Copy an item within your working copy (just schedules the copy; nothing goes into the repository until you commit):

$ svn copy foo.txt bar.txt
A         bar.txt
$ svn status
A  +   bar.txt

Copy an item from the repository to your working copy (just schedules the copy; nothing goes into the repository until you commit):

$ svn copy file:///tmp/repos/test/far-away near-here
A         near-here

Tip

This is the recommended way to resurrect a dead file in your repository!

And finally, copying between two URLs:

$ svn copy file:///tmp/repos/test/far-away \
> file:///tmp/repos/test/over-there -m "remote copy."
Committed revision 9.

Tip

This is the easiest way to tag a revision in your repository; just svn copy that revision (usually HEAD) into your tags directory.

$ svn copy file:///tmp/repos/test/trunk \
>          file:///tmp/repos/test/tags/0.6.32-prerelease \
>          -m "tag tree"
Committed revision 12.

Name

delete

Synopsis

svn delete path ...
svn delete URL ...

Items specified by path are scheduled for deletion upon the next commit. Files (and directories that have not been committed) are immediately removed from the working copy. The command will not remove any unversioned or modified items; use the --force option to override this behavior.

Items specified by URL are deleted from the repository via an immediate commit. Multiple URLs are committed atomically.

Alternate names: del, remove, rm

Changes: working copy if operating on files; repository if operating on URLs

Accesses repository: only if operating on URLs

Options

--editor-cmd editor

--encoding enc

--file file, -F file

--force

--force-log

--keep-local

--message text, -m text

--quiet (-q)

--targets filename

--with-revprop property

Name

diff

Synopsis

svn diff [-r N[:M]] [--old old-tgt] [--new new-tgt] [path ...]
svn diff -r N:M URL
svn diff [-r N[:M]] URL1[@N] URL2[@M]

Display the differences between two paths. The three different ways you can use svn diff are:

svn diff [-r N[:M]] [--old old-tgt] [--new new-tgt] [path ...]

Display the differences between old-tgt and new-tgt. If paths are given, they are treated as relative to old-tgt and new-tgt, and the output is restricted to differences in only those paths. old-tgt and new-tgt may be working copy paths or URL[@rev]. old-tgt defaults to the current working directory, and new-tgt defaults to old-tgt. N defaults to BASE or, if old-tgt is a URL, to HEAD. M defaults to the current working version or, if new-tgt is a URL, to HEAD. svn diff -r N sets the revision of old-tgt to N, whereas svn diff -r N:M also sets the revision of new-tgt to M.

svn diff -r N:M URL

A shorthand for svn diff -r N:M --old=URL --new=URL.

svn diff [-r N[:M]] URL1[@N] URL2[@M]

A shorthand for svn diff [-r N[:M]] --old=URL1 --new=URL2.

If target is a URL, then revisions N and M can be given either via the --revision option or by using @ notation as described earlier.

If target is a working copy path, then the --revision option means:

--revision N:M

The server compares target@N and target@M.

--revision N

The client compares target@N against the working copy.

No --revision option

The client compares the base and working copies of target.

If the alternate syntax is used, the server compares URL1 and URL2 at revisions N and M respectively. If either N or M are omitted, a value of HEAD is assumed.

By default, svn diff ignores the ancestry of files and merely compares the contents of the two files being compared. If you use --notice-ancestry, the ancestry of the paths in question is taken into consideration when comparing revisions. (That is, if you run svn diff on two files with identical contents but different ancestry you will see the entire contents of the file as having been removed and added again.)

Alternate names: di

Changes: nothing

Accesses repository: for obtaining differences against anything but the BASE revision in your working copy.

Options

--change args, -c args

--changelist name, -cl name

--depth arg

--diff-cmd cmd

--extensions args, -x args

--force

--new new-target

--no-diff-deleted

--notice-ancestry

--old old-target

--revision rev, -r rev

--summarize

--xml

Examples

Compare BASE and your working copy:

$ svn diff COMMITTERS
Index: COMMITTERS
=================================================
==================
--- COMMITTERS  (revision 4404)
+++ COMMITTERS  (working copy)
...

See how your working copy’s modifications compare against an older revision:

$ svn diff -r 3900 COMMITTERS
Index: COMMITTERS
=================================================
==================
--- COMMITTERS  (revision 3900)
+++ COMMITTERS  (working copy)
...

Use --diff-cmd cmd and -x to pass arguments directly to the external diff program:

$ svn diff --diff-cmd /usr/bin/diff -x "-i -b" COMMITTERS
Index: COMMITTERS
=================================================
==================
0a1,2
> This is a test
>

Name

export

Synopsis

svn export [-r rev] URL [path]
svn export path1 path2

The first form exports a clean directory tree into path from the repository specified by URL, at revision rev if it is given — otherwise at HEAD. If path is omitted, the last component of the URL is used for the local directory name.

The second form exports a clean directory tree from the working copy specified by path1 into path2. All local changes are preserved, but files not under version control are not copied.

This command will also take the unique --native-eol option.

Alternate names: none

Changes: local disk

Accesses repository: only if exporting from a URL

Options

--depth arg

--force

--ignore-externals

--native-eol format

--quiet (-q)

--revision rev, -r rev

Name

help

Synopsis

svn help [subcommand ...]

Provide a quick usage summary. With subcommand, provide information about the given subcommand.

Alternate names: ?, h

Changes: nothing

Accesses repository: no

Name

import

Synopsis

svn import [path] URL

Recursively commit a copy of path to URL. If path is omitted, . is assumed. Parent directories are created in the repository as necessary.

Alternate names: none

Changes: repository

Accesses repository: yes

Options

--auto-props

--depth arg

--editor-cmd editor

--encoding enc

--file file, -F file

--force

--force-log

--message text, -m text

--no-auto-props

--no-ignore

Examples

Import the local directory myproj into the root of your repository:

$ svn import -m "New import" myproj \
> http://svn.red-bean.com/repos/test
Adding         myproj/sample.txt
...
Transmitting file data .........
Committed revision 16.

Import the local directory myproj into trunk/vendors in your repository. The directory trunk/vendors need not exist before you import into it; svn import will recursively create directories for you:

$ svn import -m "New import" myproj \
> http://svn.red-bean.com/repos/test/trunk/vendors/myproj
Adding         myproj/sample.txt
...
Transmitting file data .........
Committed revision 16.

After importing data, note that the original tree is not under version control. To start working, you still need to svn checkout a fresh working copy of the tree.

Name

info

Synopsis

svn info [path ...]
svn info URL

Print information about paths in your working copy or specified URLs, including:

- Path

- Name

- URL

- Repository root

- Repostiory UUID

- Revision

- Node kind

- Last changed author

- Last changed revision

- Last changed date

- Last token

- Lock owner

- Lock created (date)

- Lock expires (date)

- Schedule

- Copied from URL

- Copied from rev

- Text last updated

- Properties last updated

- Checksum

Alternate names: none

Changes: nothing

Accesses repository: no

Options

--changelist name, -cl name

--depth arg

--incremental

--revision rev, -r rev

--targets filename

--xml

Name

list

Synopsis

svn list [target ...]

List each target file and the contents of each target directory as they exist in the repository. If target is a working copy path, the corresponding repository URL is used. The default target is ., meaning the repository URL of the current working-copy directory.

With --verbose, the following fields show the status of the item:

- Revision number of the last commit

- Author of the last commit

- Size (in bytes)

- Date and time of the last commit

Alternate names: ls

Changes: nothing

Accesses repository: yes

Options

--depth arg

--incremental

--revision rev, -r rev

--verbose (-v)

--xml

Examples

To see what files a repository has without downloading a working copy:

$ svn list http://svn.red-bean.com/repos/test/support
README.txt
INSTALL
examples/
...

Pass the --verbose option for additional information:

$ svn list --verbose file:///tmp/repos
16 sally         28361 Jan 16 23:18 README.txt
27 sally             0 Jan 18 15:27 INSTALL
24 harry               Jan 18 11:27 examples/

Name

lock

Synopsis

svn lock path ...
svn lock URL

Set a lock token on a specified file to prevent other users or even the same user on another system from updating the file. Only the system with the lock token may commit changes. Locks are useful when working on binary files that cannot be merged. By default, Subversion’s locks are not strict, however. Locks can be broken or taken over by other users by using the --force option.

Alternate names: none

Changes: working copy; repository

Accesses repository: yes

Options

--encoding enc

--file file, -F file

--force

--force-log

--message text, -m text

--targets filename

Name

log

Synopsis

svn log [path]
svn log URL [path ...]

The default target is the path of your current directory. If no arguments are supplied, svn log shows the log messages for all files and directories inside of (and including) the current working directory of your working copy. You can refine the results by specifying a path, one or more revisions, or any combination of the two. The default revision range for a local path is BASE:1.

If you specify a URL alone, the command prints log messages for everything that the URL contains. If you add paths past the URL, only messages for those paths under that URL are printed. The default revision range for a URL is HEAD:1.

With --verbose, svn log also prints all affected paths with each log message. With --quiet, svn log does not print the log message body itself (this is compatible with --verbose).

Each log message is printed just once, even if more than one of the affected paths for that revision were explicitly requested. Logs follow copy history by default. Use --stop-on-copy to disable this behavior, which can be useful for determining branch points.

Alternate names: none

Changes: nothing

Accesses repository: yes

Options

--change arg, -c arg

--incremental

--limit num, -l num

--quiet (-q)

--revision rev, -r rev

--stop-on-copy

--targets filename

--use-merge-history, -g

--verbose (-v)

--with-all-revprops

--with-revprop property

--xml

Examples

To see the log messages for all the paths that changed in your working copy, run svn log from the top:

$ svn log
----------------------------------------------------------
--------------
r20 | harry | 2003-01-17 22:56:19 −0600 (Fri, 17 Jan 2003)
| 1 line

Tweak.
----------------------------------------------------------
--------------
r17 | sally | 2003-01-16 23:21:19 −0600 (Thu, 16 Jan 2003)
| 2 lines
...

If you don’t have a working copy handy, you can log a URL:

$ svn log http://svn.red-bean.com/repos/test/foo.c
----------------------------------------------------------
--------------
r32 | sally | 2003-01-13 00:43:13 −0600 (Mon, 13 Jan 2003)
| 1 line

Added defines.
----------------------------------------------------------
--------------
r28 | sally | 2003-01-07 21:48:33 −0600 (Tue, 07 Jan 2003)
| 3 lines
...

If you run svn log on a specific path and provide a specific revision and get no output at all:

$ svn log -r 20 http://svn.red-bean.com/untouched.txt
----------------------------------------------------------
--------------

That just means that the path was not modified in that revision. If you log from the top of the repository, or know the file that changed in that revision, you can specify it explicitly:

$ svn log -r 20 touched.txt
----------------------------------------------------------
--------------
r20 | sally | 2003-01-17 22:56:19 −0600 (Fri, 17 Jan 2003)
| 1 line

Made a change.
----------------------------------------------------------
--------------

Name

merge

Synopsis

svn merge sourceURL1[@N] sourceURL2[@M] [wcpath]
svn merge sourceWCPATH1@N sourceWCPATH2@M [wcpath]
svn merge -r N:M source [path]

In the first form, the source URLs are specified at revisions N and M. These are the two sources to be compared. The revisions default to HEAD if omitted.

In the second form, the URLs corresponding to the source working copy paths define the sources to be compared. The revisions must be specified.

In the third form, source can be a URL or working-copy item, in which case the corresponding URL is used. This URL, at revisions N and M, defines the two sources to be compared.

wcpath is the working-copy path that will receive the changes. If wcpath is omitted, a default value of “.” is assumed, unless the sources have identical basenames that match a file within “.”, in which case, the differences are applied to that file.

Unlike svn diff, this command takes the ancestry of a file into consideration when performing a merge operation. This is very important when you’re merging changes from one branch into another and you’ve renamed a file on one branch but not the other.

Alternate names: none

Changes: working copy

Accesses repository: only if working with URLs

Options

--accept arg

--change arg, -c arg

--depth arg

--diff3-cmd cmd

--dry-run

--extensions args, -x args

--force

--ignore-ancestry

--quiet (-q)

--record-only

--reintegrate

--revision rev, -r rev

Examples

Merge a branch back into the trunk (assuming that you have a working copy of the trunk and that the branch was created in revision 250):

$ svn merge -r 250:HEAD \
> http://svn.red-bean.com/repos/branches/my-branch
U  myproj/tiny.txt
U  myproj/thhgttg.txt
U  myproj/win.txt
U  myproj/flo.txt

If you branched at revision 23, and you want to merge changes from the trunk into your branch, you could do this from inside the working copy of your branch:

$ svn merge -r 23:30 file:///tmp/repos/trunk/vendors
U  myproj/thhgttg.txt
...

To merge changes to a single file:

$ cd myproj
$ svn merge -r 30:31 thhgttg.txt
U  thhgttg.txt

Name

mergeinfo

Synopsis

svn mergeinfo sourceURL[@rev] [target ...]

Query information about merges or potential merges between sourceURL and target. By default it shows merged information. The option --show-revs can be used to get information about eligible merges.

Alternate names: none

Changes: nothing

Accesses repository: yes

Options

--revision rev, -r rev

--show-revs arg

Examples

Find out which changesets your trunk directory has already received as well as what changesets it’s still eligible to receive:

$ svn mergeinfo branches/test
Path: branches/test
Source path: /trunk
Merged ranges: r2:13
Eligible ranges: r13:15

Name

mkdir

Synopsis

svn mkdir path ...
svn mkdir URL ...

Create a directory with a name given by the final component of the path or URL. A directory specified by a working copy path is scheduled for addition in the working copy. A directory specified by a URL is created in the repository via an immediate commit. Multiple directory URLs are committed atomically. In both cases, all the intermediate directories must already exist.

Alternate names: none

Changes: working copy; repository if operating on a URL

Accesses repository: only if operating on a URL

Options

--editor-cmd editor

--encoding enc

--file file, -F file

--force-log

--message text, -m text

--parents

--quiet (-q)

--with-revprop property

Name

move

Synopsis

svn move src dst

This command moves (renames) a file or directory in your working copy or in the repository.

Tip

This command is equivalent to an svn copy followed by svn delete.

WC→WC

Move and schedule a file or directory for addition (with history).

URL→URL

Complete server-side rename.

Tip

Subversion does not support moving between working copies and URLs. In addition, you can move files only within a single repository; Subversion does not support cross-repository moving.

Alternate names: mv, rename, ren

Changes: working copy; repository if operating on a URL

Accesses repository: only if operating on a URL

Options

--editor-cmd editor

--encoding enc

--file file, -F file

--force

--force-log

--message text, -m text

--revision rev, -r rev

--revprop

--with-revprop property

Name

propdel

Synopsis

svn propdel propname [path ...]
svn propdel propname --revprop -r rev [URL]

This removes properties from files, directories, or revisions. The first form removes versioned properties in your working copy, while the second removes unversioned remote properties on a repository revision.

Alternate names: pdel, pd

Changes: working copy; repository only if operating on a URL

Accesses repository: only if operating on a URL

Options

--changelist name, -cl name

--depth arg

--quiet (-q)

--revision rev, -r rev

--revprop

Examples

Delete a property from a file in your working copy:

$ svn propdel svn:mime-type some-script
property 'svn:mime-type' deleted from 'some-script'.

Delete a revision property:

$ svn propdel --revprop -r 26 release-date
property 'release-date' deleted from repository revision
'26'

Name

propedit

Synopsis

svn propedit propname path ...
svn propedit propname --revprop -r rev [URL]

Edit one or more properties using your favorite editor. The first form edits versioned properties in your working copy, while the second edits unversioned remote properties on a repository revision.

Alternate names: pedit, pe

Changes: working copy; repository only if operating on a URL

Accesses repository: only if operating on a URL

Options

--editor-cmd editor

--encoding enc

--force

--force-log

--password pass

--revision rev, -r rev

--revprop

--with-revprop property

Name

propget

Synopsis

svn propget propname [path ...]
svn propget propname --revprop -r rev [URL]

Print the value of a property on files, directories, or revisions. The first form prints the versioned property of an item or items in your working copy, while the second prints the unversioned remote property on a repository revision.

Alternate names: pget, pg

Changes: working copy; repository only if operating on a URL

Accesses repository: only if operating on a URL

Options

--changelist name, -cl name

--depth arg

--revision rev, -r rev

--revprop

--strict

--xml

Name

proplist

Synopsis

svn proplist [path ...]
svn proplist --revprop -r rev [URL]

List all properties on files, directories, or revisions. The first form lists versioned properties in your working copy, while the second lists unversioned remote properties on a repository revision.

Alternate names: plist, pl

Changes: working copy; repository only if operating on a URL

Accesses repository: only if operating on a URL

Options

--changelist name, -cl name

--depth arg

--quiet (-q)

--revision rev, -r rev

--revprop

--verbose (-v)

--xml

Examples

You can use svn proplist to see the properties on an item in your working copy:

$ svn proplist foo.c
Properties on 'foo.c':
svn:mime-type
svn:keywords
owner

But with the --verbose flag, svn proplist is extremely handy, as it also shows you the values for the properties:

$ svn proplist --verbose foo.c
Properties on 'foo.c':
svn:mime-type : text/plain
svn:keywords : Author Date Rev
owner : sally

Name

propset

Synopsis

svn propset propname [propval] path ...
svn propset propname --revprop -r rev [propval] [URL]

Set propname to propval on files, directories, or revisions. The first example creates a versioned, local property change in the working copy, and the second creates an unversioned, remote property change on a repository revision. The new property value, propval, may be provided literally, or using the -F valfile option.

Alternate names: pset, ps

Changes: working copy; repository only if operating on a URL

Accesses repository: only if operating on a URL

Options

--changelist name, -cl name

--depth arg

--encoding enc

--file file, -F file

--force

--quiet (-q)

--revision rev, -r rev

--revprop

--targets filename

Examples

Set the mimetype on a file:

$ svn propset svn:mime-type image/jpeg foo.jpg
property 'svn:mime-type' set on 'foo.jpg'

On a Unix system, if you want a file to have the executable permission set:

$ svn propset svn:executable ON somescript
property 'svn:executable' set on 'somescript'

Warning

By default, you cannot modify revision properties in a Subversion repository. Your repository administrator must explicitly enable revision property modifications by creating a hook named pre-revprop-change.

Name

resolve

Synopsis

svn resolve path ...

Remove the conflicted state on working-copy files or directories. This command does not semantically resolve conflict markers; instead it replaces path and then removes conflict-related artifact files. Use the --accept argument to specify what version to use when replacing path. This command allows path to be committed again by telling Subversion that the conflicts have been resolved. Use it after you have resolved the conflict in the file. You can pass the following arguments to the --accept option:

Alternate names: none

Changes: working copy

Accesses repository: no

Options

--accept arg

--depth arg

--quiet (-q)

--recursive, -R

--targets filename

Example

If you get a conflict on an update, your working copy will contain three additional files:

$ svn update
Conflict discovered in 'foo.c'.
Select: (p) postpone, (df) diff-full, (e) edit,
(h) help for more options: p
C    foo.c
Updated to revision 31
$ svn resolve --accept mine-full foo.c
Resolved conflicted state of 'foo.c'

Tip

You can just remove the conflict files and commit, but svn resolve fixes up some bookkeeping data in the working-copy administrative area in addition to removing the conflict files, so you should use this command.

Name

resolved

Synopsis

svn resolved path ...

Deprecated. Remove the conflicted state on working-copy files or directories. Symantically it is the same as 'svn resolve --accept working path', which you should now use instead.

Alternate names: none

Changes: working copy

Accesses repository: no

Options

--depth arg

--quiet (-q)

--recursive (-R)

--targets filename

Name

revert

Synopsis

svn revert path ...

Revert any local changes to a file or directory, and resolve any conflicted states. svn revert reverts not only the contents of an item in your working copy, but also any property changes. Finally, you can use it to undo any scheduling operations that you may have done (e.g., files scheduled for addition or deletion can be unscheduled).

Alternate names: none

Changes: working copy

Accesses repository: no

Options

--changelist name, -cl name

--depth arg

--quiet (-q)

--recursive (-R)

--targets filename

Examples

Discard changes to a file:

$ svn revert foo.c
Reverted foo.c

If you want to revert a whole directory of files, use the --depth=infinity flag:

$ svn revert --depth=infinity .
Reverted newdir/afile
Reverted foo.c
Reverted bar.txt

Warning

If you provide no targets to svn revert, it does nothing; to protect you from accidentally losing changes in your working copy, svn revert requires you to provide at least one target.

Name

status

Synopsis

svn status [path ...]

Print the status of working-copy files and directories. With no arguments, it prints only locally modified items (no repository access). With --show-updates, add working revision and server out-of-date information. With --verbose, print full revision information on every item.

The first five columns in the output are each one character wide, and each column gives you information about different aspects of each working-copy item.

The first column indicates that an item was added, deleted, or otherwise changed:

space

No modifications.

A

Item is scheduled for addition.

D

Item is scheduled for deletion.

M

Item has been modified.

R

Item has been replaced in your working copy. This means the file was scheduled for deletion, and then a new file with the same name was scheduled for addition in its place.

C

The contents of the item conflicts with updates received from the repository.

X

Item is related to an externals definition.

I

Item is being ignored (e.g., with the svn:ignore property).

?

Item is not under version control.

!

Item is missing (e.g., you moved or deleted it without using svn). This also indicates that a directory is incomplete (a checkout or update was interrupted).

~

Item is versioned as a directory but has been replaced by a file, or vice versa.

The second column tells the status of a file’s or directory’s properties:

space

No modifications.

M

Properties for this item have been modified.

C

Properties for this item are in conflict with property updates received from the repository.

The third column is populated only if the working copy directory is locked:

space

Item is not locked.

L

Item is locked.

The fourth column is populated only if the item is scheduled for addition-with-history:

space

No history scheduled with commit.

+

History scheduled with commit.

The fifth column is populated only if the item is switched relative to its parent:

space

Item is a child of its parent directory.

S

Item is switched.

The sixth column is populated with lock information:

space

When --show-updates is used, the file is not locked. Otherwise, it merely means that the file is not locked in this working copy.

K

File is locked in this working copy.

O

File is locked by another user or in another working copy. This will only appear when --show-updates is used.

T

File is locked in this working copy, but the lock has been stolen and is invalid. The file is locked in the repository. This will only appear when --show-updates is used.

B

File is locked in this working copy, but the lock has been broken and is invalid. The file is no longer locked. This will only appear when --show-updates is used.

If you pass the --show-updates option, then out-of-date information appears in the seventh column:

space

The item in your working copy is up to date.

*

A newer revision of the item exists on the server.

The remaining fields are variable width and delimited by spaces. The working revision is the next field if the --show-updates or --verbose options are passed.

If the --verbose option is passed, the last committed revision and last committed author are displayed next.

The working-copy path is always the final field, so it can include spaces.

Alternate names: stat, st

Changes: nothing

Accesses repository: only if using --show-updates

Options

--changelist name, -cl name

--depth arg

--ignore-externals

--incremental

--no-ignore

--non-recursive (-N)

--quiet (-q)

--show-updates (-u)

--no-ignore

--xml

Examples

To find out what changes you have made to your working copy:

$ svn status wc
M     wc/bar.c
A  +   wc/qax.c

To find out what files in your working copy are out of date, pass the --show-updates option (this does not make any changes to your working copy). Here you can see that wc/foo.c has changed in the repository since we last updated our working copy:

$ svn status --show-updates wc
M           965    wc/bar.c
*     965    wc/foo.c
A  +         965    wc/qax.c
Status against revision:    981

Tip

--show-updates places an asterisk only next to items that are out of date (that is, items that will be updated from the repository if you run svn update). --show-updates does not cause the status listing to reflect the repository’s version of the item.

And finally, the most information you can get out of the status subcommand:

$ svn status --show-updates --verbose wc
M           965       938 sally        wc/bar.c
* 965       922 harry        wc/foo.c
A  +         965       687 harry        wc/qax.c
965       687 harry        wc/zig.c
Head revision:   981

Name

switch

Synopsis

svn switch URL [path]

This subcommand updates your working copy to mirror a new URL--usually a URL that shares a common ancestor with your working copy, although not necessarily. This is the Subversion way to move a working copy to a new branch.

As with most subcommands, you can limit the scope of the switch operation to a particular tree depth using the --depth option. Alternatively, you can use the --set-depth option to set a new “sticky” working copy depth on the switch target. Currently, the depth of a working copy directory can only be increased (telescoped more deeply); you cannot make a directory more shallow.

Alternate names: sw

Changes: working copy

Accesses repository: yes

Options

--accept arg

--depth arg

--diff3-cmd cmd

--force

--ignore-externals

--quiet (-q)

--relocate

--revision rev, -r rev

--set-depth arg

Examples

If you’re currently inside the directory vendors, which was branched to vendors-with-fix, and you’d like to switch your working copy to that branch:

$ svn switch http://svn.red-bean.com/repos/branches/ \
> vendors-with-fix .
U  myproj/foo.txt
U  myproj/bar.txt
U  myproj/baz.c
U  myproj/qux.c
Updated to revision 31.

And to switch back, just provide the URL to the location in the repository from which you originally checked out your working copy:

$ svn switch http://svn.red-bean.com/repos/trunk/vendors .
U  myproj/foo.txt
U  myproj/bar.txt
U  myproj/baz.c
U  myproj/qux.c
Updated to revision 31.

Tip

You can just switch part of your working copy to a branch if you don’t want to switch your entire working copy.

Sometimes an administrator might change the “base location” of your repository; in other words, the contents of the repository don’t change, but the main URL used to reach the root of the repository does. For example, the hostname may change, or the URL schema, or perhaps just the path that leads to the repository. Rather than checking out a new working copy, you can have the svn switch command “rewrite” the beginnings of all the URLs in your working copy. Use the --relocate command to do the substitution. No file contents are changed, nor is the repository contacted. It’s similar to running a sed script over your working copy .svn/ directories, which runs s/OldRoot/NewRoot/:

$ cd /tmp
$ svn checkout file:///tmp/repos test
A  test/a
A  test/b
...

$ mv repos newlocation
$ cd test/

$ svn update
svn: Unable to open an ra_local session to URL
svn: Unable to open repository 'file:///tmp/repos'

$ svn switch --relocate file:///tmp/
repos file:///tmp/newlocation .
$ svn update
At revision 3.

Name

unlock

Synopsis

svn unlock path ...
svn unlock URL

Remove the lock token from the specified files. This command will print a warning if the target is locked by another user or no lock token exists, but will continue to unlock files it can unlock. Use the --force option to break a lock belonging to another user or working copy.

Alternate names: none

Changes: working copy; repository

Accesses repository: yes

Options

--force

--targets filename

Name

update

Synopsis

svn update [PATH ...]

svn update brings changes from the repository into your working copy. If no revision is given, it brings your working copy up to date with the HEAD revision. Otherwise, it synchronizes the working copy to the revision given by the --revision option.

For each updated item Subversion prints a line starting with a specific character reporting the action taken. These characters have the following meaning:

A

Added

B

Broken lock (third column only)

D

Deleted

U

Updated

C

Conflicted

G

Merged

E

Existed

A character in the first column signifies an update to the actual file, while updates to the file’s properties are shown in the second column. Lock information is printed in the third column.

Tip

If you want to examine an older revision of a single file, you may want to use svn cat.

Alternate names: up

Changes: working copy

Accesses repository: yes

Options

--accept arg

--changelist name, -cl name

--depth arg

--diff3-cmd cmd

--editor-cmd editor

--force

--ignore-externals

--quiet (-q)

--revision rev, -r rev

--set-depth arg

Repository Administration: svnadmin

svnadmin is the administrative tool for monitoring and repairing your Subversion repository.

Common svnadmin Options

--bdb-log-keep

(Berkeley DB specific) Disable automatic log removal of database logfiles.

--bdb-txn-nosync

(Berkeley DB specific) Disable use of fsync( ) when committing database transactions.

--bypass-hooks

Bypass the repository hook system.

--clean-logs

Remove unused Berkeley DB logs.

--force-uuid

By default, when loading data into a repository that already contains revisions, svnadmin ignores the UUID from the dump stream. This option causes the repository’s UUID to be set to the UUID from the stream.

--ignore-uuid

By default, when loading an empty repository, svnadmin uses the UUID from the dump stream. This option causes that UUID to be ignored.

--incremental

Dump a revision only as a diff against the previous revision, instead of the usual full text.

--parent-dir dir

When loading a dumpfile, root paths at dir instead of /.

--quiet

Do not show normal progress; show only errors.

--revision rev, -r rev

Specify a particular revision to operate on.

Common svnadmin Subcommands

The svnadmin command creates and administers the repository. As such, it always operates on local paths, not on URLs.

Name

create

Synopsis

svnadmin create repos_path

Create a new, empty repository at the path provided. If the provided directory does not exist, it is created for you.

Options

--bdb-log-keep

--bdb-txn-nosync

Example

Creating a new repository is just this easy:

$ svnadmin create /usr/local/svn/repos

Name

deltify

Synopsis

svnadmin deltify [-rlower[:upper]]repos_path

svnadmin deltify only exists in 1.0.x due to historical reasons. This command is deprecated and no longer needed.

It dates from a time when Subversion offered administrators greater control over compression strategies in the repository. This turned out to be a lot of complexity for very little gain, and the feature was deprecated.

Options

--quiet

--revision rev, -r rev

Name

dump

Synopsis

svnadmin dump repos_path [-r lower[:upper]] [--incremental]

Dump the contents of filesystem to standard output in a dumpfile portable format, sending feedback to standard error. Dump revisions lower rev through upper rev. If no revisions are given, dump all revision trees. If only lower is given, dump that one revision tree.

Options

--incremental

--quiet

--revision rev, -r rev

Examples

Dump your whole repository:

$ svnadmin dump /usr/local/svn/repos
SVN-fs-dump-format-version: 1
Revision-number: 0
* Dumped revision 0.
Prop-content-length: 56
Content-length: 56
...

Incrementally dump a single transaction from your repository:

$ svnadmin dump /usr/local/svn/repos -r 21 --incremental
* Dumped revision 21.
SVN-fs-dump-format-version: 1
Revision-number: 21
Prop-content-length: 101
Content-length: 101
...

Name

help

Synopsis

svnadmin help [subcommand ...]

Provide a quick usage summary. With subcommand, provide information about the given subcommand.

Alternate names: ?, h

Name

hotcopy

Synopsis

svnadmin hotcopy old_repos_path new_repos_path

This subcommand makes a full hot backup of your repository, including all hooks, configuration files, and, of course, database files. If you pass the --clean-logs option, svnadmin performs a hotcopy of your repository, and then removes unused Berkeley DB logs from the original repository. You can run this command at any time and make a safe copy of the repository, regardless of whether other processes are using the repository.

Option

--clean-logs

Name

list-dblogs

Synopsis

svnadmin list-dblogs repos_path

List Berkeley DB logfiles. Berkeley DB creates logs of all changes to the repository, which allow it to recover in the face of catastrophe. Unless you enable DB_LOGS_AUTOREMOVE, the logfiles accumulate, although most are no longer used and can be deleted to reclaim disk space.

Name

list-unused-dblogs

Synopsis

svnadmin list-unused-dblogs repos_path

List unused Berkeley DB logfiles (see svnlook list-dblogs).

Example

Remove all unused logfiles from a repository:

$ svnadmin list-unused-dblogs /path/to/repos | xargs rm
## disk space reclaimed!

Name

load

Synopsis

svnadmin load repos_path

Read a dumpfile-formatted stream from standard input, committing new revisions into the repository’s filesystem. Send progress feedback to standard output.

Options

--force-uuid

--ignore-uuid

--parent-dir

--quiet (-q)

Examples

This shows the beginning of loading a repository from a backup file (made, of course, with svn dump):

$ svnadmin load /usr/local/svn/restored < repos-backup
<<< Started new txn, based on original revision 1
* adding path : test ... done.
* adding path : test/a ... done.
...

Or, to load into a subdirectory:

$ svnadmin load --parent-dir new/subdir/for/project \
>   /usr/local/svn/restored < repos-backup
<<< Started new txn, based on original revision 1
* adding path : test ... done.
* adding path : test/a ... done.
...

Name

lslocks

Synopsis

svnadmin lslocks repos_path [path]

Print descriptions of all locks in repository repos_path underneath path. If path isn’t given it defaults to the root directory of the repository.

Name

lstxns

Synopsis

svnadmin lstxns repos_path

Print the names of all uncommitted transactions.

Name

recover

Synopsis

svnadmin recover repos_path

Run this command if you get an error indicating that your repository needs to be recovered. This command requires a database lock. Normally failure to obtain a lock will cause an error. Use the --wait option to cause the command to wait indefinitely for a database lock.

Options

--wait

Name

rmlocks

Synopsis

svnadmin rmlocks repos_path locked_path...

Unconditionally remove locks from each locked path.

Name

rmtxns

Synopsis

svnadmin rmtxns repos_path txn_name ...

Delete outstanding transactions from a repository.

Options

--quiet (-q)

Examples

Remove all uncommitted transactions from your repository, using svn lstxns to provide the list of transactions to remove:

$ svnadmin rmtxns /usr/local/svn/repos/ \
>`svnadmin lstxns /usr/local/svn/repos/`

Name

setlog

Synopsis

svnadmin setlog repos_path -r revision file

Set the log message on revision revision to the contents of file.

This is similar to using svn propset --revprop to set the svn:log property on a revision, except that you can also use the option --bypass-hooks to avoid running any pre- or post-commit hooks, which is useful if the modification of revision properties has not been enabled in the pre-revprop-change hook.

Warning

Revision properties are not under version control, so this command permanently overwrites the previous log message.

Options

--bypass-hooks

--revision rev, -r rev

Example

Set the log message for revision 19 to the contents of the file msg:

$ svnadmin setlog /usr/local/svn/repos/ -r 19 msg

Name

setrevprop

Synopsis

svnadmin setrevprop repos_path -r revision name file

Set the property name on revision revision to the contents of file.

Options

--revision rev, -r rev

Example

Set the revision property repository-photo to the contents of the file repo.png:

$ svnadmin setrevprop /var/svn/repos/ -r 0 repository-
photo repo.png

Name

setuuid

Synopsis

svnadmin setuuid repos_path [new_uuid]

Reset the repository UUID to new_uuid. If no new uuid is given generate a new one.

Name

verify

Synopsis

svnadmin verify repos_path

Run this command to verify the integrity of your repository. This iterates through all revisions in the repository by internally dumping all revisions and discarding the output.

Examining the Repository: svnlook

svnlook is a command-line utility for examining different aspects of a Subversion repository. It does not make any changes to the repository. svnlook is typically used by the repository hooks, but a repository administrator might find it useful for diagnostic purposes.

Since svnlook works via direct repository access (and thus can only be used on the machine that holds the repository), it refers to the repository with a path, not a URL.

If no revision or transaction is specified, svnlook defaults to the youngest (most recent) revision of the repository.

svnlook Options

Options in svnlook are global, just as in svn and svnadmin; however, most options apply to only one subcommand because the functionality of svnlook is (intentionally) limited in scope.

--copy-info

Used with the changed command to show detailed copy source information.

--no-diff-deleted

Do not print differences for deleted files. The default behavior when a file is deleted in a transaction/revision is to print the same differences that you would see if you had left the file but removed all the content.

--no-diff-added

Do not print differences for added files. The default behavior is to print the same differences that you would see if you added the entire contents of an existing but empty file.

--revision rev, -r rev

Examine revision number rev.

--revprop

Operate on a revision property rather than the property of a file or directory. You must also specify a revision using --revision when using this option.

--show-ids

Show the filesystem node revision IDs for each path in the filesystem tree.

--transaction tid, -t tid

Examine transaction ID tid.

svnlook Subcommands

Name

author

Synopsis

svnlook author repos_path

Print the author of a revision or transaction in the repository.

Options

--revision rev, -r rev

--transaction tid, -t tid

Name

cat

Synopsis

svnlook cat repos_path path_in_repos

Print the contents of a file.

Options

--revision rev, -r rev

--transaction tid, -t tid

Name

changed

Synopsis

svnlook changed repos_path

Print the paths that were changed in a particular revision or transaction, as well as an svn update-style status letter in the first column: A for added, D for deleted, and U for updated (modified).

Options

--copy-info

--revision rev, -r rev

--transaction tid, -t tid

Example

Show a list of all the changed files in revision 39 of a test repository:

$ svnlook changed -r 39 /usr/local/svn/repos
A   trunk/vendors/deli/
A   trunk/vendors/deli/chips.txt
A   trunk/vendors/deli/sandwich.txt
A   trunk/vendors/deli/pickle.txt

Name

date

Synopsis

svnlook date repos_path

Print the datestamp of a revision or transaction in a repository.

Options

--revision rev, -r rev

--transaction tid, -t tid

Name

diff

Synopsis

svnlook diff repos_path

Print GNU-style differences of changed files and properties in a repository. If a file has a nontextual svn:mime-type property, the differences are explicitly not shown.

Options

--no-diff-added

--no-diff-deleted

--revision rev, -r rev

--transaction tid, -t tid

Name

dirs-changed

Synopsis

svnlook dirs-changed repos_path

Print the directories that were themselves changed (property edits) or whose file children were changed.

Options

--revision rev, -r rev

--transaction tid, -t tid

Name

help

Synopsis

svnlook help [subcommand]
svnlook -h [subcommand]
svnlook -? [subcommand]

Provide a quick usage summary. With subcommand, provide information about the given subcommand.

Alternate names: ?, h

Name

history

Synopsis

svnlook history repos_path [path_in_repos]

Print information about the history of a path in the repository (or the root directory if no path is supplied).

Options

--limit num, -l num

--revision rev, -r rev

--show-ids

Example

This shows the history output for the path /tags/1.0, as of revision 20 in our sample repository.

$ svnlook history -r 20 /usr/local/svn/repos /tags/1.0 \
> --show-ids
REVISION   PATH <ID>
--------   ---------
19   /tags/1.0 <1.2.12>
17   /branches/1.0-rc2 <1.1.10>
16   /branches/1.0-rc2 <1.1.x>
14   /trunk <1.0.q>
...

Name

info

Synopsis

svnlook info repos_path

Print the author, datestamp, log message size, and log message.

Options

--revision rev, -r rev

--transaction tid, -t tid

Name

lock

Synopsis

svnlook lock repos_path path_in_repos

Print available information about existing lock for path_in_repos. If no lock exists, print nothing.

Name

log

Synopsis

svnlook log repos_path

Print the log message.

Options

--revision rev, -r rev

--transaction tid, -t tid

Name

propget

Synopsis

svnlook propget repos_path propname path_in_repos

List the value of a property on a path in the repository.

Alternate names: pg, pget

Options

--revision rev, -r rev

--transaction tid, -t tid

Example

Show the value of the seasonings property on the file /trunk/sandwich in the HEAD revision:

$ svnlook pg /usr/local/svn/repos seasonings /trunk/
sandwich
mustard

Name

proplist

Synopsis

svnlook proplist repos_path path_in_repos

List the properties of a path in the repository. With --verbose, show the property values too.

Alternate names: pl, plist

Options

--revision rev, -r rev

--revprop

--transaction tid, -t tid

--verbose (-v)

Examples

Show the names of properties set on the file /trunk/README in the HEAD revision:

$ svnlook proplist /usr/local/svn/repos /trunk/README
original-author
svn:mime-type

This is the same command as in the previous example, but this time it shows the property values as well:

$ svnlook proplist --verbose /usr/local/svn/repos \
> /trunk/README
original-author : fitz
svn:mime-type : text/plain

Name

tree

Synopsis

svnlook tree repos_path [path_in_repos]

Print the tree, starting at path_in_repos (if supplied; at the root of the tree otherwise), optionally showing node revision IDs.

Options

--full-paths

--non-recursive, -N

--revision rev, -r rev

--show-ids

--transaction tid, -t tid

Example

This shows the tree output (with node IDs) for revision 40 in our sample repository:

$ svnlook tree -r 40 /usr/local/svn/repos --show-ids
/ <0.0.2j>
trunk/ <p.0.2j>
vendors/ <q.0.2j>
deli/ <1g.0.2j>
egg.txt <1i.e.2j>
soda.txt <1k.0.2j>
sandwich.txt <1j.0.2j>

Name

uuid

Synopsis

svnlook uuid repos_path

Print the UUID for the repository. The UUID is the repository’s Universal Unique IDentifier. The Subversion client uses this identifier to differentiate between one repository and another.

Name

youngest

Synopsis

svnlook youngest repos_path

Print the youngest revision number of a repository.

Providing Remote Access: svnserve

svnserve allows access to Subversion repositories using the svn network protocol. You can run svnserve either as a standalone server process, or by having another process--such as inetd, xinetd, or sshd--start it for you.

Once the client has selected a repository by transmitting its URL, svnserve reads a file named conf/svnserve.conf in the repository directory to determine repository-specific settings, such as what authentication database to use and what authorization policies to apply. The details are provided in Version Control with Subversion.

svnserve Options

Unlike the previous commands we’ve described, svnserve has no subcommands; svnserve is controlled exclusively by options.

--daemon, -d

Run in daemon mode. svnserve backgrounds itself, and accepts and serves TCP/IP connections on the svn port (3690, by default).

--foreground

When used together with -d, this option causes svnserve to stay in the foreground. This option is mainly useful for debugging.

--help, -h

Display a usage summary and exit.

--inetd, -i

Use the standard input/standard output file descriptors, as appropriate for a server running out of inetd.

--listen-host=host

Listen on the interface specified by host, which may be either a hostname or an IP address.

--listen-once, -X

Accept one connection on the svn port, serve it, and exit. This option is mainly useful for debugging.

--listen-port=port

Listen on port when run in daemon mode.

--pid-file filename

Write process ID to filename.

--root= root, -r= root

Set the virtual root for repositories served by svnserve to root. The pathname in URLs provided by the client are interpreted relative to this root and are not allowed to escape this root.

--threads, -T

When running in daemon mode, spawn a thread instead of a process for each connection. The svnserve process still backgrounds itself at startup time.

--tunnel, -t

Run in tunnel mode, which is just like the inetd mode of operation (serve one connection over standard input/standard output), except that the connection is considered to be pre-authenticated with the username of the current UID. This flag is selected by the client when running over a tunnelling agent such as ssh.

--tunnel-user username

Used with -tunnel to specify an alternate username for pre-authentication.

Chapter 14. The Git Version Control System

Git is a powerful, open source, distributed version control system (DVCS). It is not considered as user-friendly as Subversion but has many advanced features, including elegant merges of contributions from multiple independent sources and the ability to access the entire project history, even when not connected to a central server.

This chapter covers the following topics:

- Conceptual overview

- Using Git: a quick tour

- The Git command line client: git

Version control was introduced in Chapter 12, which contains a comparison of Subversion, Git, and other popular systems. A more thorough discussion on Git can be found in Jon Loeliger’s Version Control with Git (O’Reilly).

Conceptual Overview

Git was originally created in 2005 by Linus Torvalds as a system for managing changes to the Linux kernel. Although it is used for many of the same tasks as other version control systems like Subversion, Git’s internal workings are very different. It’s important to understand some of these concepts in order to use Git successfully.

Git maintains a repository; a directory structure that tracks the historical contents of a set of files. Generally, the repository is stored in a .git directory (or another directory named by $GIT_DIR) along with the files themselves.

Unlike other version control systems, Git does not enforce the concept of a “central repository.” Instead, every set of files tracked by Git has its own .git repository, and revisions can be easily pushed and pulled from one repository to another.

The set of files currently being tracked by Git is called the working tree. The working tree is where most of your daily work takes place. By default, the working tree starts in the parent directory of the .git directory. (You can override this by setting $GIT_WORK_TREE.) The operation of creating a working tree from a repository is called checking out the files, which is done by git checkout. After modifying the files in the working tree, you save the changes back to the repository by committing them with git commit (this is also called checking in).

Unlike other systems, Git introduces an extra, intermediate state between the repository and the working tree called the index. (You might see the index called the cache in a few places, but this terminology is obsolete and should be avoided.) Initially, the index tracks the set of files as they were at checkout time. As you become confident that changes you made to the working tree are correct, you add them to the index using git add. Then, when the set of changes forms a coherent batch, you commit the index into the repository (along with a log message) using git commit. The main advantage of this two-step process is it’s easy to limit a commit to only some of the changes you’ve been working on, which leads to more coherent individual commits. Git’s working style — including the index — encourages many small commits instead of large batches.

Git Repository Format

The set of commits in a Git repository is stored in the form of a directed acyclic graph, or DAG. This simply means that each commit can reference one or more earlier “parent” commits, and more than one commit can refer to the same parents. The word “acyclic” refers to the fact that the structure is not allowed to contain loops; no parent commit can refer back to a commit that lists it as a parent.

The structure of the DAG defines the repository’s history. Normally, each commit has exactly one parent, which describes the repository exactly as it was before the new commit was made. By comparing a commit to its parent, you can produce a diff, which is a precise set of changes that were applied to the parent in order to produce the new version.

Some commits have more than one parent. These commits are called merge commits because they express a merging of two separate branches of history. If two people have a copy of a particular repository and start making commits, those two histories will start to diverge, which is called forking. Eventually, someone will need to rejoin the two histories into one, which is called merging. (As with other version control systems, you can also create additional named branches in each repository if you want. For example, you might create a maintenance branch for each major release of your software.)

Referring to Commits

Each commit in Git can be uniquely identified by its commitid, a SHA-1 hash code made up of 40 hexadecimal digits. Unlike revisions in centralized systems like Subversion, Git revision numbers cannot be sequential, since there’s no central server to assign the sequential IDs. Because it’s impossible for a human to remember strings of 40 digits, Git provides several more convenient ways to refer to commits.

Any Git command that can accept a revision can accept any of the following forms:

Full 40-digit hash

You can always simply supply the full 40-digit hash code, such as da87b5990c03a799ae7a581c2edb1287dba08a43.

Abbreviated hash

Since the 40 digits of a hash code are effectively random, it’s very unlikely (though not impossible) that there will be more than one commit with the same hash. Thus, you can refer to any commit by the first few digits of its name, as long as only one commit starts with those digits. People often choose seven digits as a reasonably safe length. For example, da87b59.

Tags

Using the git tag command, you can create user-friendly names for individual commits. For example, if you released version v1.1 of your software after making commit da87b59, you could run git tag v1.1 da87b59 so that in the future, you can always refer to a commit named v1.1. Tag names can be shared between repositories, but you have to do it explicitly using git push and git pull.

Local branches

Branches are similar to tags, in that they name a particular commit. However, branches are special because if you check out a branch and make a new commit, the branch advances automatically to point at the new commit.

Unlike with other version control systems, branch names in Git are maintained locally for every copy of a repository. That means if you clone someone else’s repository, you take a copy of the branch called master (the default Git branch name). They may continue committing to their master branch, and you might commit to yours, and then there will exist two branches called master, each with different contents. You can resync them using git push and git pull.

Remote tracking branches

When you clone a central repository, you will frequently want to keep track of the branches as they exist in that respository, even as you make changes to them in your own repository. Git helps do this by naming repositories using the git remote command. After that, a particular branch on a particular remote would be named remotename/branchname. (Git automatically creates a remote named origin to identify the repository you originally cloned from, and the default branch in a repository is usually master. So you might have a local branch called master corresponding to a remote tracking branch called origin/master.)

HEAD

HEAD is a special name that always refers to the currently checked-out commit.

FETCH_HEAD

FETCH_HEAD is a special name that refers to the most recent commit retrieved by git fetch.

commit^n notation

For any commit, you can refer to its n-th direct parent by giving its name (using any acceptable form of a commit name, such as a branch name, tag, or hash), followed by ^, followed by the parent number you want. Most commits (other than merge commits) have only one parent, so if n is omitted, the immediate parent is returned. For example, da87b59^ is the first parent of da87b59; HEAD^2^1 is the first parent of the second parent of HEAD; origin/master^^^^ is four parents up from origin/master, taking the first parent at each step.

commit˜n notation

You can refer to a parent n steps up the tree using commit˜n notation. For example, HEAD˜4 is four parents up from HEAD, and is equivalent to HEAD^^^^. Note that you can combine ˜ and ^ notation, so HEAD^2˜4 is four steps up the tree from the second direct parent of HEAD.

branch@{n} notation

Because branch names can be retargeted at any time to refer to a different commit, you run the risk of accidentally losing a lot of work if you change or delete a branch name incorrectly. branch@{n} notation is designed to fix this; it refers to the commit branch referred to n commits ago. For example, if you use git reset or git merge and then change your mind, you can refer to the commit before the most recent change using HEAD@{1}.

Unlike ^ and ˜ notation, the name here must really be a branch name, not an arbitrary commit, since it makes no sense to refer to the old meaning of a particular commit. However, you can use ^ and ˜ on the output of commit@{n}, however. For example, HEAD@{1}^2˜4.

You can see the history of a branch name in a format suitable for use with commit@{n}, using git reflog.

Using Git: A Quick Tour

Git permits a staggering number of different workflow styles, from “almost centralized” (everyone frequently pushes and pulls to the same central server) to entirely email-based (people exchange patches using a mailing list). It would be impossible to explain all the different Git workflows here, so we’ll focus on just one: a simple push/pull workflow with a single shared repository.

Before You Start

Before you start using Git for the first time, you need to set two global configuration values, user.email and user.name, or else you won’t be able to make new commits. Here’s how:

$ git config --global user.name 'John Smith'
$ git config --global user.email 'jsmith@example.com'

These settings will remain in place across all your repositories, so you don’t have to reset them every time. You can also override them on a per-repository basis if you want, by running the commands in a particular repository and omitting the --global option.

Example: The Linux Kernel Repository

As our first example, let’s clone a copy of the Linux kernel into /tmp/linux-2.6:

$ cd /tmp
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/
linux-2.6.git linux-2.6
Initialized empty Git repository in /tmp/linux-2.6/.git/
remote: Counting objects: 1177432, done.
remote: Compressing objects: 100% (189064/189064), done.
remote: Total 1177432 (delta 982454), reused 1176803 (delta 981879)
Receiving objects: 100% (1177432/1177432), 288.00 MiB | 406 KiB/s, done.
Resolving deltas: 100% (982454/982454), done.
Checking out files: 100% (27842/27842), done.

Now you have a copy of the entire Linux kernel and its development history, including many different tags and branches. You’ve started out on branch master, which is the latest version. Check out the v2.6.20 tag to get an older version:

$ cd linux-2.6
$ git checkout v2.6.20
Checking out files: 100% (33554/33554), done.
Note: moving to 'v2.6.20' which isn't a local branch
If you want to create a new branch from this checkout, you may do so
(now or later) by using -b with the checkout command again. Example:
git checkout -b <new_branch_name>
HEAD is now at 62d0cfc... Linux 2.6.20

You can’t make changes to tags, and you haven’t created a local branch for your work, so Git has given you what it calls a disconnected HEAD. You can make commits, but they won’t be attached to any branch at all. That’s a bit dangerous, since it’s easy to lose track of your work that way. Let’s name our work so it doesn’t get lost:

$ git checkout -b my-test-branch
Switched to a new branch "my-test-branch"

And look at the list of local branches:

$ git branch
master
* my-test-branch

You can make a test commit:

$ echo 'hello world' >hello.txt
$ git add hello.txt
$ git commit -m 'my first hello commit'
Created commit 22b0a19: my first hello commit
1 files changed, 1 insertions(+), 0 deletions(-)
create mode 100644 hello.txt

Remember, this new commit hasn’t been shared with anyone; you’ve only committed it to your local repository.

Try pulling in the changes from v2.6.20 to v2.6.21:

$ git pull origin v2.6.21
Merge made by recursive.
...
$ ls hello.txt
hello.txt

All the changes from v2.6.21 have been merged into your branch, but your new hello.txt is still there too. Success! If you had permission to push your new branch back to the central kernel repository, which you probably don’t, you could do it now:

$ git push origin my-test-branch
Counting objects: 228, done.
Delta compression using 2 threads.
Compressing objects: 100% (165/165), done.
Writing objects: 100% (228/228), 38.66 KiB, done.
Total 228 (delta 142), reused 77 (delta 60)
To git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
linux-2.6
* [new branch]      my-test-branch -> my-test-branch

Someone could then pull your branch into theirs and receive your hello.txt changes.

Creating and Sharing a New Repository

If you have a project that isn’t already in Git, you will need to first create a local repository for it. Let’s say you have a directory called my-project in which you already have a set of files. You want to keep it under version control. Here’s what you do:

$ cd my-project
$ git init
Initialized empty Git repository in .git/
$ git add .
$ git commit -m 'Initial commit'

(The git add command above won’t work unless there is at least one file to add, and git commit won’t work until you’ve git added at least one file.)

For personal projects, that might be all you need; you can now create commits, branches, and tags, compare differences, and so on.

If you want to share your project with someone else, however, you will need to create a bare repository (i.e., one with no work tree of its own) and give other people access to it. In this example, we’ll create a new bare repository in /home/git/my-project.git, copied from /tmp/my-project, and give access to everyone in the mygroup Unix group:

$ git clone --bare /tmp/my-project /home/git/my-project.git
Initialized empty Git repository in .git/
$ cd /home/git/my-project.git
$ git config core.sharedRepository group
$ chgrp -R mygroup .
$ chmod -R g+rwX .

By convention, bare repositories have pathnames that end in a .git suffix. This is because they don’t contain a .git subdirectory — the .git subdirectory contents are in the root of the bare repository, since there’s no work tree.

People in mygroup can now git clone /home/git/my-project.git and push and pull from it.

If you want to host an open source project that everyone on the Internet can share, you have several options:

git daemon

You can run the Git daemon on your server. The git daemon command is beyond the scope of this book, but you can find instructions in git help daemon.

Gitosis

Gitosis is a separate tool that lets you create a single SSH account and give multiple people access to a Git repository through that.

git shell

The git shell command (see git help shell) is included with Git and does a similar job to Gitosis. Most people prefer Gitosis.

http://github.com

A commercial service, github.com, offers free hosting services for open source projects and reasonably priced hosting of proprietary projects.

Gitorious

Gitorious is an open source tool similar to github.com. You can use it to create your own github.com-like hosting service.

http://repo.or.cz

repo.or.cz was the original public Git hosting service. It provides basic push/pull access, although it isn’t as user friendly as the other alternatives.

Because Git repositories are fully distributed, you can choose to host your project in more than one place at a time for added reliability, in case a server is unavailable or loses its data.

The Git Command Line Client: git

The git Command

Everything you do with Git is accomplished using the git command. The git main program doesn’t actually do anything itself; instead, it runs subcommands based on the first word on the command line, often executing a subprogram based on that name. For example, if you run git add, Git might end up executing a program called git-add. In fact, if you create additional git-* commands in your $PATH, Git will add them to its repertoire automatically.

Git contains a daunting number of subcommands — well over 100 of them. Most of these commands are meant to be used internally to create other subcommands. We’ll cover only the most important commands in this book.

Accessing Git’s Online Help

You can ask the git command for help using the git help command. By default, it just gives a list of the most common commands:

$ git help
The most commonly used git commands are:
add           Add file contents to the index
apply         Apply a patch on a git index file and a working tree
archive       Create an archive of files from a named tree
...

You can also get a complete list of all the commands:

$ git help -a
git commands available in '/usr/bin'
------------------------------------------
add                 gui                 reflog
add--interactive    hash-object         relink
am                  http-fetch          remote
...

Finally, you can get the Unix manpage for a particular command (every Git command, even the obscure ones, has a manpage). For example, to get help for the git add command:

$ git help add

git Subcommands

Name

add

Synopsis

git add filename ...

Add or update a file in the index so its changes will be committed upon the next call to git commit. This is called staging the change. Unlike other systems, Git commits only the exact file contents that you have added, so if you make further changes to a file, you will need to add it again before running git commit.

With the -p option, Git lets you stage individual changes (“hunks”) interactively, even inside a particular file. You can use this to help break your commits into smaller, more understandable pieces.

Options

-n (no-op)

-v (verbose)

-f (force)

-p (partial)

Examples

To stage a new or updated file in the index:

$ git add myfile.c

To stage all the files in the current directory, except the ones ignored by .gitignore:

$ git add.

To add a file even though it is ignored by .gitignore:

$ git add myfile.o
The following paths are ignored by one of your .gitignore
files:
myfile.o
Use -f if you really want to add them.
fatal: no files added
$ git add -f myfile.o

To add only part of a file:

$ git add -p README
diff --git a/README b/README
index 42644cd..e2ad5c3 100644
--- a/README
+++ b/README
@@ −1 +1,2 @@
...
Stage this hunk [y,n,q,a,d,/,e,?]? y

Name

archive

Synopsis

git archive [--remote=repository-path] [--format=zip] revision -- [path ...] >outputfile

Create a tar or zip format archive from the current repository or from the repository at repository-path if --remote is specified. The default output file format is (uncompressed) tar, but git archive can also produce a zip file instead if you specify --format=zip.

git archive always writes the new archive to standard output, so you should redirect or pipe its output somewhere.

You must specify the revision from which to take the files. If you want to use the current revision, use HEAD.

If you specify one or more paths, only those paths are included in the produced archive.

Options

--list

--remote

--format=tar|zip

Examples

To list the available options for --format:

$ git archive --list
tar
zip

To create a tar.gz file of the currently checked-out revision:

$ git archive HEAD | gzip >my-release.tar.gz

To create a zip file of tag v1.2 in a repository from another computer named myserver (where you have Unix shell access via ssh):

$ git archive --format=zip --remote=myserver:src/myapp.git
v1.2 >myapp-1.2.zip

Name

bisect

Synopsis

git bisect start [bad-commit [good-commit ...]] -- [path ...]
git bisect bad [commit ...]
git bisect good [commit ...]
git bisect skip [commit ...]
git bisect reset
git bisect view
git bisect run cmd [args ...]

Go back in history to find the first commit that introduced a problem. git bisect uses a binary search algorithm to narrow down which commit caused a problem using as few steps as possible. If there are n commits to consider, git bisect can find the exact culprit with approximately log2 n attempts. For example, with 100 commits, it will take about 7 tries; with 1,000 commits, it will take about 10 tries.

git bisect start [bad-commit [good-commit ...] -- [path ...]

Use this command to start the bisection. You can optionally specify one known bad-commit (which exhibits the problem) and one or more known good-commits (which do not exhibit the problem). If you know the bug is in a particular set of files or directory, specify them as paths to further narrow the set of commits to consider.

git bisect bad [commit ...]

Mark the given commit(s) as bad and check out the next candidate. If no commits are provided, the default is the currently checked-out HEAD.

git bisect good [commit ...]

Mark the given commit(s) as good and check out the next candidate. If no commits are provided, the default is the currently checked-out HEAD.

git bisect skip [commit ...]

Mark the given commit(s) as untestable and check out the next candidate. You need this if some other bug exists in the current commit that prevents you from testing the bug you’re looking for. If no commits are provided, the default is the currently checked-out HEAD.

git bisect reset

Abort the bisection and check out the commit you were using when you ran git bisect start.

git bisect view

Show the current bisection status using gitk.

git bisect run cmd [args ...]

Continue the bisection automatically by running the given cmd on each candidate. If the command returns an error, the commit is considered bad; otherwise, it is considered good.

Examples

To look for a problem when you know revisions v2.0 and v1.1 are good, but the current version is bad, and the bug is probably in the mymodule subdirectory:

$ git bisect start HEAD v2.0 v1.1 -- mymodule
Bisecting: 100 revisions left to test after this (roughly 7 steps)
[fa16ab36ad014bcc03acc4313bb0918fb241b54d] Fix the widget
$ make test
...
$ git bisect bad
Bisecting: 50 revisions left to test after this (roughly 6 steps)
[49cf82288aac5f0dcb152e2d75cd340e48d9e760] Change some bits
$ make test
...
$ git bisect good
fa16ab36ad014bcc03acc4313bb0918fb241b54d is first bad
commit

To find a bug that was introduced somewhere between v1.1 and v2.0, and that could be in any file:

$ git bisect start
$ git bisect good v1.1
$ git bisect bad v2.0
Bisecting: 97 revisions left to test after this (roughly 7 steps)
[fa16ab36ad014bcc03acc4313bb0918fb241b54d] Fix the widget
$ git bisect run make test
...
1f73862f3b63bbc9f0a8a8a12dd58e1a39a3355f is first bad commit
bisect run success

Name

branch

Synopsis

git branch [-r] [-a] [--contains commit]
git branch [-f] [--track] branchname [commit]
git branch -m oldname newname
git branch -d|-D [-r] branchname

List, create, rename, and delete branches.

git branch [-r] [-a] [--contains commit]

List the existing branches. By default, lists only local branches (.git/refs/heads/*). With -r, list remote tracking branches instead (.git/refs/remotes/*/*). With -a, list all local and remote tracking branches. With --contains, list only the branches that contain the given commit.

git branch [-f] [--track|--no-track] branchname [commit]

Create a new branch, branchname, that points at the given commit. The default for commit is HEAD. If branchname already exists, the operation will fail unless -f is specified. If you specify --track (the default in newer versions of Git) and commit is a remote tracking branch, you will be able to type simply git merge or git pull in the future to merge remote changes into your branch.

Tip

This command does not check out your new branch. If you want to create a new branch and check it out in one step, use git checkout -b.

git branch -m|-Moldnamenewname

Rename a branch from oldname to newname. If newname already exists, -m will fail while -M will overwrite it.

git branch -d|-D [-r]branchname

Delete branchname. If -r is specified, branchname is a remote tracking branch (.git/refs/remotes/*/*); otherwise it is a local branch (.git/refs/heads/*). If you use -d, the branch will only be deleted if your current HEAD already includes everything in branchname; otherwise, it will fail. If you use -D, this safety check doesn’t occur.

Examples

To get the list of all branches:

$ git branch -a

To create a new branch that starts off pointing at your current HEAD:

$ git branch savepoint1

To later delete the savepoint1 branch:

$ git branch -d savepoint1

To create and check out a new branch test based on remote tracking branch origin/master:

$ git branch --track test origin/master
$ git checkout test
Switched to branch 'test'

Name

checkout

Synopsis

git checkout [revision] path ...

Copy files from the repository into your working tree and possibly switch branches. git checkout does one of four different things, depending on which options are provided:

revision but no path

Switch branches to the one named by revision. If files are modified in the working tree and also changed in the new branch, the operation will fail. The next commit will be in the new branch.

If revision is a valid commit but not the name of a local branch, Git still switches HEAD to the given commit but does not give the new branch a name. This is called a detached HEAD. You can later name the new branch with git checkout -b.

In either case, if the -b option is given, a new branch is created from the given revision, and Git switches to that branch.

path(s) but no revision

Destroys all working tree changes in the named files or directories, replacing them with their contents from the index.

revision and path(s)

Destroys all working tree changes in the named files or directories, replacing them with their contents from the given revision. This does not switch branches; instead, it replaces contents of the given files in the index. The next git commit, will affect the same branch as before, but the named paths will be considered modified.

no revision and no path(s)

No changes. Prints a list of files that have been modified in the working tree.

Options

-q(quiet)

-f(force)

-b new_branch_name

--track (-t)

--no-track

-m (merge)

Examples

To revert all the files in directory docs to their version from the index:

$ git checkout docs

To switch to the branch called new-feature, which must already exist:

$ git checkout new-feature
Switched to branch "new-feature"

To switch to the remote branch origin/master, creating a new branch called new-feature:

$ git checkout -b new-feature origin/master
Branch new-feature set up to track remote branch refs/
remotes/origin/master.
Switched to a new branch "new-feature"

Name

cherry-pick

Synopsis

git cherry-pick commit

Take the changes from an individual commit (usually one from another branch) and apply it to the current branch. Note that unlike git merge, git cherry-pick applies only a single change, not all the history leading up to that change.

The newly created commit is completely independent of the original, although it has the same commit message by default. git cherry-pick commit is the rough equivalent of git show commit | patch -p1

Options

-e, --edit

-x (extend commit message)

-m parent-number

-n, --no-commit

-s, --signoff

Examples

To cherry-pick commit 1a48191 onto the current branch and edit the commit message:

$ git cherry-pick -e 1a48191
Finished one cherry-pick.

Name

clean

Synopsis

git clean -n|-f [-d] [-x]

Removes files from the work tree that are not in the Git index. By default, it only removes files that are not listed in .gitignore and does not remove directories. (To undo work tree changes to files that are in the index, use git checkout.)

You must provide one of -n or -f.

Options

-n (print only, do not remove)

-f (force removal of files)

-d (also remove extra directories)

-x (also remove files skipped by .gitignore)

-X (only remove files skipped by .gitignore)

-q (quiet)

Examples

To remove all extra files in the work tree so the only files remaining are ones that would be there after a fresh git clone:

$ git clean -f -d -x
Removing foo

To see what would happen if you ran the above command:

$ git clean -n -d -x
Would remove foo

Name

clone

Synopsis

git clone repository [local-directory]

Make a copy of repository (which can be a local or remote Git repository) in local-directory. By default, if repository is on the local filesystem, Git will use hardlinks to copy the .git/objects folder to minimize disk space waste.

Available forms for repository are:

/path/repo.git

rsync://hostname/path/repo.git

http://hostname/path/repo.git

https://hostname/path/repo.git

git://host/path/repo.git

ssh://host/path/repo.git

ssh://user@host:port/path/repo.git

host:path/repo.git

user@host:path/repo.git

Options

-s, --shared

--no-hardlinks

--reference other-parent-repository

-q, --quiet

-n, --no-checkout

--bare

-o origin-name, --origin origin-name

--depth shallow-clone-depth

Examples

To clone the Linux kernel repository:

$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git linux-2.6

Name

commit

Synopsis

git commit [-- file ...]

Commit the changes that have already been staged in the index, updating HEAD.

If -a is given, all changed files in the work tree — not only staged changes — will be committed. (-a is the common behavior in systems like Subversion.)

If files are specified, exactly those files are committed, regardless of the state of the index.

You cannot commit a file for the first time, even with -a, unless it has first been added with git add.

Options

-a (all files, not just added ones)

--amend

-m commit-message, --message=commit-message

-F commit-message-file

-q, --quiet

-s, --signoff

Examples

To commit changes only to files in the mylib directory:

$ git commit -- mylib
Created commit 90716b6: my new commit
1 files changed, 13 insertions(+), 0 deletions(-)
create mode 100644 test-file

Name

config

Synopsis

git config [--global] --list
git config [--global] name
git config [--global] name value

List, get, or set configuration values. If --global is given, uses your account-wide default settings (in ˜/.gitconfig); otherwise uses the settings for the current repository (in .git/config). Instead of using git config, you can also just view or edit these files directly.

The most important settings are:

core.autocrlf

If true, converts LF line endings to CRLF on files when checking out and converts the line endings back to LF when committing.

core.bare

Makes this repository a bare repository, which means it has no work tree. (Public shared repositories are usually bare.)

core.sharedRepository

Set to either all, group, or false. If group, the files in .git will be group readable and writable. If all, the files will also be readable (but not writable) by everyone.

core.editor

The path of your favourite text editor, for editing commit messages. The $EDITOR environment variable overrides this.

gc.autopacklimit

Controls how frequently Git will automatically run git gc after common operations. To disable it completely, use 0.

rerere.enabled

When committing a conflicted merge, Git will remember how you resolved the conflict and attempt to reuse the recorded resolution if it encounters it again in the future.

user.email

Your email address. This will be attached to commit messages automatically. The $EMAIL environment variable overrides this.

user.name

You full name. This will be attached to commit messages automatically. The $GIT_COMMITTER_NAME and $GIT_AUTHOR_NAME environment variables override this.

Options

--unset

Examples

To set your email address and name for future commits:

$ git config --global user.name 'John Smith'
$ git config --global user.email 'jsmith@example.com'

To list all your global settings:

$ git config --global --list
user.name=John Smith
user.email=jsmith@example.com
gc.autopacklimit=0

Name

diff

Synopsis

git diff first-commit [second-commit] [-- path ...]
git diff --cached [first-commit] [-- path ...]

Show the differences between two revisions. If paths are specified, restricts the comparison to only the given files or directories.

The default first-commit is HEAD.

The default second-commit is normally the work tree. With --cached, the default second-commit is the index.

Options

--name-only

--name-status

--stat (show diffstat instead of patch)

-a, --text

-M (detect renames)

-C (detect copies and renames)

--find-copies-harder

-R (reverse patch)

-w, --ignore-all-space

--exit-code

-Un, --unified=n

Examples

To see which changes are already staged in the index:

$ git diff --cached

To see which changes are in the work tree but not yet staged:

$ git diff

To see a summary of changes between two tags (v1.1 and v2.0):

$ git diff --stat v1.1 v2.0

To see the changes between v1.1 and the current work tree:

$ git diff v1.1

To see the changes between v1.1 and HEAD:

$ git diff v1.1 HEAD

Name

fetch

Synopsis

git fetch [remote-name]
git fetch repository [remoteref[:localref]]

Fetch commits from a remote Git repository and adds it to the local one.

In the first form, fetch all branches and tags from the given remote-name (a remote repository set up using git remote). The default remote name is origin.

In the second form, fetch a particular remoteref from repository and store it as local branch localref. The default localref is FETCH_HEAD. The default remoteref is HEAD.

Options

-f, --force

-n, --no-tags

-t, --tags

Examples

To fetch the latest Linux kernel release and compare it against your current work tree:

$ git fetch git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git linux-2.6 master
From git://git.kernel.org/...
* branch            master -> FETCH_HEAD
$ git diff FETCH_HEAD

To update all the remote tracking branches attached to the remote named origin:

$ git fetch origin
remote: Counting objects: 15, done.
remote: Compressing objects: 100% (10/10), done.
remote: Total 10 (delta 8), reused 0 (delta 0)
Unpacking objects: 100% (10/10), done.
From git://git.kernel.org/...
6544ab2..e3498f3  master     -> origin/master

To retrieve the branch test1 from someone’s repository and save it as the local branch mytest1:

$ git fetch git://git.kernel.org/... test1:mytest1

Name

gc

Synopsis

git gc [--prune] [--aggressive]

Pack the .git/objects directory to save disk space and increase speed.

git gc is run automatically from time to time, so it is rarely needed unless you want to use the --prune or --aggressive options or want to force packing to happen at a particular time (such as before making a backup).

Options

--aggressive (take extra time to save even more space)

--prune (delete unused objects)

Examples

To aggressively repack the current repository and save as much space as possible:

$ git gc --aggressive --prune
Generating pack...
Done counting 3299 objects.
Deltifying 3299 objects...
100% (3299/3299) done
Writing 3299 objects...
100% (3299/3299) done
Total 3299 (delta 2225), reused 0 (delta 0)
Pack pack-4eb8f89a145f826ef93923fe97c4ab23bd8abb62 created.
Removing unused objects 100%...
Done.

Name

gitk

Synopsis

gitk [git-log options...]

Display a graphical browser showing the Git history. gitk takes all the same options as git log.

Examples

To show the history of all changes to the mylib directory on branches test1 and test2, but leave out all changes that are included in v1.1:

$ gitk test1 test2 ^v1.1 -- mylib

Name

grep

Synopsis

git grep [-e] pattern [--cached|commit ...] [-- path ...]

Search the given commits for the given regular expression pattern(s).

If no commits are specified, normally searches the current work tree. With --cached, searches the index instead. If paths are specified, restricts the search to the given files or directories.

The main advantage of git grep over plain grep is that it ignores files (such as compiler output and editor backups) that have not been added with git add.

When multiple patterns are specified (using -e), the default combination is --or, unless --and or --not is specified.

Options

-e pattern

--and

--or

--not

(

)

-E (act like egrep)

-F (act like fgrep)

-i, --ignore-case

-v, --invert-match

-w, --word-regexp

-l, --files-with-matches

-L, --files-without-matches

Examples

To search the work tree for lines containing chicken without considering case:

$ git grep -i chicken

To search the top of branches test1 and test2 for lines containing alpha and either beta or gamma:

$ git grep -e alpha --and \( -e beta -e gamma \) test1 test2

To search only the mylib directory for files starting with the word chicken:

$ git grep '^chicken' -- mylib

Name

init

Synopsis

git init [-q] [--bare] [--shared=false|group|all]

Create a new Git repository in the current directory.

Options

-q, --quiet

--bare

--shared=false|group|all

Examples

To create a new repository with default settings:

$ git init

To create a new bare repository that will be shared with everyone in your Unix group:

$ git init -bare --shared=group

Name

log

Synopsis

git [revision ...] [-- path ...]

Show the commit history. If paths are specified, show only the history related to the given files or directories. If revisions are specified, show the history starting from the given revisions. The default revision is HEAD. With --all, the default is to show all revisions in all local branches.

Each revision can be specified in one of the following formats:

commit

Include the history for the given commit.

^commit

Exclude the history starting at the given commit.

a..b

Includes all commits in b that are not in a. Equivalent to b ^a.

a...b

Includes all commits in a and b that are not in both.

Options

--all

-p (show patch)

-Un, --unified=n

-a, --text

--raw

--stat

-M (detect renames)

-C (detect copies)

--find-copies-harder

-R (reverse patch)

-w, --ignore-all-space

-n, --max-count=n (show up to only n commits)

--pretty=(oneline|short|medium|full|fuller|email|raw|format:...)

--abbrev-commit

--full-history

--no-merges

--first-parent

--parents

--left-right

--graph

--author=regex

--committer=regex

--grep=regex

--reverse

Examples

To show the commits on this branch, starting with the most recent:

$ git log
commit 3ad3a1c1866bef36461d549d87fe39babe412d61
Author: John Smith <jsmith@example.com>
Date:   Sun Jan 18 18:41:32 2009 −0500

Make some changes.

commit 529fc80df85a5ec7c88552bcb27bc0770a84e336
Author: John Smith <jsmith@example.com>
Date:   Sun Jan 17 12:13:06 2009 −0500

Do the first thing.
...

To show what was changed by the most recent commit:

$ git log −1 -p
diff --git a/server/hello.html b/server/hello.html
index 63ede62..e26d280 100644
--- a/server/hello.html
+++ b/server/hello.html
@@ −1,17 +1 @@
...

To show all commits in all local branches where the commit message contains the word hello:

$ git log --grep=hello --all
commit 3ad3a1c1866bef36461d549d87fe39babe412d61
Author: John Smith <jsmith@example.com>
Date:   Sun Jan 18 18:41:32 2009 −0500

Undo changes to hello.html.
...

Name

merge

Synopsis

git merge commit ...

Merge one or more other branches into the current HEAD. For each specified commit, Git calculates the set of changes on that branch that are not currently in HEAD and attempts to apply those changes to the current HEAD. If the changes cannot be applied successfully, Git will leave conflicts in the index, which you will need to resolve by hand (using an editor, git add, and git commit).

Almost always, you will supply exactly one commit. In some situations, you may wish to merge more than one branch at the same time; this is called an octopus merge and is allowed only if none of the merges cause any conflicts. It is equivalent to merging the given commits one by one, except that the merged result produces only one new commit.

You can override the merge strategy to be used, but this is almost never necessary. When more than one commit is specified, the only allowed strategy is octopus.

Normally, Git combines the branch histories so git log will show all the commits from all branches that have been merged. With --squash, it eliminates the history of the branches other than HEAD. This simplifies the git log output, but prevents successful merges from that branch in the future, so it is usually a bad idea.

Options

--no-commit

--squash

--log

--no-ff

-s (resolve|recursive|octopus|ours|subtree)

-m msg

Examples

To merge feature branches feature1 and feature2 into your current branch using an octopus merge:

$ git merge feature1 feature2
Already up-to-date with
aa871d4ef9657e03b2ef7053dc13a16777955499
Trying simple merge with
bdd84225b4f7c282731aed540171e7cbe392c00d
Merge made by octopus.
58 files changed, 1371 insertions(+), 195 deletions(−)

To merge the branch production into the current HEAD, resulting in a conflict:

$ git merge production
Auto-merging testfile.c
Auto-merging server/hello.html
CONFLICT (content): Merge conflict in server/hello.html
Auto-merging test2.c
Recorded preimage for 'server/hello.html'
Automatic merge failed; fix conflicts and then commit the result.

To resolve the conflict above and commit the completed merge:

(edit server/hello.html)
$ git add server/hello.html
$ git commit

Name

mv

Synopsis

git mv oldfile newfile
git mv oldfiles ... newdir

Rename oldfile to newfile or move a series of oldfiles into the directory newdir, which must already exist. git mv updates both the work tree and the index.

Tip

There is no need for a git cp (copy) command. Just copy the file using Unix cp and git add. Git is still able to track the history of files moved and copied in this way.

Options

-f (overwrite even if newfile exists)

-n, --dry-run

Examples

To rename file1.c to file1b.c:

$ git mv file1.c file1b.c

To move file1.c and file2.c into the mylib directory:

$ git mv file1.c file2.c mylib/

Name

pull

Synopsis

git pull
git pull repository branch

Fetch the given branch then merge it into HEAD. git pull is just a short form for git fetch followed by git merge.

If no repository or branch is specified, git pull attempts to pull from the remote tracking branch associated with your current branch, if any. (Associations are set up using the --track option when creating a branch with git branch. You can also add them later with git config.)

The repository can be a local repository path, a repository URL (see git clone), or a remote name (see git remote). The branch must be a valid branch or tag name in the remote repository.

For more information about how pull works, see git fetch and git merge.

Options

--no-commit

--squash

--log

--no-ff

-s (resolve|recursive|octopus|ours|subtree)

--tags

--no-tags

Examples

To pull the latest Linux kernel changes into your current branch:

$ git pull git://git.kernel.org/pub/scm/linux/kernel/git/
torvalds/linux-2.6.git master
From git://git.kernel.org/...
* branch            master     -> FETCH_HEAD
Merge made by recursive.
21 files changed, 932 insertions(+), 66 deletions(-)

Name

push

Synopsis

git push [--all] [--tags] [repository [localref][:remoteref]]

Push changes from one or more branches or tags into the specified remote repository.

Repository can be a local repository path, a repository URL (see git clone), or a remote name (see git remote). If repository is omitted, it defaults to origin.

If localref is omitted, it defaults to pushing all the refs that currently exist on the remote. For example, if you have local branches named A, B, C, and D, and the remote has branches named A, C, and E, then Git will push branches A and C unless you specify a specific localref.

As an alternative to providing localref, you can provide --all or --tags. With --all, Git pushes all the local branches. With --tags, Git pushes all the local tags.

If remoteref is omitted, it defaults to the same name as localref. If you supply remoteref, it needs to be the full refname, such as refs/heads/master, not just the base branch name.

If you supply a remoteref without a localref, Git deletes remoteref in the remote repository. This is useful if the remote end refuses to update a ref because it is not a fast forward; you can delete the remote ref, and then re-create it.

Options

--all

--tags

--dry-run

--thin

Examples

To push the current branch (master) to the remote named origin:

$ git push origin master

To push all local branches to the default remote (origin), as long as they already exist there:

$ git push

To push all the local branches to a particular remote repository:

$ git push --all server:/git/myrepo.git

To delete the branch test1 on a remote named myremote:

$ git push myremote :test1

To push the current HEAD to a branch named test1 on myremote:

$ git push myremote HEAD:refs/heads/test1

Name

rebase

Synopsis

git rebase [-i] [--onto onto-commit] base-commit [switch-branch]
git rebase --continue | --skip | --abort

Automatically cherry-pick a series of commits between base-commit and switch-branch onto onto-commit, leaving the result in switch-branch.

If switch-branch is omitted, the default is HEAD. If onto-commit is omitted, the default is base-commit.

Warning

Using git rebase can completely disrupt future merges to and from the rebased branch. Use git rebase only for changing commits that have never been shared with others, such as before a new branch has been pushed to a shared repository.

git rebase is a powerful alternative to git merge. You can use it to simplify and rewrite the history of your changes in order to make them easier to review, audit, and share. However, because git rebase rewrites the history of your repository, misuse can cause hard-to-resolve errors, including duplicate commits and merge conflicts.

You can imagine git rebase as a series of commands that looks something like this:

git checkout switch-branch
git reset --hard onto-commit
for commit in base-commit..switch-branch
git cherry-pick commit
done

The end result is a new branch that contains onto-branch plus a linear series of commits (i.e., with no merges). The new commits consist of all the commits that were previously part of switch-branch but not base-commit.

With -i, git rebase opens an interactive editor before the rebase operation starts. The editor contains a list of all the commits in base-commit..switch-branch. You can rearrange the list, add/delete individual entries, or merge (squash) multiple commits into a single one, thus allowing you to produce a set of commits that is easier for others to review.

During a rebase operation, cherry-picking a particular commit may result in a conflict. In that case, you need to do one of the following:

- Resolve the conflict, commit it with git commit, and then run git rebase --continue.

- Run git rebase --skip to skip this commit entirely.

- Run git rebase --abort to cancel the rebase operation and change the Git history back to the way it started.

Options

-i, --interactive

--onto onto-commit

-p, --preserve-merges

Examples

To take all the patches in HEAD that are not in origin/master, and apply them on top of the current origin/master:

$ git rebase origin/master

To do the same as the above, but interactively reorder, edit, and squash the patches:

$ git rebase -i origin/master

To take all the patches in the feature1 branch that are not in origin/master, and add them on top of feature2, resulting in a new feature1:

$ git rebase --onto feature2 origin/master feature1

To do the same as the above in two steps for clarity:

$ git checkout feature1
$ git rebase --onto feature2 origin/master

To resolve a conflict that arose during the rebase operation:

(edit test1.c)
$ git add test1.c
$ git commit
$ git rebase --continue

Name

reflog

Synopsis

git reflog show [branch]

Show entries from the reflog, which tracks changes to local refs (branches). If branch is omitted, shows the reflog for HEAD.

The reflog tracks the “history of history.” Although commands like git reset can be used to undo a commit, the old commit still stays around in the reflog until it eventually expires. This allows you to undo many Git operations you might have performed by accident.

You can refer to entries in the reflog using branch@{n} notation. For example, HEAD@{5} means to use HEAD as it existed five changes ago.

Examples

To list all the recent changes to HEAD:

$ git reflog

To undo the most recent merge operation:

$ git reset HEAD@{1}

Name

remote

Synopsis

git remote add [-f] name repository-url
git remote rm name
git remote show name
git remote prune [--dry-run] name
git remote update [name ...]

Manipulate remotes, which act as short forms for tracking repository URLs and branches. This command takes one of several forms:

git remote add name repository-url

Register a new remote name at repository-url. With -f, also git fetch the set of remote branches from the new remote.

git remote rm name

Unregister the remote name.

git remote show name

Show information about the given remote name.

git remote prune name

Delete remote tracking branches that no longer exist on the remote name. To prevent accidental data loss, remote tracking branches in the local repository are never deleted unless you run this command.

git remote update [name ...]

Equivalent to running git fetch name for each of the names individually. If no names are provided, fetches all the registered remotes.

Examples

To show information about the remote named origin (which is created automatically by git clone):

$ git remote show origin
* remote origin
URL: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
HEAD branch: master
Remote branches:
master     tracked
production tracked
Local branches configured for 'git pull':
master     merges with remote master
production merges with remote production
Local refs configured for 'git push':
master     pushes to master     (up to date)
production pushes to production (local out of date)

To replace origin with a pointer to a new server and fetch the branches on the new server:

$ git remote rm origin
$ git remote add -f origin myserver:/git/myproj.git
Updating origin
From myserver:/git/myproj.git
* [new branch]      master     -> origin/master
* [new branch]      production -> origin/production

To update all registered remotes:

$ git remote update
Updating origin

Name

reset

Synopsis

git reset [--soft|--hard] [commit] [-- path ...]

If no paths are given, update HEAD to point at the given commit. This can be used to undo one or more commits as if they had never happened. If paths are given, HEAD is not changed; only the listed files and directories are modified.

Warning

git reset is extremely dangerous and can cause you to lose track of portions of your repository’s history. Use it only on branches that have never been shared with anyone else. If you make a mistake with git reset, you can usually undo it using git reflog.

With --soft, neither the index nor the work tree are modified, and only the HEAD pointer is changed. Thus, the difference between HEAD and the index is the set of changes needed to convert the new HEAD into the original HEAD. If you then run git commit, a new commit will be created that changes the files back to the way they were before you ran git reset.

With --hard, both the index and the work tree are modified to match the given commit; any changes from the given commit to HEAD are lost.

If neither --soft nor --hard is specified, then the index is updated, but not the work tree.

Examples

To undo the most recent commit without losing the changes to the files themselves (so they can be committed again):

$ git reset HEAD^

To change the current branch to point at the same place as origin/master, destroying anything else that might have happened in the current branch previously:

$ git reset --hard origin/master

To undo the above git reset operation by recovering the previous HEAD from the reflog:

$ git reset --hard HEAD@{1}

To undo the most recent five commits and recommit their changes as a single commit:

$ git reset --soft HEAD˜5
$ git commit

Name

revert

Synopsis

git revert [-n] commit

Create a new commit that reverses the effect of commit.

Options

-n, --no-commit

-s, --signoff

Examples

To undo the most recent commit:

$ git revert HEAD
[master ae3f932] Revert "Say hello."
1 files changed, 0 insertions(+), 50 deletions(-)

To undo commit ae3f932, even if it is not the most recent commit:

$ git revert ae3f932
[master ae3f932] Revert "Say hello."
1 files changed, 0 insertions(+), 50 deletions(-)

Name

rm

Synopsis

git rm [-f] [-r] -- path ...

Remove files from the work tree and index. They will be permanently removed when you run git commit.

With -f, forces removal of a file even if it doesn’t match HEAD. With -r, removes entire directories and all their contained files.

Options

-f (force)

-r (recursive)

--cached (ignore work tree)

-n, --dry-run

Examples

To remove the mylib directory:

$ git rm -r mylib
rm 'mylib/test1.c'
rm 'mylib/test2.c'

Name

stash

Synopsis

git stash
git stash list
git stash show [stashid]
git stash apply [stashid]

Save, list, or reapply the set of uncommitted changes from a work tree and index.

This command takes one of four forms:

git stash

Save the current set of uncommitted changes and undo them. The index and work tree are reset to match HEAD.

git stash list

Show the list of all stashes that have previously been saved.

git stash show [stashid]

Show the exact set of changes that are saved as stashid. If stashid is omitted, uses the most recently saved changes.

git stash apply [stashid]

Brings back the changes from the given stashid and applies them to the current index and work tree. If stashid is omitted, uses the most recently saved changes.

Examples

To save the current set of uncommitted changes, switch branches, and apply those changes to the new branch:

$ git stash
Saved working directory and index state "WIP on master: 44951b7... Say hello"
(To restore them type "git stash apply")
HEAD is now at 44951b7 Say hello

$ git checkout feature1
Switched to a new branch "feature1"

$ git stash apply
Removed test1.c

Name

status

Synopsis

git status [path ...]

Check what would happen if you ran git commit. If paths are specified, check what would happen if you ran git commit paths.

Examples

To check the status of the current branch:

$ git status
# On branch master
# Changed but not updated:
#   (use "git add <file>..." to update what will be
committed)
#
#       modified:   test1.c
#       modified:   test2.c
#
no changes added to commit (use "git add" and/or "git
commit -a")

To see what would happen if you ran git commit test1.c:

$ git status test1.c
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   test1.c
#
# Changed but not updated:
#   (use "git add <file>..." to update what will be
committed)
#
#       modified:   test2.c
#

Name

tag

Synopsis

git tag [-a|-s|-u gpg-key-id] [-f] [-m msg | -F msg-file]
tagname commit
git tag -d tagname
git tag -l [glob-pattern]
git tag -v tagname ...

Manipulate tags. A tag is simply a user-friendly name for a particular commit. The command takes one of four forms:

git tag [-a|-s|-u gpg-key-id] [-m msg | -F msg-file] tagname commit

Create a new tag named tagname based on the given commit. With -a, the tag is annotated (i.e., it has a commit message attached) but not signed. With -s or -u, the tag is annotated and signed with the default or specified gpg private key, respectively. With -m or -F, use the given commit message or filename containing the commit message, respectively. If none of -a, -s, or -u is specified, the tag has no annotation. (Tags you shared with other people should always have an annotation and should usually be gpg signed.)

git tag -d tagname

Delete the given tagname from the local repository. Note that if the tag has already been pushed to a remote repository, there is no way to make sure everyone erases it.

git tag -l [glob-pattern]

List all the tags matching the glob-pattern. If glob-pattern is omitted, lists all the tags.

git tag -v tagname ...

Verifies the gpg signature of each requested tag.

Examples

To mark the current version with a v1.1 tag and sign it with your gpg key:

$ git tag -s v1.1 HEAD

To delete the v1.1 tag (only useful if it has never been pushed):

$ git tag -d v1.1

To list all tags for version 1.x:

$ git tag -l 'v1.*'

Chapter 15. Virtualization Command-Line Tools

This chapter covers common tools used with Linux to run many virtual servers on a single physical server. We cover the two dominant hypervisors used with Linux: Xen and KVM. We also cover libvirt-based tools used to manage both Xen and KVM. Although it isn’t strictly a Linux solution, VMware uses a Linux operating system for the Service Console of their ESX server and recent vSphere products, so we have included basic console commands they provide.

This chapter covers the following topics:

- Conceptual overview

- Basic virtualization operations

- The Xen Hypervisor

- The KVM Hypervisor

- The libvirt virtualization API

- VMware command line interface

We do not provide a tutorial or in-depth information on virtualization here. This is meant as a quick reference to virtualization concepts, commands, and utilities. Refer to the following locations for more in-depth coverage on each of these technologies.

The Xen hypervisor

http://www.xen.org/

The KVM hypervisor

http://www.linux-kvm.org/

libvirt virtualization API

http://libvirt.org/

VMware Documentation

http://www.vmware.com/support/pubs/

Conceptual Overview

All of the virtualization programs we cover in this chapter provide full system virtualization. They use a software layer to present a virtualized hardware system. This layer, called the virtual machine monitor (VMM) or hypervisor, makes it possible to run multiple operating systems simultaneously. The operating system at the base — running directly on the hardware and interacting with it directly — is called the host, and the software instances that run on top of it — interacting only indirectly with hardware — are called the guests.

Virtualization isn’t a new topic. As a means to divide a computer’s resources into multiple running environments, virtualization has been around since the 60s. Back then, IBM used it to partition mainframe computers into separate virtual machines, allowing it to run multiple applications and processes simultaneously. Although low-cost PC hardware generally replaced mainframe hardware virtualization in the 80s and 90s, virtual machines were still commonly used to provide a virtualized environment for a process: e.g., creating a security sandbox or providing greater portability. The Java Virtual Machine (JVM) is a good example of process virtualization. This kind of virtualization also includes tools like chroot and virtfs.

Another popular type of virtualization creates a new instance of the same operating system on top of the host. This technology is often called containers. It typically includes such projects as Solaris Zones and User Mode Linux (UML). We don’t cover containers in this chapter.

Here, we cover the tools of industrial-strength server virtualization. The solutions in this chapter offer environments that look like complete, independent hardware computers even though they are just software instances running on a common hardware base. While hardware costs for PCs remain fairly low, systems with multiple CPUs or CPU cores can easily handle the task of running dozens of highly available virtualized servers simultaneously. Businesses use virtualization to reduce deployment and administration costs. Many businesses also use virtualized-desktop systems to replace physical desktops, simplifying management tasks throughout the company.

Configuring virtualization requires administrative access to systems, CPUs with built-in virtualization technology, or even modified operating systems. The tools covered here are intended for large-scale server deployments. Although these tools might allow you to run an alternative operating system on your desktop or notebook, if you are just looking to run a single guest you will find that easier to do with another kind of tool. VMware Player or VirtualBox, for example, both run in user space, require no kernel modifications or special CPU, and are available for free.

System Requirements

To run the tools covered in this chapter you should have at minimum:

- A processor that supports virtualization technology (Intel VT or AMD-V). Support should be enabled in the system BIOS.

- At least 2 GB of memory.

- At least 6 GB of disk space.

Xen can run paravirtualized guests without virtualization technology in the CPU, but it requires it for full virtualization. You can check whether your existing CPU supports virtualization by grepping /proc/cpuinfo as follows:

$ egrep '(vmx|svm)'  /proc/cpuinfo

If nothing shows up, your CPU does not support virtualization. If something does appear, you may still need to enable it in BIOS to use it.

Each solution has additional requirements or limitations. Before making a hardware purchase you should check the requirements and supported hardware for the solution you plan to use.

If you want to support migration (moving a running guest from one host to another) you will also want some kind of shared-storage solution. That might be an iSCSI or SAN volume to which all servers have access. You don’t need that to get started though.

Virtualization Technology

In full virtualization, the guest operating system doesn’t need to be aware that it is running in a virtual environment. It interacts with the virtual hardware in the same way it would physical hardware. Some tasks in a fully virtualized environment, however, are computationally expensive. One way to handle the expensive tasks is to use a modified processor that performs these tasks for the hypervisor.

Paravirtualization provides another way to handle these expensive tasks. In paravirtualization the guest operating system is modified to hand these expensive tasks to the hypervisor, which can handle the task without having to emulate hardware.

Network Concepts

For your virtual server to connect to the Internet it must have a way to use the physical connection of the host. Xen, KVM, and VMware will all create a default bridge interface to handle mapping the virtual systems to the physical interface. A virtual machine could also be assigned directly to a physical device, but for most situations a bridge is what you want. More complex network configurations can be made by defining a kind of virtual switch or router. We will cover some commands that can do this here.

libvirt Tools and Terminology

Xen, KVM, and other Linux-based hypervisors support a single generic API called libvirt. For most tasks, it doesn’t matter which Linux hypervisor you are using. You can use the same basic tools. libvirt has its own terminology which will be helpful to know when reading the libvirt section.

- A node is a single physical machine.

- A hypervisor is a layer of software that virtualizes a node, providing a set of virtual machines that may differ from the node itself.

- A domain is an instance of an operating system running on a virtualized machine provided by the hypervisor.

Throughout this chapter, though, we’ll stick to more common industry terminology, referring to a domain as a guest and the node running the guest as a host.

Basic Virtualization Operations

The complexity of virtualization prevents us from covering everything in a small chapter within this book. Fortunately, developers have written tools that handle much of the complexity for you. They have worked hard to make the defaults do the right thing for your system and have written scripts to simplify the tasks. Here we cover the higher-order tools that will help you create and manage virtual systems and networks.

Creating Virtual Systems

For VMware you will use the VI Client GUI interface to create your virtual systems. We won’t cover that task here. With Xen and KVM you can use virt-manager’s virt-install to install a new guest. At minimum you must tell virt-install:

- the name of the new guest domain

- whether the guest will be paravirtualized or fully virtualized (-p or -v)

- the amount of RAM to give to the new system (-r)

- what to use as a system disk and if creating a disk, how large it should be (-f and -s)

- whether to support graphics or not (--vnc or --nographics)

- where to find the installation files (-c, -l, or --pxe)

virt-install will prompt for any values you do not provide to it on the command line. The name should be a short unique identifier; whatever helps you distinguish it from other virtual machines controlled by the same hypervisor. Paravirtualization or full virtualization depends on what your OS supports. If you do not have an installation already prepared for virtualization, you need full virtualization.

The system disk can be stored anywhere in your filesystem. Use a full path to specify where, or just a filename to have it stored in the default location for your hypervisor.

You will need a way to connect to the new system. See the section Graphic and Console Interfaces in Graphic and Console Interfaces. If you are installing a fully virtualized system, use the --vnc option. If you aren’t installing on a system running X Window System, you may need to connect to your guest remotely from a system that does. If you are installing a paravirtualized system and the guest system supports it, you can use either --vnc or --nographics. If using --nographics fails, you may need to use virsh to destroy the domain and start over as you will have no way to connect to it.

What you use for installation files will depend on what kind of virtualization you are using. For a fully virtualized system you may want to install from a CDROM drive or an installation disk ISO. You can use the -c option to point to a physical device on the host (/dev/cdrom) or to an ISO file.

To install a paravirtualized Linux or UNIX system, you will instead use the -l option with virt-install to point to the location of the initial boot image. For some distributions, you can point this to an ISO image, but the -l option does not configure a virtual CDROM, so after the boot you will need to tell the install program where to find a mirror of the installation media. You can use HTTP, NFS, or FTP to connect to that media. This means you will have already had to have set up a server to provide these files. You can quickly prepare an installation ISO for this by mounting it via the loop back device and either exporting the directory via NFS or serving the files through HTTP. We’ll provide examples.

virt-install has many other options that can help you customize your virtual server. If you are using KVM, you might want to use the --accelerate option to better take advantage of the hypervisor. You might want to use --os-type option to optimize guest configuration. You can provide more detailed information on how to configure the network interface (without any options, it just connects the guest to the default bridge interface). See virt-install’s entry in this chapter for further information.

Some distributions come with wrapper-scripts that call virt-install with default options to install a basic Linux operating system. Ubuntu, for example, provides a vm-builder script that will install a stripped-down version of Ubuntu, ready to run.

Examples

Mounting a Red Hat ISO for export via NFS:

# mkdir /mount/rhel5.3
# mount -o ro,loop RHEL-5.3.iso /mount/jeos-8
# exportfs *:/mount/rhel5.3/

Mounting a Red Hat ISO for HTTP access:

# mkdir /var/www/html/rhel5.3
# mount -o ro,loop RHEL-5.3.iso /var/www/html/rhel5.3

Full virtualization install from an installation iso:

# virt-install -name rhel-fv -v -r 256 -f /images/rhel-fv.img -s 8 -vnc \
-c RHEL-5.3.iso

Paravirtual installation via HTTP using a serial console:

# virt-install -name rhel-pv -p -r 256 -f /images/rhel-pv.img -s 6  \
--nographics -l http://example.com/rhel-5.3/

Managing Virtual Systems

While hypervisors can control the starting and stopping of virtual machines, they can’t always shut them down gracefully. You may want to power off your systems by connecting to each system and initiating a shutdown in the normal way. Sometimes you can’t do that, though, and you need to do the virtual equivalent of pulling the plug on a system that isn’t responding. The commands listed here cover these basic operations.

Xen and KVM virtual guests can be managed with virsh commands. Use virsh list --all to get a list of all managed domains. The start, shutdown, reboot, and destroy commands are your virtual power and reset buttons. From the service console in Vmware’s ESX server you can do similar things with vmware-cmd.

Graphic and Console Interfaces

You need some way to interact with the virtual systems. Generally, you will use a VNC or SDL graphic interface set up by your guest installation tool. VMware provides its own client software to handle this. For Xen and KVM you will likely use the VNC client virt-viewer or the GUI management tool virt-manager to connect to a virtual system. As an alternative, you could interact with a virtual system through a text-based console connected to a virtual system’s serial device. The virt-install command has a --nographics option that will attempt to set this console up for you, but it works only with paravirtualized guests. If your guest system has a properly functioning network connection, you may also be able to use ssh to connect to it.

Configuring Networks

Your basic network options are to use bridging or Network Address Translation (NAT). In bridging, a special bridge interface transparently connects your virtual interfaces to your host’s physical interface(s). Your virtual servers will share the physical interface.

Using NAT, your virtual servers are assigned private network IP addresses, and another interface then provides the NAT for your system. This NAT interface is essentially a bridge as well. A bridge is really any interface used to hook your virtual interfaces up to your physical interfaces. Still, these two approaches are commonly referred to as bridging and NAT.

VMware uses a third option. It creates a virtual switch to which you connect your guests’ interfaces. The default switch, however, simply bridges the switch to the server’s network interface card. Neither Xen or KVM come with a ready-made virtual switch solution, although some vendors may offer virtual switch solutions you could add to your system.

Upon installation of the hypervisor and libvirt, most distributions will automatically configure basic networking support. They will likely configure both a NAT and bridge interface. Xen’s tools will use the bridge interface by default, but virt-manager’s tools will likely use NAT.

The approach you want to use will depend on the kind of system on which you have installed the host operating system. If you are installing on a system that might frequently change networks (for example, a notebook you move between home and work) or want to keep your virtual systems separate from your physical network, you will probably want NAT. If you are using a wireless card, you must use NAT. Bridging will not work with wireless interfaces because wireless chipsets reject foreign MAC addresses. If you are installing on a server and want your virtual systems to interact with your network the way any physical system would, you want to use bridging.

While we don’t cover it in this chapter, the Net:Bridge or (bridge-utils) package contains the brctl command. This command can help you build and manage more complex bridges. You can find more information on this package at:

http://www.linuxfoundation.org/en/Net:Bridge

We highly recommend you read that page and explore the tool if you want to dig any deeper into configuring your bridges.

The basic concept to keep in mind for virtual networking is that your host systems will have interfaces for physical devices, virtual devices, and bridge devices. What they are named by default depends on your distribution and hypervisor. The following are the interfaces you might find running if you used ifconfig on a CentOS system running Xe0.

vifX.Y

A vif interface on the host connects to the virtual interface on a guest domain. Consider it the server’s representation of that virtual Network Interface Card (NIC). vif0.0 is Domain-0’s first interface. vif0.1 would be its second. vif1.0 is the first interface on the first running guest (Domain 1).

eth0

The virtual interface for Domain-0, which is connected to vif0.0.

peth0

This device performs packet distribution for guest systems, including Domain-0. It is bound to the bridge device, the physical network card. It has no IP address of its own, but instead acts as a simple switch. This is how packets get to the appropriate vif device.

xenbr0

Xen’s default bridge device that connects vif interfaces to the physical interface (peth0).

virbr0

An interface providing NAT. This is the default bridge device for virt-manager tools. You may need to enable packet forwarding in Domain-0 to make this device work.

You will likely find these devices on an Ubuntu system running KVM:

eth0

The physical interface for the host. Note that it doesn’t have an IP address. The host’s interface is bridged to this device.

vnet0

An interface providing NAT. The default bridge device for virt-manager.

vnetX

Interfaces connected to a guest’s virtual interface, where X is numbered 1 or higher. These are bridged through vnet0 by default.

br0

The host system’s bridge device. This one has the host’s IP address and connects to the physical interface, eth0.

You can set the interface to be used by a virtual domain when using virt-install with the --network option.

MAC Addresses

You may want to set a MAC address on a virtual interface manually. This is a special hexadecimal number that uniquely identifies your interface card. If not set, your configuration tool will generate a random number for it, but knowing what it will be ahead of time can help you configure DHCP or a PXE boot. With -virt-install you can set it with the --mac option. VMware’s VI Client provides an option as well.

There are some restrictions. The first three sets of numbers in a MAC address identify the vendor. When setting them, use the following vendor addresses:

Xen

00:16:3e

KVM/Qemu

54:52:00

VMware

12:50:56 AM

Making Changes to Virtual Machines

VMware’s VI Client can be used to edit virtual machine configurations. Making changes to a virtual machine under Xen or KVM can be a little trickier. You can make some changes (such as memory settings) using xm or virsh. For more complex changes with Xen, you could change the configuration files located under /etc/xen/. These are in a text format, and most of the settings you will want to change will be easy to figure out.

virsh provides one common way to make complex changes:

1. Run virsh dumpxml to get an XML configuration file for the domain you wish to change.

2. Use a text editor to edit the XML file.

3. Shut down the virtual system if it is still running.

4. Run virsh define to remove the old configuration from the hypervisor and replace it with the configuration in your edited XML file.

You can now start the domain with your new configuration.

Creating and Manipulating Disk Image Files

Tools such as virt-install will create disks as needed when installing a new virtual server, but you might want to add a disk to an existing server. One common form of disk image for virtual machines is a sparse file. The simplest tool for creating this is the dd command documented in Chapter 3. For instance, to create a 10,000 MB sparse file suitable for use as a disk image you can use the following command:

# dd if=/dev/zero of=newdisk.img bs=1M seek=10000 count=1

Change the system’s configuration file to add the new drive. You can use the guest’s system tools (such as fdisk) to configure the new disk.

You can easily increase the size of a sparse file by using dd to create a new sparse file then append the existing file with the new file. Don’t try this with an image file currently in use by a running guest, though: shut down the guest system first. Here we use dd and cat to add a 5000 MB extension to the original image.

# dd if=/dev/zero of=diskextension.img bs=1M seek=5000 count=1
# cat diskextension.img >> newdisk.img

You will need to use a tool appropriate to the guest operating system to take advantage of the new space. For example, resize2fs makes the space available to an ext3 filesystem.

For more advanced features on a disk image, you can use qemu-img, a tool we don’t document here. It can create and convert disk images to a several different formats, including to VMware’s .vmdk format. If you are using KVM you should already have it installed on your system. If you do not, you can install it via the qemu package.

Xen

Xen is the most common hypervisor used on Red Hat Advanced Server 5, Fedora, and distributions based on these, such as CentOS 5. Assuming you are using one of these, to use Xen you must install the xen and kernel-xen packages from your package repository:

# yum install xen kernel-xen

Other operating systems will probably have similar packages. Some offer a groupinstall that will include all the necessary packages:

# yum groupinstall Virtualization

Once installed, reboot your system using the Xen kernel. You may want to modify your /boot/grub/grub.conf file to boot the Xen kernel by default. Usually this means changing the default= entry to default=0, where 0 refers to the first boot configuration described by the file. See Chapter 4 for details on configuring grub and modifying the grub.conf file.

The installation of the previously mentioned packages should also configure two services to run: the Xen daemon (xend) and the xendomains script that the system uses to automatically start and stop your guest domains.

Once the new kernel and xend service is running, you should be able to run the command

# xm list

to list your current nodes. At first you will have one domain running, Domain-0.

To understand Domain-0, it helps to know that your system is not really running Linux directly. It’s running Xen’s own kernel, a virtual machine monitor based on the Nemesis microkernel. Xen’s kernel doesn’t provide an administrative interface; it depends on a modified operating system running as a guest to do this. This privileged guest also provides guest domains access to hardware devices. In our case, Domain-0 is running a modified version of Linux. Your OS is actually the controlling domain in a cluster of guest domains.

In Xen, these other guest domains are referred to as unprivileged domains, or DomU (the U stands for unprivileged). Domain-0 can also delegate control of hardware devices to other privileged domains, but that’s a more advanced topic we won’t cover here.

Paravirtualization and Architecture

Xen supports paravirtualized guests that run on the same architecture as Domain-0. Thus, if Domain-0 is running X86_64, paravirtualized guests must be X86_64 as well. To run a 32-bit guest on a 64-bit system, you must run it fully virtualized.

Like Domain-0, paravirtualized Linux guests run the Xen kernel instead of the regular kernel.

Xen Networking

Mixing libvirt and Xm tools can lead to some confusion when it comes to networking. Guest domains installed using Xen’s tools bridge to device xenbr0 by default. Those installed by libvirt’s virt-install bridge to device virbr0. To cut down on confusion and take full advantage of libvirt, you may want to disable Xen’s bridge networking altogether. Details on how to configure networking for Xen using libvirt can be found on the libvirt wiki: http://wiki.libvirt.org/page/Networking. Altertnatively you can tell virt-install to bridge to device xenbr0 using the -w option (-w bridge:xenbr0).

Xen Commands

Xen has its own special commands for installing and managing domains, but for most things you can use the libvirt tools documented in this chapter. Here, we will cover the most commonly used xm subcommands and the xentop command.

Name

xm

Synopsis

xm [options] command

Xen hypervisor management interface. Generally you will use virsh to control VMs, but there are a few useful functions you can get from xm but not virsh. We cover the most common commands here.

xm can be used to configure virtual machine access rights and security policies. Policies are given labels and the labels applied to domains. This is an advanced topic we do not cover in this book.

Commands

console domain

Connect to serial console on domain, if available. Use ctrl-] to exit a console.

create [-c] configfile [settings]

Start the guest domain described in configfile. This command is generally used to start a previously installed domain that is not currently running. By default, a domain will have a configuration file of the same name in /etc/xen/. You can specify the configfile with a full path, or a path relative to /etc/xen/. The configuration file, a Python executable file, largely consists of name=value pairs. These can also be given in a space--separated list on the command line. The manpage for xmdomain.cfg contains details on configuration file format and valid entries. The -c option causes xm to connect to the console as soon as the machine starts.

destroy domain

Immediately kill any running instance of the domain and free its resources to the hypervisor. (You usually want to use shutdown instead.)

dmesg [-c]

Print the Xen message buffer. This buffer contains informational, warning, and error messages. The -c option clears the message buffer.

help [--long]

Print a list of xm commands. If --long is given, print all commands grouped by function.

info

Print information about host system.

list [options] [domains]

List information about one or more domains (a space-separated list of domain names, ids or UUIDs). This is a more verbose listing than that provided by libvirt. It includes resource allocation and running time information.

Options

-l, --long

Print detailed information about domains in a format that can easily be consumed by external programs.

--label

Include security label information.

log

Print the contents of the xend log. This log is also found at /var/log/xen/xend.log.

top

Run the xentop command (described next).

list [options] [domains]

List information about one or more domains (a space-separated list of domain names, ids or UUIDs). This is a more verbose listing than that provided by libvirt. It includes resource -allocation and running time information as well as state. There are six possible states: running, blocked, paused, shutdown, crashed, and dying.

Options

-l, --long

Print detailed information about domains in a format that can easily be consumed by external programs.

--label

Include security label information.

pause domain

Cease hypervisor scheduling for domain.

shutdown [options] domain

Begin a graceful shutdown on domain. For guests that support this, it is the same as running shutdown on the guest. It may not succeed. By default, the command does not wait for the shutdown to complete. xm list will reveal the guest’s current state.

Options

-a

Print detailed information about domains in a format that can easily be consumed by external programs.

-w

Wait for domain to complete shutdown before exiting.

unpause domain

Resume hypervisor scheduling for domain.

Name

xentop

Synopsis

xentop [options]

Provide frequently updated information about current domains. This program performs a function similar to the Linux top command, only with information about the hypervisor and domains instead of processes. Its various options change what information is displayed. Like top, xentop also has some interactive commands to change what information xentop displays as it runs.

Options

-b, --batch

Run in batch mode; don’t accept command-line input. Useful for sending output to another command or to a file.

-d seconds, --delay=seconds

Set the delay between refreshes. Default is 3.

-i num, --iterations=num

Update display num times, then exit.

-n, --networks

Show network information.

-r, --repeat-header

Repeat the table header before each domain.

-v, --vcpus

Show virtual CPU information.

-x, --vbds

Show virtual block device information.

Interactive commands

All interactive commands are case-insensitive.

B

Toggle display of virtual block device information.

D

Prompt for a new delay setting.

N

Toggle display of network information.

Q, Esc

Quit.

R

Toggle display of table header before each domain.

S

Change sort order by cycling through the available columns.

V

Toggle display of virtual CPU information.

Up, Down

Scroll through displayed domains.

KVM

The Kernel-based Virtual Machine (KVM) is a full virtualization hypervisor for Linux. The work of the KVM hypervisor is handled by the Linux kernel. Each guest in KVM runs as a process and can be managed by Linux tools such as top and kill.

KVM isn’t a complete virtualization solution. It depends on both the libvirt tools for management and the open source processor emulator QEMU for hardware emulation. Therefore, you will need those installed as well.

KVM is the most popular hypervisor on Ubuntu distributions. Assuming you are using Ubuntu, you can use apt-get to install the necessary packages:

$ sudo apt-get install kvm libvirt-bin ubuntu-vm-builder qemu bridge-utils

You may also want the virt-viewer and virt-manager packages, though these will require the X Window System as well. As of Ubuntu version 8.10 (Intrepid) you can install the meta package ubuntu-virt-server for the basic tools mentioned previously and ubuntu-virt-mgmt for the GUI management tools.

You will likely want to provide your controlling user account with access to network devices created by libvirt. Use usermod to add your account to the libvirtd user group.

Restart your system. If all goes well, you should be able to run the following command without error:

$ virsh -c qemu:///system list

Also check to make sure KVM is working:

sudo kvm

This will confirm that you have enabled virtualization support in BIOS properly.

QEMU

QEMU is really its own virtualization solution that works in user space. Combining it with KVM speeds it up considerably, providing a robust hypervisor running at the kernel level. QEMU comes with some of its own commands for the installation and launching of virtual systems. Some older tutorials show how to use them. We won’t cover those here; instead use libvirt tools to handle these tasks.

Ubuntu Builder Scripts

Ubuntu comes with tools to help you quickly build guest systems. In older systems these tools are in the ubuntu-vm-builder package; in newer systems, they are in the python-vm-builder package. These tools handle the defaults for installing a simple Ubuntu guest. In most cases all you need to provide is a name for your new domain.

libvirt and Red Hat Virtual Machine Manager

The libvirt virtualization API provides an open source programming interface to hypervisors like Xen and KVM. It comes with virsh, a management interface for controlling hypervisors. A closely related project, the Red Hat Virtual Machine Manager application, is a collection of tools built using libvirt. This includes a few command-line tools as well as the GUI virt-manager application.

Whether you are using Xen or KVM, these libvirt based tools will handle most of the tasks of creating and managing your guests. Except for some minor differences in what each hypervisor supports and the connection string used to get to the hypervisor, these commands work the same regardless of what hypervisor you choose. You’ll want to know these tools well.

XML Configuration Files

libvirt uses XML files to define or describe the capabilities and configuration of domains, networks, and hardware devices. Many of the command tools expect to receive information from an XML file. You don’t have to know the XML tags to get started, as the tools will build the required files for you, but you may want to edit an XML file directly to change the configuration of a guest.

The XML formats, as well as more in-depth information on virsh and the API, can be found on the libvirt website: http://libvirt.org.

Connection URIs

To control a hypervisor, libvirt tools must first connect to it. You will use a URI to specify the location of the hypervisor. For KVM use a qemu:// URI and for Xen use xen://. For backwards compatibility virsh will also accept just plain xen, which it will treat as xen:///. If no connection option is given, virsh will try to connect to the URI given in the environment variable LIBVIRT_DEFAULT_URI. If none exists, it will probe the defaults in whatever hypervisor drivers it has available.

You can also make a connection to a remote server. For security reasons you will usually use SSH to do this by using an xen+ssh:// or qemu+ssh:// URI.

Connection URI Examples

Connect to the local Xen hypervisor:

xen:///

Use SSH to connect to the Xen hypervisor running on xenhost.yoyodyne.com:

xen+ssh://xenhost.yoyodyne.com/

Connect as root to the local KVM hypervisor:

qemu:///system

Connect as an unprivileged user to the local KVM hypervisor:

qemu:///session

Use SSH to connect as user john to the KVM hypervisor on kvmhost.yoyodyne.com.

ssh+qemu://john@kvmhost.yoyodyne.com/system

Remote GUI control

Installing the X Window System on your server nodes will consume resources you might rather give to a virtual machine, as well as increase the security risk to your servers. Instead, consider creating a server to control your nodes. That system can be a desktop system with a full X Window installation. Install the libvirt tools and virt-manager to that system and use a URI connection string to connect to your client. Using SSH will keep the connection secure. Use the VIRSH_DEFAULT_CONNECT_URI environment variable to hold the connection string. virsh will look there before trying the default connection URIs.

You may have problems connecting with virt-manager over SSH. If you launch virt-manager as an unprivileged user, it will usually try to switch you to the root user. This will clear environment settings like your ssh-agent settings. If prompted for the root password, select the “run unprivileged” option. This will preserve your current SSH settings. You don’t need to run as root because you aren’t controlling a hypervisor on the local system. For privileged access you will connect to a privileged user on the remote node.

At this time, virt-manager does not support creating new guests on remote systems. But you can manage your system just fine.

IP Forwarding and libvirt Networking

libvirt’s default network configures an isolated bridge device to be used by guest domains. This default bridge creates a private network for the virtual machines, but does not connect that private network to your physical network. The simplest way to complete that connection is to enable IP Forwarding in the kernel. You can quickly enable IP Forwarding using sysctl like so:

# sysctl -w net.ipv4.ip_forward=1

To set your system to enable IP forwarding upon bootup, edit the net.ipv4.ip_forward setting in /etc/sysctl.conf.

While IP forwarding can get you running quickly, for production environments you probably want to configure a more robust bridge network. Information on creating bridge networks for libvirt can be found on the libvirt wiki at:

http://wiki.libvirt.org/page/Networking

libvirt and Virtual Machine Manager Commands

Name

virsh

Synopsis

virsh [options] [command [command-options]]

libvirt management interface. virsh uses the libvirt API to connect to a hypervisor and manipulate the configuration and state of virtual machines controlled by that hypervisor. If invoked with a command, it will execute the command and then exit. If invoked without a command, virsh enters a shell mode from which you can execute commands.

This manager will work with any hypervisor that has libvirt support. However, not all virsh commands are supported by all hypervisors. Nor will they work on all guests. Still, if a hypervisor can do something, you can generally use virsh to do it. Some hypervisors, including Xen, come with their own tools for managing virtual machines, but we still recommend you use virsh instead.

Most virsh commands expect a domain option. A domain refers to a virtual machine. You can use the virtual machine’s name or UUID. If the machine is running, it should also have an ID number within the hypervisor, and you can use this for the domain option as well. Use the list command to see names and IDs of domains managed by the hypervisor.

Options

--c uri, --connect=uri

Connect to a hypervisor specified by uri.

-d level, --debug=level

Set the level of debugging information to be printed to standard output. Accepted values are 0–5. 0 disables debugging messages and is the default. 5 prints all debugging messages.

-h, --help

Print a brief description of options and commands.

-l file, --log=file

Log debugging information and errors to the specified file.

-q, --quiet

Quiet mode. Do not print informational messages to standard out.

-r, --readonly

Connect to hypervisor in read-only mode.

-t, --timing

Print timing information.

-v, --version

Print version information, and exit.

Commands

attach-device domain xmlfile

Attach device defined in xmlfile to domain.

attach-disk domain source target [options]

Attach disk device to domain. source and target are paths for the files and devices.

Options

--driver name

Set the driver name attribute. Valid values include file, tap (network tap), or phy (physical).

--subdriver type

Set the driver type attribute. The valid values depend on the driver. It’s common to use aio with the tap driver.

--mode mode

Set the mode of device. Valid values include readonly and shareable.

--type type

Set the type of device. Valid values include cdrom and floppy.

attach-interface domain type source [options]

Attach interface device to domain. Usually type will be either network or bridge. The source is the host’s network or bridge device to which the virtual network should connect, or default, to use the default gateway.

Options

--mac macaddress

Assign an address to the virtual interface.

--target name

Assign the target interface name to use in the guest.

--script path

Provide the path to a script to handle the bridge.

autostart [--disable] domain

Automatically start domain at system boot.

capabilities

Print hypervisor capabilities in XML format.

connect [uri] [--readonly]

Connect or reconnect to a hypervisor.

console domain

If a serial console is available on domain, connect to it. Use ctrl-] to exit a console.

create xmlfile

Start a domain described in the specified xmlfile.

start domain

Start an inactive domain.

destroy domain

Immediately kill any running instance of the domain and free its resources to the hypervisor. (You usually want to use shutdown instead.)

define xmlfile

Add persistent domain information described in the specified XML file. The domain is added but not started.

detach-devicedomain file

Detach device defined in file.

detach-disk domain target

Detach disk device target from domain.

detach-interface domain type [--mac macaddress]

Detach network interface from domain. Use macaddress to distinguish between multiple interfaces of the specified type.

domblkstat domain device

Print basic stats for block device on domain.

domid domain

Given the domain name, print the domain’s ID.

domifstat domain interface

Print basic stats for network interface device on domain.

dominfo domain

Print basic information on domain.

domuuid domain

Print the domain’s UUID.

domname domain

Given the domain ID, print the domain’s name.

domstate domain

Print the domain’s state.

dump domain file

Dump domain’s core to file.

dumpxml domain

Print the domain’s information in XML. Output is suitable for use with the create and define commands.

freecell [number]

Print available memory on the machine, or if specified, available memory in Non-Uniform Memory Access (NUMA) cell number.

help [command]

Print a list of available commands or information on a specified command.

hostname

Print the hypervisor’s hostname.

list [option]

Print a list of active domains and their current state. Use option --inactive to list inactive domains, or --all to list both active and inactive domains. There are six possible states: running, blocked, paused, shutdown, crashed, and dying.

migrate [--live] domain destination [transport]

Migrate a domain to a new destination host. The destination should be given as a connection URI. If the transport method differs it can be given as a separate URI, though this isn’t usually necessary. Use --live to migrate an active domain without interruption.

net-autostart [--disable] network

Automatically start network at system boot.

net-create xmlfile

Create and activate a network described in the specified xmlfile.

net-define xmlfile

Define a network described in the specified xmlfile but don’t start it.

net-destroy network

Immediately stop an active network.

net-dumpxml network

Print the network’s information in XML.

net-list [option]

Print a list of active networks. Use option --inactive to list inactive networks, or --all to list both active and inactive networks.

net-name uuid

Print the name of the network specified by uuid.

net-start network

Start a previously defined but inactive network.

net-undefine network

Remove network’s definition.

net-uuid name

Print the UUID of the network specified by name.

nodeinfo

Print basic information about the physical system.

quit

Exit virsh’s interactive terminal.

reboot domain

Reboot the domain as if a reboot command was run from the console.

restore file

Restore a domain from a domain state saved in file by the save command.

resume domain

Resume execution of a suspended domain.

save domain file

Save a domain’s state to file. This will suspend the domain, similar to hibernating a system.

schedinfo [options] domain

Set or show CPU scheduler settings.

Options

--weight n

Set scheduler weight. Valid values of n are between 1 and 65535.

--cap percent

Set the maximum percent that any one physical CPU domain can consume.

setmem domain size

Change domain’s current memory allocation to the size given in kilobytes.

setmaxmem domain size

Change domain’s maximum memory allocation to the size given in kilobytes. The new size can’t be larger than was specified when the virtual machine was created.

setvcpus domain n

Change the number of active virtual CPUs. n cannot exceed the number of CPUs specified in domain’s configuration file at boot time.

shutdown domain

Shut down the domain as if the shutdown command was run from the console.

suspend domain

Pause execution of domain.

ttyconsole domain

Print domain’s tty console device if it has one.

undefine domain

Remove domain’s definition.

uri

Print hypervisor’s URI.

vcpuinfo domain

Print information about domain’s virtual CPU.

vcpupin domain vcpu cpulist

Control domain virtual CPU affinity. Assign the given vcpu number to the physical cpulist given as a comma-separated list of numbers or number ranges: e.g., 0,2 or 0–2,5,6.

version

Print library API version number and the hypervisor URI.

vncdisplay domain

Print the IP address and port number of domain’s display, if available.

Name

virt-clone

Synopsis

virt-clone [options]

Clone a virtual machine. virt-clone copies hard drives and duplicates the virtual hardware configuration of an existing virtual machine. Elements that must be unique, such as the MAC address of a virtualized network interfaces, are updated so as to avoid conflicts with the old system. This system to be cloned must be shut off, as an active system cannot be safely cloned.

If no options are given, virt-clone will query for the needed information.

virt-clone writes debugging information to $HOME/.virtinst/virt-clone.log.

Options

--connect=uri

The hypervisor connection uri.

-d, --debug

Print debugging information to standard output.

-f path, --file=path

The path to the file, disk partition, or logical volume to use to store the new guests virtual disk. If the original system has multiple disks, this option should be run once per disk.

--force

Run without prompting. Assume a yes response to any yes/no prompt. For all other prompts, exit.

-n name, --name=name

The new domain name for the copied system.

-o domain, --original=domain

The name or UUID of the original domain to copy.

--preserve-data

Preserves any data that exists on the target of an -f option.

-m address, --mac=address

The new hardware MAC address for the network interface on the copied system.

-u uuid, --uuid=uuid

The new uuid for the copied system. This is a 32-digit hexadecimal number. If not specified, a random UUID is used.

Name

virt-image

Synopsis

virt-image [options] xmlfile

Create a guest machine from the image descriptor in xmlfile. Attributes for the new guest are taken from the descriptor file, although some missing information can be provided on the command line. Command-line options supersede information in the image descriptor file.

Options

--boot=n

If image has multiple boot descriptors, use descriptor n. The first descriptor is descriptor 0. When omitted, the one that best fits the current hypervisor is chosen.

--check-cpu

Warn if the number of virtual CPUs for the guest exceeds the number of physical CPUs in the host system.

--connect=uri

The hypervisor connection uri.

-d, --debug

Print debugging information to standard output.

-h, --help

Print information on the command and options, then exit.

-k map, --keymap=map

Set the map to use for the graphical console. By default, an English keymap is used.

-m address, --mac=address

The hardware MAC address for the network interface on the copied system. If none is specified or the address is given as RANDOM, assign a random address.

-n name, --name=name

The domain name for the new guest.

--noacpi

Disable Advanced Configuration and Power Interface (ACPI).

--noapic

Disable Advanced Programmable Interrupt Controller (APIC).

--nographics

Do not set up graphic support.

-r size, --ram=size

Allocate size in megabytes of memory for guest.

--sdl

Use Simple DirectMedia Layer for graphic access.

-u uuid, --uuid=uuid

The uuid for the new guest system. This is a 32-digit hexa-decimal number. If not specified, a random UUID is used.

--vnc

Use permanent port n for VNC instead of a random port. Note that specifying a port may cause clashes with other guests.

--vncport=n

Use port n for VNC. Note that specifying a port may cause clashes with other guests.

--vcpus n

Configure the new system with n virtual CPUs.

-w type[:name], --network=type[:name]

Configure the guest’s network connection. The type of network may be bridge, network, or user. For bridge and network you should also provide the network name as configured in the hypervisor. (Use virsh net-list to see configured network names.) user is supported by qemu’s unprivileged mode. It provides limited NAT by way of SliRP, a SLIP/PPP emulator.

Name

virt-install

Synopsis

virt-install [options]

Create a guest machine completely from the command line. Virt-install does not require an XML image descriptor file. virt-install will prompt for any required information not provided on the command line. Following is the required information.

Options

--accelerate

Use KVM or KQEMU kernel acceleration if available. Recommended when the guest OS is compatible.

--boot=n

If an image has multiple boot descriptors, use descriptor n. The first descriptor is descriptor 0. When omitted, the one that best fits the current hypervisor is chosen.

-c path, --cdrom=path

File to use for virtual CDROM device. The file may be an ISO file, CDROM device, or a URL that refers to an ISO image to fetch.

--check-cpu

Warn if the number of virtual CPUs for the guest exceeds the number of physical CPUs in the host system.

--connect=uri

The hypervisor connection uri.

--cpuset=set

Allow guest to use only the given set of CPUs. A set is a comma-separated list of numbers or number ranges: e.g., 0,2 or 0–2,5,6.

-d, --debug

Print debugging information to standard output.

-f path, --file=path

Required. The path to the file, disk partition, or logical volume to use to store the new guest’s virtual disk. If the original system has multiple disks, this option should be given once per disk.

-h, --help

Print information on the command and options, then exit.

-k map, --keymap=map

Set the keymap to use for the virtual console. By default, an English keymap is used.

-l path, --location=path

Specify the location of the installation source. path may be given as a URI. Use this instead of -c when installing from a kernel/initrd pair instead of a CDROM. Required for installing paravirtualized guests.

--livecd

The guest will always use a live CDROM image. Configure guest to boot from CDROM drive by default. Commonly used with --nodisks option.

-m address, --mac=address

The hardware MAC address for the network interface on the copied system. If none is specified or address is given as RANDOM, assign a random address.

-n name, --name=name

Required. The domain name for the new guest.

--noacpi

Disable Advanced Configuration and Power Interface (ACPI).

--noapic

Disable Advanced Programmable Interrupt Controller (APIC).

--noautoconsole

Don’t automatically launch a console for the installation. By default, virt-install launches a VNC client or virsh console to connect to the guest.

--nodisks

Guest is being created without disks. Do not prompt for disk setup.

--nographics

Don’t prompt for virtual console setup if neither --sdl nor --vnc is specified. Set up a text based console on the first serial port (or equivalent console device) instead.

--nonsparse

Fully allocate space for the virtual disk. This takes longer to initialize, but results in a faster disk and ensures you don’t run out of space. Recommended.

--os-type=type

Optimize guest for the specified guest OS type. Valid values for type include linux, windows, unix, and other.

-p, --paravirt

Guest will be a paravirtualized system.

--pxe

Use PXE boot protocol to load initial kernel.

-r size, --ram=size

Required. Allocate size in megabytes of memory for guest.

-s size, --file-size=size

Required when creating a new file. Create a file of size in gigabytes. Size may be given as a decimal, for example: 2.5. By default, virt-install creates a sparse file. The full size will be allocated, though, if used with the --nonsparse option.

--sdl

Set up a virtual console and export it using Simple Direct-Media Layer (SDL).

-u uuid, --uuid=uuid

The uuid for the new guest system. This is a 32-digit hexa-decimal number. If not specified, a random UUID is used.

-v, --hvm

Configure guest with full virtualization. Don’t use paravirtualization if available.

--vnc

Set up a virtual console and export it using VNC.

--vncport=n

Use permanent port n for VNC instead of a random port. Note that specifying a port may cause clashes with other guests.

--vcpus n

Configure new system with n virtual CPUs.

-w type[:name], --network=type[:name]

Configure guest’s network connection. The type of network may be bridge, network, or user. For bridge and network you should also provide the network name as configured in the hypervisor. (Use virsh net-list to see configured network names.) user is supported by qemu’s unprivileged mode. It provides limited NAT by way of SliRP, a SLIP/PPP emulator. If this option is omitted, a single NIC is created to a bridge device or to the default network. Specify the option multiple times to set up multiple network interfaces.

-x kernelargs, --extra-args=kernelargs

Pass additional kernel arguments to a Linux kernel. Used with the -l option. Commonly used to pass a Kickstart file to the kernel.

Name

virt-viewer

Synopsis

virt-viewer [options] domain

Use VNC to open the console of a virtual machine. The domain may be given by name, ID, or UUID.

Options

--c uri, --connect=uri

Connect to a hypervisor specified by uri.

--d, --direct

Don’t tunnel the VNC connection over SSH, even if the connection URI uses SSH.

--v, --verbose

Print information about the connection to standard output.

--w, --wait

Wait for the domain to start up before connecting to the console.

Name

virt-manager

Synopsis

virt-manager [options]

Launch GUI virtual machine manager. This manager visually displays domain and hypervisor stats. Like virsh, it can manage domains, and when run on the same system as the hypervisor, it can even be used to configure new systems. It has a couple of useful options for controlling how it starts.

Options

--c uri, --connect=uri

Connect to a hypervisor specified by uri.

--no-fork

Run without forking a new process. This can be useful for debugging connection problems.

VMware ESX 3.5

While VMware isn’t exactly a Linux product and isn’t free, it does provide access to a Service Console, which is something like Xen’s Domain-0. The Service Console runs a modified version of Red Hat Enterprise Server 3.0. So even though it is a commercial product, we want to include some information on it in this chapter.

Here, we will cover useful Service Console commands for administrators using the commercial ESX 3.5 product. VMware has also provided a free version of ESX, named ESXi. ESXi does not technically have a Service Console, though you can launch an unsupported Linux interface similar to the Service Console that has many of the same commands. Many of the commands listed in this section will work in the unsupported console, although in keeping with the unsupported nature of this console, nothing is guaranteed. VMware also provides a remote command line interface (rCLI), which is a collection of Perl utilities that mostly mimic the Service Console commands.

As we are writing this, VMware is preparing to release vSphere, the new version of ESX. It too, has a Service Console and remote CLI, the vCLI. VMware has deprecated some commands in vSphere moving functionality to the vCLI. still, they continue to provide the Service Console for troubleshooting and technical support sessions. Most of what we document here still works in vSphere.

You will need to install ESX or ESXi on a bare system. Its installation is nearly identical to an older Red Hat installation. Given your network information, it should be able to configure a default network switch that will provide your guest systems with network access.

ESX Management Client

While we cover some of the common commands below, you won’t use these for most of your management tasks. Once installed and booted, the initial screen will give you a URL you can connect to in order to perform some basic configuration. That URL will also direct you to where you can find a Virtual Infrastructure Client (VI Client) to manage your ESX server. It’s that client you will use to manage your servers. VI Client runs on Microsoft Windows.

Virtual Center

If you are using VMware servers, you are probably going to use multiple servers to take advantage of the High Availability features VMware offers, such as Vmotion. To coordinate those servers you will need to run a Microsoft Windows Server system with VMware’s virtual center installed. It’s rumored that vSphere will have a Linux-based Virtual Center, but this has not been announced for the initial release. It still requires Microsoft Windows.

VMware is GUI driven and VMware expects you will primarily use VI Client to interact with your systems. You will need to run at least one windows system to manage VMware ESX servers. The Service Console won’t let you get around this requirement. However, when your network stops working right or you need to take a closer look at a system’s performance, you will be glad to have the service console available.

VMware Networking

When configuring a virtual network switch, you will configure three different network connection types: Virtual Machine, VMkernel, and Service Console. VMware refers to these as different kinds of port groups. A port group specifies port configuration options, such as VLAN tagging or bandwidth limitations for devices assigned to that group. The switch handles the mapping of virtual devices to physical devices. In a default installation of ESX you should have a Service Console and Virtual Machine port group.

The Service Console port group provides network access to the service console and is used by the virtual center or VI Client to control the server. The Virtual Machine port group is a default port group that will bridge your virtual machines to your physical network devices. Each network card on a virtual machine must be assigned to a virtual machine port group. For a high availability cluster of ESX servers, you will need to add a VMkernel port group as well. This is the port group the hypervisors will use to speak with each other and for moving virtual machines between servers.

Physical interfaces on a server are given a name beginning with vmnic. The service console’s interfaces are given names beginning with vswif. Both of these will show up if you run ifconfig from the service console.

We won’t cover virtual switch configuration further, but these terms will help you better understand the network and switch-related commands.

Shared Disks

To run multiple ESX servers, you need a shared data store. It can be SAN-based block storage (e.g., Fibre Channel or iSCSI) or a NAS connection (NFS), but you need some place the servers can all access the same data. For block storage, VMware uses a shared filesystem, vmfs, which is designed to handle multiple systems reading and writing to the same drive.

Snapshots

ESX can take snapshots of a running system. This process essentially freezes machine state and begins tracking changes to the system in a separate file. Later you can apply those changes or discard them to revert your system to the state it had when you took the snapshot. This is commonly used to test a configuration change or system update.

Because it preserves a system’s state at a specific time, you want your virtual machine doing as little as possible when taking the snapshot. Activity such as network file transfers and database transactions will fail if you decide to revert to the snapshot. Depending on virtual machine configuration, some disk activity may not be included in the snapshot.

The file tracking changes can grow quickly, so you will need sufficient space to hold the file, and you will probably not want to keep snapshots for very long. Having a snapshot may also limit your ability to migrate a system between servers.

Restoring the snapshot on a new system may not work. VMware will generate warnings when you try to migrate a system with a snapshot. Generally you want to remove all snapshots before migration.

VMware Tools

Paravirtualization on ESX depends on VMware tools. This is a collection of drivers and daemons that allow the hypervisor to communicate with the guest system. VMware tools can synchronize the guests clock with the ESX server’s clock, initiate graceful shutdowns when needed, provide better access to an X Window System running on a guest, and more. You almost always want to install these.

ESX Server Commands

Most commands for ESX server begin with either vm or esx. Commands that begin with vm all have something to do with manipulating virtual machines. Commands that begin with esx manipulate the server and its configuration. The commands may have more options than those we document here. Here, we focus on the most useful commands and command options.

Name

esxcfg-firewall

Synopsis

esxcfg-firewall [options]

Configure a firewall for the service console. ESX uses iptables to provide the firewall. Don’t use the iptables command to configure it, though; use this command instead. In its default configuration, it denies all incoming or outgoing connections except for the ports required for the server to function:

--allowIncoming

Allow incoming connections by default.

--allowOutgoing

Allow outgoing connections by default.

--blockIncoming

Block incoming connections by default.

--blockOutgoing

Block outgoing connections by default.

-c port type direction, --close port,type,direction

Close a port. The type may be tcp or udp, The direction may be in or out.

-d [service], --disableService [service]

Close the ports required by the specified service.

-e [service], --enableService [service]

Open the ports required by the specified service.

-h, --help

Print a usage message. This is the default if no options are given.

-l, --load

Load current firewall settings into iptables.

-q [service], --query [service]

Print all current settings or the state of a service specified by name. Instead of a service you can query the default settings for incoming or outgoing packets.

-o port type direction name, --open port,type,direction,name

Open a port. The type may be tcp or udp, The direction may be in or out. You must give the service you have opened a name.

-r, --resetDefaults

Reset all parameters to the installed defaults.

-s, --services

List known service names.

Example

Allow vmware-cmd to connect to remote hosts by opening outgoing connections to port 443:

# esxcfg-firewall -o 443,tcp,out,vmware-cmd

Name

esxcfg-vswif

Synopsis

esxcfg-vswif options [interface]

Configure the service console network interface. Don’t use ifconfig or manipulate /etc/sysconfig/network-script files directly; use this command instead. Service console interface names start with vswif followed by a number. For example: vswif0 or vswif1.

Options

-a, --add

Add a service console interface. Requires the --ip and --portgroup options.

-b address, --broadcast address

Set the broadcast address.

-d, --del

Remove a service console interface.

-D, --disable-all

Disable all service console interfaces.

-e, --enable

Enable a disabled interface.

-E, --enable-all

Enable all service console interfaces.

-i address, --ip address

Set the IP address for the interface. You can also specify DHCP for address.

-l, --list

List service console interfaces along with current configuration and state.

-n mask, --netmask mask

Set the netmask.

-p name, --portgroup name

Set the interface’s portgroup name.

-s, --disable

Disable an interface.

Name

esxcfg-vswitch

Synopsis

esxcfg-vswitch options [switch]

Configure a virtual switch. The virtual switch handles port groups and VLAN tagging, and sets the uplink for virtual port groups. By default, there is a single virtual switch: vSwitch0. You can add additional switches and assign them to different physical network interfaces.

Options

-a, --add

Add a new virtual switch. You must provide a switch name.

-A name, --add-pg name

Add port group name to the switch.

-b, --get-cdp

Print the current Cisco Discovery Protocol (CDP) for the switch.

-B status, --set-cdp status

Set the CDP status for the switch. This may be down, listen, advertise, or both.

-d, --delete

Delete a virtual switch. If the switch has any ports in use, this will fail.

-D name, --del-pg name

Remove port group name from the switch.

-l, --list

List switches and their port groups.

-L interface, --link interface

Attach an uplink interface to a virtual switch. This should be an unused physical interface or vmnic.

-m size, --mtu size

Set the size of the Maximum Transfer Unit (MTU) for the switch. This will affect all interfaces attached to the virtual switch.

-M interface, --add-pg-uplink interface

Add an uplink interface to a port group.

-N interface, --del-pg-uplink interface

Remove an uplink interface from a port group.

-p name, --pg name

Specify name of the port group to use with the --vlan option. Specify ALL to apply to all port groups on the switch.

-U interface, --unlink interface

Remove an uplink interface from a virtual switch.

-v id, --vlan id

Set the VLAN id for a port group. Use with the --pg option. Setting id to 0 disables VLAN tagging for the port group.

Name

esxcfg-nics

Synopsis

esxcfg-nics options [interface]

Display information about physical network interfaces and manage some interface settings.

Options

-a, --auto

Set the interface to auto-negotiate speed and duplex settings.

-d mode, --duplex mode

Set duplex mode for the interface. Value may be full or half.

-l, --list

Print current configuration of all network interfaces on the system.

-s n, --speed n

Set the speed of the interface to n. Valid values are 10, 100, 1000, or 10000 and are measured in megabits per second.

Name

esxtop

Synopsis

esxtop [options]

Provide frequently updated information about resource usage on the ESX server. This program performs a function similar to the Linux top command. Where top shows information on processes and process IDs, esxtop shows information on hypervisor resource pools, and resource pool groups. A resource pool is any item the hypervisor must schedule. For example, each virtual CPU, has a resource pool ID, and each virtual processor on a single virtual machine belongs to the same resource pool group.

esxtop’s various options change what information is displayed. Like top, esxtop also offers interactive commands to change what information it displays as it runs. esxtop has more interactive commands than we’ll show here. We are just covering the basic screens and common commands. The h command, however, will always show you the currently valid interactive commands.

Options

-a

Override configuration file settings and show all statistics.

-b

Run in batch mode; don’t accept command-line input. Useful for sending output to another command or to a file.

-c file

Use alternative configuration file. This also becomes the default file for the interactive command W.

-d seconds

Set the delay between refreshes. Default is 3.

-n num

Update display num times, then exit.

-s

Secure mode. Disable the interactive command s.

Interactive commands

#

Prompt for number of rows to show.

c

Switch to CPU resource screen.

d

Switch to storage device screen.

f, F

Add or remove fields.

h

Show information on currently available commands.

m

Switch to memory resource screen.

o, O

Change field order.

Q, Esc

Quit.

s

Prompt for a new delay setting.

n

Switch to network resource usage screen.

v

Switch to virtual machine disk usage screen.

W

Write a configuration file matching current setup to ˜/.esxtop3rc.

Name

vmware-cmd

Synopsis

vmware-cmd [options][vmxpath command]

Console-based virtual machine manager. This command can work on the local system, or connect to a remote system using the Simple Object Access Protocol (SOAP). To connect to a remote system you may need to alter your firewall settings on the system issuing the commands so that it will allow outgoing connections to port 443. See the example in esxcfg-firewall.

The guest you want to work on is identified by the full path to its .vmx configuration file (vmxpath). The path must include the UUID of the vmfs volume and so can be quite long. Use the -l option to get the correct path for all registered virtual machines. While vmware-cmd has options for getting and setting virtual machine configuration values, we don’t cover those here.

Options

-h

Print basic usage and commands.

-H host

Connect to remote host. This can be given as a domain name or IP address.

-s [un]register configfile

Add or remove the guest described in .vmx file found at path from server control.

-l

List virtual machines registered with server.

-O port

Connect to alternative port, specified by port number. The default is port 443.

-P password

Provide password for the user specified in the -U option.

-q

Quiet mode. Minimize output.

-U username

Connect with the given username.

-v

Verbose mode.

Command

Return values for the command generally show the command function and whether they succeed (value 1) or fail (value 0.) Power-related commands generally take an option power operation mode of soft, hard, or trysoft. soft power operations use vmware-tools to generally do the right thing to the guest, such as gracefully shutting it down before pulling the virtual plug, or running special scripts to prepare the system for suspension. hard operations just perform the requested action immediately. trysoft operations will attempt to use vmware-tools for its operations, but if that fails, will force the operation without using tools.

connectdevice name

Connect device name to system. Valid device names can be found in the system’s .vmx configuration file.

createsnapshot name description quiesce memory

Take a snapshot of the system, setting the new snapshot’s name and description. If these values contain spaces, enclose them in quotes. You can quiesce drive activity and save memory state while taking the snapshot. quiesce and memory should be 0 for false or 1 for true. You usually will want both to be 1.

getstate

Report whether the virtual machine is off, on, suspended, or stuck.

getuptime

Report how long, in minutes, a machine has been running.

hassnapshot

Report whether virtual machine has a snapshot.

reset [mode]

Restart virtual machine.

removesnapshots

Apply saved changes and delete all snapshots.

revertsnapshot

Discard changes and restore virtual machine to most recent snapshot. Begin tracking changes again from the snapshot state.

start [mode]

Power up virtual machine.

stop [mode]

Power off virtual machine.

suspend

Save virtual machine’s state and suspend its operation.

Examples

List registered virtual machines:

vmware-cmd -l

Register the yoyodyne system with the hypervisor:

vmware-cmd -s register /vmfs/volumes/uuid/yoyodyne/
yoyodyne.vmx

Start a registered virtual machine:

vmware-cmd /vmfs/volumes/uuid/yoyodyne/yoyodyne.vmx start

Create a snapshot of the yoyodyne system:

vmware-cmd /vmfs/volumes/uuid/yoyodyne/yoyodyne.vmx \
createsnapshot beforeupdate "state before system update" 1 1

Connect a virtual IDE CDROM to yoyodyne system:

vmware-cmd /vmfs/volumes/uuid/yoyodyne/yoyodyne.vmx \
connectdevice ide0:0

Name

vmkfstools

Synopsis

vmkfstools options [target]

Manipulate disk images and vmfs filesystems. As with other commands, you generally use VI Client to perform these tasks. But you must use the command line when importing a disk from another VMware product, such as VMware Workstation. Use this command to create or extend a VMFS system or to extend, rename, or remove a disk image. It can also set or query disk image properties. Use vmkfstools instead of mv and cp to move and copy virtual disks.

You generally do not want to perform virtual disk operations on disks currently in use by a virtual machine. Shut down virtual machines first. Changes in a virtual disk will often require changes in a virtual machine’s configuration or changes in the virtual machine’s operating system. One example is changing virtual machine partition information to take advantage of an extended disk.

Targets

The target will be a device, partition, or file, depending on what you intend to do.

device

A device target will begin with /vmfs/devices/, the mount point of the device filesystem. This will include SAN-based disks, logical volumes, and SCSI devices attached to the ESX server.

partition

A partition target begins with vmhba followed by numbers that signify adapter:target: LUN:partition[:filepath]. For example, vmhba0:1:14:2 would be the 2nd partition of LUN 14 on target 1 HBA 0. You can also target a file on a partition by appending the filepath.

path

A path target is simply a path to a .vmdk virtual disk file. This path can be given relative to the /vmfs directory. The path to the file target isn’t required if it is in the current working directory.

Options

We have grouped options that are commonly used together, generally following the order used in the manpages.

VMFS options:

-b size, --blocksize size

Set new VMFS volume block size. Default is 1m for 1 megabyte. Other valid options are 2m, 4m and 8m. Used with the -C option.

-C type, --createfs type

Create a VMFS filesystem on a partition target. In ESX 3.5, the only valid type is vmfs3.

-S label, -setfsname label

Set the label for a new VMFS filesystem. This is used only with the -C option.

-Z partition, --extendfs partition

Extend existing vmfs3 filesystem by adding the specified partition to it. vmfs3 filesystems can have at most 32 partitions.

-P, --queryfs

List attributes of a VMFS filesystem. The target of this command may be the path to any directory or file on a VMFS filesystem.

-h, --human-readable

Used in conjunction with the -P option. Print sizes in a more easily read form.

Virtual disk options:

-c size, --createvirtualdisk size

Create a new virtual disk of the specified size in bytes (by default). You can also append g, m, or k to give numbers in gigabytes, megabytes, or kilobytes, respectively. For example: 8g for 8 gigabytes.

-a [type], --adaptertype [type]

Specify adapter type to use with the virtual disk. The only valid types are buslogic or lsilogic. Default is buslogic, but for Linux you probably want lsilogic.

-d format, --diskformat format

Set virtual disk format. This option is used when creating and cloning virtual disks (-c and -i options). See later options for valid virtual disk formats. When cloning, this option can be used to specify the format of the target disk; for example, when cloning a VMFS virtual disk file to a 2 GB sparse file useable by other VMware products.

-U, --deletevirtualdisk

Delete a virtual disk and any associated files.

-E source, --renamevirtualdisk source

Rename source virtual disk and associated files to target.

-i source, --clonevirtualdisk source

Clone source virtual disk and associated files to target. This is commonly used to import disks from other VMware products. You can use -d to specify the format of the source.

-X size, --extendvirtualdisk size

Extend an existing disk to the specified size in bytes (by default). You can also append g, m, or k to give numbers in gigabytes, megabytes, or kilobytes respectively. This action will break snapshots and the guest will need some way to recognize and take advantage of the new disk size (such as by resizing a partition with resize2fs).

-r device, --createrdm device

Create a virtual raw device mapping. (See the following section, Virtual disk formats.) Give device as the full path to a device under /vmfs/devices.

-q, --queryrdm

Print attributes of an existing raw disk mapping.

-z device, --createrdmpassthrough device

Create a physical raw device mapping. (See the following section, Virtual disk formats.) Give device as the full path to a device under /vmfs/devices.

-g, --geometry

Print geometry information for a virtual disk.

-w, --writezeroes

Initialize a virtual disk with zeroes. This will wipe any existing data from the disk.

-j, --inflatedisk

Convert a thin virtual disk to a preallocated virtual disk, preserving existing data and zeroing out unallocated blocks.

Virtual disk formats

This section lists the valid target disk formats to use with the -d option when creating or cloning a virtual disk. Created disks may be in any of the ESX vmdk formats. When cloning a disk, use -d if you need to export to an alternate format or target a raw device.

ESX vmdk formats:

zeroedthick

Allocate all space and wipe any previous contents of that space during virtual machine read and write operations. This is the default format.

eagerzeroedthick

Like zeroedthick, only the allocated space is wiped at creation time.

thick

Allocate all space, but don’t bother cleaning any existing content on the disk.

thin

Supply and zero out space for the filesystem as it is used by the virtual machine.

VMware compatible formats:

2gbsparse

Sparse disk with 2 GB maximum extent size (the Virtual disk will be split into 2 GB sections). This is a useful format when writing to disks that don’t support files larger than 2 GB.

monosparse

One monolithic disk file.

monoflat

One monolithic flat file.

Raw device mappings:

rdm:device

Virtual raw device mapping. These are treated by a guest as any other virtual disk.

rdmp:device

Physical raw device mapping. A virtual machine is given direct access to a physical raw device and interacts with it as it would any SCSI device. LUN listing requests are virtualized, however, so only the system that owns the virtual device can access it.

raw:device

A raw SCSI device, like a tape archive or an unmapped LUN.

Examples

Export a VMFS virtual disk to 2 GB sparse file:

# vmkfstools -i original.vmdk -d 2gbsparse new.vmdk

Index

A note on the digital index

A link in an index entry is displayed as the section title in which that entry appears. Because some sections have multiple index markers, it is not unusual for an entry to have several links to the same section. Clicking on any link will take you directly to the place in the text in which the marker appears.

Symbols

#!shell directive,

#define statements, generating template of, Options

#pragma implementation directive, Pragma directives

#pragma interface directive, Warning options

& (ampersand), Quoting, Command Forms

background execution, Quoting, Command Forms

command redirection, Simple redirection

repeat substitute command in ex,

reuse text matched by pattern, Replacement Patterns

&& (ampersand, double), Command Forms

AND operator for commands, Command Forms

AND operator, in expressions, , Built-in Variables

:set command, Miscellaneous Commands

< (left angle bracket) less than operator, , Built-in Variables

< or > (angle brackets), Quoting, Command Forms

command redirection, Quoting, Command Forms

shift commands in ex,

<= (left angle bracket, equals sign) less than or equal operator, Built-in Variables

> (right angle bracket), , Built-in Variables

greater than operator, , Built-in Variables

output redirection,

>= (right angle bracket, equals sign) greater than or equal operator, Built-in Variables

>> (right angle bracket, double) append output,

@include directive, gawk, Profiling

\< or \> (backslash, angle brackets) match beginning or end of word, Search Patterns

\a alert escape sequence, Quoting, Arrays, Pattern Addressing Examples, Variable and Array Assignment

\A time escape sequence, Arrays

\b backspace escape sequence, Quoting, Variable and Array Assignment

\B escape sequence, Search Patterns, Pattern Addressing Examples

\b escape sequence, Search Patterns, Pattern Addressing Examples

\c control character escape sequence, Quoting

\D date escape sequence, Arrays

\d date escape sequence, Arrays

\d decimal escape sequence, Pattern Addressing Examples

\E escape character, pattern matching, Replacement Patterns

\e escape character, pattern matching, Replacement Patterns

\E escape sequence, Quoting

\e escape sequence, Quoting, Arrays

\f form feed escape sequence, Quoting, Pattern Addressing Examples, Variable and Array Assignment

\h hostname escape sequence, Arrays

\j jobs escape sequence, Arrays

\l basename escape sequence, Arrays

\L escape character, pattern matching, Replacement Patterns

\l escape character, pattern matching, Replacement Patterns

\n escape character, pattern matching, Search Patterns, Replacement Patterns

\n newline escape sequence, Quoting, Arrays, Pattern Addressing Examples, Variable and Array Assignment

\o octal escape sequence, sed, Pattern Addressing Examples

\r carriage return escape sequence, Arrays, Pattern Addressing Examples, Variable and Array Assignment

\s shell escape sequence, Arrays

\t tab escape sequence, Quoting, Variable and Array Assignment

\T time escape sequence, Arrays

\t time escape sequence, Arrays

\U escape character, pattern matching, Replacement Patterns

\u escape character, pattern matching, Replacement Patterns

\u username escape sequence, Arrays

\V release escape sequence, Arrays

\v version escape sequence, Arrays

\v vertical tab escape sequence, Quoting, Pattern Addressing Examples, Variable and Array Assignment

\W current directory escape sequence, Arrays

\w current directory escape sequence, Arrays

\W escape character, pattern matching, Search Patterns

\w escape character, pattern matching, Search Patterns

\W escape sequence, Pattern Addressing Examples

\w escape sequence, Pattern Addressing Examples

\x hexadecimal escape sequence, Quoting, Pattern Addressing Examples, Variable and Array Assignment

|& (vertical bar, ampersand) output directed to coprocess, gawk-Specific Features,

A

a command, sed, Basic Editing,

abbreviate command, ex, Address Symbols

accept command,

access command,

access mode for files, checking,

access permissions, changing, Options

account command, ftp, Options

account command, mailx, Compose-mode commands

aclocal command,

aconnect command, Options

ACPI (Advanced Configuration and Power Interface),

displaying information about, Options

events from, informing user programs of,

acpi command, Options

acpid daemon,

add command, git, Accessing Git’s Online Help

add command, svn, svn Subcommands

addition operator (+), Built-in Variables

addr add command, ip, Options

addr del command, ip, Options

addr show command, ip, Options

addr2line command,

Address Resolution Protocol (ARP), TCP/IP Administration,

addresses of lines, ex, Sample .exrc File,

addresses, program, translating to filenames and line numbers,

Advanced Linux Sound Architecture (see ALSA),

Advanced Package Tool (see APT),

Advanced Power Management (APM) hardware, handling events from,

agetty command,

alias command, Bash,

alias command, lftp, Options

alias command, mailx, Compose-mode commands

aliases,

assigning,

removing,

aliases database, rebuilding,

alnum character class, Filename Metacharacters, Search Patterns

alpha character class, Filename Metacharacters, Search Patterns

ALSA (Advanced Linux Sound Architecture), Options

MIDI files,

playing, Options

recording,

mixer,

connecting to one or more sound cards, Options

controlling, Options

ports, reading and writing MIDI files to, Options

sound cards, advanced configuration settings for, Options

sound files,

playing, Options

recording,

alsactl command, Options

alsamixer command, Options

alternates (alt) command, mailx, Compose-mode commands

amidi command, Options

amixer command, Options

ampersand (&), Quoting, Command Forms

background execution, Quoting, Command Forms

command redirection, Simple redirection

repeat substitute command in ex,

reuse text matched by pattern, Replacement Patterns

ampersand, double (&&),

AND operator, in expression,

AND operator, in expressions, Built-in Variables

for commands, Command Forms

anacron command, Options

AND operator (&&), Command Forms

for commands, Command Forms

in expression,

and() function, gawk, Group Listing of awk Functions and Commands

angle brackets (< or >), Quoting, Command Forms

(see also left angle bracket; right angle bracket), Options

command redirection, Quoting, Command Forms

shift commands in ex,

anon command, lftp, Options

ANSI/VT100 terminal emulation,

Apache web server, The Excitement of Linux

benefits of using with Linux, The Excitement of Linux

user authentication files for, creating or updating, Options

aplay command, Options

aplaymidi command, Options

APM (Advanced Power Management) hardware, handling events from,

apmd command,

append command, ex, Examples

append command, ftp, Options

apropos command, Parameters

APT (Advanced Package Tool), Parameters, Package Management

(see also aptitude command, Debian; synaptic command, Debian), Parameters

apt command, Parameters

apt-cache command, Debian, Scripts

apt-cdrom command, Debian, Options

apt-config command, Debian, Commands

apt-extracttemplates command, Debian, Commands

apt-file script, Debian, Scripts

apt-ftparchive command, Debian,

apt-get command, Debian, Options

apt-rdepends script, Debian, Scripts

apt-sortpkgs command, Debian, Options

aptitude command, Debian, Package Management, Options

ar command,

arch command,

Arch system, Source Code Management Systems

architecture for package, Package Management

architecture type, printing,

archive command, git, Examples

archives, Example

(see also packages),

copying files to or from tape or disk, Options

copying files to or restoring from, Options

index for, generating,

maintaining,

of Debian packages, Files

of RPM packages, Plugins and yum-utils

arecord command,

arecordmidi command,

args command, ex, Examples

arguments on command-line,

checking,

printing, Options

shifting, Options

arithmetic expressions, Command Forms, Arithmetic Expressions,

arithmetic for loop,

ARP (Address Resolution Protocol), TCP/IP Administration,

arp command,

arrays, Other Shell Variables,

Bash, Other Shell Variables,

gawk, Variable and Array Assignment

AS (autonomous system), IP Addresses

as command, Options

ASCII codes of keys, printing, Options

ascii command, ftp, Options

ASCII format, displaying files in,

asort() function, gawk, Group Listing of awk Functions and Commands

asorti() function, gawk, Group Listing of awk Functions and Commands

assembly source files, generating object files from, Options

assignment operators, gawk, Built-in Variables

associative arrays, Arrays

Bash, Other Shell Variables

gawk, Variable and Array Assignment

asterisk (*), Arguments

in filename, Arguments

match multiple instances of a character, Filenames Versus Patterns

multiplication operator, Built-in Variables

* (asterisk), Filenames Versus Patterns

in filename, Arguments

match multiple instances of a character, Filenames Versus Patterns

multiplication operator, Built-in Variables

asterisk, double (**) exponentiation operator, Built-in Variables

** (asterisk, double) exponentiation operator, Built-in Variables

asterisk, equals sign (*=) assignment operator, Built-in Variables

*= (asterisk, equals sign) assignment operator, Built-in Variables

asterisk, parentheses (*()) in filename, Filename Metacharacters

*() (asterisk, parentheses) in filename, Filename Metacharacters

asterisks, equals sign (**=) assignment operator, Built-in Variables

**= (asterisks, equals sign) assignment operator, Built-in Variables

at command, Options

at command, lftp, Options

at sign (@) execute register command in ex,

@ (at sign) execute register command in ex,

at sign, parentheses (@()) in filename, Filename Metacharacters

@() (at sign, parentheses) in filename, Filename Metacharacters

atan2() function, gawk,

atd command,

atq command,

atrm command,

audio files, Options

playing, Options

recording,

recording to CDs, Options, Examples, Options

recording to DVDs, Options, Options

authentication,

adding RSA or DSA identities to agent, Escape characters

gathering keys from multiple hosts, Options

hold private keys for public key authentication,

keys, managing,

author command, svnlook,

autoconf command, ,

autoheader command, Options

automake command, Options

autonomous system (AS), IP Addresses

autoreconf command, Options

autoscan command, Options

autoupdate command,

auto_resume built-in variable, Other Shell Variables

awk, GNU (see gawk language), Profiling

AWKPATH environment variable, gawk, Profiling

B

b command, sed, Branching Commands,

background execution of commands, Quoting, Command Forms, ,

backing up files,

backslash (\), Quoting

escape character, Bash shell, Quoting

escape character, pattern matching, Replacement Patterns

escape character, prompt strings, Arrays

backslash parentheses (\(...\)) save enclosed subpattern, Search Patterns

\(...\) (backslash parentheses) save enclosed subpattern, Search Patterns

\ (backslash), Quoting

escape character, Bash shell, Quoting

escape character, pattern matching, Replacement Patterns

escape character, prompt strings, Arrays

backslash, angle brackets (\< or \>) match beginning or end of word, Search Patterns

backslash, apostrophe (\') escape character, pattern matching, Search Patterns

\' (backslash, apostrophe) escape character, pattern matching, Search Patterns

backslash, backtick (\`) escape character, pattern matching, Search Patterns

\` (backslash, backtick) escape character, pattern matching, Search Patterns

backslash, braces (\{...\}) enclosing range of characters to match, Filenames Versus Patterns

\{...\} (backslash, braces) enclosing range of characters to match, Filenames Versus Patterns

backslash, semicolon (\;...;) enclosing pattern address in sed, Pattern Addressing

\;...; (backslash, semicolon) enclosing pattern address in sed, Pattern Addressing

backtick (`) command substitution, Quoting, Command Forms

` (backtick) command substitution, Quoting, Command Forms

backup files, restoring,

badblocks command,

base64 command, Options

basename command, Options

BASH built-in variable, Built-in Shell Variables

Bash shell, , The Bash Shell

arguments for, Arguments

arithmetic expressions, Command Forms, Arithmetic Expressions,

arrays, Other Shell Variables

background execution, Quoting,

built-in commands, executing bypassing functions, Options

built-in variables, Built-in Shell Variables

character classes, Filename Metacharacters

command execution, Job Control

command forms, Command Forms

command history, Command History, Options, Options

command redirection, Quoting, Command Forms

command substitution, Quoting, Command Forms

command-line options for, Options

commands, enabling or disabling, Options

commands, list of, Command Execution

coprocesses, Multiple redirection

debugger, Built-in Shell Variables

escape character, Quoting

filenames, metacharacters for, Arguments

functions, Functions

help on commands for, Options

home directories for, Special Files

invoking, The Bash Shell

job control, Job Control

line-edit mode, Command History

options for, setting or unsetting, Options

POSIX notation in, Filename Metacharacters

programmable completion, Programmable Completion, Options

prompt strings, Arrays

quoting special characters in, Filename Metacharacters

restricted shells, Restricted Shells

startup files for, Arguments

suspending, Settable shell options

variable substitution, Quoting, Variables

version of, covered in this book, The Bash Shell

websites about, The Bash Shell

BASH_ARGC built-in variable, Built-in Shell Variables

BASH_ARGV built-in variable, Built-in Shell Variables

BASH_COMMAND built-in variable, Built-in Shell Variables

BASH_EXECUTION_STRING built-in variable, Built-in Shell Variables

BASH_LINENO built-in variable, Built-in Shell Variables

BASH_REMATCH built-in variable, Built-in Shell Variables

BASH_SOURCE built-in variable, Built-in Shell Variables

BASH_SUBSHELL built-in variable, Built-in Shell Variables

BASH_VERSINFO built-in variable, Built-in Shell Variables

BASH_VERSION built-in variable, Built-in Shell Variables

batch command,

Bautts, Tony (Linux Network Administrator’s Guide), Overview of TCP/IP, Overview of Firewalls and Masquerading

bc compiler,

bdelete command, ex, Examples

Beebe, Nelson H.F. (Classic Shell Scripting), The Bash Shell

bell command, ftp, Options

Berkeley C shell, The Bash Shell

Berkeley Internet Name Domain (BIND), Routing daemons

Berkeley Software Distribution (BSD), Commands on Linux, Sources and Licenses

bg command, Bash,

BGP (Border Gateway Protocol), IP Addresses

binary command, ftp, Options

BIND (Berkeley Internet Name Domain), DNS and BIND

bind command, Bash,

BIND DNS server, sending commands to, Options

binder process, NIS, Options

bindtextdomain() function, gawk,

biod daemon, Administering NFS

bisect command, git,

bison command, Other symbols

blame command, svn, svn Subcommands

blank character class, Filename Metacharacters, Search Patterns

block files, creating,

blocklist command, GRUB,

blocks group, printing information about,

bookmark command, lftp, Options

books and publications, Overview of Firewalls and Masquerading

Building Internet Firewalls (Zwicky; Cooper; Chapman), Overview of Firewalls and Masquerading

Classic Shell Scripting (Robbins; Beebe), The Bash Shell

GNU Emacs Pocket Reference (Cameron), Pattern Matching

Internetworking with TCP/IP (Comer), Overview of TCP/IP

Learning GNU Emacs (Cameron et al.), Pattern Matching, Modes

Learning Red Hat Enterprise Linux and Fedora (McCarty), What This Book Offers

Learning the bash Shell (Newham), The Bash Shell

Learning the Unix Operating System (Peek; Todino-Gonguet; Strang), xvii, Overview of Firewalls and Masquerading

Linux iptables Pocket Reference (Purdy), Overview of Firewalls and Masquerading

Linux Journal, xviii, Overview of TCP/IP, Overview of Firewalls and Masquerading

Linux Magazine, xviii, Overview of TCP/IP, Overview of Firewalls and Masquerading

Linux Network Administrator’s Guide (Bautts; Dawson; Purdy), Overview of TCP/IP, Overview of Firewalls and Masquerading

Managing Projects with GNU Make (Mecklenburg), Configuration options

Mastering Regular Expressions (Friedl), Pattern Matching

Perl 5 Pocket Reference (Vromans), Pattern Matching

Perl in a Nutshell (Patwardhan et al.), Pattern Matching

Regular Expression Pocket Reference (Stubblebine), Pattern Matching

Running Linux (Dalheimer; Welsh), Commands on Linux

TCP/IP Network Administration (Hunt), Overview of TCP/IP

Version Control with Subversion (Pilato et al.), The Subversion Version Control System

boot command, GRUB,

boot loader, The Boot Process

boot sector, The Boot Process

booting, Boot Methods

dual booting, Boot Methods, Boot Methods, Options

GRUB, Boot Methods, lilo Command Options

kernel options during, Dual-Booting Linux and Windows 2000/XP/Vista

LILO, Boot Methods, The Boot Process

virtualization for, Boot Methods

bootp command, GRUB, GRUB Commands

Border Gateway Protocol (BGP), IP Addresses

Bourne shell, The Bash Shell

Bourne-Again SHell (see Bash shell), Command Forms

braces ({...}), Command Forms

enclosing command grouping, Command Forms

enclosing nested pattern address in sed, Pattern Addressing

enclosing procedures in gawk, Important gawk Options

enclosing range of characters to match, Filenames Versus Patterns

{...} (braces), Command Forms

enclosing command grouping, Command Forms

enclosing nested pattern address in sed, Pattern Addressing

enclosing procedures in gawk, Important gawk Options

enclosing range of characters to match, Filenames Versus Patterns

brackets ([...]), Other Shell Variables

enclosing array elements, Other Shell Variables

enclosing characters to match, Filenames Versus Patterns

enclosing expressions, Settable shell options

in filename, Arguments

[...] (brackets), Other Shell Variables

enclosing array elements, Other Shell Variables

enclosing characters to match, Filenames Versus Patterns

enclosing expressions, Settable shell options

in filename, Arguments

brackets, double ([[...]]) enclosing expressions,

[[...]] (brackets, double) enclosing expressions,

branch command, git, Examples

branches, for source code management system, Introduction and Terminology, Basic Version-Control Operations

branches, in Git, Conceptual Overview, Examples

merging, , Examples

pushing,

tracking changes to,

brctl command, Configuring Networks

break command, Bash, Options

break command, gawk,

break command, gdb, Common commands

bridge-utils package, Configuring Networks

bridging, Configuring Networks

BSD (Berkeley Software Distribution), Commands on Linux, Sources and Licenses

bt command, gdb, Common commands

buffer command, ex, Examples

buffer-manipulation commands, Emacs, Capitalization Commands

buffers command, ex, Examples

Building Internet Firewalls (Zwicky; Cooper; Chapman), Overview of Firewalls and Masquerading

built-in commands (see commands, Bash), Built-in Shell Variables

built-in variables, Built-in Shell Variables

built-in variables, gawk, Simple Pattern-Procedure Examples

builtin command, Bash, Options

bunzip2 command, Options

bye command, ftp, Options

bzcat command, Options

bzcmp command, Options

bzdiff command, Options

bzgrep command, Options

bzip2 command, Options

bzip2 files, Options

(see also compressed files), Options

bzip2recover command, Options

bzless command, Examples

bzmore command, Examples

C

c command, gdb, Common commands

c command, sed, Basic Editing,

C language,

generating from RPC code,

preprocessor for, Options

c++ compiler (see g++ compiler), Quoting

c++filt command, Examples

C-h command (help), Emacs, Notes on the Tables

cache command, lftp, Options

cache command, mailx, Compose-mode commands

cal command, Options

calendar, printing, Options

caller command, Bash, Options

cameras, reading images from, Options

Cameron, Debra, Pattern Matching

GNU Emacs Pocket Reference, Pattern Matching

Learning GNU Emacs, Pattern Matching, Modes

capitalization commands, Emacs, Capitalization Commands

caret (^), Built-in Variables

exponentiation operator, Built-in Variables

match at beginning of line or string, Filenames Versus Patterns

^ (caret), Filenames Versus Patterns

exponentiation operator, Built-in Variables

match at beginning of line or string, Filenames Versus Patterns

caret, equals sign (^=) assignment operator, Built-in Variables

^= (caret, equals sign) assignment operator, Built-in Variables

case command, Bash, Options

case command, ftp, Options

cat command, Options

cat command, GRUB,

cat command, svn,

cat command, svnlook,

cc compiler (see gcc compiler),

cd command, Bash,

cd command, ex, Examples

cd command, ftp, Options

cd command, gdb, Common commands

CD-Rs, writing in DAO mode, Options

CDDA (Compact Disc Digital Audio), Options

converting to WAV, Options

converting to WAV format,

cdda2wav command, Options

cdparanoia command, Options

CDPATH built-in variable, Built-in Shell Variables

cdrdao command, Options

cdrecord command, Examples

CDs, File Management

commands for, list of, File Management

converting from CDDA to WAV format,

ejecting, Options

reading and writing, Options, Options

recording audio files to, Options, Examples

recording data files to, Examples

recording data or audio to, Options

cdup command, ftp, Options

center command, ex,

centering commands, Emacs, Centering Commands

cfdisk command, Examples

chage command, Commands

chainloader, GRUB: The Grand Unified Bootloader

chainloader command, GRUB,

chains, Overview of Firewalls and Masquerading

change command, ex,

changed command, svnlook,

changelist command, svn,

Chapman, D. Brent (Building Internet Firewalls), Overview of Firewalls and Masquerading

character classes, Filename Metacharacters

Bash, Filename Metacharacters

pattern matching, Search Patterns

character files, creating,

chattr command, Options

chdir (c) command, mailx, Compose-mode commands

check-update command, yum, General options

checkout command, git,

checkout command, svn, Examples

checksums, calculating and printing, Options

cherry-pick command, git,

chfn command, Attributes

chgrp command, Attributes

chkconfig command, Options

chmod command, Options

chmod command, ftp, Options

chown command, Examples

chpasswd command, Options

chroot command, Options

chrt command, Options

chsh command, Options

chvt command, Options

CIDR (Classless Inter-Domain Routing), IP Addresses

cksum command, Options

Classic Shell Scripting (Robbins; Beebe), The Bash Shell

classify command, mailx, Command-mode commands

Classless Inter-Domain Routing (CIDR), IP Addresses

clean command, git,

clean command, yum,

cleanup command, svn, Examples

clear command, Options

clear command, gdb, Common commands

clearing screen, Options

client, NIS, Administering NIS

client/server model, for source code management system, Introduction and Terminology

clocks, Common Commands

commands for, list of, Common Commands

reading or setting,

clone command, git,

close command, ex,

close command, ftp, Commands

close command, lfpt, Commands

close() function, gawk,

cmp command,

cmp command, GRUB,

cntrl character class, Filename Metacharacters, Search Patterns

code examples in this book, using, xix, Source Code Management Systems

Codeville system, Source Code Management Systems

col command,

colcrt command, Examples

colon (:),

null command,

preceding ex commands, Sample .exrc File

preceding label, sed, Branching Commands

: (colon),

null command,

preceding ex commands, Sample .exrc File

preceding label, sed, Branching Commands

color command, GRUB, GRUB Commands

colrm command, Examples

column command, Examples

columns,

formatting input into, Examples

removing from file, Examples, Options

COLUMNS built-in variable, Built-in Shell Variables

Comer, Douglas E. (Internetworking with TCP/IP), Overview of TCP/IP

comm command, Examples

command command, Bash,

command command, lftp, Commands

command mode, Conceptual Overview, Command Mode

command-line arguments,

checking,

printing, Options

shifting, Options

commands, The Excitement of Linux, What This Book Offers

Bash, Command Execution

aliases for, assigning,

aliases for, removing,

conditional execution of, Options, Options

coprocessing, Multiple redirection

enabling or disabling, Options

executing, Job Control

executing based on signals, Examples

executing in current process,

executing, bypassing aliases or functions, Options,

forms of, Command Forms

hash table for,

history of, Command History, Options, Options

programmable completion for, Options

redirection of, Quoting, Command Forms

substitution of, Quoting, Command Forms

type of, determining, Signals

deleting queued jobs of,

displaying manual pages for, Options

Emacs, Absolutely Essential Commands, Help Commands

buffer-manipulation, Capitalization Commands

capitalization, Capitalization Commands

centering, Centering Commands

completions for, Modes

deletion, Cursor-Movement Commands

file-handling, Notes on the Tables

help, Notes on the Tables, Centering Commands

indentation, Indentation Commands

jobs, Window Commands

listing, Notes on the Tables

macro, Macro Commands

paragraph, Paragraphs and Regions

region, Paragraphs and Regions

search, Search Commands

shell, Special Shell Characters

stopping, Paragraphs and Regions

transposition, Paragraphs and Regions

undoing, Paragraphs and Regions

windows, Capitalization Commands

word-abbreviation, Capitalization Commands

ex, Address Symbols

line addresses in, Sample .exrc File,

options for, Address Symbols

syntax for, Sample .exrc File

executing and timing the execution, Expression tests

executing as superuser,

executing at scheduled times, Directives

executing at specific time and date, Options

executing even after logging out, Options

executing in a new session, Options

executing in batch from standard input,

executing on remote host, Options

executing periodically, Options

executing queued jobs of,

executing remotely, Options

executing repeatedly,

executing with arguments from standard input, Track options and arguments

executing with lower priority,

executing with specific options, Options

executing within ftp, Options

for clocks, Common Commands

for communications, Sources and Licenses

for comparisons, Comparisons

for daemons, Common Commands

for file management, Comparisons

for filesystems, Managing Filesystems

for hardware, Daemons

for host information, Daemons

for installation, Installation

for kernel, Managing Filesystems

for mail, Installation

for media, File Management

for networking, Managing the Kernel

for NFS administration, TCP/IP Administration

for NIS administration, TCP/IP Administration

for NIS maps, NIS Maps

for printing, Printing, Managing the Kernel

for process management, Starting and Stopping the System

for program maintenance, Programming

for programming, File Management

for searching, Programming

for security, Managing the Kernel

for shell programming, Shell Programming

for storage, Shell Programming

for system administration, Common Commands

for system integrity, Managing the Kernel

for system logging, System Activity and Process Management

for system status, Shell Programming

for TCP/IP administration, Overview of Networking

for TCP/IP troubleshooting, Serial-line communication

for text processing, System Status

for user management, System Activity and Process Management

full pathnames for execution of,

GRUB, The GRUB Shell

help on, Linux Commands

list of, by category, Sources and Licenses

listing queued jobs of,

locating files for, Options

options for, entering, Linux Commands

output from, sending to both standard output and files,

scheduling, System Activity and Process Management

sending to BIND DNS server, Options

tracing system calls and signals for, Examples

commands command, gdb, Common commands

comments, Other symbols

in bc, Function keywords

in C, nested, warnings for, Options, Warning options

in database map input file, Options

in DNS update requests, Options

in file containing format strings, Options

in gawk, Group Listing of awk Functions and Commands

in GRUB configuration file, Using grub-install

in history expansion, Other Shell Variables

in LILO configuration files, The LILO Configuration File

in MAC address input file, File-type characters

in makefiles, Options

in RPM package manifest file, Query options

in sed scripts, Branching Commands

in shell scripts, Command Execution

in xinetd input, Configuration files

commit command, git,

commit command, svn,

communications, commands for, Sources and Licenses

Compact Disc Digital Audio (see CDDA),

comparison operators,

comparisons, commands for, Comparisons

compgen command, Bash, Options

compl() function, gawk,

complete command, Bash, Examples, Options

completion, programmable, Examples, Options

COMPREPLY built-in variable, Built-in Shell Variables

compress command, logrotate, Options

compresscmd command, logrotate, Options

compressed files, Options

bzip2 files, Options

comparing, Options

compressing executable files, Options

compressing files with Lempel-Ziv coding,

reading and then writing to standard output, Options

renaming, Options

uncompressing and searching,

uncompressing and then paging through,

uncompressing and then recompressing in .gz format, Commands

uncompressing files, Options

compressext command, logrotate, Options

compressoptions command, logrotate, Options

COMP_CWORD built-in variable, Built-in Shell Variables

COMP_LINE built-in variable, Built-in Shell Variables

COMP_POINT built-in variable, Built-in Shell Variables

COMP_WORDBREAKS built-in variable, Built-in Shell Variables

COMP_WORDS built-in variable, Built-in Shell Variables

concatenation operator, Built-in Variables

Concurrent Versions System (CVS), Usage Models

conditional execution of commands, Options

case command, Options

if command, Options

short-circuit operations for, Command Forms

config command, git, Examples

configfile command, GRUB,

configuration of vi editor, Miscellaneous Commands

configuration script,

generating from m4 macros,

updating, Options

conflict, in source code management system, Introduction and Terminology

console command, xm, Xen

contact information for this book, xxi, Conceptual Overview

containers technology, Conceptual Overview

context-free grammar, converting to tables, Configuration files

continue command, Bash, Options

continue command, gawk,

conventions used in this book, xx, Overview of Firewalls and Masquerading

Cooper, Simon (Building Internet Firewalls), Overview of Firewalls and Masquerading

coproc reserved word, Multiple redirection

coprocesses, Bash, Multiple redirection

coprocesses, gawk, gawk-Specific Features

copy (co) command, mailx, Command-mode commands

copy and move commands, Changing and deleting text

copy command, ex,

copy command, logrotate, Configuration commands

copy command, svn,

copy-modify-merge model, Subversion, Basic Version-Control Operations

copyleft (see GPL), Basic Version-Control Operations

copytruncate command, logrotate, Configuration commands

cos() function, gawk,

cp command,

cpio command, Options

cpp command, Options

cr command, ftp, Commands

CRC (cyclic redundancy check) checksum, computing, Options

create command, logrotate, Configuration commands

create command, svnadmin, Common svnadmin Subcommands

create command, xm, Xen

cron command, Package Management

crond command, Directives

crontab command, Directives

csh shell, The Bash Shell

csplit command,

CSSC system, Other Source Code Management Systems

ctags command, Arguments

Ctrl key (C-), Emacs, Modes

CUPS printer queues, configuring, Configuration commands

cupsd command, Options

current working directory,

changing,

printing, Options

cursor (point) location, Emacs, Modes

cursor-movement commands, Emacs, Cursor-Movement Commands

cut and paste (kill and yank), Emacs, Modes

cut command, Options

cut-and-paste utility for Linux console,

CVS (Concurrent Versions System), Usage Models

cyclic redundancy check (CRC) checksum, computing, Options

D

d command, sed, Basic Editing,

D command, sed, Branching Commands,

daemons, Overview of Networking

commands for, list of, Common Commands

nfsd daemons, Daemons

routing daemons, Routing daemons

daily command, logrotate, Configuration commands

Dalheimer, Matthias Kalle (Running Linux), Commands on Linux

DAO (disk-at-once) mode, Options

database maps for sendmail, creating, Options

database of files, searching, Environment variables

databases, searching for a specific key, HFS options

date and time,

current date and time, printing,

retrieving from specific host(s) on network, Options

date command,

date command, svnlook,

Dawson, Terry (Linux Network Administrator’s Guide), Overview of TCP/IP, Overview of Firewalls and Masquerading

dbm database files, Overview of NIS

dbm file, NIS, creating or dumping, Special target names

dcgettext() function, gawk,

dcngettext() function, gawk,

dd command, Format, MAC Addresses

dd command, GRUB, Installing GRUB

deallocv command, Options

Debian Package Manager, Package Management, rpmbuild options

commands for, Scripts

files used by, Files

interactive frontend for (see dselect command, Debian), Package Management, rpmbuild options

lower-level packaging tool for (see dpkg-deb command, Debian), Package Management, rpmbuild options

naming conventions for, Package Management, rpmbuild options

package flags, Package Flags

package priorities, Files

package states, Package Priorities

scripts for, Scripts

debug command, ftp, Commands

debug command, GRUB,

debugfs command, Options

debugger, Built-in Shell Variables

Bash, Built-in Shell Variables

gdb,

debuginfo-install plugin, yum,

decimal format, displaying files in,

declare command, Bash, Options

decoding, base64, Options

decrement operator (--), Built-in Variables

decryption (see encryption and decryption), The GRUB Configuration File

default command, GRUB, The GRUB Configuration File

delaycompress command, logrotate, Configuration commands

delete (d) command, mailx, Command-mode commands

delete command, ex,

delete command, ftp, Commands

delete command, gawk,

delete command, gdb, Common commands

delete command, svn, Examples

deletion commands, Emacs, Cursor-Movement Commands

deltify command, svnadmin, Common svnadmin Subcommands

dependencies for packages, Package Management, Package Management

dependency file, creating, Requests

deplist command, yum,

depmod command, Requests

desktop environments, What This Book Offers

desktop system, Linux as, The Excitement of Linux

destroy command, xm, Commands

devdump command, Options

device command, GRUB, GRUB Commands

device map, GRUB, GRUB: The Grand Unified Bootloader

devices, File-type characters

assigning interfaces to, File-type characters

displaying contents of, Options

formatting,

formatting as ext2 filesystem, Options

paging, turning off, Options

paging, turning on, Options

swapping, turning off, Options

swapping, turning on, Options

volume name for, determining, Slab mode fields

df command,

dhcp command, GRUB,

diff command,

diff command, git, Examples

diff command, svn,

diff command, svnlook,

diff3 command, Options

dig command, Routing daemons,

digit character class, Filename Metacharacters, Search Patterns

dir command, Query options

dir command, ftp, Commands

dircolors command, Query options

directories, Options

adding to stack, Options

contents of, listing verbosely,

creating,

deleting, Options

listing contents of, Query options,

lost+found directory, creating,

moving or renaming, Operations

printing stack for, Options

printing top directory from stack,

removing from path, Options

Dired (Directory Editor) mode, Emacs, Modes

dirname command, Options

dirs command, Bash, Options

dirs-changed command, svnlook,

DIRSTACK built-in variable, Built-in Shell Variables

disaster recovery data, storing, Options

disconnect command, ftp, Commands

disk image files, for virtualization, MAC Addresses

disk usage,

auditing, Options

available space, determining,

printing, ,

quota statistics for, printing,

reporting on,

disk-at-once (DAO) mode,

disown command, Bash, Options

display command, gdb, Common commands

displayapm command, GRUB,

displaymem command, GRUB,

distributions of Linux, The Excitement of Linux

division operator (/), Built-in Variables

dmesg command, Options

dmesg command, xm, Commands

DNS (Domain Name System), Routing daemons

DNS servers, querying,

do command, gawk,

do reserved word, Bash, Options

document formatting (see groff command), Exit codes

document processing, gs command for, Exit codes

doexec command, Options

$ (dollar sign), Built-in Variables

field reference, Operators

last input line as pattern address in sed, Pattern Addressing

match at end of line or string, Filenames Versus Patterns

preceding built-in variables, Built-in Shell Variables

preceding macros in ftp, Options

variable substitution, Quoting

dollar sign ($), Built-in Variables

field reference, Operators

last input line as pattern address in sed, Pattern Addressing

match at end of line or string, Filenames Versus Patterns

preceding built-in variables, Built-in Shell Variables

preceding macros in ftp, Options

variable substitution, Quoting

${...} (dollar sign, braces), Other Shell Variables

enclosing arrays, Other Shell Variables

enclosing variable substitution, Variables

dollar sign, braces (${...}), Other Shell Variables

enclosing arrays, Other Shell Variables

enclosing variable substitution, Variables

$(()) (dollar sign, double parentheses) arithmetic substitution, Command Forms, Arithmetic Expressions

dollar sign, double parentheses ($(())) arithmetic substitution, Command Forms, Arithmetic Expressions

$() (dollar sign, parentheses) command substitution, Command Forms

dollar sign, parentheses ($()) command substitution, Command Forms

Domain Name System (DNS), DNS and BIND

domain names, Example

contact for, finding, Example

definition of, Routing daemons

domain nameserver,

querying, Options

updating, Options

domainname command,

domains, DNS and BIND

definition of, Routing daemons

NIS, Overview of NIS

done reserved word, Bash, Options

dosfsck command,

dot (.),

end message, mailx,

match single character, Filenames Versus Patterns

read and execute file command,

. (dot),

end message, mailx,

match single character, Filenames Versus Patterns

read and execute file command,

double quotes (“...”) enclosing special characters, Quoting

“...” (double quotes) enclosing special characters, Quoting

down command, gdb, Common commands

downloading files from Internet,

dp (dt) command, mailx, Command-mode commands

dpkg command, Debian, Options

(see also Debian Package Manager), Scripts

dpkg-architecture script, Debian, Scripts

dpkg-buildpackage script, Debian, Scripts

dpkg-checkbuilddeps script, Debian, Scripts

dpkg-deb command, Debian, Package Management, Options

dpkg-distaddfile script, Debian, Scripts

dpkg-divert script, Debian, Scripts

dpkg-genchanges script, Debian, Scripts

dpkg-gencontrol script, Debian, Scripts

dpkg-name script, Debian, Scripts

dpkg-parsechangelog script, Debian, Scripts

dpkg-preconfigure script, Debian, Scripts

dpkg-query command, Debian, Options

dpkg-reconfigure script, Debian, Scripts

dpkg-scanpackages script, Debian, Scripts

dpkg-shlibdeps script, Debian, Scripts

dpkg-source script, Debian, Scripts

dpkg-split command, Debian, Options

dpkg-statoverride script, Debian, Scripts

DSA identities, adding to authentication agent, Escape characters

dselect command, Debian, Package Management, Options

du command,

dual booting, Boot Methods, Boot Methods, Options

dump command, Options

dump command, GRUB,

dump command, svnadmin, Common svnadmin Subcommands

dumpe2fs command,

dumpiso command,

dumpkeys command,

dvdrecord command, Options

DVDs, File Management

commands for, list of, File Management

ejecting, Options

recording, Options, Options

E

e command, sed, Basic Editing,

e2fsck command, Options

e2image command, Options

e2label command,

EasyBCD software, Options

echo command,

echo command, Bash, Options

ed editor, metacharacters supported by, Replacement Patterns

edit (e) command, mailx, Command-mode commands

edit command, ex,

edit commands, Insert Commands

EDITOR built-in variable, Built-in Shell Variables

editors (see ed editor; Emacs editor; ex editor; sed editor; vi editor; vim editor),

edquota command,

EGP (Exterior Gateway Protocol), IP Addresses

egrep command, Options, Replacement Patterns

eject command, Options

elevator algorithm, setting latency for,

ELF (Executable and Linking Format) object files,

elvis editor, The vi, ex, and vim Editors

elvtune command,

EMACS built-in variable, Built-in Shell Variables

emacs command, Notes on the Tables

Emacs editor, , The Emacs Editor

commands, Capitalization Commands

buffer-manipulation, Capitalization Commands

capitalization, Capitalization Commands

centering, Centering Commands

completions for, Modes

cursor-movement, Cursor-Movement Commands

deletion, Cursor-Movement Commands

file-handling, Notes on the Tables

help, Notes on the Tables, Centering Commands, Help Commands

indentation, Indentation Commands

jobs, Window Commands

list of, alphabetic by keystroke, Help Commands

list of, alphabetic by name, Meta-Key Sequences

list of, most important, Notes on the Tables

listing, Notes on the Tables

macro, Macro Commands

paragraph, Paragraphs and Regions

region, Paragraphs and Regions

search, Search Commands

shell, Special Shell Characters

stopping, Paragraphs and Regions

transposition, Paragraphs and Regions

undoing, Paragraphs and Regions

windows, Capitalization Commands

word-abbreviation, Capitalization Commands

Ctrl key notation (C-), Modes

file buffers in, Modes

invoking, Notes on the Tables

kill and yank (cut and paste) in, Modes

mark location in, Modes

Meta key notation (M-), Modes

modes in, The Emacs Editor

point (cursor) location in, Modes

windows in, Modes

embed command, GRUB,

embedded versions of Linux, The Excitement of Linux

enable command,

enable command, Bash, Options

encoding, base64, Options

encryption and decryption with GNU Privacy Guard, HFS options

(see also security), Configuration commands

endscript command, logrotate, Configuration commands

Enter key, print next line command in ex,

ENV built-in variable, Built-in Shell Variables

env command,

environment variables,

printing, Options

setting,

substituting in shell string or script,

environment, displaying,

envsubst command,

equals sign (=), Built-in Variables

assignment operator, Built-in Variables

command in sed, Basic Editing, Branching Commands

print line number command in ex,

= (equals sign), Built-in Variables

assignment operator, Built-in Variables

command in sed, Basic Editing, Branching Commands

print line number command in ex,

esac reserved word, Bash, Options

escape sequences, Quoting

gawk, Variable and Array Assignment

pattern matching, Search Patterns

ESX management client, for VMware, VMware ESX 3.5

ESX server commands, for VMware, Snapshots

esxcfg-firewall command, VMware, Snapshots

esxcfg-nics command, VMware,

esxcfg-vswif command, VMware,

esxcfg-vswitch command, VMware, Options

esxtop command, VMware,

etags command,

EUID built-in variable, Built-in Shell Variables

eval command, Bash, Options

ex editor, Options, The vi, ex, and vim Editors, Conceptual Overview, Sample .exrc File

command options, Address Symbols

command syntax, Sample .exrc File

command-line options, Conceptual Overview

commands, Address Symbols

exiting, Command-Line Options

invoking, Command-Line Options, Sample .exrc File

line addresses in, Sample .exrc File,

pattern matching metacharacters supported by, Replacement Patterns

examples in this book, using, xix,

! (exclamation point),

execute command in ex,

execute command, mailx, Compose-mode commands

history expansion character, Command History

logical negation operator, Built-in Variables

negating pipeline, Command Execution

NOT operator for commands, Command Forms

preceding commands in ftp, Options

exclamation point (!),

execute command in ex,

execute command, mailx, Compose-mode commands

history expansion character, Command History

logical negation operator, Built-in Variables

negating pipeline, Command Execution

NOT operator for commands, Command Forms

preceding commands in ftp, Options

!= (exclamation point, equal) not equal operator, Built-in Variables

exclamation point, equal (!=) not equal operator, Built-in Variables

!() (exclamation point, parentheses) in filename, Filename Metacharacters

exclamation point, parentheses (!()) in filename, Filename Metacharacters

!~ (exclamation point, tilde) match negation of regular expression, Built-in Variables

exclamation point, tilde (!~) match negation of regular expression, Built-in Variables

exec command, Bash,

Executable and Linking Format (ELF) object files,

executable files, compressing, Options

exit (ex, x) command, mailx, Command-mode commands

exit command, Bash,

exit command, gawk,

exp() function, gawk,

expand command, Options

exponentiation operator (^ or **), Built-in Variables

export command, Bash,

export command, svn, Examples

expr command,

expressions, evaluating, , Options, , Settable shell options

ext2 filesystem, Options

checking and repairing, Options

debugging, Options

formatting devices as, Options

label for, displaying,

printing block and superblock information,

resizing, Options

storing disaster recovery data for, Options

tuning parameters of, Options

ext3 filesystem, Managing Filesystems

debugging, Options

formatting devices as,

printing block and superblock information,

extended Internet services daemon,

extended regular expressions, searching with, Options

Extensible Filesystem (see XFS), Configuration commands

extension command, logrotate, Configuration commands

extension() function, gawk,

Exterior Gateway Protocol (EGP), IP Addresses

eXternal Data Representation (XDR), Administering NIS

F

factor command, Examples

fallback command, GRUB, The GRUB Configuration File

false command, Examples

false command, Bash, Options

Fast Lexical Analyzer Generator,

FAT filesystem, Managing Filesystems

fc command, Bash, Command History, Options

fc-cache command, Examples

fc-list command,

FCEDIT built-in variable, Built-in Shell Variables

fdisk command,

fetch command, git,

fflush() function, gawk,

fg command, Bash, Options

fgconsole command, Commands

fgrep command, Commands

fi reserved word, Bash,

field reference ($), gawk, Built-in Variables

FIFO pipes, creating,

FIGNORE built-in variable, Built-in Shell Variables

file (fi) command, mailx, Command-mode commands

file command, Commands

file command, ex,

file inclusion, gawk, Profiling

filenames, Options

checking validity of, Options

database of, searching, Environment variables

metacharacters for, Arguments

temporary,

validity and portability of,

files,

(see also directories; paths),

access mode for, checking,

access permissions for, changing, Options

attributes of, changing, Options

attributes of, listing, Options

backing up,

base64 encoding or decoding, Options

byte count for, Options

classifying, Commands

columns in, removing, Examples

comparing, ,

comparing and finding differences between, Key bindings

comparing lines common to, Examples

compressing,

compressing and decompressing, Options

computing or checking MD5 checksums for,

concatenating, Options

conditions of, testing for, Settable shell options

converting into tables for parsing, Other symbols

converting to alternate character encoding, Options

converting to tables, Configuration files

copying,

copying and converting format of, Format

copying or restoring from archives, Options

copying securely, Options

copying to or from remote systems,

creation mask for, displaying or setting,

deleting,

deleting files older than a specific access time,

displaying in hex, octal, decimal, or ASCII,

displaying one screen at a time, Options, Options

downloading from Internet,

dumping, in octal format by default, Options

executable, compressing, Options

formatting into columns, Examples

group for, changing, Attributes

line count for, Options

linking, Commands

locating, Options

maintaining in archives,

management of, commands for, Comparisons, Notes on the Tables

merging,

merging corresponding lines of, Options

moving or renaming, Operations

overwriting, to make contents unrecoverable, Options

ownership of, changing, Examples

paginating, suitable for printing, Files

paging through, , Options

paging, turning off, Options

printing,

printing first few lines of,

printing last ten lines of, Options

printing lines in reverse order,

processes using, identifying, Options

recompiling and relinking based on dependencies, Configuration options

reformatting to a specific width, Options, Options

remote file distribution,

removing by unlinking,

removing columns or fields from, Options

removing duplicate adjacent lines in,

renaming, Options

restoring from backup,

reversing characters in each line of, Options

searching, Commands

searching for files meeting specific conditions, Examples

searching for printable strings in, Options

searching for strings at beginning of lines, Configuration commands

searching with extended regular expressions, Options

separating into context-based sections,

sorted, joining, Interactive commands

sorting lines of,

sorting strings in, Options

splitting into equal-sized segments, Options

swapping, turning off, Options

transferring to and from remote sites, , Configuration file format,

unchanged, verifying,

uncompressing, Options

updating access and modification times to current time, Field descriptions

updating across a network,

word count for, Options

filesystem checker, for MS-DOS filesystems,

filesystem types, Managing Filesystems

filesystems, Managing Filesystems

(see also NFS), Examples

checking and repairing, Options, Options

commands for, list of, Managing Filesystems

creating on a device,

debugging, Options

displaying contents of, Options

ISO9660/Joliet/HFS, generating, Common commands,

mounting, Examples,

quotas for, enforcing, Options

quotas for, turning off enforcement of,

quotas, editing,

unmounting, Options

writing buffers to disk, Options

find command, Examples

find command, GRUB,

firewalls, Serial-line communication

book about, Overview of Firewalls and Masquerading

rules, printing, Options

rules, restoring, Target extensions

firstaction command, logrotate, Configuration commands

fixmbr command, The Boot Process

flex command, Examples

floppy disks, ejecting, Options

fmt command, Options

fold command, Options

fold command, ex,

foldclose command, ex,

folder (fold) command, mailx, Command-mode commands

folders command, mailx, Command-mode commands

foldopen command, ex,

font conventions used in this book, xx, Examples

font information caches, creating, Examples

fonts, listing,

for command, Bash,

for command, gawk, ,

foreground, moving job to, Options

form command, ftp, Commands

formail command, Options

forward (fwd) command, mailx, Command-mode commands

frame command, gdb, Common commands

free command, Options

free disk space, determining,

Free Software Foundation (see FSF), Pattern Matching

Friedl, Jeffrey E.F. (Mastering Regular Expressions), Pattern Matching

from (f) command, mailx, Command-mode commands

fsck command, Options

fsck.ext2 command, Options

FSF (Free Software Foundation), What This Book Offers

fstest command, GRUB,

ftp command,

(see also sftp command), Commands

ftpd command, Commands

FUNCNAME built-in variable, Built-in Shell Variables

function command, Bash,

function command, gawk,

functions, Functions

declaring,

defining,

deleting,

exiting and returning status from,

listing for source file,

overloading, decoding symbols for, Examples

source and line number for, Options

user-defined, gawk, Octal and Hexadecimal Constants in gawk

fuser command, Options

G

G command, sed, Basic Editing,

g command, sed, Basic Editing,

g++ compiler,

gateways, Gateways and Routing

gawk command,

gawk language, The gawk Programming Language

array assignment, Variable and Array Assignment

built-in variables, Simple Pattern-Procedure Examples

command-line options for, Standard Options

command-line syntax for, Conceptual Overview

commands for, Internationalization

coprocesses, gawk-Specific Features

escape sequences, Variable and Array Assignment

file inclusion for, Profiling

functions for, Internationalization

hexadecimal constants in, Octal and Hexadecimal Constants in gawk

implementation limits of, Internationalization

internationalization for, Profiling

invoking, Command-Line Syntax

octal constants in, Octal and Hexadecimal Constants in gawk

operators, Built-in Variables

output redirection,

pattern matching metacharacters supported by, Replacement Patterns

patterns in, Important gawk Options, Patterns

procedures in, Important gawk Options, Patterns

profiling, Profiling

sockets, Coprocesses and Sockets

user-defined functions, User-Defined Functions

variable assignment, Built-in Variables

gc command, git,

gcc compiler,

gdb debugger, Pragma directives

General Public License (see GPL), Common commands

genisoimage command, Common commands

gensub() function, gawk,

geometry command, GRUB,

get command, ftp, Commands

getent command, HFS options

getkeycodes command, HFS options

getline command, gawk,

getopts command, Bash,

getpwnam( ) function, Arguments

getpwuid( ) function, Arguments

gettext, GNU, Profiling

GhostScript,

git command, Creating and Sharing a New Repository

add subcommand, Accessing Git’s Online Help

archive subcommand, Examples

bisect subcommand,

branch subcommand, Examples

checkout subcommand,

cherry-pick subcommand,

clean subcommand,

clone subcommand,

commit subcommand,

config subcommand, Examples

diff subcommand, Examples

fetch subcommand,

gc subcommand,

gitk subcommand, Examples

grep subcommand, Examples

help subcommand, Accessing Git’s Online Help

init subcommand, Examples

log subcommand, Examples

merge subcommand, Examples

mv subcommand, Examples

pull subcommand, Examples

push subcommand,

rebase subcommand, Examples

reflog subcommand,

remote subcommand,

reset subcommand, Examples

revert subcommand, Examples

rm subcommand, Examples

stash subcommand,

status subcommand,

tag subcommand, Examples

git daemon, Creating and Sharing a New Repository

git shell, Creating and Sharing a New Repository

Git version control system, Source Code Management Systems, The Git Version Control System

branches in, Conceptual Overview,

merging, , Examples

pushing,

tracking changes to,

checking in (committing) files, Conceptual Overview, Example: The Linux Kernel Repository,

cherry-picking commits, , Examples

finding problem in,

referring to commits, Conceptual Overview

remotely,

reversing, Examples

searching commits, Examples

testing results of,

undoing, Examples

checking out files, Conceptual Overview, Example: The Linux Kernel Repository,

command line for, Creating and Sharing a New Repository

configuring, Examples

differences, generating, Examples

help for, Accessing Git’s Online Help

history, displaying, Examples, Examples

hosting projects, Creating and Sharing a New Repository

index for, Conceptual Overview

adding or updating files in, Accessing Git’s Online Help

removing files from, Examples

remotes for,

repositories for, The Git Version Control System, Conceptual Overview

cloning,

creating, Example: The Linux Kernel Repository, Examples

creating archive from, Examples

packing,

subcommands for, Accessing Git’s Online Help

tags for, Referring to Commits, Examples

uncommitted changes, working with,

user name and email for, Referring to Commits

working tree for, Conceptual Overview

cleaning,

removing files from, Examples

, Conceptual Overview, Example: The Linux Kernel Repository,

github.com service, Creating and Sharing a New Repository

gitk command, git, Examples

Gitorious tool, Creating and Sharing a New Repository

Gitosis tool, Creating and Sharing a New Repository

glob command, ftp, Commands

global command, ex,

GLOBIGNORE built-in variable, Built-in Shell Variables

GNOME desktop, Sources and Licenses

GNU Arch system, Source Code Management Systems

GNU awk (see gawk language), Pattern Matching

GNU Emacs (see Emacs editor), Profiling

GNU Emacs Pocket Reference (Cameron), Pattern Matching

GNU gettext, Profiling

GNU makefiles, creating from template files, Options

GNU Privacy Guard application, HFS options

GNU project, Commands on Linux

GNU sed editor (see sed editor), Introduction

GNU utilities documentation, website for, xvii, Introduction

GNU/Linux, Introduction

(see also Linux), Command-mode commands

good (go) command, mailx, Command-mode commands

gpasswd command, HFS options

gpg command, HFS options

gpgsplit command, Other commands

gpgv command,

GPL (General Public License), What This Book Offers

gpm command,

gprof command,

GRand Unified Bootloader (see GRUB), Filename Metacharacters, Search Patterns

graph character class, Filename Metacharacters, Search Patterns

graphical desktop environments for Linux, Commands on Linux

graphical tools for Linux, Commands on Linux

greater than (>) operator,

grep command, Options, Replacement Patterns

grep command, git, Examples

groff command, Examples

group ID, displaying information about, Options

groupadd command, Environment variables

groupdel command,

groupinfo command, yum,

groupinstall command, yum,

grouplist command, yum,

groupmod command,

groupremove command, yum,

groups, Attributes

changing for files, Attributes

changing for user,

creating, Environment variables

creating shadowed groups from, Exit codes

listing for users,

managing, HFS options

modifying,

removing,

removing corrupt and duplicate entries in,

space allowed on disk for,

GROUPS built-in variable, Built-in Shell Variables

groups command,

grpck command,

grpconv command, Exit codes

GRUB (GRand Unified Bootloader), Boot Methods, lilo Command Options

boot CD for, Installing GRUB

boot floppy for, Installing GRUB

commands for, The GRUB Shell

configuration file, Using grub-install, Boot-Time Kernel Options, Boot-Time Kernel Options

device map, GRUB: The Grand Unified Bootloader

installation stages, GRUB: The Grand Unified Bootloader

installing, Installing GRUB

menu interface, Using the Menu Interface

naming conventions, GRUB: The Grand Unified Bootloader

shell, The GRUB Configuration File

grub command, GRUB, Installing GRUB, The GRUB Configuration File

grub-install shell script, GRUB: The Grand Unified Bootloader, Creating a GRUB boot floppy

grub-md5-crypt command, GRUB, The GRUB Configuration File

gs command, Exit codes

gsub() function, gawk,

gunzip command, Options

gzexe command, Options

gzip command,

H

H command, sed, Basic Editing,

h command, sed, Basic Editing,

H hostname escape sequence, Arrays

halt command, Options

halt command, GRUB,

hard drive, Options

parameters for, reading or setting, Options

partitioning, Examples, Options

hard links, Options

hardware, Daemons

commands for, list of, Daemons

performance improvements on, The Excitement of Linux

supported by Linux, The Excitement of Linux

hardware clock, reading or setting,

hash command, Bash,

hash command, ftp, Commands

# (hash sign), Group Listing of awk Functions and Commands

preceding comments in gawk, Group Listing of awk Functions and Commands

preceding comments in LILO configuration file, The LILO Configuration File

preceding comments in sed scripts, Branching Commands

preceding comments in shell scripts, Command Execution

hash sign (#), Command Execution

preceding comments, Command Execution

preceding comments in gawk, Group Listing of awk Functions and Commands

preceding comments in LILO configuration file, The LILO Configuration File

preceding comments in sed scripts, Branching Commands

hdparm command, Options

head command,

header for packages, Plugins and yum-utils

headers (h) command, mailx, Command-mode commands

headers+ (h+) command, mailx, Command-mode commands

headers- (h-) command, mailx, Command-mode commands

Hello Protocol, IP Addresses

help command (C-h), Emacs, Notes on the Tables

help command, Bash, Options

help command, ftp, Commands

help command, git, Accessing Git’s Online Help

help command, GRUB,

help command, ip, Options

help command, mailx, Command-mode commands

help command, svn,

help command, svnadmin, Examples

help command, svnlook,

help command, xm, Commands

help command, yum,

help commands, Emacs, Notes on the Tables, Centering Commands, Help Commands

hexadecimal constants, gawk, Octal and Hexadecimal Constants in gawk

hexadecimal format,

displaying files in,

printing host ID in, Options

hexdump command,

HFS filesystem, generating, Common commands,

hiddenmenu command, GRUB, The GRUB Configuration File

hide command, ex,

hide command, GRUB,

histchars built-in variable, Other Shell Variables

HISTCMD built-in variable, Built-in Shell Variables, Built-in Shell Variables

HISTCONTROL built-in variable, Other Shell Variables

HISTFILE built-in variable, Other Shell Variables

HISTFILESIZE built-in variable, Other Shell Variables

HISTIGNORE built-in variable, Other Shell Variables

history command, Bash, Options

history command, svnlook,

history expansion character (!), Command History

history of commands, Command History, Options, Options

HISTSIZE built-in variable, Other Shell Variables

HISTTIMEFORMAT built-in variable, Other Shell Variables

hoclock command,

hold (ho) command, mailx, Command-mode commands

hold space, sed, sed Operation

HOME built-in variable, Other Shell Variables

home directories, determining, Arguments

host command, Routing daemons, Options

host ID, printing in hexadecimal format, Options

HOSTFILE built-in variable, Other Shell Variables

hostid command, Options

HOSTNAME built-in variable, Built-in Shell Variables

hostname command, Options

hosts, Daemons

information about, commands for, Daemons

name of, displaying or setting, Options

printing information about, Options

HOSTTYPE built-in variable, Built-in Shell Variables

hotcopy command, svnadmin, Examples

htdigest command, Options

hunspell command, Options

Hunt, Craig (TCP/IP Network Administration), Overview of TCP/IP

hypervisor, Conceptual Overview, Virtualization Technology

(see also virtualization tools), Compose-mode commands

hyphen (-), Compose-mode commands

previous command, mailx, Compose-mode commands

subtraction operator, Built-in Variables

unary minus operator, Built-in Variables

- (hyphen), Compose-mode commands

previous command, mailx, Compose-mode commands

subtraction operator, Built-in Variables

unary minus operator, Built-in Variables

hyphen(s) (- or --) preceding command options, Linux Commands

- or -- (hyphen(s)) preceding command options, Linux Commands

hyphen, double (--) decrement operator, Built-in Variables

-- (hyphen, double) decrement operator, Built-in Variables

hyphen, equals sign (-=) assignment operator, Built-in Variables

-= (hyphen, equals sign) assignment operator, Built-in Variables

I

i command, sed, Basic Editing,

I/O latency for elevator algorithm,

I/O scheduling class, setting, Options

IANA (Internet Assigned Numbers Authority), IP Addresses

IBM Journaled Filesystem (see JFS), Domain names

ICANN (Internet Corporation for Assigned Names and Numbers), Domain names

icedax command,

ICMP (Internet Control Message Protocol), Overview of TCP/IP

iconv command, Options

id command, Options

idle command, ftp, Commands

IEEE 1394 packets, dumping,

if command, Bash, Options

if command, gawk,

ifconfig command, Domain names, Options

ifconfig command, GRUB,

ifempty command, logrotate, Configuration commands

IFS built-in variable, Other Shell Variables

igawk (inclusion gawk), Profiling

ignore command, mailx, Command-mode commands

IGNOREEOF built-in variable, Other Shell Variables

image command, ftp, Options

IMAP (Interactive Mail Access Protocol) server daemon,

imap command, mailx, Command-mode commands

imapd command,

import command, svn,

impsprobe command, GRUB,

in operator, for array membership, Built-in Variables

include command, logrotate, Configuration commands

inclusion gawk (igawk), Profiling

InCrEdible Digital Audio eXtractor (see icedax command), Built-in Variables

increment operator (++), Built-in Variables

indentation commands, Emacs, Window Commands

index() function, gawk,

index, for Git, Conceptual Overview

adding or updating files in, Accessing Git’s Online Help

removing files from, Examples

inetd command,

info command,

info command, gdb, Common commands

info command, svn, Examples

info command, svnlook,

info command, xm, Commands

info command, yum,

init command, git, Examples

init daemon, Upstart, Options

init program, Starting and Stopping the System

initctl command, Options

initrd command, GRUB, The GRUB Configuration File, , Boot-Time Kernel Options

inode, printing contents of, Options

input command, ftp, Commands

INPUTRC built-in variable, Other Shell Variables

insert command, ex,

insert commands, Marks

insert mode, Conceptual Overview, Command Mode

insmod command, Options

install command,

install command, GRUB,

install command, yum,

installation, commands for, Installation

int() function, gawk,

integer comparisons, testing for, String conditions

Intel Multiprocessor Specification,

Interactive Mail Access Protocol (IMAP) server daemon,

interfaces, assigning to a device, File-type characters

internationalization, gawk, Profiling

Internet Assigned Numbers Authority (IANA), IP Addresses

Internet Control Message Protocol (ICMP), Overview of TCP/IP

Internet Corporation for Assigned Names and Numbers (ICANN), Domain names

Internet protocols, Overview of Networking

Internet services daemon,

Internetworking with TCP/IP (Comer), Overview of TCP/IP

interprocess communication (see IPC),

ionice command, Options

ioprobe command, GRUB,

IP address,

contact for, finding, Example

definition of, Overview of TCP/IP

ip command, Domain names, Options

IP ports, mapping to RPC program numbers, Options

IPC (interprocess communication), Common arguments

removing message queues, Common arguments

removing semaphore arrays, Common arguments

removing shared memory segments, Common arguments

reporting on, Options

ipcrm command, Common arguments

ipcs command, Options

iptables (see netfilter), Overview of Firewalls and Masquerading, Target extensions

iptables command, Overview of Firewalls and Masquerading, Options

iptables-restore command, Overview of Firewalls and Masquerading, Target extensions

iptables-save command, Overview of Firewalls and Masquerading, Options

IPv4 addresses, Overview of TCP/IP

IPv6 addresses, IP Addresses

ISO9660 images,

displaying content of, Options

displaying information about, Options

displaying length of, Options

verifying integrity of, Options

ISO9660/Joliet/HFS filesystem, generating, Common commands,

isodump command, Options

isoinfo command, Options

isosize command, Options

isovfy command, Options

ispell command, Options

J

JFS (Journaled Filesystem), Installation

job control, Job Control

Emacs commands for, Window Commands

listing jobs, Options

moving job to foreground, Options

removing job from job list, Options

terminating jobs,

waiting for background jobs to finish,

jobs command, Bash, Options

join command, Interactive commands

join command, ex,

Journaled Filesystem (see JFS), Common commands

jump command, gdb, Common commands

jumps command, ex,

junk (j) command, mailx, Command-mode commands

K

k command, ex,

kbdrate command,

kbd_mode command,

kernel, Introduction

commands for, list of, Managing Filesystems

loading modules into, Options

messages, displaying, prioritizing, and logging, Options

parameters, displaying or modifying, Options

kernel command, GRUB, The GRUB Configuration File, The GRUB Configuration File,

Kernel-based Virtual Machine (see KVM hypervisor), Options

keyboard,

assigning keycode events to scancodes, Options

driver translation tables, printing information about,

mode for, printing or setting,

printing keycodes, scancodes, or ASCII codes of keys pressed, Options

rate, setting,

Unicode mode for,

keycodes, HFS options

mapping table for, HFS options

printing, Options

keymaps, loading, Options

keys, authentication, Options

gathering public and private keys from multiple, Options

generating, managing, and converting,

holding private keys for public authentication,

keyword substitutions, in source code management system, Introduction and Terminology

kill and yank (cut and paste), Emacs, Modes

kill command,

kill command, Bash,

kill command, gdb, Common commands

killall command, Options

klogd command, Options

Korn shell, The Bash Shell

ksh shell, The Bash Shell

KVM hypervisor, KVM

building guest systems, Ubuntu Builder Scripts

changing virtual machine configurations, MAC Addresses

device interfaces for, Configuring Networks

graphic interface for, Managing Virtual Systems

installing, Interactive commands

libvirt used with (see libvirt virtualization API), Managing Virtual Systems

managing virtual systems, Managing Virtual Systems

QEMU used with, Interactive commands

website for, Virtualization Command-Line Tools

L

l command, sed, Basic Editing,

LANG built-in variable, Other Shell Variables

last command, Options

lastaction command, logrotate, Configuration commands

lastb command, Options

lastlog command,

latency in elevator algorithm, setting,

lcd command, ftp, Commands

LC_ALL built-in variable, Other Shell Variables

LC_COLLATE built-in variable, Other Shell Variables

LC_CTYPE built-in variable, Other Shell Variables

LC_MESSAGES built-in variable, Other Shell Variables

LC_NUMERIC built-in variable, Other Shell Variables

ld command,

ldconfig command, Options

ldd command, Options

Learning GNU Emacs (Cameron et al.), Pattern Matching, Modes

Learning Red Hat Enterprise Linux and Fedora (McCarty), What This Book Offers

Learning the bash Shell (Newham), The Bash Shell

Learning the Unix Operating System (Peek; Todino-Gonguet; Strang), xvii, Options

LED flag settings, displaying or changing, Options

left angle bracket (<) less than operator, , Built-in Variables

left angle bracket, equals sign (<=) less than or equal operator, Built-in Variables

left command, ex,

Lempel-Ziv coding (LZ77), compressing files using,

length() function, gawk,

less command, Options

less than operator (<),

lesskey command, Commands

let command, Bash, Arithmetic Expressions,

lexical analysis program, generating, Examples

lftp command, Configuration file format

lftpget command, Commands

libraries,

examining and updating, Options

shared, displaying program requirements for, Options

libvirt virtualization API, System Requirements, libvirt and Red Hat Virtual Machine Manager

connection URIs for hypervisor, Ubuntu Builder Scripts

networking for, Connection URI Examples

remote GUI control for, Connection URI Examples

virsh commands,

virt-clone command, Options

virt-image command, Options

virt-install command, Options

virt-manager command, Options

virt-viewer command, Options

website for, Virtualization Command-Line Tools, Ubuntu Builder Scripts

XML configuration files for, Ubuntu Builder Scripts

licenses for Linux, What This Book Offers

(see also GPL), The Boot Process, Kernel options

LILO (Linux Loader), Boot Methods, The Boot Process

boot errors, lilo Command Options

configuration file, LILO: The Linux Loader, The LILO Configuration File, Boot-Time Kernel Options, Boot-Time Kernel Options

global options, Global options

image options, Image options

kernel options, Kernel options

rescue CD for, making, The Boot Process

lilo command, LILO: The Linux Loader, Kernel options

line-edit mode, Bash, Command History

LINENO built-in variable, Built-in Shell Variables

LINES built-in variable, Other Shell Variables

link command, Commands

link set command, ip, Options

link show command, ip, Options

Linux, Introduction

as desktop system, The Excitement of Linux

benefits of, Introduction

commands, The Excitement of Linux, What This Book Offers

compared to Unix, Introduction

distributions of, The Excitement of Linux

embedded versions of, The Excitement of Linux

hardware supported by, The Excitement of Linux

history of, Introduction

installing, book about, xvii, What This Book Offers

licenses for, What This Book Offers

performance improvements by, The Excitement of Linux

source code for, Sources and Licenses

starting, Starting and Stopping the System

stopping, Starting and Stopping the System

support for, The Excitement of Linux

Linux Gazette website, xvii, Overview of Firewalls and Masquerading

Linux Insider website, xvii, Overview of Firewalls and Masquerading

Linux iptables Pocket Reference (Purdy), Overview of Firewalls and Masquerading

Linux Loader (see LILO), Overview of TCP/IP, Overview of Firewalls and Masquerading

Linux Magazine, xviii, Overview of TCP/IP, Overview of Firewalls and Masquerading

Linux Network Administrator’s Guide (Bautts; Dawson; Purdy), Overview of TCP/IP, Overview of Firewalls and Masquerading

Linux Today website, xvii,

Linux Weekly News website, xvii,

list command, ex,

list command, gdb, Common commands

list command, mailx, Command-mode commands

list command, svn,

list command, xm, Commands

list command, yum,

list-dblogs command, svnadmin, Examples

list-unused-dblogs command, svnadmin, Examples

ln command, Commands

load command, svnadmin, Examples

loaded modules, listing,

loadkeys command, Options

local command, Bash,

local variables, Bash,

locale command,

locale settings, printing,

localinstall command, yum,

localizing gawk programs, Profiling

localupdate command, yum,

locate command, Environment variables

lock command, GRUB, The GRUB Configuration File,

lock command, svn,

lock command, svnlook,

lockfile command, Options

log command, git, Examples

log command, svn,

log command, svnlook,

log command, xm, Commands

log message, for source code management system, Introduction and Terminology

log() function, gawk,

logger command, Options

logging (see system logging),

logging in, Options

to remote host, Options

to remote system, securely, Options

to tty port,

logical AND operator (&&),

logical negation operator (!), Built-in Variables

logical operators,

logical OR operator (||),

login shell,

changing, Options

exiting,

logins,

bad attempts at, displaying, Options

for system accounts, displaying times of,

most recent, printing, Options

printing list of, Options

printing summary of, Slab mode fields

logout command, Bash,

logrotate command, Options

look command, Configuration commands

loop devices, setting up and controlling, Configuration commands

loops,

exiting from, Options

for command,

skipping remaining commands in, Options

until command,

while command,

losetup command, Configuration commands

lost+found directory, creating,

lower character class, Filename Metacharacters, Search Patterns

lpadmin command, Configuration commands

lpinfo command,

lpmove command,

lpq command,

lpr command,

lprm command, Options

lpstat command,

ls command, Query options,

ls command, ftp, Commands

lsattr command, Options

lshift() function, gawk,

lslocks command, svnadmin, Examples

lsmod command,

lspci command, Options

lstxns command, svnadmin, Examples

lsusb command,

LZ77 (Lempel-Ziv coding), compressing files using,

M

M-x Tab (command names list) command, Emacs, Notes on the Tables

m4 command,

m4 macros,

combining into one file,

generating configuration script from,

generating template of #define statements from, Options

MAC address, for virtualization, MAC Addresses

macdef command, ftp, Commands

MACHTYPE built-in variable, Built-in Shell Variables

macro commands, Macros

macro commands, Emacs, Centering Commands

macro processor,

macros, Options

executing in ftp, Options

in package spec file, RPM Package Concepts

listing for source file,

magnetic tape drive, controlling,

mail,

aliases database, rebuilding,

aliases, printing, Options

commands for, list of, Installation

reading or sending, Options, Options

remote mail, receiving, Options

sendmail queue, listing messages in, Options

sendmail statistics, reporting, Options

mail (m) command, mailx, Command-mode commands

MAIL built-in variable, Other Shell Variables

mail command, Options

mail command, logrotate, Configuration commands

mail transfer agent (MTA),

mailbox format, filtering input into, Options

MAILCHECK built-in variable, Other Shell Variables

mailfirst command, logrotate, Configuration commands

maillast command, logrotate, Configuration commands

MAILPATH built-in variable, Other Shell Variables

mailq command, Options

mailstats command, Options

mailx command, Options

make command, Configuration options

makeactive command, GRUB,

makecache command, yum,

makedbm command, Special target names

makefiles, Options

creating from template files, Options

executing, Configuration options

makemap command, Options

man command, Options

Managing Projects with GNU Make (Mecklenburg), Configuration options

manpath command,

manual pages, Options

displaying, Options

path to, determining,

searching for keyword, Options

searching short descriptions for strings, Parameters

map command, ex,

map command, GRUB,

mapfile command, Bash,

maps, NIS, Overview of NIS

mark command, ex, Examples

mark location, Emacs, Modes

marks command, ex, Examples

masquerading, Overview of Firewalls and Masquerading

master boot record (see MBR), Pattern Matching

Mastering Regular Expressions (Friedl), Pattern Matching

match() function, gawk,

mbox command, mailx, Command-mode commands

MBR (master boot record), Boot Methods

installing GRUB boot loader on, GRUB: The Grand Unified Bootloader, Creating a GRUB boot floppy, Using grub-install

installing LILO boot loader on, The Boot Process

restoring, The Boot Process

McCarty, Bill (Learning Red Hat Enterprise Linux and Fedora), What This Book Offers

MD5 checksums for files, computing or checking,

md5crypt command, GRUB, The GRUB Configuration File,

md5sum command,

mdelete command, ftp, Commands

mdir command, ftp, Commands

Mecklenburg, Robert (Managing Projects with GNU Make), Configuration options

media (see CDs; DVDs), Options

memory maps, displaying for a process, Options

memory usage, statistics about, Options

menu items, providing to user,

merge command,

merge command, git, Examples

merge command, svn,

mergeinfo command, svn, Examples

mesg command,

message queues, IPC, removing, Common arguments

Meta key (M-), Emacs, Modes

Meta key handling, displaying or setting, Options

metacharacters in pattern matching, Pattern Matching

mget command, ftp, Commands

MIDI files, Options

playing, Options

reading and writing to ALSA ports, Options

recording,

MIDI ports, connecting to route events, Options

mirror command, lftp, Commands

missingok command, logrotate, Configuration commands

mixer, ALSA, Options

connecting to ALSA sound card(s), Options

controlling, Options

mkdir command,

mkdir command, ftp, Commands

mkdir command, svn, Examples

mkdosfs command,

mke2fs command, Options

mkexrc command, ex, Examples

mkfifo command,

mkfs command,

mkfs.ext3 command,

mkisofs command,

mkisofs command, GRUB, Installing GRUB

mklost+found command,

mknod command,

mkrescue command, The Boot Process

mkswap command,

mktemp command,

mktime() function, gawk,

mls command, ftp, Commands

mode command, ftp, Commands

modinfo command,

modprobe command,

modtime command, ftp, Commands

module command, GRUB,

modulenounzip command, GRUB,

modules,

loading,

loading into kernel, Options

printing information about,

unloading, Options

modulus operator (%), Built-in Variables

monotone system, Other Source Code Management Systems

monthly command, logrotate, Configuration commands

more command, Options

mount command, Administering NFS, Examples

mountd command,

mountd daemon, Administering NFS

mouse server for Linux console,

move (mv) command, mailx, Command-mode commands

move command, ex, Examples

move command, svn,

movement commands, Movement Commands

mt command,

MTA (mail transfer agent), Options

Multiboot Specification, lilo Command Options

multiplication operator (*), Built-in Variables

mv command, Operations

mv command, git, Examples

N

n command, sed, Basic Editing,

N command, sed, Branching Commands,

name command, Bash,

name service, Name Service

named daemon, Routing daemons

named pipes (FIFO), making,

namei command, Options

nameif command, File-type characters

nameserver, DNS and BIND, Options

naming conventions, GRUB: The Grand Unified Bootloader

GRUB, GRUB: The Grand Unified Bootloader

packages, Package Management

NAT (Network Address Translation), Managing Virtual Systems

nc command, File-type characters

neigh add command, ip, Options

neigh chg command, ip, Commands

neigh del command, ip, Commands

neigh flush command, ip, Commands

neigh list command, ip, Commands

neigh repl command, ip, Commands

Net:Bridge package, Configuring Networks

netcat command (see nc command), Overview of Firewalls and Masquerading

netfilter (iptables), Overview of Firewalls and Masquerading

books about, Overview of Firewalls and Masquerading

filtering rules, configuring, Options

netstat command, Options

network, Overview of Networking

(see also NFS; NIS), Managing Virtual Systems

administration, book about, xvii, Managing the Kernel

commands for, list of, Managing the Kernel

configuring for virtualization, Managing Virtual Systems

confirming response of remote hosts on,

devices, manipulating, Options

dumping headers and packets of network traffic, Examples

interface, configuring, Domain names, Options

packet capture files for, reading and manipulating, Options

reading and writing data across, File-type characters

serial lines, attaching as network interfaces, Options

status of, displaying, Options

TCP/IP administration, Overview of Networking, TCP/IP Administration

updating files across,

Windows-based, Linux server supporting, The Excitement of Linux

Network Address Translation (NAT), Configuring Networks

Network File System (see NFS), Examples

Network Information System (see NIS), Examples

new command, ex, Examples

newaliases command,

newer command, ftp, Commands

newgrp command,

Newham, Cameron (Learning the bash Shell), The Bash Shell

newline character, as word separator, Quoting

newsgroups, xviii,

newusers command,

next (n) command, mailx, Command-mode commands

next command, ex, Examples

next command, gawk,

next command, gdb, Common commands

nextfile command, gawk,

NFS (Network File System), Overview of Firewalls and Masquerading

administering, Administering NFS

commands for, list of, TCP/IP Administration

daemons, Administering NFS

exporting filesystems, Administering NFS

module, launching threads for,

mounting filesystems, Administering NFS

server, displaying information about, Options

statistics on, printing,

nfsd command,

nfsd daemons, Daemons

nfstat command,

NIC names, finding contact for, Example

nice command,

NIS (Network Information System), Overview of NIS

administering, Administering NIS

client, setting up, Administering NIS

commands for, list of, TCP/IP Administration, Overview of NIS

domain, setting or displaying name of,

domains, Overview of NIS

login password for, changing,

maps, Overview of NIS

password file, modifying,

server, setting up, Administering NIS

servers, Overview of NIS

services, checking configuration for, Options

user accounts, NIS User Accounts

NIS binder process,

NIS database,

creating, Options

printing specific values in, Options

NIS dbm file, creating or dumping, Special target names

NIS map,

forcing propagation of, Options

printing values of keys,

transferring from server to local host, , Options

version of, determining, Options

NIS server,

hostname of, determining,

setting for ypbind command, Options

NIS+, Overview of NIS

nlist command, ftp, Commands

nm command,

nmap command, ftp, Commands

nocompress command, logrotate, Configuration commands

nocopy command, logrotate, Configuration commands

nocopytruncate command, logrotate, Configuration commands

nocreate command, logrotate, Configuration commands

nodelaycompress command, logrotate, Configuration commands

nohlsearch command, ex,

nohup command, Options

nomail command, logrotate, Configuration commands

nomissingok command, logrotate, Configuration commands

noolddir command, logrotate, Configuration commands

nosharedscripts command, logrotate, Configuration commands

NOT operator (!) for commands, Command Forms

notifempty command, logrotate, Configuration commands

nroff command, formatting output from, , Examples

nslookup command, Options

nsupdate command, Options

ntrans command, ftp, Commands

null command (:),

number command, ex,

numbers, printing in sequence, Options

nvi editor, The vi, ex, and vim Editors

O

objcopy command, Interactive commands

objdump command, Options

object files,

combining into executable object module,

copying, Interactive commands

displaying information about, Options

generating from assembly source files, Options

removing symbols from, Options

size of, printing,

octal constants, gawk, Octal and Hexadecimal Constants in gawk

octal format, displaying files in,

od command, Options

olddir command, logrotate, Configuration commands

OLDPWD built-in variable, Built-in Shell Variables

online documentation, displaying,

only command, ex,

open command, ex,

open command, ftp, Commands

OpenPGP-format messages, splitting into packets, Other commands

OpenPGP-signed files, checking signature of,

openvt command, Arguments

operating system, printing information about, Options

operators, Operators

arithmetic, Arithmetic Expressions

comparison,

gawk, Built-in Variables

logical,

OPTARG built-in variable, Built-in Shell Variables

OPTERR built-in variable, Other Shell Variables

OPTIND built-in variable, Built-in Shell Variables

OR operator (||), Command Forms

for commands, Command Forms

for expressions, , Built-in Variables

or() function, gawk,

OSTYPE built-in variable, Built-in Shell Variables

output redirection, gawk,

ownership of files, changing, Examples

P

P command, sed, Basic Editing, Branching Commands,

p command, sed,

package managers, Package Management

(see also APT; Debian Package Manager; RPM; yum program),

package-cleanup plugin, yum,

packages, Package Management

Debian, rpmbuild options

archive of, Files

cache for, managing, Scripts

files used by, Files

flags for, Package Priorities

generating,

managing, Options, Options

naming conventions for, rpmbuild options

priorities of, Files

querying, Options

sorting records in, Options

sources for, adding, Options

splitting, Options

states of, Package Priorities

dependencies for, Package Management

naming conventions for, Package Management

RPM, Yum: Yellowdog Updater Modified

archive of, Plugins and yum-utils

building, The rpmbuild Command

header for, Plugins and yum-utils

managing with rpm command, RPM Package Concepts

managing with yum, Package Management

repository of, Package Management

signature verification for, Plugins and yum-utils

spec file for, Plugins and yum-utils

signature verification for, Package Management

user privileges required for, Package Management

packets,

IEEE394, dumping,

tracing path to host taken by, Special characters,

pager command, GRUB,

paragraph commands, Emacs, Paragraphs and Regions

paravirtualization, Virtualization Technology, Xen, VMware Tools

parentheses ((...)), Quoting, Command Forms

enclosing group of commands, Quoting, Command Forms

enclosing group of regular expressions, Search Patterns

(...) (parentheses), Quoting, Command Forms

enclosing group of commands, Quoting, Command Forms

enclosing group of regular expressions, Search Patterns

partnew command, GRUB,

parttype command, GRUB,

passwd command, Arguments

password command, GRUB, The GRUB Configuration File,

passwords,

changing, Options

created shadowed entries for,

creating or changing, Arguments

expirations for, changing, Commands

information stored with, changing, Attributes

removing corrupt or duplicate entries, Options

paste (yank), Emacs, Modes

paste command, Options

patch command,

patches, applying,

PATH built-in variable, Other Shell Variables

pathchk command, Options

paths, Options

checking validity of, Options

following to terminal point, Options

for current working directory, printing,

printing only leading directory components from, Options

removing leading directory components from, Options

pattern addressing, sed, Pattern Addressing

pattern matching, , Pattern Matching

character classes in, Search Patterns

escape sequences in, Search Patterns

metacharacters in, Pattern Matching

replacement patterns, Replacement Patterns

search patterns, Search Patterns

searching and replacing, examples of, Examples of Searching

searching files with extended regular expressions, Options

searching files with regular expressions, Options

searching, examples of, Metacharacters, Listed by Program

pattern space, sed, sed Operation

patterns, gawk, Important gawk Options, Patterns

Patwardhan, Nathan (Perl in a Nutshell), Pattern Matching

pause command, GRUB,

pause command, xm, Options

pccardctl command,

PCI (Peripheral Component Interconnect) devices, listing, Options

PCMCIA sockets, controlling,

PDF (Portable Document Format) language, interpreter for, Exit codes

Peek, Jerry (Learning the Unix Operating System), xvii, Built-in Variables

% (percent sign), Programmable Completion

modulus operator, Built-in Variables

preceding job ID in commands, Programmable Completion

reuse previous replacement pattern, Replacement Patterns

percent sign (%), Built-in Variables

modulus operator, Built-in Variables

preceding job ID in commands, Programmable Completion

reuse previous replacement pattern, Replacement Patterns

%= (percent sign, equals sign) assignment operator, Built-in Variables

percent sign, equals sign (%=) assignment operator, Built-in Variables

performance, Linux improving, The Excitement of Linux

Peripheral Component Interconnect (PCI) devices, listing, Options

Perl 5 Pocket Reference (Vromans), Pattern Matching

Perl in a Nutshell (Patwardhan et al.), Pattern Matching

permuted indexes,

pgawk (profiling gawk), gawk-Specific Features

pidof command,

Pilato, C. Michael (Version Control with Subversion), The Subversion Version Control System

ping command,

pipe (pi) command, mailx, Command-mode commands

pipe character (|), Quoting, Command Forms

pipes,

named pipes (FIFO), making,

negating result of, Command Execution

PIPESTATUS built-in variable, Built-in Shell Variables

plugins for yum program,

plus sign (+), Built-in Variables

addition operator, Built-in Variables

match one or more instances, Search Patterns

unary plus operator, Built-in Variables

+ (plus sign), Built-in Variables

addition operator, Built-in Variables

match one or more instances, Search Patterns

unary plus operator, Built-in Variables

plus sign, double (++) increment operator, Built-in Variables

++ (plus sign, double) increment operator, Built-in Variables

+= (plus sign, equals sign) assignment operator, Built-in Variables

plus sign, parentheses (+()) in filename, Filename Metacharacters

+() (plus sign, parentheses) in filename, Filename Metacharacters

plus, equals sign (+=) assignment operator, Built-in Variables

pmap command, Options

PNM (Portable aNyMap) format, writing images to, Options

point (cursor) location, Emacs, Modes

Point-to-Point Protocol (PPP), Overview of TCP/IP, Serial-line communication, Options

popd command, Bash,

Portable aNyMap (PNM) format, writing images to, Options

Portable Document Format (PDF) language, interpreter for, Exit codes

portmap command, Options

portmap daemon, Administering NFS

POSIX notation, in Bash, Filename Metacharacters, Command Forms

POSIXLY_CORRECT built-in variable, Other Shell Variables

postrotate command, logrotate, Configuration commands

PostScript language, interpreter for, Exit codes

poweroff command, Options

PPID built-in variable, Built-in Shell Variables

PPP (Point-to-Point Protocol), Overview of TCP/IP, Serial-line communication, Options

pppd command, Options

pppd daemon, Serial-line communication

pr command, Files

praliases command, Options

prerotate command, logrotate, Configuration commands

preserve (pre) command, mailx, Command-mode commands

preserve command, ex,

previous command, ex,

prime factors, calculating, Examples

Print (P) command, mailx, Command-mode commands

print (p) command, mailx, Command-mode commands

print character class, Filename Metacharacters, Search Patterns

print command, ex,

print command, gawk, ,

print command, gdb, Common commands

print jobs,

cancelling, Options

moving to a new destination,

print queues,

accepting,

CUPS, configuring, Configuration commands

displaying status of,

rejecting, Options

print scheduler, starting, Options

print spool queue, displaying information about,

printenv command, Options

printer drivers, printing information about,

printers,

enabling,

printing information about,

tuning device parameters for, Options

printf command, Options

printf command, Bash, Options

printf() function, gawk, ,

printing, commands for, File Management, Managing the Kernel,

priority of processes, controlling,

privileges required for packages, Package Management

procedures, gawk, Important gawk Options, Patterns

process IDs, Options

determining for specific files or filesystems, Options

displaying for programs,

processes,

active, reporting on, Arguments

managing, commands for, Starting and Stopping the System

memory maps for, displaying, Options

most CPU-intensive, displaying information about, Options

priority of, controlling,

real-time scheduling for, changing, Options

terminating, ,

terminating all processes, Options

processor affinity mask, retrieving or setting, Examples

profile data for an object, displaying,

profiling, gawk, gawk-Specific Features

program addresses, translating to filenames and line numbers,

programmable completion, Programmable Completion, Options

programming, File Management

(see also gawk language; source code management systems), Commands

commands for, list of, File Management

maintenance of, commands for, Programming

prompt command, ftp, Commands

prompt strings, Arrays

PROMPT_COMMAND built-in variable, Other Shell Variables

propdel command, svn,

propedit command, svn,

properties, Subversion, Key Features

propget command, svn,

propget command, svnlook,

proplist command, svn,

proplist command, svnlook,

propset command, svn, Examples

protocols, Internet, Overview of Networking

provides command, yum,

proxy command, ftp, Commands

ps command, Arguments

PS1 built-in variable, Other Shell Variables, Arrays

PS2 build-in variable, Arrays

PS2 built-in variable, Other Shell Variables

PS3 built-in variable, Other Shell Variables

PS4 built-in variable, Other Shell Variables, Arrays

pseudonyms (links) for files,

ptx command,

ptype command, gdb, Common commands

pull command, git, Examples

punct character class, Filename Metacharacters, Search Patterns

Purdy, Gregor, Overview of Firewalls and Masquerading

Linux iptables Pocket Reference, Overview of Firewalls and Masquerading

Linux Network Administrator’s Guide, Overview of TCP/IP, Overview of Firewalls and Masquerading

push command, git,

pushd command, Bash, Options

put command, ex,

put command, ftp, Commands

pwck command, Options

pwconv command,

PWD built-in variable, Built-in Shell Variables

pwd command,

pwd command, Bash, Options

pwd command, ftp, Commands

pwd command, gdb, Common commands

python-vm-builder package, Ubuntu Builder Scripts

Q

Q command, sed, Basic Editing,

q command, sed, Basic Editing,

qall command, ex,

QEMU, combining with KVM hypervisor, Interactive commands

qemu-img tool, Creating and Manipulating Disk Image Files

question mark (?), Arguments

help command, mailx, Compose-mode commands

in filename, Arguments

match zero or one instance, Search Patterns

? (question mark), Arguments

help command, mailx, Compose-mode commands

in filename, Arguments

match zero or one instance, Search Patterns

question mark, colon (?:) conditional expression, Built-in Variables

?: (question mark, colon) conditional expression, Built-in Variables

question mark, parentheses (?()) in filename, Filename Metacharacters

?() (question mark, parentheses) in filename, Filename Metacharacters

quit (q) command, mailx, Command-mode commands

quit command, ex,

quit command, ftp, Options

quit command, gdb, Common commands

quit command, GRUB,

quota command,

quotacheck command, Options

quotaoff command,

quotaon command, Options

quotas, Options

exceeding limit, sending messages to users regarding,

setting, Options

quotastats command,

quote command, ftp, Commands

quoting special characters in Bash, Filename Metacharacters

R

R command, sed, Basic Editing,

r command, sed, Basic Editing,

rand() function, gawk,

RANDOM built-in variable, Built-in Shell Variables

ranlib command,

RARP (Reverse Address Resolution Protocol), Overview of TCP/IP

rarp command, GRUB,

rcp command,

RCS (Revision Control System), Usage Models

rdate command, Options

rdist command, Options

rdistd command, Options

read command, Bash, Options

read command, ex,

read command, GRUB,

readcd command, Options

readelf command,

readline library, managing,

readlink command, Options

readom command, Options

readonly command, Bash,

real-time scheduling for processes, changing, Options

rebase command, git, Examples

reboot command, Options

reboot command, GRUB,

recover command, ex,

recover command, svnadmin, Examples

Red Hat Package Manager (see RPM), Ubuntu Builder Scripts

Red Hat Virtual Machine Manager, libvirt and Red Hat Virtual Machine Manager

redirection of commands, Command Forms

redo command, ex,

reflog command, git,

reget command, ftp, Commands

region commands, Emacs, Paragraphs and Regions

Regular Expression Pocket Reference (Stubblebine), Pattern Matching

regular expressions, Pattern Matching

(see also pattern matching),

reinstall command, yum,

reject command, Options

relational operators, gawk, Built-in Variables

release of package, Package Management

remainder operator (%), Built-in Variables

remote command, git,

remote file distribution,

remote host, logging in to, Options

remote hosts, confirming responses of,

Remote Procedural Call (RPC) language, generating C code from,

Remote Procedure Call (RPC), Administering NIS

remote procedure call (RPC) activity, statistics on,

remote shell server,

remote systems, accessing, Runlevels

remotehelp command, ftp, Commands

remotestatus command, ftp, Commands

remove (rem) command, mailx, Command-mode commands

remove command, yum,

rename (ren) command, mailx, Command-mode commands

rename command, Options

rename command, ftp, Commands

renice command,

replacement patterns, metacharacters for, Search Patterns

replacing, with pattern matching, Examples of Searching

Reply (R) command, mailx, Command-mode commands

reply (r) command, mailx, Command-mode commands

REPLY built-in variable, Built-in Shell Variables

replyall command, mailx, Command-mode commands

repo-graph plugin, yum,

repo-rss plugin, yum,

repo.or.cz hosting service, Creating and Sharing a New Repository

repoclosure plugin, yum,

repodiff plugin, yum,

repolist command, yum,

repomanage plugin, yum,

repoquery plugin, yum,

repositories, for Git, The Git Version Control System, Conceptual Overview

cloning,

creating, Example: The Linux Kernel Repository, Examples

creating archive from, Examples

packing,

repository, for source code management system, Source Code Management: An Overview, The Subversion Version Control System

repository, of RPM packages, Package Management

reposync plugin, yum, Plugins and yum-utils

repotrack plugin, yum, Plugins and yum-utils

repquota command,

reset command, Options

reset command, ftp, Commands

reset command, git, Examples

resize command, ex,

resize2fs command, Options

resolve command, svn,

resolved command, svn,

resolvedep command, yum,

resolver, DNS and BIND

resource limits, printing,

resources (see books and publications; website resources), Command-mode commands

respond command, mailx, Command-mode commands

restart command, ftp, Commands

restore command,

restricted shells, Restricted Shells

retain command, mailx, Command-mode commands

return command, Bash,

return command, gawk,

rev command, Options

Reverse Address Resolution Protocol (RARP), Overview of TCP/IP

reverse-search command, gdb, Common commands

revert command, git, Examples

revert command, svn,

Revision Control System (RCS), Usage Models

revision of package, Package Management

rewind command, ex,

rexec command, Options

rexecd command, Options

right angle bracket (>), , Built-in Variables

greater than operator, , Built-in Variables

output redirection,

right angle bracket, double (>>) append output,

right angle bracket, equals sign (>=) greater than or equal operator, Built-in Variables

right angle brackets (> or >>) in cat command, Options

> or >> (right angle brackets) in cat command, Options

right command, ex,

RIP (Routing Information Protocol), IP Addresses

rlogin command, Options

rlogind command, Options

rm command, Options

rm command, git, Examples

rmail command, Options

rmdir command, Options

rmdir command, ftp, Commands

rmlocks command, svnadmin, Examples

rmmod command, Options

rmtxns command, svnadmin, Examples

rndc command, Options

Robbins, Arnold (Classic Shell Scripting), The Bash Shell

root command, GRUB,

root directory, changing, Options

rootnoverify command, GRUB,

rotate command, logrotate, Configuration commands

route add command, ip, Commands

route chg command, ip, Commands

route command, Commands

route del command, ip, Commands

route events, connecting MIDI ports to, Options

route list command, ip, Commands

route repl command, ip, Commands

routed daemon, Routing daemons

routing daemons, Routing daemons

Routing Information Protocol (RIP), IP Addresses

routing tables, Routing daemons,

routing, controlling, Options

RPC (Remote Procedure Call), RPC and XDR

activity of, statistics on,

generating C code from,

program numbers, Options

mapping to IP ports, Options

mapping to universal addresses, Options

reporting information for programs,

rpcbind command, Options

rpcbind daemon, Administering NFS

rpcgen command,

rpcinfo command,

RPM (Red Hat Package Manager), Package Management, Plugins and yum-utils

database rebuild options for, Verify options

examples of, Signature-check options

freshen options for, Install, upgrade, and freshen options

install options for, The rpm Command

naming conventions for, Package Management

options for, The rpm Command

package-query options for, Package-selection options

package-selection options for, Query options

query options for, Query options

rpm command syntax for, RPM Package Concepts

rpmbuild command syntax and options for, The rpmbuild Command

signature-check options for, Verify options

uninstall options for, Package-query options

upgrade options for, The rpm Command

verify options for, Package-query options

rpm command, Options, RPM Package Concepts

rpmbuild command, RPM, Plugins and yum-utils, The rpmbuild Command

RSA identities, adding to authentication agent, Escape characters

rsh command, Options

rshd command, Options

rshift() function, gawk,

rsync command,

rsyslogd command,

run command, gdb, Common commands

runique command, ftp, Commands

runlevel command, Options

runlevels, Starting and Stopping the System

changing,

specifying services to be run at, Options

Running Linux (Dalheimer; Welsh), Commands on Linux

S

s command, sed, Basic Editing,

sandbox, for source code management system, Introduction and Terminology, Basic Version-Control Operations

SANE (Scanner Access Now Easy),

sane-find-scanner command, Options

save (s) command, mailx, Command-mode commands

savedefault command, GRUB,

saveignore command, mailx, Command-mode commands

saveretain command, mailx, Command-mode commands

saving files, vi, Changing and deleting text

sbnext command, ex,

sbuffer command, ex,

scancode-to-keycode mapping table,

scancodes, printing, Options

scanimage command, Options

Scanner Access Now Easy (SANE), Options

detecting scanners, Options

scanners, Options

detecting by SANE, Options

reading images from, Options

SCCS (Source Code Control System), Usage Models

scheduling commands, System Activity and Process Management

scp command, Options

screen command, Options

script command, Key bindings

scripts in package spec file, RPM Package Concepts

SCSI scanners, detecting by SANE, Options

sdiff command, Key bindings

search command, gdb, Common commands

search command, yum,

search commands, Emacs, Paragraphs and Regions

search patterns, metacharacters for, Filenames Versus Patterns

searching, Programming

commands for, list of, Programming

with pattern matching, Metacharacters, Listed by Program, Examples of Searching

Second Extended Filesystem (see ext2 filesystem), Built-in Shell Variables

SECONDS built-in variable, Built-in Shell Variables

secure copying of files, Options

secure login to remote system, Options

security, Managing the Kernel

(see also authentication; signature verification), Options

commands for, list of, Managing the Kernel

encryption with GNU Privacy Guard, HFS options

website about, xvii, Options

sed command, Options

sed editor, The sed Editor

branching commands, Branching Commands

command syntax for, GNU sed Options

editing commands, Basic Editing

hold space for, sed Operation

input for, The sed Editor, sed Operation, Basic Editing, Branching Commands

input/output commands, Basic Editing

invoking, Command-Line Syntax

line information commands, Basic Editing

multiline input commands, Branching Commands

options for, sed Operation

pattern addressing, Pattern Addressing

pattern matching metacharacters supported by, Replacement Patterns

pattern space for, sed Operation

yanking and putting commands, Basic Editing

seen command, mailx, Command-mode commands

select command, Bash,

semaphore arrays, IPC, removing, Common arguments

semaphore files, creating, Options

semicolon (;) command separator, Quoting, Command Forms

; (semicolon) command separator, Quoting, Command Forms

sendmail command, Options

database maps for, creating, Options

mail aliases for, printing, Options

sendport command, ftp, Commands

sensor chips, displaying readings and configuring, Configuration options

sensors command, Configuration options

seq command, Options

serial command, GRUB,

Serial Line IP (SLIP), Serial-line communication

serial lines, attaching as network interfaces, Options

servers, NIS, Overview of NIS, Administering NIS

services, managing runlevels for, Options

set (se) command, mailx, Command-mode commands

set command, Bash, Example

set command, ex,

set command, lftp, Commands

set variable command, gdb, Common commands

setkey command, GRUB, Options

setkeycodes command, Options

setleds command, Options

setlog command, svnadmin, Examples

setmetamode command, Options

setquota command, Options

setrevprop command, svnadmin, Examples

setsid command, Options

setterm command, Options

setup command, GRUB, Using grub-install,

setuuid command, svnadmin, Examples

sftp command,

SGI Extensible Filesystem (see XFS), Options, The Bash Shell, The Bash Shell

sh shell, Options, The Bash Shell, The Bash Shell

SHA1 checksums, computing or checking, Options

sha1sum command, Options

shadow files,

creating or updating from passwords,

removing corrupt and duplicate entries in, , Options

shadowed groups, creating, Exit codes

shared memory segments, IPC, removing, Common arguments

sharedscripts command, logrotate, Configuration commands

shell (sh) command, mailx, Command-mode commands

SHELL built-in variable, Other Shell Variables

shell command, ex,

shell command, yum,

shell commands, Emacs, Window Commands

shell conditions, testing for, String conditions

shell scripts, Command Execution

comments in, Command Execution

exiting,

SHELLOPTS built-in variable, Built-in Shell Variables

shells, What This Book Offers, The Bash Shell

(see also Bash shell), Options

changing, Options

creating with effective user ID, Special settings

invoking in a script,

programming, commands for, Shell Programming

starting on remote host, Options

shift command, Bash, Options

SHLVL built-in variable, Built-in Shell Variables

shopt command, Bash, Options

show (Sh) command, mailx, Command-mode commands

showkey command, Options

showmount command, Administering NFS, Options

shred command, Options

shutdown command, Options

shutdown command, xm, Options

shutting down the system, Options, Options, Options, Options

signal command, gdb, Common commands

signature verification, HFS options

of OpenPGP-signed files,

of packages, Package Management, Plugins and yum-utils

with GNU Privacy Guard, HFS options

Simple Mail Transport Protocol (SMTP), Overview of TCP/IP

Simple Network Management Protocol (SNMP), Overview of TCP/IP

sin() function, gawk,

single quotes ('...') enclosing special characters, Quoting

‘...’ (single quotes) enclosing special characters, Quoting

site command, ftp, Commands

size command,

size command, ftp, Commands

size command, logrotate, Configuration commands

size command, mailx, Command-mode commands

slab cache information, displaying in real time,

slabtop command,

slash (/) division operator, Built-in Variables

/ (slash) division operator, Built-in Variables

slash, equals sign (/=) assignment operator, Built-in Variables

/= (slash, equals sign) assignment operator, Built-in Variables

Slashdot website, xvii, Pattern Addressing

slashes (/.../) enclosing pattern address in sed, Pattern Addressing

/.../ (slashes) enclosing pattern address in sed, Pattern Addressing

slattach command, Options

sleep command, Options

sleep for a specified time, Options

SLIP (Serial Line IP), Serial-line communication

SMTP (Simple Mail Transport Protocol), Overview of TCP/IP

snext command, ex,

SNMP (Simple Network Management Protocol), Overview of TCP/IP

sockets, gawk language, gawk-Specific Features

sort command,

sorted files, joining, Interactive commands

sorting strings in a file, Options

sound cards, ALSA, Options

advanced configuration settings for, Options

connecting to ALSA mixer, Options

sound files, Options

playing, Options

recording,

recording to CDs, Options, Examples, Options

recording to DVDs, Options, Options

Source Code Control System (SCCS), Usage Models

source code for Linux, Sources and Licenses

source code management systems, Source Code Management: An Overview

checking files in or out, Introduction and Terminology

client/server model for, Introduction and Terminology

Codeville, Source Code Management Systems

copy, modify, merge model for, Introduction and Terminology

CSSC, Other Source Code Management Systems

CVS, Usage Models

Git (see Git Version Control System), Source Code Management Systems

GNU Arch, Source Code Management Systems

locking model for, Introduction and Terminology

merging changes in, Introduction and Terminology

monotone system, Other Source Code Management Systems

RCS, Usage Models

SCCS, Usage Models

Subversion (see Subversion Version Control System), Settable shell options

source command, Bash, Settable shell options

source command, ex,

source command, mailx, Command-mode commands

source files, listing function and macro names in, Arguments,

space character class, Filename Metacharacters, Search Patterns

space character, as word separator, Quoting

spec file for package, Plugins and yum-utils

spell checkers, Options, Options

splashimage command, GRUB, Options

split command, Options

split command, ex,

split() function, gawk, Variable and Array Assignment,

sprevious command, ex,

sprintf() function, gawk, ,

sqrt() function, gawk,

srand() function, gawk,

ssh command, Options

ssh-add command, Escape characters

ssh-agent command,

ssh-keygen command,

ssh-keyscan command, Options

sshd command, Options

Stallman, Richard (founder of FSF), Sources and Licenses

standard input,

determining terminal connected to, Options

reading a line from, Options

start command, logrotate, Configuration commands

starting the system, Starting and Stopping the System

startup files for Bash, Arguments

stash command, git,

stat command, Options

statd command, Examples

status command, ftp, Commands

status command, git,

status command, svn,

status line, Status-Line Commands

step command, gdb, Common commands

stop command, ex,

stopping commands, Emacs, Paragraphs and Regions

stopping the system, Starting and Stopping the System

storage, commands for, Shell Programming

strace command, Examples

Strang, John (Learning the Unix Operating System), xvii,

stream editor (see sed editor),

strftime() function, gawk,

string conditions, testing for, File conditions

strings, Options

completions for, generating, Options

converting initial whitespace to tabs, Options

printing with specific format, Options

sorting, Options

translating characters in,

writing to standard output, Options

strings command, Options

strip command, Options

strtonum() function, gawk, Octal and Hexadecimal Constants in gawk,

struct command, ftp, Commands

stty command, Options

Stubblebine, Tony (Regular Expression Pocket Reference), Pattern Matching

su command, Special settings

sub() function, gawk,

subdomains, DNS and BIND

substitute command, ex,

substr() function, gawk,

subtraction operator (-), Built-in Variables

Subversion version control system, Source Code Management Systems, The Subversion Version Control System

atomic commits, Basic Version-Control Operations

authors of files, showing, svn Subcommands

book about, The Subversion Version Control System

branching in, Basic Version-Control Operations, Key Features

checking in (committing) changes, Basic Version-Control Operations, Using Subversion: A Quick Tour,

checking out files, Using Subversion: A Quick Tour, Examples

conflicts, handling of, Basic Version-Control Operations, ,

copy-modify-merge model used by, Basic Version-Control Operations

copying files,

differencing files, Key Features, Using Subversion: A Quick Tour,

directories, creating, Examples

directory versioning, Basic Version-Control Operations

displaying file contents,

help for,

keywords for, Special File Properties

locking files, , , Examples

logging for,

merging files, , Examples

moving (renaming) files,

networks used with, Basic Version-Control Operations

obtaining, Special File Properties

projects, svn Subcommands

adding files and directories to, svn Subcommands

creating, Special File Properties

deleting files and directories from, Examples

grouping files into collections,

properties (metadata) for, Basic Version-Control Operations, Key Features,

remote access for,

repository for, The Subversion Version Control System, Repository Administration: svnadmin

exporting from, Examples

importing to,

listing contents of,

sandbox for, Basic Version-Control Operations

svn command line, Using Subversion: A Quick Tour

svn subcommands, Common svn Options

svnadmin command, Repository Administration: svnadmin

svnadmin subcommands, Common svnadmin Subcommands

svnlook command,

svnlook subcommands,

svnserv command,

tags in, Basic Version-Control Operations, Key Features

working copy, Examples

cleaning, Examples

printing information about, Examples

status of,

updating, Examples,

sudo command,

sum command, Options

Sun Yellow Pages (YP), Overview of NIS

sunique command, ftp, Commands

superblock, printing information about,

supernetting, IP Addresses

superuser, executing commands as,

support for Linux, The Excitement of Linux

suspend command, Bash, Settable shell options

suspend command, ex,

sview command, ex,

svn command, Subversion, Using Subversion: A Quick Tour

svn subcommands, Subversion, Common svn Options

svnadmin command, Subversion, Repository Administration: svnadmin

svnadmin subcommands, Subversion, Common svnadmin Subcommands

svnlook command, Subversion,

svnlook subcommands, Subversion,

svnserv command, Subversion,

swapoff command, Options

swapon command, Options

swapspace, creating,

switch command, svn, Examples

symbol table, printing in alphabetical order,

symbolic links, Options, Options

synaptic command, Debian, Package Management, Options

sync command, Options

sysctl command, Options

sysklogd command, Options

syslogd command,

system access commands, Window Commands

system administration, commands for, Common Commands

system command, ftp, Commands

system control messages, displaying, Options

system integrity, commands for, Managing the Kernel

system load,

averages of, graphing,

averages of, printing,

system logging, Options

adding entries to log, Options

commands for, Miscellaneous

manipulating logfiles, Options

system messages, , Options

system status, Shell Programming

commands for, list of, Shell Programming

time running, printing,

usage, printing summary of, Slab mode fields

System V init (SysVinit), Starting and Stopping the System

system() function, gawk,

systime() function, gawk,

SysVinit (System V init), Starting and Stopping the System

T

t command, ex,

T command, sed, Branching Commands,

t command, sed, Branching Commands,

tabooext command, logrotate, Configuration commands

tabs, Quoting

as word separator, Quoting

converting initial whitespace to, Options

converting to spaces, Options

tac command,

tag command, ex,

tag command, git, Examples

tags, Introduction and Terminology

Git, Referring to Commits, Examples

Subversion, Basic Version-Control Operations

tags command, ex,

tail command, Options

tailf command, Options

talk command, Options

tape drive, controlling,

tapes, ejecting, Options

tar command, Options

taskset command, Examples

tbl command, formatting output from, , Examples

TCP/IP, TCP/IP Administration

books about, Overview of TCP/IP

commands for, list of, Overview of Networking, Serial-line communication

configuring, Domain names

gateways, Gateways and Routing

IP addresses, Overview of TCP/IP

name service, Name Service

routing daemons, Routing daemons

troubleshooting, Serial-line communication

TCP/IP Network Administration (Hunt), Overview of TCP/IP

tcpdump command, Examples

tcpslice command, Options

tcsh shell, The Bash Shell

tee command,

telinit command,

telnet command, Runlevels

telnetd command, Options

temporary filename, generating,

tenex command, ftp, Commands

TERM built-in variable, Other Shell Variables

terminal, Options

as standard input, determining, Options

attributes, setting, Options

I/O options, setting, Options

initializing, Options

resetting, Options

terminal command, GRUB, Options

terminal emulation,

terminal session, typescript of, Key bindings

test command, Options

test command, Bash, Settable shell options

testload command, GRUB, Options

testvbe command, GRUB, Options

text patterns (see pattern matching), System Status

text processing, commands for, System Status

TEXTDOMAIN environment variable, gawk, Profiling

tftpserver command, GRUB,

Third Extended Filesystem (see ext3 filesystem), Command-mode commands

thread (th) command, mailx, Command-mode commands

threads, launching for NFS module,

tilde (~), Arguments

in filename, Arguments

match regular expression, Operators

replace regular expression command in ex,

reuse previous replacement pattern, Replacement Patterns

tilde escape commands, mailx, Command-line options

~ (tilde), Arguments

in filename, Arguments

match regular expression, Operators

replace regular expression command in ex,

reuse previous replacement pattern, Replacement Patterns

tilde escape commands, mailx, Command-line options

tilde, hyphen (~-) in filename, Arguments

~- (tilde, hyphen) in filename, Arguments

tilde, plus sign (~+) in filename, Arguments

~+ (tilde, plus sign) in filename, Arguments

time (see date and time),

time command, Expression tests

time command, Bash, Examples

time system has been running, printing,

TIMEFORMAT built-in variable, Other Shell Variables

timeout command, GRUB, The GRUB Configuration File

times command, Bash, Examples

title command, GRUB, The GRUB Configuration File

tload command,

TMOUT built-in variable, Other Shell Variables

tmpwatch command,

Todino-Gonguet, Grace (Learning the Unix Operating System), xvii,

tolower() function, gawk,

top command, Options

top command, mailx, Command-mode commands

top command, xm, Commands

Torvalds, Linus (developer of Linux), Introduction

touch command, Field descriptions

touch command, mailx, Command-mode commands

toupper() function, gawk,

tr command,

trace command, ftp, Commands

tracepath command, Special characters

traceroute command,

translating characters in a string,

translation tables of keyboard driver,

transposition commands, Emacs, Paragraphs and Regions

trap command, Bash, Examples

tree command, svnlook,

trigger scriptlets in package spec file, RPM Package Concepts

troff command (see groff command), Options

true command, Options

true command, Bash, Signals

tset command, Options

tsort command, Options

tty command, Options

tty port, logging in to,

tune2fs command, Options

tunelp command, Options

Type (T) command, mailx, Command-mode commands

type (t) command, mailx, Command-mode commands

type command, Bash, Signals

type command, ftp, Commands

typescript of terminal session, Key bindings

U

ubuntu-virt-mgmt package, Interactive commands

ubuntu-virt-server package, Interactive commands

ubuntu-vm-builder package, Ubuntu Builder Scripts

UDP (User Datagram Protocol), Overview of TCP/IP

UID built-in variable, Built-in Shell Variables

ul command, Options

ulimit command, Bash,

umask command, Bash,

umask command, ftp, Commands

umount command, Administering NFS, Options

unabbreviate command, ex,

unalias command, Bash,

unalias command, mailx, Command-mode commands

uname command, Options

unanswered command, mailx, Command-mode commands

unary minus operator (-), Built-in Variables

unary plus operator (+), Built-in Variables

uncollapse (unc) command, mailx, Command-mode commands

uncompresscmd command, logrotate, Configuration commands

undelete (u) command, mailx, Command-mode commands

underscores, translating to underlining, Options

undisplay command, gdb, Common commands

undo command, ex,

undoing commands, Emacs, Paragraphs and Regions

unexpand command, Options

ungood command, mailx, Command-mode commands

unhide command, ex,

unhide command, GRUB,

Unicode mode for keyboard,

unicode_start command,

unicode_stop command,

uniq command,

universal addresses, mapping RPC program numbers to, Options

Universal Serial Bus (USB) devices, listing,

Universal Unique Identifier (see UUID), Introduction

Unix, compared to Linux, Introduction

unjunk command, mailx, Command-mode commands

unlink command,

unlock command, svn,

unmap command, ex,

unread (U) command, mailx, Command-mode commands

unset (uns) command, mailx, Command-mode commands

unset command, Bash,

until command, Bash,

until command, gdb, Common commands

up command, gdb, Common commands

up2date program, Package Management

update command, svn,

update command, yum,

upgrade command, yum,

upper character class, Filename Metacharacters, Search Patterns

uppermem command, GRUB, Options

Upstart, Starting and Stopping the System

Upstart init daemon, Options

uptime command,

URLs, fetching, Commands

USB (Universal Serial Bus) devices, listing,

USB scanners, detecting by SANE, Options

Usenet newsgroups, xviii, Administering NIS

user accounts, NIS, Administering NIS

user authentication files, creating or updating, Options

user command, ftp, Commands

User Datagram Protocol (UDP), Overview of TCP/IP

user groups, xix, Options

user ID, displaying information about, Options

user-defined functions, gawk, Octal and Hexadecimal Constants in gawk

useradd command,

userdel command, Options

usermod command, Options

users,

(see also groups), Options

adding or updating,

changing groups for,

creating or updating,

current, printing ID of, Example

deleting, Options

interactive conversations with, Track options and arguments

logged in, listing,

logged in, printing summary of, Slab mode fields

mailing regarding exceeded quotas,

modifying account information for, Options

number of logged in, printing,

space allowed on disk for,

talking to another user, Options

writing a message to all users, Slab mode fields

users command, Options

usleep command, Options

UUID (Universal Unique Identifier),

creating,

uuid command, svnlook,

uuidgen command,

V

v command, ex,

v command, sed, Basic Editing,

variable substitution, Quoting, Variables

variables, Built-in Shell Variables

built-in, Built-in Shell Variables

declaring, Options

exporting to make global,

forcing expansion of, Options

gawk, Simple Pattern-Procedure Examples, Built-in Variables

local,

reading an input line and assigning to, Options

readonly,

setting or printing, Example

unsetting,

vbeprobe command, GRUB, Options

vdir command,

verbose command, ftp, Commands

verify (verif) command, mailx, Command-mode commands

verify command, svnadmin,

version command, ex,

version control system (see source code management system), The Subversion Version Control System

Version Control with Subversion (Pilato et al.), The Subversion Version Control System

version of package, Package Management

vertical bar (|), Search Patterns

match either one or the other, Search Patterns

output directed to next command,

pipe character, Quoting, Command Forms

| (vertical bar), Search Patterns

match either one or the other, Search Patterns

output directed to next command,

pipe character, Quoting, Command Forms

vertical bar, ampersand (|&) output directed to coprocess, gawk-Specific Features,

vertical bar, double (||), Command Forms

OR operator for commands, Command Forms

OR operator, in expressions, , Built-in Variables

|| (vertical bar, double), Command Forms

OR operator for commands, Command Forms

OR operator, in expressions, , Built-in Variables

VFAT filesystem, Managing Filesystems

vi, vi Commands

(see also specific commands), Common commands

for user management

:set command, Miscellaneous Commands

copy and move, Changing and deleting text

edit, Edit Commands

insert, Insert Commands

macros, Macros

movement, Movement Commands

multiple files, accessing, Saving and Exiting

saving files, Changing and deleting text

system access, Window Commands

window, Window Commands

waiting before execution of, Options

vi command, , Conceptual Overview

vi editor, The vi, ex, and vim Editors

command-line options, Conceptual Overview

commands, Status-Line Commands

:set command, Miscellaneous Commands

copy and move, Changing and deleting text

edit, Insert Commands

insert, Marks

line numbering, Searches

macros, Macros

marks, Searches

movement, Movement Commands

multiple files, accessing, Saving and Exiting

on status line, Status-Line Commands

saving files, Changing and deleting text

syntax for, Command-Line Options

system access, Window Commands

window, Window Commands

configuration of, Miscellaneous Commands

exiting, Command-Line Options, Changing and deleting text

invoking, Conceptual Overview

modes, Conceptual Overview, Review of vi Operations

pattern matching metacharacters supported by, Replacement Patterns

video mode, setting,

vidmode command,

view command, ex,

vile editor, The vi, ex, and vim Editors

vim command,

vim editor, The vi, ex, and vim Editors, Conceptual Overview

command-line options, Conceptual Overview

visual mode, Visual mode (vim only)

virsh commands, Managing Virtual Systems, MAC Addresses, Ubuntu Builder Scripts,

virt-clone command, Options

virt-image command, Options

virt-install command, libvirt Tools and Terminology, Managing Virtual Systems, MAC Addresses, Xen, Options

virt-manager command, Options

virt-manager package, Managing Virtual Systems, Interactive commands, Ubuntu Builder Scripts, Connection URI Examples

virt-viewer command, Options

virt-viewer package, Managing Virtual Systems, Interactive commands

virtual center, for VMware, VMware ESX 3.5

virtual console,

deallocating, Options

determining number of, Commands

virtual machine monitor (VMM), Conceptual Overview

virtual memory statistics, printing,

Virtual PC, Boot Methods

virtual terminal,

executing commands on, Arguments

Meta key handling for,

switching to, Options

virtualization method for booting, Boot Methods

virtualization tools, Conceptual Overview

connection to Internet, System Requirements

console interface for, Managing Virtual Systems

creating virtual systems, libvirt Tools and Terminology

disk image files for, MAC Addresses

for a single guest, Conceptual Overview

graphic interface for, Managing Virtual Systems

KVM (see KVM hypervisor), System Requirements

libvert tools, System Requirements

libvirt (see libvirt virtualization API), MAC Addresses

MAC address for, MAC Addresses

managing virtual systems, Creating Virtual Systems

migration support for, System Requirements

network configuration for, Managing Virtual Systems

paravirtualization, Virtualization Technology

system requirements for, Conceptual Overview

VMware (see VMware), Options

Xen (see Xen hypervisor), Options

visual (v) command, mailx, Command-mode commands

VISUAL built-in variable, Other Shell Variables

visual command, ex,

visual mode, vim, Syntax of vi Commands

vmkfstools command, VMware, Examples

VMM (virtual machine monitor), Conceptual Overview

vmstat command,

VMware, VMware ESX 3.5

changing virtual machine configurations, MAC Addresses

ESX management client for, VMware ESX 3.5

ESX server commands, Snapshots

graphic interface for, Managing Virtual Systems

managing virtual systems, Managing Virtual Systems

networking for, VMware Networking

paravirtualization with, Snapshots

shared disks for, VMware Networking

snapshots, Snapshots

virtual center for, VMware ESX 3.5

virtual switch for networking, Managing Virtual Systems

website for, Virtualization Command-Line Tools

VMware server, Boot Methods

vmware-cmd command, VMware, Managing Virtual Systems, Interactive commands

volname command, Slab mode fields

volume name for device, determining, Slab mode fields

Vromans, Johan (Perl 5 Pocket Reference), Pattern Matching

vSphere, VMware ESX 3.5

vsplit command, ex,

W

w command, Slab mode fields

W command, sed, Basic Editing,

w command, sed, Basic Editing,

wait command, Bash,

wait command, lftp, Commands

wall command, Slab mode fields

wall command, ex,

warnquota command,

watch command,

watch command, gdb, Common commands

WAV format, converting to CDDA, Options,

wc command, Options

website resources, xvii–xix, Source Code Management Systems

Arch system, Source Code Management Systems

Bash debugger, Built-in Shell Variables

Bash shell, The Bash Shell

Codeville system, Source Code Management Systems

CSSC system, Other Source Code Management Systems

for this book, xxi, Ubuntu Builder Scripts

GNU utilities documentation, xvii, Ubuntu Builder Scripts

libvirt virtualization API, Ubuntu Builder Scripts

Linux Today, xvii, Other Source Code Management Systems

Linux Weekly News, xvii, Other Source Code Management Systems

monotone system, Other Source Code Management Systems

netfilter, Overview of Firewalls and Masquerading

online support, xviii, Special File Properties

Slashdot, xvii, Special File Properties

Subversion, Special File Properties

Usenet newsgroups, xviii, Conceptual Overview

user groups, xix, Conceptual Overview

vim editor, Conceptual Overview

virtualization tools, Virtualization Command-Line Tools

weekly command, logrotate, Configuration commands

Welsh, Matt (Running Linux), Commands on Linux

wget command,

whatis command, Options

whatis command, gdb, Common commands

whereis command, Options

which command,

while command, Bash,

while command, gawk,

whitespace, converting to tabs, Options

who command,

whoami command, Example

whois command, Example

window commands, Window Commands

window commands, Emacs, Capitalization Commands

Windows, Managing Filesystems

accessing files from Linux, Installation

as host OS with Linux as guest, Boot Methods

booting with GRUB, GRUB: The Grand Unified Bootloader

booting with LILO, The Boot Process

dual booting Linux with, Boot Methods, Options

Linux as challenge to, Introduction

networking on, Linux providing, The Excitement of Linux

restoring original boot loader, The Boot Process

wnext command, ex,

wodim command, Options

word character class, Filename Metacharacters

word-abbreviation commands, Emacs, Capitalization Commands

working tree, for Git, Conceptual Overview

cleaning,

removing files from, Examples

wq command, ex,

wqall command, ex,

write (w) command, mailx, Command-mode commands

write a message to all users, Slab mode fields

write command, Track options and arguments

write command, ex,

write messages, controlling receipt of,

X

X command, ex,

x command, mailx, Command-mode commands

x command, sed, Basic Editing,

X Window System, Commands on Linux

xargs command, Track options and arguments

xdigit character class, Filename Metacharacters, Search Patterns

XDR (eXternal Data Representation), RPC and XDR

Xen hypervisor, Creating and Manipulating Disk Image Files

changing virtual machine configurations, MAC Addresses

device interfaces for, Configuring Networks

graphic interface for, Managing Virtual Systems

installing, Creating and Manipulating Disk Image Files

libvirt used with (see libvirt virtualization API), Managing Virtual Systems

managing virtual systems, Managing Virtual Systems

networking for, Xen Networking

paravirtualization with, Xen

website for, Virtualization Command-Line Tools

xentop command, Options

xm command, Xen

xentop command, Options

XFS (Extensible Filesystem), Installation

xinetd command,

xit (x) command, mailx, Command-mode commands

xit command, ex,

xm command, Xen, Xen

xor() function, gawk,

Y

y command, sed, Basic Editing,

yacc command, Configuration files

yank (paste), Emacs, Modes

yank command, ex,

yes command, Options

youngest command, svnlook,

YP (Yellow Pages), Overview of NIS

ypbind command, Options

ypcat command, Options

ypinit command, Options

ypmatch command,

yppasswd, Options

yppasswdd command,

yppoll command, Options

yppush command, Options

yps server, Overview of NIS

ypserv command,

ypserv server, Overview of NIS

ypset command, Options

yptest command, Options

ypwhich command,

ypxfr command,

ypxfrd command, Options

yum program, Package Management, Package Management

command syntax and options for, Package Management

commands used in, General options

configuration for, Package Management

plugins for,

yum-builddep plugin, yum, Plugins and yum-utils

yum-complete-transaction plugin, yum, Plugins and yum-utils

yumdownloader plugin, yum, Plugins and yum-utils

yup program, Package Management

Z

z command, ex,

z command, mailx, Command-mode commands

Z Shell, The Bash Shell

zcat command, Options

zcmp command, Options

zdiff command, Options

zforce command, Options

zgrep command,

zless command,

zmore command,

znew command, Commands

zones, printing information about, Options

zsh shell, The Bash Shell

Zwicky, Elizabeth D. (Building Internet Firewalls), Overview of Firewalls and Masquerading

About the Authors

Ellen Siever is a writer and editor specializing in Linux and other open source topics. In addition to Linux in a Nutshell, she coauthored Perl in a Nutshell. She is a long-time Linux and Unix user, and was a programmer for many years until she decided that writing about computers was more fun.

Stephen Figgins honed many of his computer skills while working as O'Reilly's book answer guy. A life long learner with many interests, Stephen draws on many resources to make difficult topics understandable and accessible.

Now living in Lawrence, Kansas, he administrates Linux servers for Sunflower Broadband, a cable company. When not found working with computers, writing, or spending time with his family, you will likely find him outdoors. Stephen teaches wilderness awareness and living skills.

Robert Love has been a Linux user and hacker since the early days. He is active in--and passionate about--the Linux kernel and GNOME desktop communities. His recent contributions to the Linux kernel include work on the kernel event layer and inotify. GNOME-related contributions include Beagle, GNOME Volume Manager, NetworkManager, and Project Utopia. Currently, Robert works in the Open Source Program Office at Google.

Robert is the author of Linux Kernel Development (SAMS 2005) and the co-author of Linux in a Nutshell (2006 O'Reilly). He is also a Contributing Editor at Linux Journal. He is currently working on a new work for O'Reilly that will be the greatest book ever written, give or take. Robert holds a B.A. in Mathematics and a B.S. in Computer Science from the University of Florida. A proud Gator, Robert was born in South Florida but currently calls home Cambridge, MA.

Arnold Robbins, an Atlanta native, is a professional programmer and technical author. He has worked with Unix systems since 1980, when he was introduced to a PDP-11 running a version of Sixth Edition Unix. He has been a heavy AWK user since 1987, when he became involved with gawk, the GNU project's version of AWK. As a member of the POSIX 1003.2 balloting group, he helped shape the POSIX standard for AWK. He is currently the maintainer of gawk and its documentation. He is also coauthor of the sixth edition of O'Reilly's Learning the vi Editor. Since late 1997, he and his family have been living happily in Israel.

Colophon

The animal featured on the cover of Linux in a Nutshell, Sixth Edition, is an Arabian horse. Known for its grace and intelligence, the Arabian is one of the oldest breeds of horse, with evidence of its existence dating back 5,000 years. The Arabian was instrumental as an ancestor to other popular breeds, most notably the Thoroughbred in the 17th and 18th centuries. One of the more distinctive horse breeds, the typical Arabian has large, expressive eyes and nostrils; small ears; and a short, sturdy back. Its stamina suits it particularly well for endurance riding, a sport dominated by the Arabian breed. Its wonderful temperament makes the Arabian an all-around favorite riding horse in North America, although it also can be found in more specialized competitions such as dressage, jumping, and reining.

The cover image is from the Dover Pictorial Archive. The cover font is Adobe ITC Garamond. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont’s TheSansMonoCondensed.

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Linux in a Nutshell

Ellen Siever

Stephen Figgins

Robert Love

Arnold Robbins

Editor

Andy Oram

Copyright © 2009 Ellen Siever, Stephen Figgins, and Robert Love

O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (http://my.safaribooksonline.com). For more information, contact our corporate/institutional sales department: (800) 998-9938 or corporate@oreilly.com.

Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of O’Reilly Media, Inc. The In a Nutshell series designation, Linux in a Nutshell, the image of an Arabian horse, and related trade dress are trademarks of O’Reilly Media, Inc.

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and O’Reilly Media, Inc. was aware of a trademark claim, the designations have been printed in caps or initial caps.

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Linux in a Nutshell

Table of Contents

Special Upgrade Offer

Preface

Organization of This Book

Other Resources

Online Documentation

Websites

Linux Journal and Linux Magazine

Usenet Newsgroups

Online Linux Support

Linux User Groups

Using Code Examples

Conventions

How to Contact Us

Safari® Books Online

Acknowledgments

1. Introduction

The Excitement of Linux

Distribution and Support

Commands on Linux

What This Book Offers

Sources and Licenses

Beginner’s Guide

Communication

Comparisons

File Management

Media

Printing

Programming

Program Maintenance

Searching

Shell Programming

Storage

System Status

Text Processing

Miscellaneous

2. System and Network Administration Overview

Common Commands

Clocks

Daemons

Hardware

Host Information

Installation

Mail

Managing Filesystems

Managing the Kernel

Networking

Printing

Security and System Integrity

Starting and Stopping the System

System Activity and Process Management

Users

Miscellaneous

Overview of Networking

TCP/IP Administration

NFS and NIS Administration

Overview of TCP/IP

IP Addresses

Gateways and Routing

Gateway protocols

Routing daemons

Routing tables

Name Service

DNS and BIND

Domain names

Configuring TCP/IP

Network interfaces

Serial-line communication

Troubleshooting TCP/IP

Overview of Firewalls and Masquerading

Overview of NFS

Administering NFS

Daemons

Exporting Filesystems

Mounting Filesystems

Overview of NIS

Servers

Domains

NIS Maps

Map Manipulation Utilities

Administering NIS

Setting Up an NIS Server

Setting Up an NIS Client

NIS User Accounts

RPC and XDR

3. Linux Commands

Alphabetical Summary of Commands

4. Boot Methods

The Boot Process

LILO: The Linux Loader

The LILO Configuration File

Global options

Image options

Kernel options

The lilo Command

lilo Command Options

LILO Boot Errors

GRUB: The Grand Unified Bootloader

Installing GRUB

Creating a GRUB boot CD

Creating a GRUB boot floppy

Using grub-install

Installing from the GRUB command line

The GRUB Configuration File

Using the Menu Interface

The GRUB Shell

GRUB Commands

Command-Line and Global Menu Commands

Command-Line and Menu-Entry Commands

Dual-Booting Linux and Windows 2000/XP/Vista

Boot-Time Kernel Options

initrd: Using a RAM Disk

5. Package Management

Yum: Yellowdog Updater Modified

The yum Command

General options

yum Command Summary

Plugins and yum-utils

The Red Hat Package Manager

RPM Package Concepts

The rpm Command

General options

Install, upgrade, and freshen options

Query options

Package-selection options

Package-query options

Uninstall options

Verify options

Database rebuild options

Signature-check options

Miscellaneous options

FTP/HTTP options

RPM Examples

The rpmbuild Command

rpmbuild options

The Debian Package Manager

Files

Package Priorities

Package and Selection States

Package Flags

Scripts

Debian Package Manager Command Summary

6. The Bash Shell

Overview of Features

Invoking the Shell

Options

Arguments

Syntax

Special Files

Filename Metacharacters

Examples

Quoting

Examples

Command Forms

Examples

Redirection Forms

Simple redirection

Redirection using file descriptors

Multiple redirection

Examples

Coprocesses

Functions

Variables

Variable Substitution

Examples

Built-in Shell Variables

Other Shell Variables

Arrays

Special Prompt Strings

Arithmetic Expressions

Operators

Examples

Command History

Line-Edit Mode

Common editing keystrokes

The fc Command

Examples

Programmable Completion

Examples

Job Control

Command Execution

Restricted Shells

Built-in Commands

7. Pattern Matching

Filenames Versus Patterns

Metacharacters

Search Patterns

Replacement Patterns

Metacharacters, Listed by Program

Examples of Searching

Examples of Searching and Replacing

8. The Emacs Editor

Conceptual Overview

Modes

Buffer and Window

Point and Mark

Kill and Yank

Notes on the Tables

Absolutely Essential Commands

Command-Line Syntax

Summary of Commands by Group

File-Handling Commands

Cursor-Movement Commands

Deletion Commands

Paragraphs and Regions

Stopping and Undoing Commands

Transposition Commands

Search Commands

Capitalization Commands

Word-Abbreviation Commands

Buffer-Manipulation Commands

Window Commands

Special Shell Characters

Indentation Commands

Centering Commands

Macro Commands

Detail Information Help Commands

Help Commands

Summary of Commands by Key

Control-Key Sequences

Meta-Key Sequences

Summary of Commands by Name

9. The vi, ex, and vim Editors

Conceptual Overview

Command-Line Syntax

Command-Line Options

Review of vi Operations

Command Mode

Insert Mode

Syntax of vi Commands

Examples

Visual mode (vim only)

Status-Line Commands

vi Commands

Movement Commands

Character

Text

Lines

Screens

Searches

Line numbering

Marks

Insert Commands

Edit Commands

Changing and deleting text

Copying and moving

Saving and Exiting

Accessing Multiple Files

Window Commands

Interacting with the System

Macros

Miscellaneous Commands

vi Configuration

The :set Command

Options Used by :set

Sample .exrc File

ex Basics

Syntax of ex Commands

Addresses

Address Symbols

Options

Alphabetical Summary of ex Commands

10. The sed Editor

Conceptual Overview

Typical Uses of sed

sed Operation

Command-Line Syntax

Standard Options

GNU sed Options

Syntax of sed Commands

Pattern Addressing

Pattern Addressing Examples

GNU sed Regular Expression Extensions

Group Summary of sed Commands

Basic Editing

Line Information

Input/Output Processing

Yanking and Putting

Branching Commands

Multiline Input Processing

Alphabetical Summary of sed Commands

11. The gawk Programming Language

Conceptual Overview

Command-Line Syntax

Standard Options

Important gawk Options

Patterns and Procedures

Patterns

Procedures

Simple Pattern-Procedure Examples

Built-in Variables

Operators

Variable and Array Assignment

Escape sequences

Octal and Hexadecimal Constants in gawk

User-Defined Functions

gawk-Specific Features

Coprocesses and Sockets

Profiling

File Inclusion

Internationalization

Implementation Limits

Group Listing of awk Functions and Commands

Alphabetical Summary of awk Functions and Commands

Output Redirections

printf Formats

12. Source Code Management: An Overview

Introduction and Terminology

Usage Models

Source Code Management Systems

Other Source Code Management Systems

13. The Subversion Version Control System

Conceptual Overview

Basic Version-Control Operations

Key Features

Special File Properties

Obtaining Subversion

Using Subversion: A Quick Tour

The Subversion Command Line Client: svn

Common svn Options

svn Subcommands

Repository Administration: svnadmin

Common svnadmin Options

Common svnadmin Subcommands

Examining the Repository: svnlook

svnlook Options

svnlook Subcommands

Providing Remote Access: svnserve

svnserve Options

14. The Git Version Control System

Conceptual Overview

Git Repository Format

Referring to Commits

Using Git: A Quick Tour

Before You Start

Example: The Linux Kernel Repository

Creating and Sharing a New Repository

The Git Command Line Client: git

The git Command

Accessing Git’s Online Help

git Subcommands

15. Virtualization Command-Line Tools

Conceptual Overview

System Requirements

Virtualization Technology

Network Concepts

libvirt Tools and Terminology

Basic Virtualization Operations

Creating Virtual Systems

Examples

Managing Virtual Systems

Graphic and Console Interfaces

Configuring Networks

MAC Addresses

Making Changes to Virtual Machines

Creating and Manipulating Disk Image Files

Xen

Paravirtualization and Architecture

Xen Networking

Xen Commands

KVM

QEMU

Ubuntu Builder Scripts

libvirt and Red Hat Virtual Machine Manager

XML Configuration Files

Connection URIs

Connection URI Examples

Remote GUI control

IP Forwarding and libvirt Networking

libvirt and Virtual Machine Manager Commands

VMware ESX 3.5

ESX Management Client

Virtual Center

VMware Networking

Shared Disks

Snapshots

VMware Tools

ESX Server Commands

Index

About the Authors

Colophon

Special Upgrade Offer

Copyright