OReilly Running Linux 5th Edition Dec 2005 ISBN 0596007604

  Running Linux, 5th Edition By Matthias Kalle Dalheimer, Matt Welsh ...............................................

  Publisher: O'Reilly Pub Date: December 2005

  ISBN: 0-596-00760-4 Pages: 972

You may be contemplating your first Linux installation. Or you may have been using Linux

for years and need to know more about adding a network printer or setting up an FTP server. Running Linux, now in its fifth edition, is the book you'll want on hand in either case. Widely recognized in the Linux community as the ultimate getting-started and problem-solving book, it answers the questions and tackles the configuration issues that frequently plague users, but are seldom addressed in other books. This fifth edition of Running Linux is greatly expanded, reflecting the maturity of the

operating system and the teeming wealth of software available for it. Hot consumer topics

such

as audio and video playback applications, groupware functionality, and spam filtering are

covered, along with the basics in configuration and management that always have made the book popular.

  Running Linux covers basic communications such as mail, web surfing, and instant

messaging, but also delves into the subtleties of network configuration--including dial-up,

ADSL, and cable modems--in case you need to set up your network manually. The book can

make you proficient on office suites and personal productivity applications--and also tells

you what programming tools are available if you're interested in contributing to these applications.

  Other new topics in the fifth edition include encrypted email and filesystems, advanced shell techniques, and remote login applications. Classic discussions on booting, package management, kernel recompilation, and X configuration have also been updated.

  

The authors of Running Linux have anticipated problem areas, selected stable and popular

solutions, and provided clear instructions to ensure that you'll have a satisfying experience

using Linux. The discussion is direct and complete enough to guide novice users, while still

providing the additional information experienced users will need to progress in their mastery of Linux.

  

Whether you're using Linux on a home workstation or maintaining a network server,

Running Linux will provide expert advice just when you need it.

  

Running Linux, 5th Edition

By Matthias Kalle Dalheimer, Matt Welsh ...............................................

  Publisher: O'Reilly Pub Date: December 2005

  

ISBN: 0-596-00760-4

Pages: 972

  

  

  

  

  

  

  

  

  

  

  

   Running Linux, Fifth Edition by Matthias Kalle Dalheimer and Matt Welsh Copyright © 2006, 2002, 1999, 1996, 1995 O'Reilly Media, Inc. All rights reserved. Printed in the United States of America. Published by O'Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472. O'Reilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (safari.oreilly.com). For more information, contact our corporate/institutional sales department: (800) 998-9938 or

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  Editor: Andy Oram

  Production Editor: Adam Witwer Production Services: Argosy Publishing Cover Designer: Edie Freedman Interior Designer: David Futato

  Printing History: May 1995: First Edition.

  August 1996: Second Edition. August 1999: Third Edition.

  December 2002: Fourth Edition. December 2005: Fifth Edition.

  Nutshell Handbook, the Nutshell Handbook logo, and the O'Reilly logo are registered trademarks of O'Reilly Media, Inc. The Linux series designations, Running Linux, images of the American West, and related trade dress are trademarks of O'Reilly Media, Inc.

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  While every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.

  ISBN: 0-596-00760-4 [M]

  Preface Technical knowledge is not enough. One must transcend techniques so that the art becomes an artless art, growing out of the unconscious.

  Daisetsu Suzuki (1870-1966) This is a book about Linux, a free, open source operating system that's changing the world of computing. In this book, we show how you can completely change the way you work with computers by exploring a powerful and free operating system. Linux goes against the traditional computing mainstream, being developed by a loosely organized group of thousands of volunteers across the Internet. Linux started as a real underground movement guerrilla hacking, if you will and brings a lot of excitement, discovery, and self-empowerment back into today's corporate-dominated computing culture. We invite you to dive in, enjoy yourself, and join the throng of people who know what it means to tweak your dot clocks and

  rdev your kernel image.

  The Zen quote at the beginning of this preface summarizes our philosophy in this book. We're targeting readers who are inquisitive and creative enough to delve full-tilt into the world of Linux, and who want to get at the heart of the system. Linux represents a rebellion against commercial and proprietary operating systems, and many of its users like living on the edge of the latest technological trends. Of course, the casual reader can set up and run a Linux system (or hundreds of them!) without much trouble, but the purpose of this book is to dig more deeply into the system to bring you completely into the Linux mentality, to reach Linux "enlightenment." Rather than gloss over messy details, we explain the concepts by which the system actually works so that you can troubleshoot problems on your own. By sharing the accumulated expertise of several Linux experts, we hope to give you enough confidence to call yourself a true Linux Guru. (Your first koan: what is the sound of one user hacking?) You have in your hands the fifth edition of Running Linux, and by most accounts this book is considered the classic text on installing, maintaining, and learning to use a Linux system. The first edition was published way back in 1996, and had its roots in a free book called Linux Installation and Getting Started, which was written by Matt Welsh and is still floating around the Internet. Since Matt conceived and wrote Running Linux, the book has gone through a lot of expansion and improvement to keep up-to-date with the latest developments in the Linux world.

  Kalle Dalheimer, a developer and consultant bringing a great deal of experience with both Linux development and desktop applications, has become the lead author on the past three editions. Other contributors over time have included Lar Kaufman (material on printing and other first-edition material), Tom Adelstein (updates to the introductory chapter and substantial material on VMWare, rdesktop, VNC, and FreeNX), Aaron Weber (GNOME, Evolution, Red Carpet, and ZENworks), Sam Hiser (OpenOffice), Jay Ts (Samba), John H. Terpstra (updates to Samba and NFS), Jeff Tranter (multimedia, sources of Linux information), Kyle Rankin (games), Breckin Loggins (GnuCash), Rod Smith (substantial printing material, including CUPS), Kyle Dent (Postfix), Terry Dawson (material on security), Brian Vincent (Wine and CodeWeaver), Chris Lawrence (Debian packaging), Vatafu Valerica (LAMP chapter), Marc Mutz (material on public-key encryption and encypted filesystems), Steffen Hansen (material on the GIMP, OpenGL, Postfix, and ProFTPd), Till Adam (material on groupware solutions for Linux), Jesper Pedersen (material on kimdaba and Procmail, updates to the Python section), Michel Boyer de la Giroday (PHP), Ivan Ristic (updates to Apache and LAMP chapters), and Jeffrey Dunitz (updates to the backup chapter). As Linux attracts more and more development, becoming increasingly appealing in new areas of use, the challenge for a book like this is to continue its mission with an ever-increasing scope. This edition is much bigger than any of the previous ones, and covers topics such as desktop tools that made only cursory appearances earlier. No book can adequately capture

  everything there is to know about Linux, so we've tried to ask

  at each turn what information is most valuable for a person exploring the system and trying to get a firm basis for further self-education. Our approach has worked remarkably well over the many editions, and we think this book will be of use to you for a long time to come. In the preface to the first edition, we said that "Linux has the potential to completely change the face of the PC operating system world." Looking back, it's clear that our prediction was right! Linux has erupted into the computing mainstream with an amazing force: it has been covered by every major media channel, has helped usher in the so-called Open Source Revolution, and is widely claimed as the most viable competitor to Microsoft's dominance in the operating systems market. Today, most estimates place the number of Linux users worldwide at well over 300 million. Linux has matured to the point where many people can dive in and start using Linux without knowing most of the hairy details behind device drivers,

  XFree86 configuration files, and bootloaders. Actually, a good Linux distribution these days is just as easy to install as its commercial competitors such as Microsoft Windows. Still, we think it's best to give you some of the behind-the-scenes views, so you have an understanding of the workings of the system, even if it's not strictly necessary for casual Linux use.

  Organization of This Book

  Each chapter of this book contains a big chunk of information. It takes you into a world of material that could easily take up several books. But we move quickly through the topics you need to know.

  of the book, "Enjoying and Being Productive on Linux,"

  introduces Linux and brings you to the point where you can do all the standard activities people do on other systems: emailing, web surfing, playing games, watching videos, and so on.

   , Introduction to Linux Tries to draw together many different threads. It explains

  why Linux came to be and what it offers that continues to attract new users and developers.

   , Preinstallation and Installation Describes preliminary tasks that you may have to do before

  installation, such as partitioning your disk, and guidance for initial Linux installation and configuration.

   , Desktop Environments Helps you get comfortable navigating the desktop and the

  most important tools, including the Evolution utility for mail, calendar, and managing contacts.

   , Basic Unix Commands and Concepts Offers a system administrator's introduction to Unix. It is

  intended to give you enough tools to perform the basic tasks you'll need to do throughout the book. Basic commands are covered, along with some tips for administrators and some concepts you should know.

   , Web Browsers and Instant Messaging Shows neat tricks and advanced uses for some of the

  popular and basic computer activities: web browsing and instant messaging.

   , Electronic Mail Clients Introduces other mail clients, for people who want to try

  something besides Evolution, and shows ways to secure email.

   , Office Suites and Personal Productivity Explains how you can be just as productive in your office

  work on Linux as on the proprietary alternatives. The main topics are the OpenOffice office suite, KOffice office suite, and the GnuCash financial application, along with an introduction to groupware.

   , Multimedia Discusses audio and video, covering concepts you'll find

  useful, configuration for systems where the tools don't work automatically, and a few common applications. The GIMP is also introduced for image manipulation.

  

of the book, "System Administration," shows you how to

  set up your Linux system and its environment for such tasks as printing and sharing files with other systems; it also shows you how to take care of your system in other ways.

   System Administration Basics Covers system administration topics such as filesystems

  and swap space that are normally handled automatically during installation, but sometimes need user intervention.

   Installing, Updating, and Compiling Programs Covers system updates, which are important both to get new features and applications and to fix security flaws.

Chapter 13 , Networking Is a basic introduction to networking, which is usually set

  up during installation but is worth understanding at a deeper level. The chapter shows you how to configure your system so that it can work on a local area network or communicate with an Internet service provider using Point- to-Point Protocol (PPP). ISDN and ADSL are also covered.

   The X Window System Shows you how to configure the X Window System, which

  underlies the desktops introduced in

Chapter 3 . We show

  you how to overcome problems you might encounter when your distribution installs the software and how to configure it for the best performance on your video hardware.

Chapter 17 , System Start and Shutdown Covers system startup and shutdown. Topics include the GRUB bootloader, which lets you choose between operating

  systems at startup time, and how to get the right services going.

   Configuring and Building the Kernel Explains how to update the kernel and its modules, which

  may be necessary to run new Linux features or get drivers installed for your hardware.

  

of the book, "Programming," starts exploring interesting

  advanced topics that make Linux a powerful asset, such as programming.

   Text Editing Offers in-depth tutorials on vi and Emacs, valuable text

  editors. Covers text processing, an alternative to using word processors to format text documents.

   Text Processing Describes tools for producing formatted documents from

  markup languages, including XML and the older languages TEX, troff, and Texinfo.

   Programming Tools Is a wide-ranging introduction to programming on Linux,

  introducing a number of languages, as well as tools that you may find it useful to understand even if you are not a programmer.

   Running Web Applications with MySQL and PHP Covers the M and P in the well-known acronym LAMP,

  introducing the basic configuration and use of MySQL and PHP for use with Apache.

Chapter 26 , Running a Secure System Covers the ProFTPD web server, which is convenient for serving documents to colleagues or the general public.

   Heterogeneous Networking and Running Windows

Programs A wealth of ways to get the best out of two diffferent environments. Appendix, Sources of Linux Information Tells you about useful online documentation for Linux and other sources of help.

  Conventions Used in This Book

  The following is a list of the typographical conventions used in this book:

  Italic

  Is used for file and directory names, command names, command-line options, email addresses and pathnames, usernames, hostnames, site names, and all new terms.

  Constant Width

  Is used in examples to show the contents of files or the output from commands, to indicate environment variables and keywords that appear in code, and for Emacs commands.

  Constant Width Bold

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

  Constant Width Italic

  Is used to indicate variable options, keywords, or text that the user is to replace with an actual value.

  This icon designates a note, which is an important aside to the nearby text.

  

This icon designates a warning relating to the nearby text.

  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 us 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: "Running Linux, Fifth Edition by Matthias Kalle Dalheimer and Matt Welsh. Copyright 2006 O'Reilly Media, Inc., 0-596-00760-4." If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at

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  How to Contact Us

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  Acknowledgments

  This book is the result of many people's efforts, and as expected, it would be impossible to list them all here. First of all, we would like to thank Andy Oram, who did an excellent job of editing, writing, and whip-cracking to get this book into shape. Apart from being the overall editor, Andy contributed the Unix tutorial chapter and the Gaim section as well as material for the X and Perl sections. It was Andy who approached us about writing for O'Reilly in the first place, and he has demonstrated the patience of a saint when waiting for our updates to trickle in. Because this book has grown so much in size and scope, its topics have become too diverse for one person, or even a small set of coauthors. Therefore, we have drawn in experts in a number of subject areas, listed near the beginning of the preface, to write substantial material. We would also like to thank the following people for their work on the Linux operating system without all of them, there wouldn't be anything to write a book about: Linus Torvalds, Richard Stallman, Donald Becker, Alan Cox, Remy Card, Eric Raymond, Ted T'so, H. J. Lu, Miguel de Icaza, Ross Biro, Drew Eckhardt, Ed Carp, Eric Youngdale, Fred van Kempen, Steven Tweedie, Patrick Volkerding, Dirk Hohndel, Matthias Ettrich, and all of the other hackers, from the kernel grunts to the lowly docos, too numerous to mention here. Special thanks to the following people for their contributions to the Linux Documentation Project, technical review of this book, or general friendliness and support: Phil Hughes, Melinda McBride, Bill Hahn, Dan Irving, Michael Johnston, Joel Goldberger, Michael K. Johnson, Adam Richter, Roman Yanovsky, Jon Magid, Erik Troan, Lars Wirzenius, Olaf Kirch, Greg Hankins, Alan Sondheim, Jon David, Anna Clark, Adam

  Goodman, Lee Gomes, Rob Walker, Rob Malda, Jeff Bates, and Volker Lendecke. For the third edition, we thank Phil Hughes, Robert J. Chassell, Tony Cappellini, Craig Small, Nat Makarevitch, Chris Davis, Chuck Toporek, Frederic HongFeng, and David Pranata for wide- ranging comments and corrections. Particularly impressive were the efforts put in by an entire team of Debian developers and users, organized for us by Ossama Othman and Julian T. J. Midgley. Julian set up a CVS repository for comments, and the book was examined collectively by him, Chris Lawrence, Robert J. Chassell, Kirk Hilliard, and Stephen Zander. For the fourth edition, we thank David Collier-Brown, Oliver Flimm, Phil Hughes, Chris Lawrence, Rich Payne, Craig Small, Jeff Tranter, and Aaron Weber for their reviews. For the fifth edition, we thank Ben Hyde, Cheridy Jollie, Chris Lawrence, Ellen Siever, and Jeff Tranter. Kalle would like to thank Valerica Vatafu from Buzau, Romania, for lots of help with the chapter about LAMP. He would also like to thank his colleagues in his company Klarälvdalens Datakonsult AB Michel Boyer de la Giroday, Tanja Dalheimer, Steffen Hansen, Jesper Pedersen, Lutz Rogowski, Karl-Heinz Zimmer, Tobias Larsson, Romain Pokrzywka, David Faure, Marc Mutz, Tobias Larsson, and Till Adam for their constructive comments on drafts of the book as well as for being general "Linux thought amplifiers."

  

Part I: Enjoying and Being Productive on

Linux This part of the book introduces Linux and brings you to

  the point where you can do all the standard activities people do on other systems: emailing, web surfing, playing games, watching videos, and so on.

Chapter 2 is worth reading even if you plan to install Linux

  from an easy-to-use distribution. Fundamental considerations, such as how much disk space to devote to different parts of your system, indicate that some planning lies behind every installation.

  The vast majority of Linux installations go well and make the features discussed in this part of the book available to system users. If you have trouble, though, the more advanced material in other parts of the book can help you, along with online documentation and more specialized texts.

  

Chapter 1. Introduction to Linux Welcome to Running Linux, Version 5! When we wrote the first

  edition of this book, Linux had barely arrived on the scene. Our task seemed simple: help readers learn the basics of a new operating system that required a pretty fixed and predictable set of tasks. Few if any observers expected Linux would become a best-of-breed operating system, supported by the vast majority of hardware and software manufacturers on the planet. Who would have known that Linux would grow from a small user base of 30,000 people in 1995 to hundreds of millions only 10 years later? People use Linux everywhere on the planet and in some cases in outer space and under the ocean.

  To the casual observer, Linux looks like a fairly simple personal computer desktop built on the same chassis as any IBM PC. People use Linux to browse the Internet, exchange email, listen to music, watch videos, and instant message their friends and coworkers. Students and office workers create documents with word processors, perform numerous tasks with spreadsheet programs, and make slide presentations. The same Linux operating system also drives sonar arrays in nuclear submarines, indexes every document on the Internet, unifies large corporate data centers, runs nearly 70% of all web sites in the world, records your television programs, works in your cellular phone, and runs the switches that allow you to connect with your friends and family anywhere on the globe. Linux runs systems on the international space station as well as the shuttles that take astronauts there. It protects you from spam and computer viruses on numerous routers and back-end systems.

  You can benefit directly from installing Linux on a system at home, at school, or in the office, and having all that power at office work, but you can also learn how to write database queries, administer a web server, filter mail for spam and viruses, automate your environment through scripting languages, access web services, and participate in the myriad of other cutting-edge activities provided by modern computing. How does Linux do all those things? Linux distributions harvest vast amounts of diverse technology, especially new and innovative developments in hardware. Developers have access to all the code that makes up the operating system. Although many people consider Linux the largest cooperative software development project in human history, Linux developers don't need to even know each other. If someone wants to write a software application, all he has to do is download the Linux code or visit its documentation site. If you started counting people who have contributed to the development of Linux and its associated projects, you would see hundreds of thousands of individuals.

  Linux and open source software developers come from many walks of life. Major computer vendors such as IBM, HP, Novell, Red Hat, Sun, Dell, and others pay portions of their staffs to work on Linux. Universities around the globe sponsor projects and foundations that contribute to Linux. The U.S. Department of Defense, NASA, and the National Security Agency have paid for numerous pieces of the Linux operating system. Developing countries such as China, Brazil, Malaysia, South Africa, and Viet Nam, to mention a few, have added to the Linux base. Industrial giants such as Germany, Australia, Japan, the United Kingdom, and others have also made their presence felt. But in the very midst of those giants, many individuals such as you and me have also contributed to Linux. During the 1990s, Linux generated more excitement in the computer field than any other development since the advent of microprocessor technology. Linux rejuvenated a dying technology sector following the fall of the dot-com boom in the informed observers worldwide, including the authors of this book. Early on, Linux inspired and captured the loyalty of its users. Technologists interested in the server side of the Internet needed to become familiar with the operating systems that ran web sites, domain name services, and email and service providers. Traditional software manufacturers priced their systems out of the range of those wanting to gain webmaster- type skills. Many people viewed Linux as a godsend because you could download it for free and gain the skills necessary to become a webmaster or system administrator while working on relatively low-cost hardware. Originally, people saw Linux as simply an operating system kernel, offering the basic services of process scheduling, virtual memory, file management, and handling of hardware peripherals such as hard drives, DVDs, printers, terminals, and so forth. Other Internet operating systems belonged to the Unix family, which became available for commercial sale only after the breakup of AT&T and the Bell Operating Systems. To skirt the legal issues surrounding AT&T's Unix, the Free Software Foundation (FSF) created a plethora of applications that performed many of the functions of basic Unix while using totally original FSF code instead of code produced by Bell Labs. This collection of FSF software was called GNU. To become a complete operating system, however, FSF needed a kernel. Although their own efforts in that area stalled, an operating system fitting the bill arose unexpectedly from efforts by a student at the University of Helsinki in Finland: Linus Torvalds. People now use the term "Linux" to refer to the complete systemthe kernel along with the many applications that it runs: a complete development and work environment including compilers, editors, graphical interfaces, text processors, games, and more. FSF proponents ask that this broader collection of software be known as "GNU/Linux."

1.1. About This Book

  This book provides an overview and guide to Linux as a desktop and a back-office system. We present information on topics to satisfy novices and wizards alike. This book should provide sufficient material for almost anyone to choose the type of installation they want and get the most out of it. Instead of covering many of the volatile technical detailsthose things that tend to change with Linux's rapid developmentwe give you the information that helps you over the bumps as you take your first steps with popular distributions, as well as background you will need if you plan to go onto more advanced Linux topics such as web services, federated identity management, high- performance computing, and so on.

  We geared this book for those people who want to understand the power that Linux can provide. Rather than provide minimal information, we help you see how the different parts of the Linux system work, so you can customize, configure, and troubleshoot the system on your own. Linux is not difficult to install and use. Many people consider it easier and faster to set up than Microsoft Windows. However, as with any commercial operating system, some black magic exists, and you will find this book useful if you plan to go beyond desktop Linux and use web services or network management services. In this book, we cover the following topics:

  The design and philosophy of the Linux operating system, and what it can do for you.

  Information on what you need to run Linux, including suggestions on hardware platforms and how to configure the operating system depending on its specified role (e.g., desktop, web server, database and/or application server).

  How to obtain and install Linux. We cover the Red Hat, SUSE, and Debian distributions in more detail than others, but the information is useful in understanding just about any distribution.

  An introduction, for new users, to the original Linux/Unix system philosophy, including the most important commands and concepts still in use. Personal productivity through slick and powerful office suites, image manipulation, and financial accounting.

  The care and feeding of the Linux system, including system administration and maintenance, upgrading the system, and how to fix things when they don't work. Expanding the basic Linux system and desktop environments with power tools for the technically inclined.

  The Linux programming environment. The tools of the trade for programming and developing software on the Linux system. Using Linux for telecommunications and networking, including the basics of TCP/IP configuration, PPP for Internet connectivity over a modem, ISDN configuration, ADSL, cable, email, news, and web accesswe even show how to configure a Linux system as a web and database server. Linux for fun: audio, video, and games.

  Many things exist that we'd love to show you how to do with Linux. Unfortunately, to cover them all, this book would be the size of the unabridged Oxford English Dictionary and would be impossible for anyone (let alone the authors) to maintain. Instead we've included the most salient and interesting aspects of the system and show you how to find out more.

  Although much of the discussion in this book is not overly technical, you'll find it easier to navigate if you have some experience with the command line and the editing of simple text files. For those who don't have such experience, we have included a short tutorial in

  of the book is an

  exploration of system administration that can help even seasoned technicians run Linux in a server mode. If you are new to Linux and want more system-oriented information, you'll want to pick up an additional guide to command-line basics. We don't dwell for long on the fundamentals, preferring instead to skip to the fun parts of the system. At any rate, although this book should be enough to get you functional and even seasoned in the use of Linux, you may have requirements that will take you into specialized areas. Seefor a list of sources of information.

1.2. Who's Using Linux?

  Application developers, system administrators, network providers, kernel hackers, students, and multimedia authors are just a few of the categories of people who find that Linux has a particular charm.

  Programmers are increasingly using Linux because of its extensibility and low costthey can pick up a complete programming environment for free and run it on inexpensive PC hardwareand because Linux offers a great development platform for portable programs. In addition to the original FSF tools, Linux can utilize a number of development environments that have surfaced over the last three years, such as Eclipse ( . Eclipse is quite a phenomenon: a tribute to both the creativity of the open source community and the fertility of a collaboration between an open source community and a major vendor (Eclipse was originally developed and released by IBM). It is an open source community focused on providing an extensible development platform and application frameworks for building software. Eclipse's tools and frameworks span the software development life cycle, including support for modeling; language development environments for Java?, C/C++, and other languages; testing and performance; business intelligence; rich client applications; and embedded development. A large, vibrant ecosystem of major technology vendors, innovative startups, universities, and research institutions and individuals extend, complement, and support the Eclipse platform.

  Networking is one of Linux's strengths. Linux has been adopted by people who run large networks because of its simplicity of management, performance, and low cost. Many Internet sites make use of Linux to drive large web servers, e-commerce applications, search engines, and more. Linux is easy to merge into a corporate or academic network because it supports common networking standards. These include both old stand- bys, such as the Network File System (NFS) and Network Information Service (NIS), and more prominent systems used in modern businesses, such as Microsoft file sharing (CIFS and related protocols) and Lightweight Directory Access Protocol (LDAP). Linux makes it easy to share files, support remote logins, and run applications on other systems. A software suite called Samba allows a Linux machine to act as a Windows server in Active Directory environments. The combination of Linux and Samba for this purpose is faster (and less expensive) than running Windows Server 2003. In fact, given the ease with which Linux supports common networking activitiesDHCP, the Domain Name System, Kerberos security, routingit's hard to imagine a corporate networking task for which it's unsuited.

  One of the most popular uses of Linux is in driving large enterprise applications, including web servers, databases, business-to-business systems, and e-commerce sites. Businesses have learned that Linux provides an inexpensive, efficient, and robust system capable of driving the most mission-critical applications. As just one example among the many publicized each month, Cendant Travel Distribution Services put its Fares application on a Linux Enterprise Server with IBM xSeries and BladeCenter servers as the hardware platforms. The move reduced expenditures by 90% while achieving 99.999% availability and handling 300 to 400 transactions per second. Linux's ease of customizationeven down to the guts of the kernelmakes the system very attractive for companies that need to exercise control over the inner workings of the system. Linux supports a range of technologies that ensure timely disk access and resistance to failure, from RAID (a set of mechanisms that allow an array of disks to be treated as a single logical storage device) to the most sophisticated storage costs of meeting new regulatory demands that require the warehousing of data for as long as 30 years. The combination of Linux, the Apache web server, the MySQL database engine, and the PHP scripting language is so common that it has its own acronymLAMP. We cover LAMP in more detail in

Chapter 25 . Kernel hackers were the first to come to Linuxin fact, the

  developers who helped Linus Torvalds create Linux are still a formidable community. The Linux kernel mailing lists see a great deal of activity, and it's the place to be if you want to stay on the bleeding edge of operating system design. If you're into tuning page replacement algorithms, twiddling network protocols, or optimizing buffer caches, Linux is a great choice. Linux is also good for learning about the internals of operating system design, and an increasing number of universities make use of Linux systems in advanced operating system courses. Finally, Linux is becoming an exciting forum for multimedia because it's compatible with an enormous variety of hardware, including the majority of modern sound and video cards. Several programming environments, including the MESA 3D toolkit (a free OpenGL implementation), have been ported to Linux; OpenGL is introduced in "Introduction to OpenGL Programming" in

Chapter 21 . The GIMP (a free Adobe Photoshop work-alike) was originally developed under Linux,

  and is becoming the graphics manipulation and design tool of choice for many artists. Many movie production companies regularly use Linux as the workhorse for advanced special- effects renderingthe popular movies Titanic and The Matrix used "render farms" of Linux machines to do much of the heavy lifting.

  Linux systems have traveled the high seas of the North Pacific, managing telecommunications and data analysis for oceanographic research vessels. Linux systems are used at research stations in Antarctica, and large "clusters" of Linux machines are used at many research facilities for complex scientific simulations ranging from star formation to earthquakes, and in Department of Energy laboratories helping to bring new sources of energy to everyone. On a more basic level, hospitals use Linux to maintain patient records and retrieve archives. The U.S. judiciary uses Linux to manage its entire infrastructure, from case management to accounting. Financial institutions use Linux for real-time trading of stocks, bonds, and other financial instruments. Linux has taken over the role that Unix used to play as the most reliable operating system.

1.3. System Features

  Linux has surpassed the features found in implementations of Unix and Windows. With the changes offered by IBM's Power Architecture, for example, Linux provides functionality for commodity hardware normally only found on the most expensive mainframes. Additionally, the latest kernels include the structure of Security Enhanced Linux (SELinux) provided by the National Security Agency ). SELinux provides the most trusted computing environment available today.

  Now add Linux's ability to provide virtualization at the kernel level. Through Xen ( ), Linux can securely execute multiple virtual machines, each running its own operating system, on a single physical system. This allows enterprises to stop server sprawl and increase CPU utilization.

1.3.1. A Bag of Features This section provides a nickel tour of Linux features.

  Linux is a complete multitasking , multiuser operating system (as are all other versions of Unix). This means that many users can be logged onto the same machine at once, running multiple programs simultaneously. Linux also supports multiprocessor systems (such as dual-Pentium motherboards), with support for _{which is great for high- performance servers and scientific applications.}

  [*] On a 32-bit architecture; on a 64-bit architecture, up to 64 CPUs are supported, and patches are available that support up to 256 CPUs.

  The Linux system is mostly compatible with a number of Unix standards (inasmuch as Unix has standards) on the source level, including IEEE POSIX.1, System V, and BSD features. Linux was developed with source portability in mind: therefore, you will probably find features in the Linux system that are shared across multiple Unix implementations. A great deal of free Unix software available on the Internet and elsewhere compiles on Linux out of the box. If you have some Unix background, you may be interested in some other specific internal features of Linux, including POSIX job control (used by shells such as the C shell, csh, and bash), pseudoterminals (pty devices), and support for national or customized keyboards using dynamically loadable keyboard drivers. Linux also supports virtual consoles , which allow you to switch between multiple login sessions from the system console in text mode. Users of the screen program will find the Linux virtual console implementation familiar (although nearly all users make use of a GUI desktop instead).

  Linux can quite happily coexist on a system that has other operating systems installed, such as Windows 95/98, Windows NT/2000/XP, Mac OS, and Unix-like operating systems such as the variants of BSD. The Linux bootloader (LILO ) and the GRand Unified Bootloader (GRUB ) allow you to select which operating system to start at boot time, and Linux is compatible with other bootloaders as well (such as the one found in Windows XP).

  Linux can run on a wide range of CPU architectures, including the Intel x86 (the whole Pentium line), Itanium, SPARC/UltraSPARC, AMD 64 ("Hammer"), ARM, PA-RISC, Alpha, PowerPC, MIPS, m68k, and IBM 390 and zSeries mainframes. Linux has also been ported to a number of embedded processors, and stripped-down versions have been built for various PDAs, including the PalmPilot and Compaq iPaq. In the other direction, Linux is being considered for top-of-the-line computers as well. Hewlett-Packard has a supercomputer with clusterssupercomputers built from arrays of PCsrun Linux as well. Linux supports various filesystem types for storing data. Some filesystems, such as the Second Extended Filesystem (ext2fs), have been developed specifically for Linux. Other Unix filesystem types, such as the Minix-1 and Xenix filesystems, are also supported. The Windows NTFS, VFAT (Windows 95/98), and FAT (MS-DOS) filesystems have been implemented as well, allowing you to access Windows files directly. Support is included for Macintosh, OS/2, and Amiga filesystems as well. The ISO 9660 CD-ROM filesystem type, which reads all standard formats of CD-ROMs, is also supported. We talk more about filesystems in

   Networking support is one of the greatest strengths of Linux, in

  terms of both functionality and performance. Linux provides a complete implementation of TCP/IP networking. This includes device drivers for many popular Ethernet cards, PPP and SLIP (allowing you to access a TCP/IP network via a serial connection or modem), Parallel Line Internet Protocol (PLIP), and ADSL. Linux also supports the modern IPv6 protocol suite, and many other protocols, including DHCP, Appletalk, IRDA, DECnet, and even AX.25 for packet radio networks. The complete range of TCP/IP clients and services is supported, such as FTP, Telnet, NNTP, and Simple Mail Transfer Protocol (SMTP), the Sun RPC protocols allowing NFS and NIS, and the Microsoft protocols allowing participation in a Microsoft domain. The Linux kernel includes complete network firewall support, allowing any Linux machine to screen network packets and prevent unauthorized access to an intranet, for example.

  It is widely held that networking performance under Linux is superior to other operating systems. We talk more about networking in

  The kernel is the guts of the operating system itself; it's the code that controls the interface between user programs and hardware devices, the scheduling of processes to achieve multitasking, and many other aspects of the system. The kernel is not a separate process running on the system. Instead, you can think of the kernel as a set of routines, constantly in memory, to which every process has access. Kernel routines can be called in a number of ways. One direct method to utilize the kernel is for a process to execute a system call, which is a function that causes the kernel to execute some code on behalf of the process. For example, the read system call will read data from a file descriptor. To the programmer, this looks like any other C function, but in actuality the code for read is contained within the kernel.

  The Linux kernel is known as a monolithic kernel, in that all core functions and device drivers are part of the kernel proper. Some operating systems employ a microkernel architecture whereby device drivers and other components (such as filesystems and memory management code) are not part of the kernelrather, they are treated as independent services or regular user applications. There are advantages and disadvantages to both designs: the monolithic architecture is more common among Unix implementations and is the design employed by classic kernel designs, such as System V and BSD. Linux does support loadable device drivers (which can be loaded and unloaded from memory through user commands); this is covered in . The Linux kernel on Intel platforms is developed to use the special protected-mode features of the Intel x86 processors (starting with the 80386 and moving on up to the current Pentium 4). In particular, Linux makes use of the protected- mode descriptor-based memory management paradigm and many of the other advanced features of these processors. Anyone familiar with x86 protected-mode programming knows that this chip was designed for a multitasking system such as