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Page 1 of 15 The Linux System Administrator's Guide The Linux System Administrator's Guide, describes the system administration aspects of using Linux. It is intended for people who know next to nothing about system administration (those saying ``what is it?''), but who have already mastered at least the basics of normal usage. This manual doesn't tell you how to install Linux; that is described in the Installation and Getting Started document. See below for more information about Linux manuals.
Chapter 1. Introduction"In the beginning, the file was without form, and void; and emptiness was upon the face of the bits. And the Fingers of the Author moved upon the face of the keyboard. And the Author said, Let there be words, and there were words."
The Linux System Administrator's Guide, describes the system administration aspects of using Linux. It is intended for people who know next to nothing about system administration (those saying ``what is it?''), but who have already mastered at least the basics of normal usage. This manual doesn't tell you how to install Linux; that is described in the Installation and Getting Started document. See below for more information about Linux manuals. System administration covers all the things that you have to do to keep a computer system in usable order. It includes things like backing up files (and restoring them if necessary), installing new programs, creating accounts for users (and deleting them when no longer needed), making certain that the filesystem is not corrupted, and so on. If a computer were, say, a house, system administration would be called maintenance, and would include cleaning, fixing broken windows, and other such things. The structure of this manual is such that many of the chapters should be usable independently, so if you need information about backups, for example, you can read just that chapter. However, this manual is first and foremost a tutorial and can be read sequentially or as a whole. This manual is not intended to be used completely independently. Plenty of the rest of the Linux documentation is also important for system administrators. After all, a system administrator is just a user with special privileges and duties. Very useful resources are the manual pages, which should always be consulted when you are not familiar with a command. If you do not know which command you need, then the apropos command can be used. Consult its manual page for more details. While this manual is targeted at Linux, a general principle has been that it should be useful with other UNIX based operating systems as well. Unfortunately, since there is so much variance between different versions of UNIX in general, and in system administration in particular, there is little hope to cover all variants. Even covering all possibilities for Linux is difficult, due to the nature of its development. There is no one official Linux distribution, so different people have different setups and many people have a setup they have built up themselves. This book is not targeted at any one distribution. Distributions can and do vary considerably. When possible, differences have been noted and alternatives given. For a list of distributions and some of their differences see http://en.wikipedia.org/wiki/Comparison_of_Linux_distributions. In trying to describe how things work, rather than just listing ``five easy steps'' for each task, there is much information here that is not necessary for everyone, but those parts are marked as such and can be skipped if you use a preconfigured system. Reading everything will, naturally, increase your understanding of the system and should make using and administering it more productive. Understanding is the key to success with Linux. This book could just provide recipes, but what would you do when confronted by a problem this book had no recipe for? If the book can provide understanding, then recipes are not required. The answers will be self evident. Like all other Linux related development, the work to write this manual was done on a volunteer basis: I did it because I thought it might be fun and because I felt it should be done. However, like all volunteer work, there is a limit to how much time, knowledge and experience people have. This means that the manual is not necessarily as good as it would be if a wizard had been paid handsomely to write it and had spent millennia to perfect it. Be warned. One particular point where corners have been cut is that many things that are already well documented in other freely available manuals are not always covered here. This applies especially to program specific documentation, such as all the details of using mkfs. Only the purpose of the program and as much of its usage as is necessary for the purposes of this manual is described. For further information, consult these other manuals. Usually, all of the referred to documentation is part of the full Linux documentation set.
1.1. Linux or GNU/Linux, that is the question.Many people feel that Linux should really be called GNU/Linux. This is because Linux is only the kernel, not the applications that run on it. Most of the basic command line utilities were written by the Free Software Foundation while developing their GNU operating system. Among those utilities are some of the most basic commands like cp, mv lsof, and dd. In a nutshell, what happened was, the FSF started developing GNU by writing things like compliers, C libraries, and basic command line utilities before the kernel. Linus Torvalds, started Linux by writing the Linux kernel first and using applications written for GNU. I do not feel that this is the proper forum to debate what name people should use when referring to Linux. I mention it here, because I feel it is important to understand the relationship between GNU and Linux, and to also explain why some Linux is sometimes referred to as GNU/Linux. The document will be simply referring to it as Linux. GNU's side of the issue is discussed on their website: The relationship - http://www.gnu.org/gnu/linux-and-gnu.html Why Linux should be GNU/Linux - http://www.gnu.org/gnu/why-gnu-linux.html GNU/Linux FAQ's - http://www.gnu.org/gnu/gnu-linux-faq.html Here are some Alternate views: http://librenix.com/?inode=2312 http://www.topology.org/linux/lingl.html http://atulchitnis.net/writings/gnulinux.php
Figure 2-1 shows some of them.Probably the most important parts of the kernel (nothing else works without them) are memory management and process management. Memory management takes care of assigning memory areas and swap space areas to processes, parts of the kernel, and for the buffer cache. Process management creates processes, and implements multitasking by switching the active process on the processor. At the lowest level, the kernel contains a hardware device driver for each kind of hardware it supports. Since the world is full of different kinds of hardware, the number of hardware device drivers is large. There are often many otherwise similar pieces of hardware that differ in how they are controlled by software. The similarities make it possible to have general classes of drivers that support similar operations; each member of the class has the same interface to the rest of the kernel but differs in what it needs to do to implement them. For example, all disk drivers look alike to the rest of the kernel, i.e., they all have operations like `initialize the drive', `read sector N', and `write sector N'. Some software services provided by the kernel itself have similar properties, and can therefore be abstracted into classes. For example, the various network protocols have been abstracted into one programming interface, the BSD socket library. Another example is the virtual filesystem (VFS) layer that abstracts the filesystem operations away from their implementation. Each filesystem type provides an implementation of each filesystem operation. When some entity tries to use a filesystem, the request goes via the VFS, which routes the request to the proper filesystem driver. A more in-depth discussion of kernel internals can be found at 1.2. Trademarks Microsoft, Windows, Windows NT, Windows 2000, and Windows XP are trademarks and/or registered trademarks of Microsoft Corporation. Red Hat is a trademark of Red Hat, Inc., in the United States and other countries. SuSE is a trademark of Novell. Linux is a registered trademark of Linus Torvalds. UNIX is a registered trademark in the United States and other countries, licensed exclusively through X/Open Company Ltd. GNU is a registered trademark of the Free Software Foundation. Other product names mentioned herein may be trademarks and/or registered trademarks of their respective companies.
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