[gentoo-doc-cvs] cvs commit: lpi-101-advanced-p4.xml - gentoo-doc-cvs

From:	Lukasz Damentko <rane@×××××××××××.org>
To:	gentoo-doc-cvs@l.g.o
Subject:	[gentoo-doc-cvs] cvs commit: lpi-101-advanced-p4.xml
Date:	Sun, 01 Jan 2006 09:01:43
Message-Id:	`200601010901.k0191Kf5022984@robin.gentoo.org`

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rane        06/01/01 09:01:19

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  Added:       xml/htdocs/doc/en/articles lpi-101-advanced-p4.xml

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                        lpi-101-intermediate-p3.xml

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  Log:

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  #115044, two new articles, xmlified by Damian Kuras (ShadoWW)

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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/lpi-101-advanced-p4.xml?rev=1.1&content-type=text/x-cvsweb-markup&cvsroot=gentoo

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plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/lpi-101-advanced-p4.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo

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Index: lpi-101-advanced-p4.xml

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===================================================================

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<?xml version="1.0" encoding="UTF-8"?>

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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">

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<!-- $Header: -->

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<guide link="/doc/en/articles/lpi-101-advanced-p4.xml" disclaimer="articles">

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<title>LPI certification 101 (release 2) exam prep, Part 4</title>

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<author title="Author">

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  <mail link="drobbins@g.o">Daniel Robbins</mail>

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</author>

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<author title="Author">

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  <mail link="chouser@g.o">Chris Houser</mail>

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</author>

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<author title="Author">

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  <mail link="agriffis@g.o">Aron Griffis</mail>

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</author>

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<abstract>

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In this tutorial, we'll introduce all popular filesystem on Linux. We'll teach

35

you how to mount and unmount devices. In next chapter you'll know how to boot

36

the system and how to work with runlevels. In next section of this tutorial,

37

we'll introduce filesystem quotas, we will teach you how to set them and how to

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configure them. By the end of this tutorial you'll know a system logs.

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</abstract>

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<!-- The original version of this article was first published on IBM

42

developerWorks, and is property of Westtech Information Services. This

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document is an updated version of the original article, and contains

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various improvements made by the Gentoo Linux Documentation team -->

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<version>1.0</version>

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<date>2005-12-17</date>

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<chapter>

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<title>Before you start</title>

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<section>

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<title>About this tutorial</title>

53

<body>

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55

<p>

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Welcome to "Advanced administration," the last of four tutorials designed to

57

prepare you for the Linux Professional Institute's 101 (release 2) exam. In

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this tutorial (Part 4), we'll bolster your knowledge of advanced Linux

59

administration skills by covering a variety of topics including Linux

60

filesystems, the Linux boot process, runlevels, filesystem quotas, and system

61

logs.

62

</p>

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64

<p>

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This tutorial is particularly appropriate for someone who may be serving as the

66

primary sysadmin for the first time, since we cover a lot of low-level issues

67

that all system administrators should know. If you are new to Linux, we

68

recommend that you start with <uri

69

link="/doc/en/articles/lpi-101-fundamentals-p1.xml">Part 1</uri> and work

70

through the series from there. For some, much of this material will be new, but

71

more experienced Linux users may find this tutorial to be a great way of

72

"rounding out" their foundational Linux system administration skills and

73

preparing for the next LPI certification level.

74

</p>

75

76

<p>

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By the end of this series of tutorials (eight in all covering the LPI 101 and

78

102 exams), you will have the knowledge you need to become a Linux Systems

79

Administrator and will be ready to attain an LPIC Level 1 certification from

80

the Linux Professional Institute if you so choose.

81

</p>

82

83

<p>

84

For those who have taken the <uri

85

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxlpi4-i.html">release

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1 version</uri> of this tutorial for reasons other than LPI exam preparation,

87

you probably don't need to take this one. However, if you do plan to take the

88

exams, you should strongly consider reading this revised tutorial.

89

</p>

90

91

<p>

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The LPI logo is a trademark of Linux Professional Institute.

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</p>

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95

</body>

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</section>

97

<section>

98

<title>About the authors</title>

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<body>

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101

<p>

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For technical questions about the content of this tutorial, contact the

103

authors:

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</p>

105

106

<ul>

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  <li>Daniel Robbins, at <mail>drobbins@g.o</mail></li>

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  <li>Chris Houser, at <mail>chouser@g.o</mail></li>

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  <li>Aron Griffis, at <mail>agriffis@g.o</mail>.</li>

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</ul>

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<p>

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Daniel Robbins lives in Albuquerque, New Mexico, and is the Chief Architect of

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<uri link="http://www.gentoo.org">Gentoo Technologies, Inc.</uri>, the creator

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of Gentoo Linux, an advanced Linux for the PC, and the Portage system, a

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next-generation ports system for Linux. He has also served as a contributing

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author for the Macmillan books Caldera OpenLinux Unleashed, SuSE Linux

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Unleashed, and Samba Unleashed. Daniel has been involved with computers in some

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fashion since the second grade, when he was first exposed to the Logo

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programming language as well as a potentially dangerous dose of Pac Man. This

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probably explains why he has since served as a Lead Graphic Artist at SONY

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Electronic Publishing/Psygnosis. Daniel enjoys spending time with his wife,

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Mary, and their daughter, Hadassah.

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</p>

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<p>

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Chris Houser, known to his friends as "Chouser," has been a UNIX proponent

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since 1994 when joined the administration team for the computer science network

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at Taylor University in Indiana, where he earned his Bachelor's degree in

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Computer Science and Mathematics. Since then, he has gone on to work in Web

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application programming, user interface design, professional video software

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support, and now Tru64 UNIX device driver programming at <uri

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link="http://www.compaq.com/">Compaq</uri>. He has also contributed to various

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free software projects, most recently to <uri

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link="http://www.gentoo.org">Gentoo Linux</uri>. He lives with his wife and two

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cats in New Hampshire.

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</p>

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<p>

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Aron Griffis graduated from Taylor University with a degree in Computer Science

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and an award that proclaimed him the "Future Founder of a Utopian UNIX

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Commune". Working towards that goal, Aron is employed by <uri

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link="http://www.compaq.com/">Compaq</uri> writing network drivers for Tru64

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UNIX, and spending his spare time plunking out tunes on the piano or developing

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<uri link="http://www.gentoo.org">Gentoo Linux</uri>. He lives with his wife

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Amy (also a UNIX engineer) in Nashua, NH.

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</p>

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</body>

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</section>

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</chapter>

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<chapter>

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<title>Filesystems, partitions, and block devices</title>

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<section>

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<title>Introduction to block devices</title>

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<body>

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<p>

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In this section, we'll take a good look at disk-oriented aspects of Linux,

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including Linux filesystems, partitions, and block devices. Once you're familar

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with the ins and outs of disks and filesystems, we'll guide you through the

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process of setting up partitions and filesystems on Linux.

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</p>

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<p>

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To begin, I'll introduce "block devices". The most famous block device is

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probably the one that represents the first IDE drive in a Linux system:

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</p>

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<pre caption="First IDE drive in Linux">

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/dev/hda

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</pre>

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<p>

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If your system uses SCSI drives, then your first hard drive will be:

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</p>

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<pre caption="First SCSI drive in Linux">

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/dev/sda

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</pre>

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</body>

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</section>

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<section>

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<title>Layers of abstraction</title>

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<body>

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<p>

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The block devices above represent an abstract interface to the disk. User

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programs can use these block devices to interact with your disk without

192

worrying about whether your drivers are IDE, SCSI, or something else. The

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program can simply address the storage on the disk as a bunch of contiguous,

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randomly-accessible 512-byte blocks. 

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</p>

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</body>

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</section>

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<section>

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<title>Partitions</title>

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<body>

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<p>

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Under Linux, we create filesystems by using a special command called

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<c>mkfs</c> (or <c>mke2fs</c>, <c>mkreiserfs</c>, etc.), specifying a

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particular block device as a command-line argument.

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</p>

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<p>

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However, although it is theoretically possible to use a "whole disk" block

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device (one that represents the entire disk) like <path>/dev/hda</path> or

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<path>/dev/sda</path> to house a single filesystem, this is almost never done

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in practice. Instead, full disk block devices are split up into smaller, more

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manageable block devices called partititons. Partitions are created using a

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tool called <c>fdisk</c>, which is used to create and edit the partition table

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that's stored on each disk. The partition table defines exactly how to split up

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the full disk.

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</p>

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</body>

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</section>

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<section>

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<title>Introducing fdisk</title>

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<body>

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<p>

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We can take a look at a disk's partition table by running <c>fdisk</c>,

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specifying a block device that represents a full disk as an argument.

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</p>

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<note>

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Alternate interfaces to the disk's partition table include <c>cfdisk</c>,

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<c>parted</c>, and <c>partimage</c>. I recommend that you avoid using

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<c>cfdisk</c> (despite what the fdisk manual page may say) because it sometimes

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calculates disk geometry incorrectly.

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</note>

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<pre caption="Using fdisk on IDE drive">

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# <i>fdisk /dev/hda</i>

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</pre>

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<pre caption="Using fidks on SCSI drive">

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# <i>fdisk /dev/sda</i>

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</pre>

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<impo>

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You should <e>not</e> save or make any changes to a disk's partition table if

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any of its partitions contain filesystems that are in use or contain important

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data. Doing so will generally cause data on the disk to be lost.

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</impo>

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</body>

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</section>

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<section>

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<title>Inside fdisk</title>

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<body>

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<p>

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Once in <c>fdisk</c>, you'll be greeted with a prompt that looks like this:

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</p>

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<pre caption="fidsk greeting prompt">

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Command (m for help):

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</pre>

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<p>

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Type <c>p</c> to display your disk's current partition configuration:

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</p>

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<pre caption="Displaying current parition configuration">

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Command (m for help): p

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Disk /dev/hda: 240 heads, 63 sectors, 2184 cylinders

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Units = cylinders of 15120 * 512 bytes

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   Device Boot    Start       End    Blocks   Id  System

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/dev/hda1             1        14    105808+  83  Linux

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/dev/hda2            15        49    264600   82  Linux swap

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/dev/hda3            50        70    158760   83  Linux

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/dev/hda4            71      2184  15981840    5  Extended

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/dev/hda5            71       209   1050808+  83  Linux

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/dev/hda6           210       348   1050808+  83  Linux

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/dev/hda7           349       626   2101648+  83  Linux

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/dev/hda8           627       904   2101648+  83  Linux

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/dev/hda9           905      2184   9676768+  83  Linux

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Command (m for help):

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</pre>

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<p>

291

This particular disk is configured to house seven Linux filesystems (each with

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a corresponding partition listed as "Linux") as well as a swap partition

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(listed as "Linux swap").

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</p>

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</body>

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</section>

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<section>

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<title>Block device and partitioning overview</title>

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<body>

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<p>

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Notice the name of the corresponding partition block devices on the left side,

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starting with <path>/dev/hda1</path> and going up to <path>/dev/hda9</path>. In

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the early days of the PC, partitioning software only allowed a maximum of four

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partitions (called primary partitions). This was too limiting, so a workaround

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called extended partitioning was created. An extended partition is very similar

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to a primary partition, and counts towards the primary partition limit of four.

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However, extended partitions can hold any number of so-called logical

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partitions inside them, providing an effective means of working around the four

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partition limit.

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</p>

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314

</body>

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</section>

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<section>

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<title>Partitioning overview, continued</title>

318

<body>

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320

<p>

321

All partitions hda5 and higher are logical partitions. The numbers 1 through 4

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are reserved for primary or extended partitions.

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</p>

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<p>

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In our example, hda1 through hda3 are primary partitions. hda4 is an extended

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partition that contains logical partitions hda5 through hda9. You would never

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actually use <path>/dev/hda4</path> for storing any filesystems directly -- it

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simply acts as a container for partitions hda5 through hda9.

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</p>

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</body>

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</section>

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<section>

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<title>Partition types</title>

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<body>

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<p>

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Also, notice that each partition has an "Id," also called a partition type.

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Whenever you create a new partition, you should ensure that the partition type

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is set correctly. 83 is the correct partition type for partitions that will be

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housing Linux filesystems, and 82 is the correct partition type for Linux swap

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partitions. You set the partition type using the t option in <c>fdisk</c>. The

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Linux kernel uses the partition type setting to auto-detect fileystems and swap

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devices on the disk at boot-time.

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</p>

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</body>

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</section>

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<section>

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<title>Using fdisk to set up partitions</title>

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<body>

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<p>

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Now that you've had your introduction to the way disk partitioning is done

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under Linux, it's time to walk through the process of setting up disk

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partitions and filesystems for a new Linux installation. In this process, we

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will configure a disk with new partitions and then create filesystems on them.

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These steps will provide us with a completely clean disk with no data on it

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that can then be used as a basis for a new Linux installation.

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</p>

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<impo>

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To follow these steps, you need to have a hard drive that does not contain any

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important data, since these steps will <e>erase</e> the data on your disk. If

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this is all new to you, you may want to consider just reading the steps, or

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using a Linux boot disk on a test system so that no data will be at risk.

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</impo>

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</body>

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</section>

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<section>

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<title>What the partitioned disk will look like</title>

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<body>

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<p>

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After we walk through the process of creating partitions on your disk, your

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partition configuration will look like this:

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</p>

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<pre caption="Look of our disk after creating partitions">

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Disk /dev/hda: 30.0 GB, 30005821440 bytes

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240 heads, 63 sectors/track, 3876 cylinders

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Units = cylinders of 15120 * 512 = 7741440 bytes

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   Device Boot    Start       End    Blocks   Id  System

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/dev/hda1    *        1        14    105808+  83  Linux

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/dev/hda2            15        81    506520   82  Linux swap

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/dev/hda3            82      3876  28690200   83  Linux

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Command (m for help):

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</pre>

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</body>

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</section>

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<section>

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<title>Sample partition commentary</title>

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<body>

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<p>

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In our suggested "newbie" partition configuration, we have three partitions.

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The first one (<path>/dev/hda1</path>) at the beginning of the disk is a small

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partition called a boot partition. The boot partition's purpose is to hold all

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the critical data related to booting -- GRUB boot loader information (if you

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will be using GRUB) as well as your Linux kernel(s). The boot partition gives

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us a safe place to store everything related to booting Linux. During normal

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day-to-day Linux use, your boot partition should remain unmounted for safety.

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If you are setting up a SCSI system, your boot partition will likely end up

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being <path>/dev/sda1</path>.

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</p>

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<p>

413

It's recommended to have boot partitions (containing everything necessary for

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the boot loader to work) at the beginning of the disk. While not necessarily

415

required anymore, it is a useful tradition from the days when the LILO boot

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loader wasn't able to load kernels from filesystems that extended beyond disk

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cylinder 1024.

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</p>

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<p>

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The second partition (<path>/dev/hda2</path>) s used for swap space. The kernel

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uses swap space as virtual memory when RAM becomes low. This partition,

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relatively speaking, isn't very big either, typically somewhere around 512 MB.

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If you're setting up a SCSI system, this partition will likely end up being

425

called <path>/dev/hda2</path>.

426

</p>

427

428

<p>

429

The third partition (<path>/dev/hda3</path>) is quite large and takes up the

430

rest of the disk. This partition is called our root partition and will be used

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to store your main filesystem that houses the main Linux filesystem. On a SCSI

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system, this partition would likely end up being <path>/dev/hda3</path>.

433

</p>

434

435

</body>

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</section>

437

<section>

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<title>Getting started</title>

439

<body>

440

441

<p>

442

Okay, now to create the partitions as in the example and table above. First,

443

enter fdisk by typing <c>fdisk /dev/hda</c> or <c>fdisk /dev/sda</c>, depending

444

on whether you're using IDE or SCSI. Then, type <c>p</c> to view your

445

current partition configuration. Is there anything on the disk that you need to

446

keep? If so, stop now. If you continue with these directions, all existing data

447

on your disk will be erased.

448

</p>

449

450

<impo>

451

Following the instructions below will cause all prior data on your disk to be

452

erased! If there is anything on your drive, please be sure that it is

453

non-critical information that you don't mind losing. Also make sure that you

454

have selected the correct drive so that you don't mistakenly wipe data from the

455

wrong drive.

456

</impo>

457

458

</body>

459

</section>

460

<section>

461

<title>Zapping existing partitions</title>

462

<body>

463

464

<p>

465

Now, it's time to delete any existing partitions. To do this, type d and hit

466

enter. You will then be prompted for the partition number you would like to

467

delete. To delete a pre-existing <path>/dev/hda1</path>, you would type:

468

</p>

469

470

<pre caption="Deleting pre-existing partition">

471

Command (m for help): <i>d</i>

472

Partition number (1-4): <i>1</i>

473

</pre>

474

475

<p>

476

The partition has been scheduled for deletion. It will no longer show up if you

477

type <c>p</c>, but it will not be erased until your changes have been saved. If

478

you made a mistake and want to abort without saving your changes, type <c>q</c>

479

immediately and hit enter and your partition will not be deleted.

480

</p>

481

482

<p>

483

Now, assuming that you do indeed want to wipe out all the partitions on your

484

system, repeatedly type <c>p</c> to print out a partition listing and then type

485

<c>d</c> and the number of the partition to delete it. Eventually, you'll end

486

up with a partition table with nothing in it:

487

</p>

488

489

<pre caption="Drives look after cleaning it">

490

491

Disk /dev/hda: 30.0 GB, 30005821440 bytes

492

240 heads, 63 sectors/track, 3876 cylinders

493

Units = cylinders of 15120 * 512 = 7741440 bytes

494

495

Device Boot    Start       End    Blocks   Id  System

496

497

Command (m for help):

498

</pre>

499

500

</body>

501

</section>

502

<section>

503

<title>Creating a boot partition</title>

504

<body>

505

506

<p>

507

Now that the in-memory partition table is empty, we're ready to create a boot

508

partition. To do this, type <c>n</c> to create a new partition, then <c>p</c>

509

to tell fdisk you want a primary partition. Then type <c>1</c> to create the

510

first primary partition. When prompted for the first cylinder, hit enter. When

511

prompted for the last cylinder, type <c>+100M</c> to create a partition 100MB

512

in size. Here's the output from these steps:

513

</p>

514

515

<pre caption="Creating a boot partition">

516

Command (m for help): <i>n</i>

517

Command action

518

e   extended

519

p   primary partition (1-4)

520

<i>p</i>

521

Partition number (1-4): <i>1</i>

522

First cylinder (1-3876, default 1):

523

Using default value 1

524

Last cylinder or +size or +sizeM or +sizeK (1-3876, default 3876): <i>+100M</i>

525

</pre>

526

527

<p>

528

Now, when you type <c>p</c>, you should see the following partition printout:

529

</p>

530

531

<pre caption="Partition printout">

532

Command (m for help): <i>p</i>

533

534

Disk /dev/hda: 30.0 GB, 30005821440 bytes

535

240 heads, 63 sectors/track, 3876 cylinders

536

Units = cylinders of 15120 * 512 = 7741440 bytes

537

538

   Device Boot    Start       End    Blocks   Id  System

539

/dev/hda1             1        14    105808+  83  Linux

540

</pre>

541

542

</body>

543

</section>

544

<section>

545

<title>Creating the swap partition</title>

546

<body>

547

548

<p>

549

Next, let's create the swap partition. To do this, type <c>n</c> to create a

550

new partition, then <c>p</c> to tell fdisk that you want a primary partition.

551

Then type <c>2</c> to create the second primary partition,

552

<path>/dev/hda2</path> in our case. When prompted for the first cylinder, hit

553

enter. When prompted for the last cylinder, type <c>+512M</c> to create a

554

partition 512MB in size. After you've done this, type <c>t</c> to set the

555

partition type, and then type <c>82</c> to set the partition type to "Linux

556

Swap." After completing these steps, typing <c>p</c> should display a partition

557

table that looks similar to this:

558

</p>

559

560

<pre caption="Partition table">

561

Command (m for help): <i>p</i>

562

563

Disk /dev/hda: 30.0 GB, 30005821440 bytes

564

240 heads, 63 sectors/track, 3876 cylinders

565

Units = cylinders of 15120 * 512 = 7741440 bytes

566

567

   Device Boot    Start       End    Blocks   Id  System

568

/dev/hda1             1        14    105808+  83  Linux

569

/dev/hda2            15        81    506520   82  Linux swap

570

</pre>

571

572

</body>

573

</section>

574

<section>

575

<title>Making it bootable</title>

576

<body>

577

578

<p>

579

Finally, we need to set the "bootable" flag on our boot partition and then

580

write our changes to disk. To tag <path>/dev/hda1</path> as a "bootable"

581

partition, type <c>a</c> at the menu and then type 1 for the partition number.

582

If you type <c>p</c> now, you'll now see that <path>/dev/hda1</path> has an "*"

583

in the "Boot" column. Now, let's write our changes to disk. To do this, type

584

<c>w</c> and hit enter. Your disk partitions are now properly configured for

585

the installation of Linux.

586

</p>

587

588

<note>

589

If fdisk instructs you to do so, please reboot to allow your system to detect

590

the new partition configuration.

591

</note>

592

593

</body>

594

</section>

595

<section>

596

<title>Extended and logical partitioning</title>

597

<body>

598

599

<p>

600

In the above example, we created a single primary partition that will contain a

601

filesystem used to store all our data. This means that after installing Linux,

602

this main filesystem will get mounted at "<path>/</path>" and will contain a

603

tree of directories that contain all our files.

604

</p>

605

606

<p>

607

While this is a common way to set up a Linux system, there is another approach

608

that you should be familiar with. This approach uses multiple partitions that

609

house multiple filesystems and are then "linked" together to form a cohesive

610

filesystem tree. For example, it is common to put <path>/home</path> and

611

<path>/var</path> on their own filesystems.

612

</p>

613

614

<p>

615

We could have made hda2 into an extended rather than a primary partition. Then,

616

we could have created the hda5, hda6, and hda7 logical partitions (which would

617

technically be contained "inside" hda2), which would house the <path>/</path>,

618

<path>/home</path>, and <path>/var</path> filesystems respectively.

619

</p>

620

621

<p>

622

You can learn more about these types of multi-filesystem configurations by

623

studying the resources listed on the next page.

624

</p>

625

626

</body>

627

</section>

628

<section>

629

<title>Partitioning resources</title>

630

<body>

631

632

<p>

633

For more information on partitioning, take a look at the following partitioning

634

tips:

635

</p>

636

637

<ul>

638

  <li>

639

    <uri link="/doc/en/articles/partition-planning-tips.xml">Partition planning

640

    tips</uri>

641

  </li>

642

  <li>

643

    <uri link="/doc/en/articles/partitioning-p2.xml">Partitioning in action:

644

    consolidating data</uri>

645

  </li>

646

  <li>

647

    <uri link="/doc/en/articles/partitioning-p1.xml">Partitioning in action:

648

    moving /home</uri>.

649

  </li>

650

</ul>

651

652

</body>

653

</section>

654

<section>

655

<title>Creating filesystems</title>

656

<body>

657

658

<p>

659

Now that the partitions have been created, it's time to set up filesystems on

660

the boot and root partitions so that they can be mounted and used to store

661

data. We will also configure the swap partition to serve as swap storage.

662

</p>

663

664

<p>

665

Linux supports a variety of different types of filesystems; each type has its

666

strengths and weaknesses and its own set of performance characteristics. We

667

will cover the creation of ext2, ext3, XFS, JFS, and ReiserFS filesystems in

668

this tutorial. Before we create filesystems on our example system, let's

669

briefly review the various filesystems available under Linux. We'll go into

670

more detail on the filesystems later in the tutorial.

671

</p>

672

673

</body>

674

</section>

675

<section>

676

<title>The ext2 filesystem</title>

677

<body>

678

679

<p>

680

ext2 is the tried-and-true Linux filesystem, but it doesn't have metadata

681

journaling, which means that routine ext2 filesystem checks at startup time can

682

be quite time-consuming. There is now quite a selection of newer-generation

683

journaled filesystems that can be checked for consistency very quickly and are

684

thus generally preferred over their non-journaled counterparts. Journaled

685

filesystems prevent long delays when you boot your system and your filesystem

686

happens to be in an inconsistent state.

687

</p>

688

689

</body>

690

</section>

691

<section>

692

<title>The ext3 filesystem</title>

693

<body>

694

695

<p>

696

ext3 is the journaled version of the ext2 filesystem, providing metadata

697

journaling for fast recovery in addition to other enhanced journaling modes,

698

such as full data and ordered data journaling. ext3 is a very good and reliable

699

filesystem. It offers generally decent performance under most conditions.

700

Because it does not extensively employ the use of "trees" in its internal

701

design, it doesn't scale very well, meaning that it is not an ideal choice for

702

very large filesystems or situations where you will be handling very large

703

files or large quantities of files in a single directory. But when used within

704

its design parameters, ext3 is an excellent filesystem.

705

</p>

706

707

<p>

708

One of the nice things about ext3 is that an existing ext2 filesystem can be

709

upgraded "in-place" to ext3 quite easily. This allows for a seamless upgrade

710

path for existing Linux systems that are already using ext2.

711

</p>

712

713

</body>

714

</section>

715

<section>

716

<title>The ReiserFS filesystem</title>

717

<body>

718

719

<p>

720

ReiserFS is a B-tree-based filesystem that has very good overall performance

721

and greatly outperforms both ext2 and ext3 when dealing with small files (files

722

less than 4k), often by a factor of 10x-15x. ReiserFS also scales extremely

723

well and has metadata journaling. As of kernel 2.4.18+, ReiserFS is now

724

rock-solid and highly recommended for use both as a general-purpose filesystem

725

and for extreme cases such as the creation of large filesystems, the use of

726

many small files, very large files, and directories containing tens of

727

thousands of files. ReiserFS is the filesystem we recommend by default for all

728

non-boot partitions.

729

</p>

730

731

</body>

732

</section>

733

<section>

734

<title>The XFS filesystem</title>

735

<body>

736

737

<p>

738

XFS is a filesystem with metadata journaling. It comes with a robust

739

feature-set and is optimized for scalability. We only recommend using this

740

filesystem on Linux systems with high-end SCSI and/or fibre channel storage and

741

a uninterruptible power supply. Because XFS aggressively caches in-transit data

742

in RAM, improperly designed programs (those that don't take proper precautions

743

when writing files to disk (and there are quite a few of them) can lose a good

744

deal of data if the system goes down unexpectedly.

745

</p>

746

747

</body>

748

</section>

749

<section>

750

<title>The JFS filesystem</title>

751

<body>

752

753

<p>

754

JFS is IBM's own high performance journaling filesystem. It has recently become

755

production-ready, and we would like to see a longer track record before

756

commenting either positively nor negatively on its general stability at this

757

point.

758

</p>

759

760

</body>

761

</section>

762

<section>

763

<title>Filesystem recommendations</title>

764

<body>

765

766

<p>

767

If you're looking for the most rugged journaling filesystem, use ext3. If

768

you're looking for a good general-purpose high-performance filesystem with

769

journaling support, use ReiserFS; both ext3 and ReiserFS are mature, refined

770

and recommended for general use.

771

</p>

772

773

<p>

774

Based on our example above, we will use the following commands to initialize

775

all our partitions for use:

776

</p>

777

778

<pre caption="Initlizing partitions">

779

# <i>mke2fs -j /dev/hda1</i>

780

# <i>mkswap /dev/hda2</i>

781

# <i>mkreiserfs /dev/hda3</i>

782

</pre>

783

784

<p>

785

We choose ext3 for our <path>/dev/hda1</path> boot partition because it is a

786

robust journaling filesystem supported by all major boot loaders. We used

787

<c>mkswap</c> for our <path>/dev/hda2</path> swap partition -- the choice is

788

obvious here. And for our main root filesystem on <path>/dev/hda3</path> we

789

choose ReiserFS, since it is a solid journaling filesystem offering excellent

790

performance. Now, go ahead and initialize your partitions.

791

</p>

792

793

</body>

794

</section>

795

<section>

796

<title>Making swap</title>

797

<body>

798

799

<p>

800

<c>mkswap</c> is the command that used to initialize swap partitions:

801

</p>

802

803

<pre caption="Initalizing swap partition">

804

# <i>mkswap /dev/hda2</i>

805

</pre>

806

807

<p>

808

Unlike regular filesystems, swap partitions aren't mounted. Instead, they are

809

enabled using the <c>swapon</c> command:

810

</p>

811

812

<pre caption="Enabling swap partition">

813

# <i>swapon /dev/hdc6</i>

814

</pre>

815

816

<p>

817

Your Linux system's startup scripts will take care of automatically enabling

818

your swap partitions. Therefore, the <c>swapon</c> command is generally only

819

needed when you need to immediately add some swap that you just created. To

820

view the swap devices currently enabled, type <c>cat /proc/swaps</c>.

821

</p>

822

823

</body>

824

</section>

825

<section>

826

<title>Creating ext2, ext3, and ReiserFS filesystems</title>

827

<body>

828

829

<p>

830

You can use the <c>mke2fs</c> command to create ext2 filesystems:

831

</p>

832

833

<pre caption="Creating ext2 filesystem">

834

# <i>mke2fs /dev/hda1</i>

835

</pre>

836

837

<p>

838

If you would like to use ext3, you can create ext3 filesystems using <c>mke2fs

839

-j</c>:

840

</p>

841

842

<pre caption="Creating ext3 filesystem">

843

# <i>mke2fs /dev/hda3</i>

844

</pre>

845

846

<note>

847

You can find out more about using ext3 under Linux 2.4 on <uri

848

link="http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html">this site</uri>

849

maintained by Andrew Morton.

850

</note>

851

852

<p>

853

To create ReiserFS filesystems, use the <c>mkreiserfs</c> command:

854

</p>

855

856

<pre caption="Creating ReiserFS filesystem">

857

# <i>mkreiserfs /dev/hda3</i>

858

</pre>

859

860

</body>

861

</section>

862

<section>

863

<title>Creating XFS and JFS filesystems</title>

864

<body>

865

866

<p>

867

To create an XFS filesystem, use the <c>mkfs.xfs</c> command:

868

</p>

869

870

<pre caption="Creating XFS filesystem">

871

# <i>mkfs.xfs /dev/hda3</i>

872

</pre>

873

874

<note>

875

You may want to add a couple of additional flags to the mkfs.xfs command: <c>-d

876

agcount=3 -l size=32m</c>. The <c>-d agcount=3</c> command will lower the

877

number of allocation groups. XFS will insist on using at least one

878

allocation group per 4GB of your partition, so, for example, if you have a 20GB

879

partition you will need a minimum agcount of 5. The <c>l size=32m</c> command

880

increases the journal size to 32MB, increasing performance.

881

</note>

882

883

<p>

884

To create JFS filesystems, use the <c>mkfs.jfs</c> command:

885

</p>

886

887

<pre caption="Creating JFS filesystem">

888

# <i>mkfs.jfs /dev/hda3</i>

889

</pre>

890

891

</body>

892

</section>

893

<section>

894

<title>Mounting filesystems</title>

895

<body>

896

897

<p>

898

Once the filesystem is created, we can mount it using the <c>mount</c> command:

899

</p>

900

901

<pre caption="Mounting filesystem">

902

# <i>mount /dev/hda3 /mnt</i>

903

</pre>

904

905

<p>

906

To mount a filesystem, specify the partition block device as a first argument

907

and a "mountpoint" as a second argument. The new filesystem will be "grafted

908

in" at the mountpoint. This also has the effect of "hiding" any files that were

909

in the <path>/mnt</path> directory on the parent filesystem. Later, when the

910

filesystem is unmounted, these files will reappear. After executing the mount

911

command, any files created or copied inside <path>/mnt</path> will be stored on

912

the new ReiserFS filesystem you mounted.

913

</p>

914

915

<p>

916

Let's say we wanted to mount our boot partition inside <path>/mnt</path>. We

917

could do this by performing the following steps:

918

</p>

919

920

<pre caption="Mounting boot partition in /mnt">

921

# <i>mkdir /mnt/boot</i>

922

# <i>mount /dev/hda1 /mnt/boot</i>

923

</pre>

924

925

<p>

926

Now, our boot filesystem is available inside /mnt/boot. If we create files

927

inside <path>/mnt/boot</path>, they will be stored on our ext3 filesystem that

928

physically resides on <path>/dev/hda1</path>. If we create file inside

929

<path>/mnt</path> but not <path>/mnt/boot</path>, then they will be stored on

930

our ReiserFS filesystem that resides on <path>/dev/hda3</path>. And if we

931

create files outside of <path>/mnt</path>, they will not be stored on either

932

filesystem but on the filesystem of our current Linux system or boot disk.

933

</p>

934

935

<p>

936

To see what filesystems are mounted, type <c>mount</c> by itself. Here is the

937

output of <c>mount</c> on one of our currently-running Linux system, which has

938

partitions configured identically to those in the example above:

939

</p>

940

941

<pre caption="Output of mount command">

942

/dev/root on / type reiserfs (rw,noatime)

943

none on /dev type devfs (rw)

944

proc on /proc type proc (rw)

945

tmpfs on /dev/shm type tmpfs (rw)

946

usbdevfs on /proc/bus/usb type usbdevfs (rw)

947

/dev/hde1 on /boot type ext3 (rw,noatime)

948

</pre>

949

950

<p>

951

You can also view similar information by typing cat <path>/proc/mounts</path>.

952

The "root" filesystem, <path>/dev/hda3</path> gets mounted automatically by the

953

kernel at boot-time, and gets the symbolic name <path>/dev/hda3</path>. On our

954

system, both <path>/dev/hda3</path> and <path>/dev/root</path> point to the

955

same underlying block device using a symbolic link:

956

</p>

957

958

<pre caption="Symbolic links">

959

# <i>ls -l /dev/root</i>

960

lr-xr-xr-x   1 root   root   33 Mar 26 20:39 /dev/root -> ide/host0/bus0/target0/lun0/part3

961

962

# <i>ls -l /dev/hda3</i>

963

lr-xr-xr-x   1 root   root   33 Mar 26 20:39 /dev/hde3 -> ide/host0/bus0/target0/lun0/part3

964

</pre>

965

966

</body>

967

</section>

968

<section>

969

<title>Even more mounting stuff</title>

970

<body>

971

972

<p>

973

So, what is this "<path>/dev/ide/host0</path>...." file? Systems like mine that

974

use the devfs device-management filesystem for <path>/dev</path> have longer

975

official names for the partition and disk block devices than Linux used to have

976

in the past. For example, <path>/dev/ide/host0/bus1/target0/lun0/part7</path>

977

is the official name for <path>/dev/hdc7</path>, and <path>/dev/hdc7</path>

978

itself is just a symlink pointing to the official block device. You can

979

determine if your system is using devfs by checking to see if the

980

<path>/dev/.devfsd</path> file exists; if so, then devfs is active.

981

</p>

982

983

<p>

984

When using the mount command to mount filesystems, it attempts to auto-detect

985

the filesystem type. Sometimes, this may not work and you will need to specify

986

the to-be-mounted filesystem type manually using the -t option, as follows:

987

</p>

988

989

<pre caption="Mounting ext3 filesystem manually with -t option">

990

# <i>mount /dev/hda1 /mnt/boot -t ext3</i>

991

</pre>

992

993

<p>or</p>

994

995

<pre caption="Mouting reiserfs filesystem manually with -t option">

996

# <i>mount /dev/hda3 /mnt -t reiserfs</i>

997

</pre>

998

999

</body>

1000

</section>

1001

<section>

1002

<title>Mount options</title>

1003

<body>

1004

1005

<p>

1006

It's also possible to customize various attributes of the to-be-mounted

1007

filesystem by specifying mount options. For example, you can mount a filesystem

1008

as "read-only" by using the "ro" option:

1009

</p>

1010

1011

<pre caption="Mouting filesystem as read-only">

1012

# <i>mount /dev/hdc6 /mnt -o ro</i>

1013

</pre>

1014

1015

<p>

1016

With <path>/dev/hdc6</path> mounted read-only, no files can be modified in

1017

<path>/mnt</path> -- only read. If your filesystem is already mounted

1018

"read/write" and you want to switch it to read-only mode, you can use the

1019

"remount" option to avoid having to unmount and remount the filesystem again:

1020

</p>

1021

1022

<pre caption="Using remount option">

1023

# <i>mount /mnt -o remount,ro</i>

1024

</pre>

1025

1026

<p>

1027

Notice that we didn't need to specify the partition block device because the

1028

filesystem is already mounted and <c>mount</c> knows that <path>/mnt</path> is

1029

associated with <path>/dev/hdc6</path>. To make the filesystem writeable again,

1030

we can remount it as read-write:

1031

</p>

1032

1033

<pre caption="Remounting filesystem as read-write">

1034

# <i>mount /mnt -o remount,rw</i>

1035

</pre>

1036

1037

<p>

1038

Note that these remount commands will not complete successfully if any process

1039

has opened any files or directories in <path>/mnt</path>. To familiarize

1040

yourself with all the mount options available under Linux, type <c>man

1041

mount</c>.

1042

</p>

1043

1044

</body>

1045

</section>

1046

<section>

1047

<title>Introducing fstab</title>

1048

<body>

1049

1050

<p>

1051

So far, we've seen how partition an example disk and mount filesystems manually

1052

from a boot disk. But once we get a Linux system installed, how do we configure

1053

that Linux system to mount the right filesystems at the right time?  For

1054

example, Let's say that we installed Gentoo Linux on our current example

1055

filesystem configuration. How would our system know how to to find the root

1056

filesystem on <path>/dev/hda3</path>? And if any other filesystems -- like swap

1057

-- needed to be mounted at boot time, how would it know which ones?

1058

</p>

1059

1060

<p>

1061

Well, the Linux kernel is told what root filesystem to use by the boot loader,

1062

and we'll take a look at the linux boot loaders later in this tutorial. But for

1063

everything else, your Linux system has a file called <path>/etc/fstab</path>

1064

that tells it about what filesystems are available for mounting. Let's take a

1065

look at it.

1066

</p>

1067

1068

</body>

1069

</section>

1070

<section>

1071

<title>A sample fstab</title>

1072

<body>

1073

1074

<p>

1075

Let's take a look at a sample <path>/etc/fstab</path> file:

1076

</p>

1077

1078

<pre caption="Sample /etc/fstab file">

1079

  &lt;fs&gt; &lt;mountpoint&gt; &lt;type&gt;    &lt;opts&gt;            &lt;dump/pass&gt;

1080

1081

/dev/hda1       /boot           ext3            noauto,noatime          1 1

1082

/dev/hda3       /               reiserfs        noatime                 0 0

1083

/dev/hda2       none            swap            sw                      0 0

1084

/dev/cdrom      /mnt/cdrom      iso9660         noauto,ro,user          0 0

1085

# /proc should always be enabled

1086

proc            /proc           proc            defaults                0 0

1087

</pre>

1088

1089

<p>

1090

Above, each non-commented line in <path>/etc/fstab</path> specifies a partition

1091

block device, a mountpoint, a filesystem type, the filesystem options to use

1092

when mounting the filesystem, and two numeric fields. The first numeric field

1093

is used to tell the <c>dump</c> backup command the filesystems that should be

1094

backed up. Of course, if you are not planning to use <c>dump</c> on your

1095

system, then you can safely ignore this field. The last field is used by the

1096

<c>fsck</c> filesystem integrity checking program, and tells it the order in

1097

which your filesystems should be checked at boot. We'll touch on <c>fsck</c>

1098

again in a few panels.

1099

</p>

1100

1101

<p>

1102

Look at the <path>/dev/hda1</path> line; you'll see that <path>/dev/hda1</path>

1103

is an ext3 filesystem that should be mounted at the <path>/boot</path>

1104

mountpoint. Now, look at <path>/dev/hda1</path>'s mount options in the opts

1105

column. The noauto option tells the system to not mount <path>/dev/hda1</path>

1106

automatically at boot time; without this option, <path>/dev/hda1</path> would

1107

be automatically mounted to <path>/boot</path> at system boot time.

1108

</p>

1109

1110

<p>

1111

Also note the noatime option, which turns off the recording of atime (last

1112

access time) information on the disk. This information is generally not needed,

1113

and turning off atime updates has a positive effect on filesystem performance.

1114

</p>

1115

1116

<p>

1117

Now, take a look at the <path>/proc</path> line and notice the defaults option.

1118

Use defaults whenever you want a filesystem to be mounted with just the

1119

standard mount options. Since <path>/etc/fstab</path> has multiple fields, we

1120

can't simply leave the option field blank.

1121

</p>

1122

1123

<p>

1124

Also notice the <path>/etc/fstab</path> line for <path>/dev/hda2</path>. This

1125

line defines <path>/dev/hda2</path> as a swap device. Since swap devices aren't

1126

mounted like filesystems, none is specified in the mountpoint field. Thanks to

1127

this <path>/etc/fstab</path> entry, our <path>/dev/hda2</path> swap device will

1128

be enabled automatically when the system starts up.

1129

</p>

1130

1131

<p>

1132

With an <path>/etc/fstab</path> entry for <path>/dev/cdrom</path> like the one

1133

above, mounting the CD-ROM drive becomes easier. Instead of typing:

1134

</p>

1135

1136

<pre caption="Mounting CD-ROM without entry in fstab">

1137

# <i>mount -t iso9660 /dev/cdrom /mnt/cdrom -o ro</i>

1138

</pre>

1139

1140

<p>

1141

We can now type:

1142

</p>

1143

1144

<pre caption="Mounting CD-ROM with entry in fstab">

1145

# <i>mount /dev/cdrom</i>

1146

</pre>

1147

1148

<p>

1149

In fact, using <path>/etc/fstab</path> allows us to take advantage of the user

1150

option. The user mount option tells the system to allow this particular

1151

filesystem to be mounted by any user. This comes in handy for removable media

1152

devices like CD-ROM drives. Without this fstab mount option, only the root user

1153

would be able to use the CD-ROM drive.

1154

</p>

1155

1156

</body>

1157

</section>

1158

<section>

1159

<title>Unmounting filesystems</title>

1160

<body>

1161

1162

<p>

1163

Generally, all mounted filesystems are unmounted automatically by the system

1164

when it is rebooted or shut down. When a filesystem is unmounted, any cached

1165

filesystem data in memory is flushed to the disk.

1166

</p>

1167

1168

<p>

1169

However, it's also possible to unmount filesystems manually. Before a

1170

filesystem can be unmounted, you first need to ensure that there are no

1171

processes running that have open files on the filesystem in question. Then, use

1172

the <c>umount</c> command, specifying either the device name or mount point as

1173

an argument:

1174

</p>

1175

1176

<pre caption="Using umount command">

1177

# <i>umount /mnt</i>

1178

</pre>

1179

1180

<p>

1181

or

1182

</p>

1183

1184

<pre caption="Using umount command">

1185

# <i>umount /dev/hda3</i>

1186

</pre>

1187

1188

<p>

1189

Once unmounted, any files in <path>/mnt</path> that were "covered" by the

1190

previously-mounted filesystem will now reappear.

1191

</p>

1192

1193

</body>

1194

</section>

1195

<section>

1196

<title>Introducing fsck</title>

1197

<body>

1198

1199

<p>

1200

If your system crashes or locks up for some reason, the system won't have an

1201

opportunity to cleanly unmount your filesystems. When this happens, the

1202

filesystems are left in an inconsistent (unpredictable) state. When the system

1203

reboots, the <c>fsck</c> program will detect that the filesystems were not

1204

cleanly unmounted and will want to perform a consistency check of filesystems

1205

listed in <path>/etc/fstab</path>.

1206

</p>

1207

1208

<impo>

1209

For a filesystem to be checked by <c>fsck</c> it must have a non-zero number in

1210

the "pass" field (the last field) in <path>/etc/fstab</path>. Typically, the

1211

root filesystem is set to a passno of 1, specifying that it should be checked

1212

first. All other filesystems that should be checked at startup time should have

1213

a passno of 2 or higher. For some journaling filesystems like ReiserFS, it is

1214

safe to have a passno of 0 since the journaling code (and not an external

1215

<c>fsck</c>) takes care of making the filesystem consistent again.

1216

</impo>

1217

1218

<p>

1219

Sometimes, you may find that after a reboot <c>fsck</c> is unable to fully

1220

repair a partially damaged filesystem. In these instances, all you need to do

1221

is to bring your system down to single-user mode and run <c>fsck</c> manually,

1222

supplying the partition block device as an argument. As <c>fsck</c> performs

1223

its filesystem repairs, it may ask you whether to fix particular filesystem

1224

defects. In general, you should say <c>y</c> (yes) to all these questions and

1225

allow <c>fsck</c> to do its thing.

1226

</p>

1227

1228

</body>

1229

</section>

1230

<section>

1231

<title>Problems with fsck</title>

1232

<body>

1233

1234

<p>

1235

One of the problems with <c>fsck</c> scans is that they can take quite a while

1236

to complete, since the entirety of a filesystem's metadata (internal data

1237

structure) needs to be scanned in order to ensure that it's consistent. With

1238

extremely large filesystems, it is not unusual for an exhaustive fsck to take

1239

more than an hour.

1240

</p>

1241

1242

<p>

1243

In order to solve this problem, a new type of filesystem was designed, called a

1244

journaling filesystem. Journaling filesystems record an on-disk log of recent

1245

changes to the filesystem metadata. In the event of a crash, the filesystem

1246

driver inspects the log. Because the log contains an accurate account of recent

1247

changes on disk, only these parts of the filesystem metadata need to be checked

1248

for errors. Thanks to this important design difference, checking a journalled

1249

filesystem for consistency typically takes just a matter of seconds, regardless

1250

of filesystem size. For this reason, journaling filesystems are gaining

1251

popularity in the Linux community. For more information on journaling

1252

filesystems, see the <uri

1253

link="http://www-106.ibm.com/developerworks/library/l-fs.html">Advanced

1254

filesystem implementor's guide, part 1: Journaling and ReiserFS</uri>.

1255

</p>

1256

1257

<p>

1258

Let's cover the major filesystems available for Linux, along with their

1259

associated commands and options.

1260

</p>

1261

1262

</body>

1263

</section>

1264

<section>

1265

<title>The ext2 filesystem</title>

1266

<body>

1267

1268

<p>

1269

The ext2 filesystem has been the standard Linux filesystem for many years. It

1270

has generally good performance for most applications, but it does not offer any

1271

journaling capability. This makes it unsuitable for very large filesystems,

1272

since <c>fsck</c> can take an extremely long time. In addition, ext2 has some

1273

built-in limitations due to the fact that every ext2 filesystem has a fixed

1274

number of inodes that it can hold. That being said, ext2 is generally

1275

considered to be an extremely robust and efficient non-journalled filesystem.

1276

</p>

1277

1278

<ul>

1279

  <li>In kernels: 2.0+</li>

1280

  <li>journaling: no</li>

1281

  <li>mkfs command: mke2fs</li>

1282

  <li>mkfs example: mke2fs /dev/hdc7</li>

1283

  <li>related commands: debugfs, tune2fs, chattr</li>

1284

  <li>performance-related mount options: noatime.</li>

1285

</ul>

1286

1287

</body>

1288

</section>

1289

<section>

1290

<title>The ext3 filesystem</title>

1291

<body>

1292

1293

<p>

1294

The ext3 filesystem uses the same on-disk format as ext2, but adds journaling

1295

capabilities. In fact, of all the Linux filesystems, ext3 has the most

1296

extensive journaling support, supporting not only metadata journaling but also

1297

ordered journaling (the default) and full metadata+data journaling. These

1298

"special" journaling modes help to ensure data integrity, not just short fscks

1299

like other journaling implementations. For this reason, ext3 is the best

1300

filesystem to use if data integrity is an absolute first priority. However,

1301

these data integrity features do impact performance somewhat. In addition,

1302

because ext3 uses the same on-disk format as ext2, it still suffers from the

1303

same scalability limitations as its non-journalled cousin. Ext3 is a good

1304

choice if you're looking for a good general-purpose journalled filesystem that

1305

is also very robust.

1306

</p>

1307

1308

<ul>

1309

  <li>In kernels: 2.4.16+</li>

1310

  <li>journaling: metadata, ordered data writes, full metadata+data</li>

1311

  <li>mkfs command: mke2fs -j</li>

1312

  <li>mkfs example: mke2fs -j /dev/hdc7</li>

1313

  <li>related commands: debugfs, tune2fs, chattr</li>

1314

  <li>performance-related mount options: noatime</li>

1315

  <li>

1316

    other mount options:

1317

  <ul>

1318

    <li>data=writeback (disable journaling)</li>

1319

    <li>

1320

    data=ordered (the default, metadata journaling and data is written out

1321

    to disk with metadata)

1322

    </li>

1323

    <li>

1324

    data=journal (full data journaling for data and metadata integrity. Halves

1325

    write performance.)

1326

    </li>

1327

  </ul>

1328

  </li>

1329

  <li>

1330

  ext3 resources:

1331

  <ul>  

1332

    <li>

1333

    <uri

1334

    link="http://www.zip.com.au/~akpm/linux/ext3/">Andrew Morton's ext3

1335

    page</uri>

1336

    </li>

1337

    <li>

1338

    <uri

1339

    link="http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html">Andrew

1340

    Morton's excellent ext3 usage documentation (recommended)</uri>

1341

    </li>

1342

    <li>

1343

    <uri

1344

    link="http://www-106.ibm.com/developerworks/linux/library/l-fs7/">#

1345

    Advanced filesystem implementor's guide, part 7: Introducing ext3</uri>

1346

    </li>

1347

    <li>

1348

    <uri

1349

    link="http://www.gentoo.org/doc/en/articles/l-afig-p8.xml">Advanced

1350

    filesystem implementor's guide, part 8: Surprises in ext3.</uri>

1351

    </li>

1352

  </ul>

1353

  </li>

1354

</ul>

1355

1356

</body>

1357

</section>

1358

<section>

1359

<title>The ReiserFS filesystem</title>

1360

<body>

1361

1362

<p>

1363

ReiserFS is a relatively new filesystem that has been designed with the goal of

1364

providing very good small file performance, very good general performance and

1365

being very scalable. In general, ReiserFS offers very good performance in most

1366

all situations. ReiserFS is preferred by many for its speed and scalability.

1367

</p>

1368

1369

<ul>

1370

  <li>In kernels: 2.4.0+ (2.4.18+ strongly recommended)</li>

1371

  <li>journaling: metadata</li>

1372

  <li>mkfs command: mkreiserfs</li>

1373

  <li>mkfs example: mkreiserfs /dev/hdc7</li>

1374

  <li>performance-related mount options: noatime, notail</li>

1375

  <li>

1376

  ReiserFS Resources:

1377

  <ul>

1378

    <li><uri link="http://www.namesys.com/">The home of ReiserFS</uri></li>

1379

    <li>

1380

    <uri

1381

    link="http://www-106.ibm.com/developerworks/library/l-fs.html">Advanced

1382

    filesystem implementor's guide, part 1: Journaling and ReiserFS</uri>

1383

    </li>

1384

    <li>

1385

    <uri

1386

    link="http://www-106.ibm.com/developerworks/library/l-fs2.html">Advanced

1387

    filesystem implementor's guide, part 2: Using ReiserFS and Linux

1388

    2.4.</uri>

1389

    </li>

1390

  </ul>

1391

  </li>

1392

</ul>

1393

1394

</body>

1395

</section>

1396

<section>

1397

<title>The XFS filesystem</title>

1398

<body>

1399

1400

<p>

1401

The XFS filesystem is an enterprise-class journaling filesystem being ported to

1402

Linux by SGI. XFS is a full-featured, scalable, journaled file-system that is a

1403

good match for high-end, reliable hardware (since it relies heavily on caching

1404

data in RAM.) but not a good match for low-end hardware.

1405

</p>

1406

1407

<ul>

1408

  <li>In kernels: 2.5.34+ only, requires patch for 2.4 series</li>

1409

  <li>journaling: metadata</li>

1410

  <li>mkfs command: mkfs.xfs</li>

1411

  <li>mkfs example: mkfs.xfs /dev/hdc7</li>

1412

  <li>performance-related mount options: noatime</li>

1413

  <li>

1414

  XFS Resources:

1415

  <ul>

1416

    <li>

1417

    <uri

1418

    link="http://oss.sgi.com/projects/xfs/">The home of XFS (sgi.com)</uri>

1419

    </li>

1420

    <li>

1421

    <uri

1422

    link="http://www-106.ibm.com/developerworks/library/l-fs9.html">Advanced

1423

    filesystem implementor's guide, part 9: Introducing XFS</uri>

1424

    </li>

1425

    <li>

1426

    <uri

1427

    link="http://www-106.ibm.com/developerworks/library/l-fs10.html">Advanced

1428

    filesystem implementor's guide, part 10: Deploying XFS.</uri>

1429

    </li>

1430

  </ul>

1431

  </li>

1432

</ul>

1433

1434

</body>

1435

</section>

1436

<section>

1437

<title>The JFS filesystem</title>

1438

<body>

1439

1440

<p>

1441

JFS is a high-performance journaling filesystem ported to Linux by IBM. JFS is

1442

used by IBM enterprise servers and is designed for high-performance

1443

applications. You can learn more about JFS at <uri

1444

link="http://www-124.ibm.com/developerworks/oss/jfs/index.html">the JFS project

1445

Web site</uri>.

1446

</p>

1447

1448

<ul>

1449

  <li>In kernels: 2.4.20+</li>

1450

  <li>journaling: metadata</li>

1451

  <li>mkfs command: mkfs.jfs</li>

1452

  <li>mkfs example: mkfs.jfs /dev/hdc7</li>

1453

  <li>performance-related mount options: noatime</li>

1454

  <li>

1455

  JFS Resources: <uri

1456

  link="http://www-124.ibm.com/developerworks/oss/jfs/index.html">the JFS

1457

  project Web site (IBM).</uri>

1458

  </li>

1459

</ul>

1460

1461

</body>

1462

</section>

1463

<section>

1464

<title>VFAT</title>

1465

<body>

1466

1467

<p>

1468

The VFAT filesystem isn't really a filesystem that you would choose for storing

1469

Linux files. Instead, it's a DOS-compatible filesystem driver that allows you

1470

to mount and exchange data with DOS and Windows FAT-based filesystems. The VFAT

1471

filesystem driver is present in the standard Linux kernel.

1472

</p>

1473

1474

</body>

1475

</section>

1476

</chapter>

1477

1478

<chapter>

1479

<title>Booting the system</title>

1480

<section>

1481

<title>About this section</title>

1482

<body>

1483

1484

<p>

1485

This section introduces the Linux boot procedure. We'll cover the concept of a

1486

boot loader, how to set kernel options at boot, and how to examine the boot log

1487

for errors. 

1488

</p>

1489

1490

</body>

1491

</section>

1492

<section>

1493

<title>The MBR</title>

1494

<body>

1495

1496

<p>

1497

The boot process is similar for all machines, regardless of which distribution

1498

is installed. Consider the following example hard disk:

1499

</p>

1500

1501

<pre caption="Structure of a hard disk">

1502

+----------------+

1503

|      MBR       |

1504

+----------------+

1505

|  Partition 1:  |

1506

| Linux root (/) |

1507

|   containing   |

1508

|   kernel and   |

1509

|     system.    |

1510

+----------------+

1511

|  Partition 2:  |

1512

|   Linux swap   |

1513

+----------------+

1514

|  Partition 3:  |

1515

|   Windows 3.0  |

1516

|  (last booted  |

1517

|    in 1992)    |

1518

+----------------+

1519

</pre>

1520

1521

<p>

1522

First, the computer's BIOS reads the first few sectors of your hard disk. These

1523

sectors contain a very small program, called the "Master Boot Record," or

1524

"MBR." The MBR has stored the location of the Linux kernel on the hard disk

1525

(partition 1 in the example above), so it loads the kernel into memory and

1526

starts it.

1527

</p>

1528

1529

</body>

1530

</section>

1531

<section>

1532

<title>The kernel boot process</title>

1533

<body>

1534

1535

<p>

1536

The next thing you see (although it probably flashes by quickly) is a line

1537

similar to the following:

1538

</p>

1539

1540

<pre caption="Boot process line">

1541

Linux version 2.4.16 (root@×××××××××××××.org) (gcc version 2.95.3 20010315 (release)) #1 Sat Jan 12 19:23:04 EST 2002

1542

</pre>

1543

1544

<p>

1545

This is the first line printed by the kernel when it starts running. The first

1546

part is the kernel version, followed by the identification of the user that

1547

built the kernel (usually root), the compiler that built it, and the timestamp

1548

when it was built.

1549

</p>

1550

1551

<p>

1552

Following that line is a whole slew of output from the kernel regarding the

1553

hardware in your system: the processor, PCI bus, disk controller, disks, serial

1554

ports, floppy drive, USB devices, network adapters, sound cards, and possibly

1555

others will each in turn report their status.

1556

</p>

1557

1558

</body>

1559

</section>

1560

<section>

1561

<title>/sbin/init</title>

1562

<body>

1563

1564

<p>

1565

When the kernel finishes loading, it starts a program called <c>init</c>. This

1566

program remains running until the system is shut down. It is always assigned

1567

process ID 1, as you can see:

1568

</p>

1569

1570

<pre caption="init process ID">

1571

$ <i>ps --pid 1</i>

1572

PID TTY          TIME CMD

1573

  1 ?        00:00:04 init.system

1574

</pre>

1575

1576

<p>

1577

The <c>init</c> program boots the rest of your distribution by running a series

1578

of scripts. These scripts typically live in <path>/etc/rc.d/init.d</path> or

1579

<path>/etc/init.d</path>, and they perform services such as setting the

1580

system's hostname, checking the filesystem for errors, mounting additional

1581

filesystems, enabling networking, starting print services, etc. When the

1582

scripts complete, <c>init</c> starts a program called <c>getty</c> which

1583

displays the login prompt, and you're good to go!

1584

</p>

1585

1586

</body>

1587

</section>

1588

<section>

1589

<title>Digging in: LILO</title>

1590

<body>

1591

1592

<p>

1593

Now that we've taken a quick tour through the booting process, let's look more

1594

closely at the first part: the MBR and loading the kernel. The maintenance of

1595

the MBR is the responsibility of the "boot loader." The two most popular boot

1596

loaders for x86-based Linux are "LILO" (LInux LOader) and "GRUB" (GRand Unified

1597

Bootloader).

1598

</p>

1599

1600

<p>

1601

Of the two, LILO is the older and more common boot loader. LILO's presence on

1602

your system is reported at boot, with the short "LILO boot:" prompt. Note that

1603

you may need to hold down the shift key during boot to get the prompt, since

1604

often a system is configured to whiz straight through without stopping.

1605

</p>

1606

1607

<p>

1608

There's not much fanfare at the LILO prompt, but if you press the &lt;tab&gt;

1609

key, you'll be presented with a list of potential kernels (or other operating

1610

systems) to boot. Often there's only one in the list. You can boot one of them

1611

by typing it and pressing &lt;enter&gt;. Alternatively you can simply press

1612

&lt;enter&gt; and the first item on the list will boot by default.

1613

</p>

1614

1615

</body>

1616

</section>

1617

<section>

1618

<title>Using LILO</title>

1619

<body>

1620

1621

<p>

1622

Occasionally you may want to pass an option to the kernel at boot time. Some of

1623

the more common options are <c>root=</c> to specify an alternative root

1624

filesystem, <c>init=</c> to specify an alternative init program (such as

1625

<c>init=/bin/sh</c> to rescue a misconfigured system), and <c>mem=</c> to

1626

specify the amount of memory in the system (for example <c>mem=512M</c> in the

1627

case that Linux only autodetects 128M). You could pass these to the kernel at

1628

the LILO boot prompt:

1629

</p>

1630

1631

<pre caption="LILO boot prompt">

1632

LILO boot: linux root=/dev/hdb2 init=/bin/sh mem=512M

1633

</pre>

1634

1635

<p>

1636

If you need to regularly specify command-line options, you might consider

1637

adding them to <path>/etc/lilo.conf</path>. The format of that file is

1638

described in the <path>lilo.conf</path>(5) man-page.

1639

</p>

1640

1641

</body>

1642

</section>

1643

<section>

1644

<title>An important LILO gotcha</title>

1645

<body>

1646

1647

<p>

1648

Before moving on to GRUB, there is an important gotcha to LILO. Whenever you

1649

make changes to <path>/etc/lilo.conf</path>, or whenever you install a new

1650

kernel, you must run <c>lilo</c>. The <c>lilo</c> program rewrites the MBR to

1651

reflect the changes you made, including recording the absolute disk location of

1652

the kernel. The example here makes use of the -v flag for verboseness:

1653

</p>

1654

1655

<pre caption="Using lilo command with -v flag">

1656

# <i>lilo -v</i>

1657

LILO version 21.4-4, Copyright (C) 1992-1998 Werner Almesberger

1658

'lba32' extensions Copyright (C) 1999,2000 John Coffman

1659

1660

Reading boot sector from /dev/hda

1661

Merging with /boot/boot.b

1662

Mapping message file /boot/message

1663

Boot image: /boot/vmlinuz-2.2.16-22

1664

Added linux *

1665

/boot/boot.0300 exists - no backup copy made.

1666

Writing boot sector.

1667

</pre>

1668

1669

</body>

1670

</section>

1671

<section>

1672

<title>Digging in: GRUB</title>

1673

<body>

1674

1675

<p>

1676

The GRUB boot loader could be considered the next generation of boot loader,

1677

following LILO. Most visibly to users, it provides a menu interface instead of

1678

LILO's primitive prompt. For system administrators, the changes are more

1679

significant. GRUB supports more operating systems than LILO, provides some

1680

password-based security in the boot menu, and is easier to administer.

1681

</p>

1682

1683

<p>

1684

GRUB is usually installed with the <c>grub-install</c> command. Once installed,

1685

GRUB's menu is administrated by editing the file

1686

<path>/boot/grub/grub.conf</path>. Both of these tasks are beyond the scope of

1687

this document; you should read the GRUB info pages before attempting to install

1688

or administrate GRUB.

1689

</p>

1690

1691

</body>

1692

</section>

1693

<section>

1694

<title>Using GRUB</title>

1695

<body>

1696

1697

<p>

1698

To give parameters to the kernel, you can press <c>e</c> at the boot menu. This

1699

provides you with the opportunity to edit (by again pressing <c>e</c>) either

1700

the name of the kernel to load or the parameters passed to it. When you're

1701

finished editing, press &lt;enter&gt; then <c>b</c> to boot with your changes.

1702

</p>

1703

1704

</body>

1705

</section>

1706

<section>

1707

<title>dmesg</title>

1708

<body>

1709

1710

<p>

1711

The boot messages from the kernel and init scripts typically scroll by quickly.

1712

You might notice an error, but it's gone before you can properly read it. In

1713

that case, there are two places you can look after the system boots to see what

1714

went wrong (and hopefully get an idea how to fix it).

1715

</p>

1716

1717

<p>

1718

If the error occurred while the kernel was loading or probing hardware devices,

1719

you can retrieve a copy of the kernel's log using the <c>dmesg</c> command:

1720

</p>

1721

1722

<pre caption="Retrieving kernel's log using dmesg command">

1723

Linux version 2.4.16 (root@×××××××××××××.org) (gcc version 2.95.3 20010315 (release)) #1 Sat Jan 12 19:23:04 EST 2002

1724

</pre>

1725

1726

<p>

1727

Hey, we recognize that line! It's the first line the kernel prints when it

1728

loads. Indeed, if you pipe the output of <c>dmesg</c> into a pager, you can

1729

view all of the messages the kernel printed on boot, plus any messages the

1730

kernel has printed to the console in the meantime. 

1731

</p>

1732

1733

</body>

1734

</section>

1735

<section>

1736

<title>/var/log/messages</title>

1737

<body>

1738

1739

<p>

1740

The second place to look for information is in the

1741

<path>/var/log/messages</path> file. This file is recorded by the syslog

1742

daemon, which accepts input from libraries, daemons, and the kernel. Each line

1743

in the messages file is timestamped. This file is a good place to look for

1744

errors that occurred during the init scripts stage of booting. For example, to

1745

see the last few messages from the nameserver:

1746

</p>

1747

1748

<pre caption="greping /var/log/messages file">

1749

# <i>grep named /var/log/messages | tail -3</i>

1750

Jan 12 20:17:41 time /usr/sbin/named[350]: listening on IPv4 interface lo, 127.0.0.1#53

1751

Jan 12 20:17:41 time /usr/sbin/named[350]: listening on IPv4 interface eth0, 10.0.0.1#53

1752

Jan 12 20:17:41 time /usr/sbin/named[350]: running

1753

</pre>

1754

1755

</body>

1756

</section>

1757

<section>

1758

<title>Additional information</title>

1759

<body>

1760

1761

<p>

1762

Additional information related to this section can be found here:

1763

</p>

1764

1765

<ul>

1766

  <li>

1767

    Tutorial: <uri

1768

    link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxgrub-i.html">Getting

1769

    to know GRUB</uri>

1770

  </li>

1771

  <li><uri link="http://en.tldp.org/HOWTO/LILO.html">LILO Mini-HOWTO</uri></li>

1772

  <li><uri link="http://www.gnu.org/software/grub/">GRUB home</uri></li>

1773

  <li>

1774

    Kernel command-line options in

1775

    <path>/usr/src/linux/Documentation/kernel-parameters.txt</path>.

1776

  </li>

1777

</ul>

1778

1779

</body>

1780

</section>

1781

</chapter>

1782

1783

<chapter>

1784

<title>Runlevels</title>

1785

<section>

1786

<title>Single-user mode</title>

1787

<body>

1788

1789

<p>

1790

Recall from the section regarding boot loaders that it's possible to pass

1791

parameters to the kernel when it boots. One of the most often used parameters

1792

is <c>s</c>, which causes the system to start in "single-user" mode. This mode

1793

usually mounts only the root filesystem, starts a minimal subset of the init

1794

scripts, and starts a shell rather than providing a login prompt.

1795

Additionally, networking is not configured, so there is no chance of external

1796

factors affecting your work.

1797

</p>

1798

1799

</body>

1800

</section>

1801

<section>

1802

<title>Understanding single-user mode</title>

1803

<body>

1804

1805

<p>

1806

So what "work" can be done with the system in such a state? To answer this

1807

question, we have to realize a vast difference between Linux and Windows.

1808

Windows is designed to normally be used by one person at a time, sitting at the

1809

console. It is effectively always in "single-user" mode. Linux, on the other

1810

hand, is used more often to serve network applications, or provide shell or X

1811

sessions to remote users on the network. These additional variables are not

1812

desirable when you want to perform maintenance operations such as restoring

1813

from backup, creating or modifying filesystems, upgrading the system from CD,

1814

etc. In these cases you should use single-user mode. 

1815

</p>

1816

1817

</body>

1818

</section>

1819

<section>

1820

<title>Runlevels</title>

1821

<body>

1822

1823

<p>

1824

In fact, it's not actually necessary to reboot in order to reach single-user

1825

mode. The <c>init</c> program manages the current mode, or "runlevel," for the

1826

system. The standard runlevels for a Linux system are defined as follows:

1827

</p>

1828

1829

<ul>

1830

  <li>0: Halt the computer</li>

1831

  <li>1 or s: Single-user mode</li>

1832

  <li>2: Multi-user, no network</li>

1833

  <li>3: Multi-user, text console</li>

1834

  <li>4: Multi-user, graphical console</li>

1835

  <li>5: same as 4</li>

1836

  <li>6: Reboot the computer.</li>

1837

</ul>

1838

1839

<p>

1840

These runlevels vary between distributions, so be sure to consult your distro's

1841

documentation.

1842

</p>

1843

1844

</body>

1845

</section>

1846

<section>

1847

<title>telinit</title>

1848

<body>

1849

1850

<p>

1851

To change to single-user mode, use the <c>telinit</c> command, which instructs

1852

<c>init</c> to change runlevels:

1853

</p>

1854

1855

<pre caption="Using telinit command">

1856

# <i>telinit 1</i>

1857

</pre>

1858

1859

<p>

1860

You can see from the table above that you can also shutdown or reboot the

1861

system in this manner. <c>telinit 0</c> will halt the computer; <c>telinit

1862

6</c> will reboot the computer. When you issue the <c>telinit</c> command to

1863

change runlevels, a subset of the <c>init</c> scripts will run to either shut

1864

down or start up system services.

1865

</p>

1866

1867

</body>

1868

</section>

1869

<section>

1870

<title>Runlevel etiquette</title>

1871

<body>

1872

1873

<p>

1874

However, note that this is rather rude if there are users on the system at the

1875

time (who may be quite angry with you). The <c>shutdown</c> command provides a

1876

method for changing runlevels in a way that treats users reasonably. Similarly

1877

to the <c>kill</c> command's ability to send a variety of signals to a process,

1878

<c>shutdown</c> can be used to halt, reboot, or change to single-user mode. For

1879

example, to change to single-user mode in 5 minutes:

1880

</p>

1881

1882

<pre caption="Changing to single-user mode with 5 minutes delay">

1883

# <i>shutdown 5</i>

1884

Broadcast message from root (pts/2) (Tue Jan 15 19:40:02 2002):

1885

The system is going DOWN to maintenance mode in 5 minutes!

1886

</pre>

1887

1888

<p>

1889

If you press &lt;control-c&gt; at this point, you can cancel the pending switch

1890

to single-user mode. The message above would appear on all terminals on the

1891

system, so users have a reasonable amount of time to save their work and log

1892

off. (Some might argue whether or not 5 minutes is "reasonable")

1893

</p>

1894

1895

</body>

1896

</section>

1897

<section>

1898

<title>"Now" and halt</title>

1899

<body>

1900

1901

<p>

1902

If you're the only person on the system, you can use "now" instead of an

1903

argument in minutes. For example, to reboot the system right now:

1904

</p>

1905

1906

<pre caption="Using shutdown command with now option">

1907

# <i>shutdown -r now</i>

1908

</pre>

1909

1910

<p>

1911

No chance to hit &lt;control-c&gt; in this case; the system is already on its

1912

way down. Finally, the -h option halts the system:

1913

</p>

1914

1915

<pre caption="Halting the system">

1916

# <i>shutdown -h 1</i>

1917

Broadcast message from root (pts/2) (Tue Jan 15 19:50:58 2002):

1918

The system is going DOWN for system halt in 1 minute!

1919

</pre>

1920

1921

</body>

1922

</section>

1923

<section>

1924

<title>The default runlevel</title>

1925

<body>

1926

1927

<p>

1928

You've probably gathered at this point that the <c>init</c> program is quite

1929

important on a Linux system. You can configure <c>init</c> by editing the file

1930

<path>/etc/initttab</path>, which is described in the inittab(5) man-page.

1931

We'll just touch on one key line in this file:

1932

</p>

1933

1934

<pre caption="Editing init configuration file">

1935

# <i>grep ^id: /etc/inittab</i>

1936

id:3:initdefault:

1937

</pre>

1938

1939

<p>

1940

On my system, runlevel 3 is the default runlevel. It can be useful to change

1941

this value if you prefer your system to boot immediately into a graphical login

1942

(usually runlevel 4 or 5). To do so, simply edit the file and change the value

1943

on that line. But be careful! If you change it to something invalid, you'll

1944

probably have to employ the <c>init=/bin/sh</c> trick we mentioned earlier.

1945

</p>

1946

1947

</body>

1948

</section>

1949

<section>

1950

<title>Additional information</title>

1951

<body>

1952

1953

<p>

1954

Additional information related to this section can be found at:

1955

</p>

1956

1957

<ul>

1958

  <li>

1959

    <uri

1960

    link="http://www.redhat.com/docs/manuals/linux/RHL-7.2-Manual/ref-guide/s1-init-boot-shutdown-init.html">

1961

    Sysvinit docs at Red Hat</uri>

1962

  </li>

1963

  <li>

1964

    <uri link="http://www.linuxdoc.org/LDP/sag/init.html">Linux System

1965

    Administrator's Guide section on init</uri>.

1966

  </li>

1967

</ul>

1968

1969

</body>

1970

</section>

1971

</chapter>

1972

1973

<chapter>

1974

<title>Filesystem quotas</title>

1975

<section>

1976

<title>Introducing quotas</title>

1977

<body>

1978

1979

<p>

1980

Quotas are a feature of Linux that let you track disk usage by user or by

1981

group. They're useful for preventing any single user or group from using an

1982

unfair portion of a filesystem, or from filling it up altogether. Quotas can

1983

only be enabled and managed by the root user. In this section, I'll describe

1984

how to set up quotas on your Linux system and manage them effectively.

1985

</p>

1986

1987

</body>

1988

</section>

1989

<section>

1990

<title>Kernel support</title>

1991

<body>

1992

1993

<p>

1994

Quotas are a feature of the filesystem; therefore, they require kernel support.

1995

The first thing you'll need to do is verify that you have quota support in your

1996

kernel. You can do this using grep:

1997

</p>

1998

1999

<pre caption="Checking kernel configuration for quota support">

2000

# <i>cd /usr/src/linux</i>

2001

# <i>grep -i quota .config</i>

2002

CONFIG_QUOTA=y

2003

CONFIG_XFS_QUOTA=y

2004

</pre>

2005

2006

<p>

2007

If this command returns something less conclusive (such as CONFIG_QUOTA is not

2008

set) then you should rebuild your kernel to include quota support. This is not

2009

a difficult process, but is outside of the scope of this section of the

2010

tutorial. If you're unfamiliar with the steps to build and install a new

2011

kernel, you might consider referencing this <uri

2012

link="/doc/en/articles/linux-kernel-compiling.xml">tutorial</uri>.

2013

</p>

2014

2015

</body>

2016

</section>

2017

<section>

2018

<title>Filesystem support</title>

2019

<body>

2020

2021

<p>

2022

Before diving into the administration of quotas, please note that quota support

2023

on Linux as of the 2.4.x kernel series is not complete. There are currently

2024

problems with quotas in the ext2 and ext3 filesystems, and ReiserFS does not

2025

appear to support quotas at all. This tutorial bases its examples on XFS, which

2026

seems to properly <uri

2027

link="http://oss.sgi.com/projects/xfs/faq.html#quotaswork">support

2028

quotas</uri>.

2029

</p>

2030

2031

</body>

2032

</section>

2033

<section>

2034

<title>Configuring quotas</title>

2035

<body>

2036

2037

<p>

2038

To begin configuring quotas on your system, you should edit

2039

<path>/etc/fstab</path> to mount the affected filesystems with quotas enabled.

2040

For our example, we use an XFS filesystem mounted with user and group quotas

2041

enabled:

2042

</p>

2043

2044

<pre caption="Configuring quotas">

2045

# <i>grep quota /etc/fstab</i>

2046

/usr/users   /mnt/hdc1    xfs    usrquota,grpquota,noauto   0 0

2047

# <i>mount /usr/users</i>

2048

</pre>

2049

2050

<p>

2051

Note that the usrquota and grpquota options don't necessarily enable quotas on

2052

a filesystem. You can make sure quotas are enabled using the <c>quotaon</c>

2053

command:

2054

</p>

2055

2056

<pre caption="Enabling quotas">

2057

# <i>quotaon /usr/users</i>

2058

</pre>

2059

2060

<p>

2061

There is a corresponding <c>quotaoff</c> command should you desire to disable

2062

quotas in the future:

2063

</p>

2064

2065

<pre caption="Disabling quotas">

2066

# <i>quotaoff /usr/users</i>

2067

</pre>

2068

2069

<p>

2070

But for the moment, if you're trying some of the examples in this tutorial, be

2071

sure to have quotas enabled.

2072

</p>

2073

2074

</body>

2075

</section>

2076

<section>

2077

<title>The quota command</title>

2078

<body>

2079

2080

<p>

2081

The <c>quota</c> command displays a user's disk usage and limits for all of the

2082

filesystems currently mounted. The -v option includes in the list filesystems

2083

where quotas are enabled, but no storage is currently allocated to the user.

2084

</p>

2085

2086

<pre caption="Using quota command">

2087

# <i>quota -v</i>

2088

2089

Disk quotas for user root (uid 0): 

2090

Filesystem  blocks   quota   limit   grace   files   quota   limit   grace

2091

 /dev/hdc1       0       0       0               3       0       0        

2092

</pre>

2093

2094

<p>

2095

The first column, blocks, shows how much disk space the root user is currently

2096

using on each filesystem listed. The following columns, quota and limit, refer

2097

to the limits currently in place for disk space. We will explain the difference

2098

between quota and limit, and the meaning of the grace column later on. The

2099

files column shows how many files the root user owns on the particular

2100

filesystem. The following quota and limit columns refer to the limits for

2101

files.

2102

</p>

2103

2104

</body>

2105

</section>

2106

<section>

2107

<title>Viewing quota</title>

2108

<body>

2109

2110

<p>

2111

Any user can use the <c>quota</c> command to view their own quota report as

2112

shown in the previous example. However only the root user can look at the

2113

quotas for other users and groups. For example, say we have a filesystem,

2114

<path>/dev/hdc1</path> mounted on <path>/usr/users</path>, with two users: jane

2115

and john. First, let's look at jane's disk usage and limits.

2116

</p>

2117

2118

<pre caption="Viewing quota for user">

2119

# <i>quota -v jane</i>

2120

2121

Disk quotas for user jane (uid 1003): 

2122

Filesystem  blocks   quota   limit   grace   files   quota   limit   grace

2123

 /dev/hdc1    4100       0       0               6       0       0

2124

</pre>

2125

2126

<p>

2127

In this example, we see that jane's quotas are set to zero, which indicates no

2128

limit.

2129

</p>

2130

2131

</body>

2132

</section>

2133

<section>

2134

<title>edquota</title>

2135

<body>

2136

2137

<p>

2138

Now let's say we want to give the user jane a quota. We do this with the

2139

<c>edquota</c> command. Before we start editing quotas, let's see how much

2140

space we have available on <path>/usr/users</path>:

2141

</p>

2142

2143

<pre caption="Checking available space on /usr/users">

2144

# <i>df /usr/users</i>

2145

2146

Filesystem           1k-blocks      Used Available Use% Mounted on

2147

/dev/hdc1               610048      4276    605772   1% /usr/users

2148

</pre>

2149

2150

<p>

2151

This isn't a particularly large filesystem, only 600MB or so. It seems prudent

2152

to give jane a quota so that she can't use more than her fair share. When you

2153

run <c>edquota</c>, a temporary file is created for each user or group you

2154

specify on the command line.

2155

</p>

2156

2157

<p>

2158

The <c>edquota</c> command puts you in an editor, which enables you to add

2159

and/or modify quotas via this temporary file.

2160

</p>

2161

2162

<pre caption="Modifying quota">

2163

# <i>edquota jane</i>

2164

2165

Disk quotas for user jane (uid 1003):

2166

Filesystem         blocks       soft       hard     inodes     soft     hard

2167

 /dev/hdc1           4100          0          0          6        0        0

2168

</pre>

2169

2170

<p>

2171

Similar to the output from the <c>quota</c> command above, the blocks and

2172

inodes columns in this temporary file refer to the disk space and number of

2173

files jane is currently using. You cannot modify the number of blocks or

2174

inodes; any attempt to do so will be summarily discarded by the system. The

2175

soft and hard columns show jane's quota, which we can see is currently

2176

unlimited (again, zero indicates no quota).

2177

</p>

2178

2179

</body>

2180

</section>

2181

<section>

2182

<title>Understanding edquota</title>

2183

<body>

2184

2185

<p>

2186

The soft limit is the maximum amount of disk usage that jane has allocated to

2187

her on the filesystem (in other words, her quota). If jane uses more disk

2188

space than is allocated in her soft limit, she will be issued warnings about

2189

her quota violation via e-mail. The hard limit indicates the absolute limit on

2190

disk usage, which a user can't exceed. If jane tries to use more disk space

2191

than is specified in the hard limit, she will get a "Disk quota exceeded"

2192

error and will not be able to complete the operation.

2193

</p>

2194

2195

</body>

2196

</section>

2197

<section>

2198

<title>Making changes</title>

2199

<body>

2200

2201

<p>

2202

So here we change jane's soft and hard limits and save the file:

2203

</p>

2204

2205

<pre caption="Changed soft and hard limits">

2206

2207

Disk quotas for user jane (uid 1003):

2208

Filesystem         blocks       soft       hard     inodes     soft     hard

2209

 /dev/hdc1           4100      10000      11500          6     2000     2500

2210

</pre>

2211

2212

<p>

2213

Running the <c>quota</c> command, we can inspect our modifications:

2214

</p>

2215

2216

<pre caption="Checking quota for user jane">

2217

# <i>quota jane</i>

2218

2219

Disk quotas for user jane (uid 1003): 

2220

Filesystem  blocks   quota   limit   grace   files   quota   limit   grace

2221

 /dev/hdc1    4100   10000   11500               6    2000    2500

2222

</pre>

2223

2224

</body>

2225

</section>

2226

<section>

2227

<title>Copying quotas</title>

2228

<body>

2229

2230

<p>

2231

You'll remember that we also have another user, john, on this filesystem. If

2232

we want to give john the same quota as jane, we can use the -p option to

2233

<c>edquota</c>, which uses jane's quotas as a prototype for all following users

2234

on the command line. This is an easy way to set up quotas for groups of users.

2235

</p>

2236

2237

<pre caption="Coping quotas">

2238

# <i>edquota -p jane john</i>

2239

# <i>quota john</i>

2240

2241

Disk quotas for user john (uid 1003): 

2242

Filesystem  blocks   quota   limit   grace   files   quota   limit   grace

2243

 /dev/hdc1       0   10000   11500               1    2000    2500        

2244

</pre>

2245

2246

</body>

2247

</section>

2248

<section>

2249

<title>Group restrictions</title>

2250

<body>

2251

2252

<p>

2253

We can also use <c>edquota</c> to restrict the allocation of disk space based

2254

on the group ownership of files. For example, to edit the quotas for the users

2255

group:

2256

</p>

2257

2258

<pre caption="Editing quotas for the users group">

2259

# <i>edquota -g users</i>

2260

Disk quotas for group users (gid 100): Filesystem blocks soft hard inodes soft hard /dev/hdc1 4100 500000 510000 7 100000 125000

2261

</pre>

2262

2263

<p>

2264

Then to view the modified quotas for the users group:

2265

</p>

2266

2267

<pre caption="Viewing modified quotas">

2268

# <i>quota -g users</i>

2269

Disk quotas for group users (gid 100): Filesystem blocks quota limit grace files quota limit grace /dev/hdc1 4100 500000 510000 7 100000 125000

2270

</pre>

2271

2272

</body>

2273

</section>

2274

<section>

2275

<title>The repquota command</title>

2276

<body>

2277

2278

<p>

2279

Looking at each users' quotas using the <c>quota</c> command can be tedious if

2280

you have many users on a filesytem. The <c>repquota</c> command summarizes the

2281

quotas for a filesystem into a nice report. For example, to see the quotas for

2282

all users and groups on <path>/usr/users</path>:

2283

</p>

2284

2285

<pre caption="Summarizing quotas">

2286

# <i>repquota -ug /usr/users</i>

2287

*** Report for user quotas on device /dev/hdc1

2288

Block grace time: 7days; Inode grace time: 7days

2289

                        Block limits                File limits

2290

User            used    soft    hard  grace    used  soft  hard  grace

2291

----------------------------------------------------------------------

2292

root      --       0       0       0              3     0     0       

2293

john      --       0   10000   11500              1  2000  2500       

2294

jane      --    4100   10000   11500              6  2000  2500       

2295

2296

*** Report for group quotas on device /dev/hdc1

2297

Block grace time: 7days; Inode grace time: 7days

2298

                        Block limits             File limits

2299

Group           used    soft    hard  grace    used  soft  hard  grace

2300

----------------------------------------------------------------------

2301

root      --       0       0      0               3     0     0       

2302

users     --    4100  500000 510000               7 100000 125000  

2303

</pre>

2304

2305

</body>

2306

</section>

2307

<section>

2308

<title>Repquota options</title>

2309

<body>

2310

2311

<p>

2312

There are a couple of other options to repquota that are worth mentioning.

2313

<c>repquota -a</c> will report on all currently mounted read-write filesystems

2314

that have quotas enabled. <c>repquota -n</c> will not resolve uids and gids to

2315

names. This can speed up the output for large lists.

2316

</p>

2317

2318

</body>

2319

</section>

2320

<section>

2321

<title>Monitoring quotas</title>

2322

<body>

2323

2324

<p>

2325

If you are a system administrator, you will want to have a way to monitor

2326

quotas to ensure that they are not being exceeded. An easy way to do this is

2327

to use <c>warnquota</c>. The <c>warnquota</c> command sends e-mail to users who

2328

have exceeded their soft limit. Typically <c>warnquota</c> is run as a

2329

cron-job.

2330

</p>

2331

2332

<p>

2333

When a user exceeds his or her soft limit, the grace column in the output from

2334

the <c>quota</c> command will indicate the grace period -- how long before the

2335

soft limit is enforced for that filesystem.

2336

</p>

2337

2338

<pre caption="Checking grace period">

2339

Disk quotas for user jane (uid 1003): 

2340

    Filesystem  blocks   quota   limit   grace   files   quota   limit   grace

2341

    /dev/hdc1   10800*  10000   11500    7days      7     2000    2500

2342

</pre>

2343

2344

<p>

2345

By default, the grace period for blocks and inodes is seven days.

2346

</p>

2347

2348

</body>

2349

</section>

2350

<section>

2351

<title>Modifying the grace period</title>

2352

<body>

2353

2354

<p>

2355

You can modify the grace period for filesystems using <c>equota</c>:

2356

</p>

2357

2358

<pre caption="Modyfing grace period">

2359

# <i>edquota -t</i>

2360

</pre>

2361

2362

<p>

2363

This puts you in an editor of a temporary file that looks like this:

2364

</p>

2365

2366

<pre caption="Looks of a grace editor">

2367

Grace period before enforcing soft limits for users:

2368

Time units may be: days, hours, minutes, or seconds

2369

Filesystem             Block grace period     Inode grace period

2370

/dev/hdc1                    7days                  7days

2371

</pre>

2372

2373

<p>

2374

The text in the file is nicely explanatory. Be sure to leave your users enough

2375

time to receive their warning e-mail and find some files to delete!

2376

</p>

2377

2378

</body>

2379

</section>

2380

<section>

2381

<title>Checking quotas on boot</title>

2382

<body>

2383

2384

<p>

2385

You may also want to check quotas on boot. You can do this using a script to

2386

run the <c>quotacheck</c> command; there is an example script in the <uri

2387

link="http://en.tldp.org/HOWTO/Quota.html">Quota Mini HOWTO</uri>. The

2388

<c>quotacheck</c> command also has the ability to repair damaged quota files;

2389

familiarize yourself with it by reading the quotacheck(8) man-page.

2390

</p>

2391

2392

<p>

2393

Also remember what we mentioned previously regarding <c>quotaon</c> and

2394

<c>quotaoff</c>. You should incorporate <c>quotaon</c> into your boot script so

2395

that quotas are enabled. To enable quotas on all filesystems where quotas are

2396

supported, use the -a option:

2397

</p>

2398

2399

<pre caption="Using -a option">

2400

# <i>quotaon -a</i>

2401

</pre>

2402

2403

</body>

2404

</section>

2405

</chapter>

2406

2407

<chapter>

2408

<title>System logs</title>

2409

<section>

2410

<title>Introducing syslogd</title>

2411

<body>

2412

2413

<p>

2414

The syslog daemon provides a mature client-server mechanism for logging

2415

messages from programs running on the system. Syslog receives a message from a

2416

daemon or program, categorizes the message by priority and type, then logs it

2417

according to administrator-configurable rules. The result is a robust and

2418

unified approach to managing logs.

2419

</p>

2420

2421

</body>

2422

</section>

2423

<section>

2424

<title>Reading logs</title>

2425

<body>

2426

2427

<p>

2428

Let's jump right in and look at the contents of a syslog-recorded log file.

2429

Afterward, we can come back to syslog configuration. The FHS (see <uri

2430

link="/doc/en/articles/lpi-101-administration-p2.xml">Part 2</uri> of this

2431

tutorial series) mandates that log files be placed in <path>/var/log</path>.

2432

Here we use the <c>tail</c> command to display the last 10 lines in the

2433

"messages" file:

2434

</p>

2435

2436

<pre caption="Reading logs">

2437

# <i>cd /var/log</i>

2438

# <i>tail messages</i>

2439

Jan 12 20:17:39 bilbo init: Entering runlevel: 3

2440

Jan 12 20:17:40 bilbo /usr/sbin/named[337]: starting BIND 9.1.3

2441

Jan 12 20:17:40 bilbo /usr/sbin/named[337]: using 1 CPU

2442

Jan 12 20:17:41 bilbo /usr/sbin/named[350]: loading configuration from '/etc/bind/named.conf'

2443

Jan 12 20:17:41 bilbo /usr/sbin/named[350]: no IPv6 interfaces found

2444

Jan 12 20:17:41 bilbo /usr/sbin/named[350]: listening on IPv4 interface lo, 127.0.0.1#53

2445

Jan 12 20:17:41 bilbo /usr/sbin/named[350]: listening on IPv4 interface eth0, 10.0.0.1#53

2446

Jan 12 20:17:41 bilbo /usr/sbin/named[350]: running

2447

Jan 12 20:41:58 bilbo gnome-name-server[11288]: starting

2448

Jan 12 20:41:58 bilbo gnome-name-server[11288]: name server starting

2449

</pre>

2450

2451

<p>

2452

You may remember from the text-processing whirlwind that the <c>tail</c>

2453

command displays the last lines in a file. In this case, we can see that the

2454

nameserver named was recently started on this system, which is named bilbo. If

2455

we were deploying IPv6, we might notice that named found no IPv6 interfaces,

2456

indicating a potential problem. Additionally, we can see that a user may have

2457

recently started GNOME, indicated by the presence of gnome-name-server.

2458

</p>

2459

2460

</body>

2461

</section>

2462

<section>

2463

<title>Tailing log files</title>

2464

<body>

2465

2466

<p>

2467

An experienced system administrator might use <c>tail -f</c> to follow the

2468

output to a log file as it occurs:

2469

</p>

2470

2471

<pre caption="Using tail -f command">

2472

# <i>tail -f /var/log/messages</i>

2473

</pre>

2474

2475

<p>

2476

For example, in the case of debugging our theoretical IPv6 problem, running the

2477

above command in one terminal while stopping and starting named would

2478

immediately display the messages from that daemon. This can be a useful

2479

technique when debugging. Some administrators even like to keep a constantly

2480

running <c>tail -f</c> messages in a terminal where they can keep an eye on

2481

system events.

2482

</p>

2483

2484

</body>

2485

</section>

2486

<section>

2487

<title>Grepping logs</title>

2488

<body>

2489

2490

<p>

2491

Another useful technique is to search a log file using the <c>grep</c> utility,

2492

described in <uri link="/doc/en/articles/lpi-101-administration-p2.xml">Part

2493

2</uri> of this tutorial series. In the above case, we might use grep to find

2494

where "named" behavior has changed:

2495

</p>

2496

2497

<pre caption="Grepping logs">

2498

# <i>grep named /var/log/messages</i>

2499

</pre>

2500

2501

</body>

2502

</section>

2503

<section>

2504

<title>Log overview</title>

2505

<body>

2506

2507

<p>

2508

The following summarizes the log files typically found in <path>/var/log</path>

2509

and maintained by syslog:

2510

</p>

2511

2512

<ul>

2513

  <li>

2514

    <path>messages</path>: Informational and error messages from general system

2515

    programs and daemons

2516

  </li>

2517

  <li>

2518

    <path>secure</path>: Authentication messages and errors, kept separate from

2519

    <path>messages</path> for extra security

2520

  </li>

2521

  <li><path>maillog</path>: Mail-related messages and errors</li>

2522

  <li><path>cron</path>: Cron-related messages and errors</li>

2523

  <li><path>spooler</path>: UUCP and news-related messages and errors.</li>

2524

</ul>

2525

2526

</body>

2527

</section>

2528

<section>

2529

<title>syslog.conf</title>

2530

<body>

2531

2532

<p>

2533

As a matter of fact, now would be a good time to investigate the syslog

2534

configuration file, <path>/etc/syslog.conf</path>. (Note: If you don't have

2535

<path>syslog.conf</path>, keep reading for the sake of information, but you may

2536

be using an alternative syslog daemon.) Browsing that file, we see there are

2537

entries for each of the common log files mentioned above, plus possibly some

2538

other entries. The file has the format facility.priority action, where those

2539

fields are defined as follows:

2540

</p>

2541

2542

<p>

2543

facility: Specifies the subsystem that produced the message. The valid keywords

2544

for facility are auth, authpriv, cron, daemon, kern, lpr, mail, news, syslog,

2545

user, uucp and local0 through local7.

2546

</p>

2547

2548

<p>

2549

priority: Specifies the minimum severity of the message, meaning that messages

2550

of this priority and higher will be matched by this rule. The valid keywords

2551

for priority are debug, info, notice, warning, err, crit, alert, and emerg.

2552

</p>

2553

2554

<p>

2555

action: The action field should be either a filename, tty (such as

2556

<path>/dev/console</path>), remote machine prefixed by @ , comma-separated list

2557

of users, or to send the message to everybody logged on. The most common action

2558

is a simple filename.

2559

</p>

2560

2561

</body>

2562

</section>

2563

<section>

2564

<title>Reloading and additional information</title>

2565

<body>

2566

2567

<p>

2568

Hopefully this overview of the configuration file helps you to get a feel for

2569

the strength of the syslog system. You should read the syslog.conf(5) man-page

2570

for more information prior to making changes. Additionally the syslogd(8)

2571

man-page supplies lots more detailed information.

2572

</p>

2573

2574

<p>

2575

Note that you need to inform the syslog daemon of changes to the configuration

2576

file before they are put into effect. Sending it a SIGHUP is the right method,

2577

and you can use the <c>killall</c> command to do this easily:

2578

</p>

2579

2580

<pre caption="Using killall command">

2581

# <i>killall -HUP syslogd</i>

2582

</pre>

2583

2584

</body>

2585

</section>

2586

<section>

2587

<title>A security note</title>

2588

<body>

2589

2590

<p>

2591

You should beware that the log files written to by syslogd will be created by

2592

the program if they don't exist. Regardless of your current umask setting, the

2593

files will be created world-readable. If you're concerned about the security,

2594

you should chmod the files to be read-write by root only. Additionally, the

2595

<c>logrotate</c> program (described below) can be configured to create new log

2596

files with the appropriate permissions. The syslog daemon always preserves the

2597

current attributes of an existing log file, so you don't need to worry about it

2598

once the file is created.

2599

</p>

2600

2601

</body>

2602

</section>

2603

<section>

2604

<title>logrotate</title>

2605

<body>

2606

2607

<p>

2608

The log files in <path>/var/log</path> will grow over time, and potentially

2609

could fill the filesystem. It is advisable to employ a program such as

2610

<c>logrotate</c> to manage the automatic archiving of the logs. The

2611

<c>logrotate</c> program usually runs as a daily cron job, and can be

2612

configured to rotate, compress, remove, or mail the log files.

2613

</p>

2614

2615

<p>

2616

For example, a default configuration of logrotate might rotate the logs weekly,

2617

keeping 4 weeks worth of backlogs (by appending a sequence number to the

2618

filename), and compress the backlogs to save space. Additionally, the program

2619

can be configured to deliver a SIGHUP to syslogd so that the daemon will notice

2620

the now-empty log files and append to them appropriately.

2621

</p>

2622

2623

<p>

2624

For more information on <c>logrotate</c>, see the logrotate(8) man page, which

2625

contains a description of the program and the syntax of the configuration file.

2626

</p>

2627

2628

</body>

2629

</section>

2630

<section>

2631

<title>Advanced topic -- klogd</title>

2632

<body>

2633

2634

<p>

2635

Before moving away from syslog, I'd like to note a couple of advanced topics

2636

for ambitious readers. These tips may save you some grief when trying to

2637

understand syslog-related topics.

2638

</p>

2639

2640

<p>

2641

First, the syslog daemon is actually part of the sysklogd package, which

2642

contains a second daemon called klogd. It's klogd's job to receive information

2643

and error messages from the kernel, and pass them on to syslogd for

2644

categorization and logging. The messages received by klogd are exactly the same

2645

as those you can retrieve using the <c>dmesg</c> command. The difference is

2646

that <c>dmesg</c> prints the current contents of a ring buffer in the kernel,

2647

whereas klogd is passing the messages to syslogd so that they won't be lost

2648

when the ring wraps around.

2649

</p>

2650

2651

</body>

2652

</section>

2653

<section>

2654

<title>Advanced topic -- alternate loggers</title>

2655

<body>

2656

2657

<p>

2658

Second, there are alternatives to the standard sysklogd package. The

2659

alternatives attempt to be more efficient, easier to configure, and possibly

2660

more featureful than sysklogd. <uri

2661

link="http://www.balabit.hu/en/downloads/syslog-ng/">Syslog-ng</uri> and <uri

2662

link="http://metalog.sourceforge.net/">Metalog</uri> seem to be some of the

2663

more popular alternatives; you might investigate them if you find sysklogd

2664

doesn't provide the level of power you need.

2665

</p>

2666

2667

<p>

2668

Third, you can log messages in your scripts using the logger command. See the

2669

logger(1) man page for more information.

2670

</p>

2671

2672

</body>

2673

</section>

2674

</chapter>

2675

2676

<chapter>

2677

<title>Summary and resources</title>

2678

<section>

2679

<title>Summary</title>

2680

<body>

2681

2682

<p>

2683

Congratulations, you've reached the end of this tutorial! Well, almost. There

2684

were a couple of topics that we were unable to include in our first four

2685

tutorials due to space limitations. Fortunately, we have a couple of good

2686

resources that will help you get up to speed on these topics in no time. Be

2687

sure to cover these particular tutorials if you are planning to get your LPIC

2688

level 1 certification.

2689

</p>

2690

2691

<p>

2692

We didn't have quite enough room to cover the important topic of system backups

2693

in this tutorial. Fortunately, IBM developerWorks already has a tutorial on

2694

this subject, called <uri

2695

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxbu-i.html">Backing up

2696

your Linux machines</uri>. In this tutorial, you'll learn how to back up Linux

2697

systems using a <c>tar</c> variant called star. You'll also learn how to use

2698

the <c>mt</c> command to control tape functions. 

2699

</p>

2700

2701

<p>

2702

The second topic that we weren't quite able to fit in was periodic scheduling.

2703

Fortunately, there's some good <uri

2704

link="http://www.ussg.iu.edu/usail/automation/cron.html">cron

2705

documentation</uri> available at Indiana University. <c>cron</c> is used to

2706

schedule jobs to be executed at a specific time, and is an important tool for

2707

any system administrator.

2708

</p>

2709

2710

<p>

2711

On the next page, you'll find a number of resources that you will find helpful

2712

in learning more about the subjects presented in this tutorial.

2713

</p>

2714

2715

</body>

2716

</section>

2717

<section>

2718

<title>Resources</title>

2719

<body>

2720

2721

<p>

2722

To find out more about quota support under Linux, be sure to check out the <uri

2723

link="http://en.tldp.org/HOWTO/Quota.html">Linux Quota mini-HOWTO</uri>.  Also

2724

be sure to consult the quota(1), edquota(8), repquota(8), quotacheck(8), and

2725

quotaon(8) man pages on your system.

2726

</p>

2727

2728

<p>

2729

Additional information to the system boot process and boot loaders can be found

2730

at:

2731

</p>

2732

2733

<ul>

2734

  <li>

2735

    IBM developerWorks' <uri

2736

    link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxgrub-i.html">Getting

2737

    to know GRUB</uri> tutorial

2738

  </li>

2739

  <li><uri link="http://en.tldp.org/HOWTO/LILO.html">LILO Mini-HOWTO</uri></li>

2740

  <li><uri link="http://www.gnu.org/software/grub/">GRUB home</uri></li>

2741

  <li>

2742

    Kernel command-line options in

2743

    <path>/usr/src/linux/Documentation/kernel-parameters.txt</path>

2744

  </li>

2745

  <li>

2746

    <uri

2747

    link="http://www.redhat.com/docs/manuals/linux/RHL-7.2-Manual/ref-guide/s1-init-boot-shutdown-init.html">Sysvinit

2748

    docs at Redhat</uri>.

2749

  </li>

2750

</ul>

2751

2752

<p>

2753

To learn more about Linux filesystems, read the multi-part advanced filesystem

2754

implementor's guide on the IBM developerWorks Linux zone, covering:

2755

</p>

2756

2757

<ul>

2758

  <li>

2759

    <uri link="http://www-106.ibm.com/developerworks/library/l-fs.html">The

2760

    benefits of journalling and ReiserFS (Part 1)</uri>

2761

  </li>

2762

  <li>

2763

    <uri

2764

    link="http://www-106.ibm.com/developerworks/library/l-fs2.html">Setting up

2765

    a ReiserFS system (Part 2)</uri>

2766

  </li>

2767

  <li>

2768

    <uri link="http://www-106.ibm.com/developerworks/library/l-fs3.html">Using

2769

    the tmpfs virtual memory filesystem and bind mounts (Part 3)</uri>

2770

  </li>

2771

  <li>

2772

    <uri link="http://www-106.ibm.com/developerworks/library/l-fs4.html">The

2773

    benefits of devfs, the device management filesystem (Part 4)</uri>

2774

  </li>

2775

  <li>

2776

    <uri

2777

    link="http://www-106.ibm.com/developerworks/library/l-fs5.html">Beginning

2778

    the conversion to devfs (Part 5)</uri>

2779

  </li>

2780

  <li>

2781

    <uri

2782

    link="http://www-106.ibm.com/developerworks/linux/library/l-fs6/">Completing

2783

    the conversion to devfs using an init wrapper (Part 6)</uri>

2784

  </li>

2785

  <li>

2786

    <uri

2787

    link="/doc/en/articles/afig-ct-ext3-intro.xml">The

2788

    benefits of the ext3 filesystem (Part 7)</uri>

2789

  </li>

2790

  <li>

2791

    <uri link="/doc/en/articles/l-afig-p8.xml">An in-depth

2792

    look at ext3 and the latest kernel updates (Part 8)</uri>

2793

  </li>

2794

  <li>

2795

    <uri

2796

    link="http://www-106.ibm.com/developerworks/linux/library/l-fs9.html">An

2797

    introduction to XFS (Part 9)</uri>.

2798

  </li>

2799

</ul>

2800

2801

<p>

2802

For more information on partitioning, take a look at the following partitioning

2803

tips on the IBM developerWorks Linux zone:

2804

</p>

2805

2806

<ul>

2807

  <li>

2808

    <uri link="/doc/en/articles/partition-planning-tips.xml">Partition planning

2809

    tips</uri>

2810

  </li>

2811

  <li>

2812

    <uri link="/doc/en/articles/partitioning-p1.xml">Partitioning in action,

2813

    Part 1</uri>

2814

  </li>

2815

  <li>

2816

    <uri link="/doc/en/articles/partitioning-p2.xml">Partitioning in action,

2817

    Part 2</uri>.

2818

  </li>

2819

</ul>

2820

2821

<p>

2822

ReiserFS Resources:

2823

</p>

2824

2825

<ul>

2826

  <li><uri link="http://www.namesys.com/">The home of ReiserFS</uri></li>

2827

  <li>

2828

    <uri

2829

    link="http://www-106.ibm.com/developerworks/library/l-fs.html">Advanced

2830

    filesystem implementor's guide, Part 1: Journalling and ReiserFS on

2831

    developerWorks</uri>

2832

  </li>

2833

  <li>

2834

    <uri

2835

    link="http://www-106.ibm.com/developerworks/library/l-fs2.html">Advanced

2836

    filesystem implementor's guide, Part 2: Using ReiserFS and Linux 2.4 on

2837

    developerWorks</uri>.

2838

  </li>

2839

</ul>

2840

2841

<p>

2842

ext3 resources:

2843

</p>

2844

2845

<ul>

2846

  <li>

2847

    <uri link="http://www.zip.com.au/~akpm/linux/ext3/">Andrew Morton's ext3

2848

    page</uri>

2849

  </li>

2850

  <li>

2851

    <uri link="http://www.zip.com.au/~akpm/linux/ext3/ext3-usage.html">Andrew

2852

    Morton's excellent ext3 usage documentation (recommended).</uri>

2853

  </li>

2854

</ul>

2855

2856

<p>

2857

XFS and JFS resources:

2858

</p>

2859

2860

<ul>

2861

  <li>

2862

    <uri link="http://oss.sgi.com/projects/xfs">SGI XFS projects page</uri>

2863

  </li>

2864

  <li>

2865

    The IBM <uri

2866

    link="http://www-124.ibm.com/developerworks/oss/jfs/index.html">JFS project

2867

    Web site</uri>.

2868

  </li>

2869

</ul>

2870

2871

<p>

2872

Don't forget <uri link="http://en.tldp.org/">linuxdoc.org</uri>. You'll find

2873

linuxdoc's collection of guides, HOWTOs, FAQs, and man pages to be invaluable.

2874

Be sure to check out <uri link="http://en.tldp.org/LDP/LG/current/">Linux

2875

Gazette</uri> and <uri

2876

link="http://en.tldp.org/linuxfocus/index.html">LinuxFocus</uri> as well.

2877

</p>

2878

2879

<p>

2880

The Linux System Administrators guide, available from <uri

2881

link="http://en.tldp.org/guides.html">Linuxdoc.org's "Guides" section</uri>, is

2882

a good complement to this series of tutorials -- give it a read! You may also

2883

find Eric S. Raymond's <uri

2884

link="http://en.tldp.org/HOWTO/Unix-and-Internet-Fundamentals-HOWTO/">Unix and

2885

Internet Fundamentals HOWTO</uri> to be helpful.

2886

</p>

2887

2888

<p>

2889

In the Bash by example article series on developerWorks, Daniel shows you how

2890

to use bash programming constructs to write your own bash scripts. This bash

2891

series (particularly Parts 1 and 2) will be excellent additional preparation

2892

for the LPIC Level 1 exam:

2893

</p>

2894

2895

<ul>

2896

  <li>

2897

    <uri

2898

    link="http://www.gentoo.org/doc/en/articles/bash-by-example-p1.xml">Bash by

2899

    example, part 1: Fundamental programming in the Bourne-again shell</uri>

2900

  </li>

2901

  <li>

2902

    <uri

2903

    link="http://www.gentoo.org/doc/en/articles/bash-by-example-p2.xml">Bash by

2904

    example, part 2: More bash programming fundamentals</uri>

2905

  </li>

2906

  <li>

2907

    <uri

2908

    link="http://www.gentoo.org/doc/en/articles/bash-by-example-p3.xml">Bash by

2909

    example, part 3: Exploring the ebuild system.</uri>

2910

  </li>

2911

</ul>

2912

2913

<p>

2914

We highly recommend the <uri

2915

link="http://www-106.ibm.com/developerworks/linux/library/l-faq/">Technical FAQ

2916

by Linux Users</uri> by Mark Chapman, a 50-page in-depth list of

2917

frequently-asked Linux questions, along with detailed answers. The FAQ itself

2918

is in PDF (Adobe Acrobat) format. If you're a beginning or intermediate Linux

2919

user, you really owe it to yourself to check this FAQ out. We also recommend

2920

the <uri

2921

link="http://www-106.ibm.com/developerworks/linux/library/l-gloss/index.html">Linux

2922

glossary for Linux users</uri>, also from Mark.

2923

</p>

2924

2925

<p>

2926

If you're not familiar with the vi editor, we strongly recommend that you check

2927

out Daniel's <uri

2928

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxvi-i.html">Vi intro

2929

-- the cheat sheet method tutorial</uri>. This tutorial will give you a gentle

2930

yet fast-paced introduction to this powerful text editor. Consider this

2931

must-read material if you don't know how to use vi.

2932

</p>

2933

2934

</body>

2935

</section>

2936

<section>

2937

<title>Feedback</title>

2938

<body>

2939

2940

<p>

2941

Please send any tutorial feedback you may have to the authors:

2942

</p>

2943

2944

<ul>

2945

  <li>Daniel Robbins, at <mail>drobbins@g.o</mail></li>

2946

  <li>Chris Houser, at <mail>chouser@g.o</mail></li>

2947

  <li>Aron Griffis, at <mail>agriffis@g.o</mail>.</li>

2948

</ul>

2949

2950

</body>

2951

</section>

2952

</chapter>

2953

</guide>

1.1                  xml/htdocs/doc/en/articles/lpi-101-intermediate-p3.xml

2958

2959

file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/lpi-101-intermediate-p3.xml?rev=1.1&content-type=text/x-cvsweb-markup&cvsroot=gentoo

2960

plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/articles/lpi-101-intermediate-p3.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo

2961

2962

Index: lpi-101-intermediate-p3.xml

2963

===================================================================

2964

<?xml version="1.0" encoding="UTF-8"?>

2965

<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">

2966

<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/articles/lpi-101-intermediate-p3.xml,v 1.1 2006/01/01 09:01:19 rane Exp $ -->

2967

2968

<guide link="/doc/en/articles/lpi-101-intermediate-p3.xml" disclaimer="articles">

2969

<title>LPI certification 101 (release 2) exam prep, Part 2</title>

2970

2971

<author title="Author">

2972

  <mail link="drobbins@g.o">Daniel Robbins</mail>

2973

</author>

2974

<author title="Author">

2975

  <mail link="chouser@g.o">Chris Houser</mail>

2976

</author>

2977

<author title="Author">

2978

  <mail link="agriffis@g.o">Aron Griffis</mail>

2979

</author>

2980

2981

<abstract>

2982

In this tutorial we'll introduce you the Linux system documentation. We will

2983

teach you how to change permissions and how to manage with Linux accounts. At

2984

the end you'll learn how to tune your enviroment.

2985

</abstract>

2986

2987

<!-- The original version of this article was first published on IBM

2988

developerWorks, and is property of Westtech Information Services. This

2989

document is an updated version of the original article, and contains

2990

various improvements made by the Gentoo Linux Documentation team -->

2991

2992

<version>1.0</version>

2993

<date>2005-12-11</date>

2994

2995

<chapter>

2996

<title>Befor You Start</title>

2997

<section>

2998

<title>About this tutorial</title>

2999

<body>

3000

3001

<p>

3002

Welcome to "Intermediate administration," the third of four tutorials designed

3003

to prepare you for the Linux Professional Institute's 101 (release 2) exam.

3004

This tutorial (Part 3) is ideal for those who want to improve their knowledge

3005

of fundamental Linux administration skills. We'll cover a variety of topics,

3006

including system and Internet documentation, the Linux permissions model, user

3007

account management, and login environment tuning.

3008

</p>

3009

3010

<p>

3011

If you are new to Linux, we recommend that you start with <uri

3012

link="/doc/en/articles/lpi-101-fundamentals-p1.xml">Part 1</uri> and <uri

3013

link="/doc/en/articles/lpi-101-administration-p2.xml">Part 2</uri>. For some,

3014

much of this material will be new, but more experienced Linux users may

3015

find this tutorial to be a great way of "rounding out" their foundational Linux

3016

system administration skills.

3017

</p>

3018

3019

<p>

3020

By the end of this series of tutorials (eight in all covering the LPI 101 and

3021

102 exams), you will have the knowledge you need to become a Linux Systems

3022

Administrator and will be ready to attain an LPIC Level 1 certification from

3023

the Linux Professional Institute if you so choose.

3024

</p>

3025

3026

<p>

3027

For those who have taken the <uri

3028

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxlpi3-i.html">release

3029

1 version</uri> of this tutorial for reasons other than LPI exam preparation,

3030

you probably don't need to take this one. However, if you do plan to take the

3031

exams, you should strongly consider reading this revised tutorial.

3032

</p>

3033

3034

</body>

3035

</section>

3036

<section>

3037

<title>About the authors</title>

3038

<body>

3039

3040

<p>

3041

For technical questions about the content of this tutorial, contact the

3042

authors:

3043

</p>

3044

3045

<ul>

3046

  <li>Daniel Robbins, at <mail>drobbins@g.o</mail></li>

3047

  <li>Chris Houser, at <mail>chouser@g.o</mail></li>

3048

  <li>Aron Griffis, at<mail>agriffis@g.o</mail>.</li>

3049

</ul>

3050

3051

<p>

3052

Residing in Albuquerque, New Mexico, Daniel Robbins is the Chief Architect of

3053

<uri link="http://www.gentoo.org/">Gentoo Linux</uri> an advanced ports-based

3054

Linux metadistribution. Besides writing articles, tutorials, and tips for the

3055

developerWorks Linux zone and Intel Developer Services, he has also served as a

3056

contributing author for several books, including Samba Unleashed and SuSE Linux

3057

Unleashed. Daniel enjoys spending time with his wife, Mary, and his daughter,

3058

Hadassah. You can contact Daniel at <mail>drobbins@g.o</mail>.

3059

</p>

3060

3061

<p>

3062

Chris Houser, known to his friends as "Chouser," has been a UNIX proponent

3063

since 1994 when he joined the administration team for the computer science

3064

network at Taylor University in Indiana, where he earned his Bachelor's degree

3065

in Computer Science and Mathematics. Since then, he has gone on to work in Web

3066

application programming, user interface design, professional video software

3067

support, and now Tru64 UNIX device driver programming at <uri

3068

link="http://www.compaq.com/">Compaq</uri>. He has also contributed to various

3069

free software projects, most recently to <uri

3070

link="http://www.gentoo.org/">Gentoo Linux</uri>).  He lives with his wife and

3071

two cats in New Hampshire. You can contact Chris at

3072

<mail>chouser@g.o</mail>.

3073

</p>

3074

3075

<p>

3076

Aron Griffis graduated from Taylor University with a degree in Computer Science

3077

and an award that proclaimed, "Future Founder of a Utopian UNIX Commune."

3078

Working towards that goal, Aron is employed by <uri

3079

link="http://www.compaq.com/">Compaq</uri> writing network drivers for Tru64

3080

UNIX, and spending his spare time plunking out tunes on the piano or developing

3081

<uri link="http://www.gentoo.org/">Gentoo Linux</uri>. He lives with his wife

3082

Amy (also a UNIX engineer) in Nashua, New Hampshire.

3083

</p>

3084

3085

</body>

3086

</section>

3087

</chapter>

3088

3089

<chapter>

3090

<title>System and network documentation</title>

3091

<section>

3092

<title>Types of Linux system documentation</title>

3093

<body>

3094

3095

<p>

3096

There are essentially three sources of documentation on a Linux system: manual

3097

pages, info pages, and application-bundled documentation in

3098

<path>/usr/share/doc</path>. In this section, we'll explore each of these

3099

sources before looking "outside the box" for more information.

3100

</p>

3101

3102

</body>

3103

</section>

3104

<section>

3105

<title>Manual pages</title>

3106

<body>

3107

3108

<p>

3109

Manual pages, or "man pages", are the classic form of UNIX and Linux reference

3110

documentation. Ideally, you can look up the man page for any command,

3111

configuration file, or library routine. In practice, Linux is free software,

3112

and some pages haven't been written or are showing their age. Nonetheless, man

3113

pages are the first place to look when you need help.

3114

</p>

3115

3116

<p>

3117

To access a man page, simply type <c>man</c> followed by your topic of inquiry.

3118

A pager will be started, so you will need to press <c>q</c> when you're done

3119

reading. For example, to look up information about the <c>ls</c> command, you

3120

would type:

3121

</p>

3122

3123

<pre caption="Searching in man page">

3124

$ <i>man ls</i>

3125

</pre>

3126

3127

<p>

3128

Knowing the layout of a man page can be helpful to jump quickly to the

3129

information you need. In general, you will find the following sections in a

3130

<c>man</c> page:

3131

</p>

3132

3133

<table>

3134

<tr>

3135

  <ti>NAME</ti>

3136

  <ti>Name and one-line description of the command</ti>

3137

</tr>

3138

<tr>

3139

  <ti>SYNOPSIS</ti>

3140

  <ti>How to use the command</ti>

3141

</tr>

3142

<tr>

3143

  <ti>DESCRIPTION</ti>

3144

  <ti>In-depth discussion on the functionality of the command</ti>

3145

</tr>

3146

<tr>

3147

  <ti>EXAMPLES</ti>

3148

  <ti>Suggestions for how to use the command</ti>

3149

</tr>

3150

<tr>

3151

  <ti>SEE ALSO</ti>

3152

  <ti>Related topics (usually man pages)</ti>

3153

</tr>

3154

</table>

3155

3156

</body>

3157

</section>

3158

<section>

3159

<title>man page sections</title>

3160

<body>

3161

3162

<p>

3163

The files that comprise manual pages are stored in <path>/usr/share/man</path>

3164

(or in <path>/usr/man</path> on some older systems). Inside that directory, you

3165

will find that the manual pages are organized into the following sections:

3166

</p>

3167

3168

<table>

3169

<tr>

3170

  <ti>man1</ti>

3171

  <ti>User programs</ti>

3172

</tr>

3173

<tr>

3174

  <ti>man2</ti>

3175

  <ti>System calls</ti>

3176

</tr>

3177

<tr>

3178

  <ti>man3</ti>

3179

  <ti>Library functions</ti>

3180

</tr>

3181

<tr>

3182

  <ti>man4</ti>

3183

  <ti>Special files</ti>

3184

</tr>

3185

<tr>

3186

  <ti>man5</ti>

3187

  <ti>File formats</ti>

3188

</tr>

3189

<tr>

3190

  <ti>man6</ti>

3191

  <ti>Games</ti>

3192

</tr>

3193

<tr>

3194

  <ti>man7</ti>

3195

  <ti>Miscellaneous</ti>

3196

</tr>

3197

</table>

3198

3199

</body>

3200

</section>

3201

<section>

3202

<title>Multiple man pages</title>

3203

<body>

3204

3205

<p>

3206

Some topics exist in more than one section. To demonstrate this, let's use the

3207

<c>whatis</c> command, which shows all the available man pages for a topic:

3208

</p>

3209

3210

<pre caption="Using whatis command">

3211

$ <i>whatis printf</i>

3212

printf               (1)  - format and print data

3213

printf               (3)  - formatted output conversion

3214

</pre>

3215

3216

<p>

3217

In this case, <c>man printf</c> would default to the page in section 1 ("User

3218

Programs"). If we were writing a C program, we might be more interested in the

3219

page from section 3 ("Library functions"). You can call up a man page from a

3220

certain section by specifying it on the command line, so to ask for

3221

<e>printf(3)</e>, we would type:

3222

</p>

3223

3224

<pre caption="Specifying section in man command">

3225

$ <i>man 3 printf</i>

3226

</pre>

3227

3228

</body>

3229

</section>

3230

<section>

3231

<title>Finding the right man page</title>

3232

<body>

3233

3234

<p>

3235

Sometimes it's hard to find the right man page for a given topic. In that case,

3236

you might try using <c>man -k</c> to search the NAME section of the man pages.

3237

Be warned that it's a substring search, so running something like <c>man -k

3238

ls</c> will give you a lot of output! Here's an example using a more specific

3239

query:

3240

</p>

3241

3242

<pre caption="Searching man using man -k command">

3243

$ <i>man -k whatis</i>

3244

apropos              (1)  - search the whatis database for strings

3245

makewhatis           (8)  - Create the whatis database

3246

whatis               (1)  - search the whatis database for complete words

3247

</pre>

3248

3249

</body>

3250

</section>

3251

<section>

3252

<title>All about apropos</title>

3253

<body>

3254

3255

<p>

3256

The example on the previous panel brings up a few more points. First, the

3257

<c>apropos</c> command is exactly equivalent to <c>man -k</c>. (In fact, I'll

3258

let you in on a little secret. When you run <c>man -k</c>, it actually runs

3259

<c>apropos</c> behind the scenes.) The second point is the <c>makewhatis</c>

3260

command, which scans all the man pages on your Linux system and builds the

3261

database for <c>whatis</c> and <c>apropos</c>. Usually this is run periodically

3262

by root to keep the database updated:

3263

</p>

3264

3265

<pre caption="Building whatis and apropos database">

3266

# <i>makewhatis</i>

3267

</pre>

3268

3269

<p>

3270

For more information on "man" and friends, you should start with its man page:

3271

</p>

3272

3273

<pre caption="Starting man page for man">

3274

$ <i>man man</i>

3275

</pre>

3276

3277

</body>

3278

</section>

3279

<section>

3280

<title>The MANPATH</title>

3281

<body>

3282

3283

<p>

3284

By default, the <c>man</c> program will look for man pages in

3285

<path>/usr/share/man</path>, <path>/usr/local/man</path>,

3286

<path>/usr/X11R6/man</path>, and possibly <path>/opt/man</path>. Sometimes, you

3287

may find that you need to add an additional item to this search path. If so,

3288

simply edit <path>/etc/man.conf</path> in a text editor and add a line that

3289

looks like this:

3290

</p>

3291

3292

<pre caption="/etc/man.conf">

3293

MANPATH /opt/man

3294

</pre>

3295

3296

<p>

3297

>From that point forward, any man pages in the <path>/opt/man/man*</path>

3298

directories will be found. Remember that you'll need to rerun <c>makewhatis</c>

3299

to add these new man pages to the whatis database.

3300

</p>

3301

3302

</body>

3303

</section>

3304

<section>

3305

<title>GNU info</title>

3306

<body>

3307

3308

<p>

3309

One shortcoming of man pages is that they don't support hypertext, so you can't

3310

jump easily from one to another. The GNU folks recognized this shortcoming, so

3311

they invented another documentation format: "info" pages. Many of the GNU

3312

programs come with extensive documentation in the form of info pages. You can

3313

start reading info pages with the <c>info</c> command:

3314

</p>

3315

3316

<pre caption="Using info command">

3317

$ <i>info</i>

3318

</pre>

3319

3320

<p>

3321

Calling <c>info</c> in this way will bring up an index of the available pages

3322

on the system. You can move around with the arrow keys, follow links (indicated

3323

with a star) using the Enter key, and quit by pressing <c>q</c>. The keys are

3324

based on Emacs, so you should be able to navigate easily if you're familiar

3325

with that editor. For an intro to the Emacs editor, see the developerWorks

3326

tutorial, <uri

3327

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxemacs-i.html">Living

3328

in Emacs</uri>.

3329

</p>

3330

3331

<p>

3332

You can also specify an info page on the command line:

3333

</p>

3334

3335

<pre caption="Specifying info command">

3336

$ <i>info diff</i>

3337

</pre>

3338

3339

<p>

3340

For more information on using the <c>info</c> reader, try reading its info

3341

page. You should be able to navigate primitively using the few keys I've

3342

already mentioned:

3343

</p>

3344

3345

<pre caption="Reading info info page">

3346

$ <i>info info</i>

3347

</pre>

3348

3349

</body>

3350

</section>

3351

<section>

3352

<title>/usr/share/doc</title>

3353

<body>

3354

3355

<p>

3356

There is a final source for help within your Linux system. Many programs are

3357

shipped with additional documentation in other formats: text, PDF, PostScript,

3358

HTML, to name a few. Take a look in <path>usr/share/doc</path> (or

3359

<path>/usr/doc</path> on older systems). You'll find a long list of

3360

directories, each of which came with a certain application on your system.

3361

Searching through this documentation can often reveal some gems that aren't

3362

available as man pages or info pages, such as tutorials or additional technical

3363

documentation. A quick check reveals there's a lot of reading material

3364

available:

3365

</p>

3366

3367

<pre caption="/usr/share/doc/">

3368

$ <i>cd /usr/share/doc</i>

3369

$ <i>find . -type f | wc -l</i>

3370

7582

3371

</pre>

3372

3373

<p>

3374

Whew! Your homework this evening is to read just half (3791) of those

3375

documents. Expect a quiz tomorrow. ;-)

3376

</p>

3377

3378

</body>

3379

</section>

3380

<section>

3381

<title>The Linux Documentation Project</title>

3382

<body>

3383

3384

<p>

3385

In addition to system documentation, there are a number of excellent Linux

3386

resources on the Internet. The <uri link="http://www.tldp.org/">Linux

3387

Documentation Project</uri> is a group of volunteers who are working on putting

3388

together the complete set of free Linux documentation. This project exists to

3389

consolidate various pieces of Linux documentation into a location that is easy

3390

to search and use.

3391

</p>

3392

3393

</body>

3394

</section>

3395

<section>

3396

<title>An LDP overview</title>

3397

<body>

3398

3399

<p>

3400

The LDP is made up of the following areas:

3401

</p>

3402

3403

<ul>

3404

  <li>

3405

    Guides - longer, more in-depth books, such as <uri

3406

    link="http://www.tldp.org/LDP/lpg/index.html">The Linux Programmer's

3407

    Guide</uri>

3408

  </li>

3409

  <li>

3410

    HOWTOs - subject-specific help, such as the <uri

3411

    link="http://www.tldp.org/HOWTO/DSL-HOWTO/index.html">DSL HOWTO</uri>

3412

  </li>

3413

  <li>

3414

    FAQs - Frequently Asked Questions with answers, such as the <uri

3415

    link="http://www.tldp.org/FAQ/faqs/BLFAQ">Brief Linux FAQ</uri>

3416

  </li>

3417

  <li>

3418

    Man pages - help on individual commands (these are the same manual pages

3419

    you get on your Linux system when you use the <c>man</c> command).

3420

  </li>

3421

</ul>

3422

3423

<p>

3424

If you aren't sure which section to peruse, you can take advantage of the

3425

search box, which allows you to find things by topic.

3426

</p>

3427

3428

<p>

3429

The LDP additionally provides a list of Links and Resources such as <uri

3430

link="http://www.tldp.org/LDP/LG/current/">Linux Gazette</uri> (see links in

3431

<uri link="#resources">Resources</uri>) and <uri

3432

link="http://www.tldp.org/linuxfocus/index.html">LinuxFocus</uri>, as well

3433

links to mailing lists and news archives.

3434

</p>

3435

3436

</body>

3437

</section>

3438

<section>

3439

<title>Mailing lists</title>

3440

<body>

3441

3442

<p>

3443

Mailing lists provide probably the most important point of collaboration for

3444

Linux developers. Often projects are developed by contributors who live far

3445

apart, possibly even on opposite sides of the globe. Mailing lists provide a

3446

method for each developer on a project to contact all the others, and to hold

3447

group discussions via e-mail. One of the most famous development mailing lists

3448

is the <uri link="http://www.tux.org/lkml/">Linux Kernel Mailing List</uri>.

3449

</p>

3450

3451

</body>

3452

</section>

3453

<section>

3454

<title>More about mailing lists</title>

3455

<body>

3456

3457

<p>

3458

In addition to development, mailing lists can provide a method for asking

3459

questions and receiving answers from knowledgeable developers, or even other

3460

users. For example, individual distributions often provide mailing lists for

3461

newcomers. You can check your distribution's Web site for information on the

3462

mailing lists it provides.

3463

</p>

3464

3465

<p>

3466

If you took the time to read the LKML FAQ at the link on the previous panel,

3467

you might have noticed that mailing list subscribers often don't take kindly to

3468

questions being asked repeatedly. It's always wise to search the archives for a

3469

given mailing list before writing your question. Chances are, it will save you

3470

time, too!

3471

</p>

3472

3473

</body>

3474

</section>

3475

<section>

3476

<title>Newsgroups</title>

3477

<body>

3478

3479

<p>

3480

Internet "newsgroups" are similar to mailing lists, but are based on a protocol

3481

called NNTP ("Network News Transfer Protocol") instead of e-mail. To

3482

participate, you need to use an NNTP client such as <c>slrn</c> or <c>pan</c>.

3483

The primary advantage is that you only take part in the discussion when you

3484

want, instead of having it continually arrive in your inbox. :-)

3485

</p>

3486

3487

<p>

3488

The newsgroups of primary interest start with comp.os.linux. You can browse the

3489

<uri link="http://www.tldp.org/links/#ng">list on the LDP site</uri>.

3490

</p>

3491

3492

<p>

3493

As with mailing lists, newsgroup discussion is often archived. A popular

3494

newsgroup archiving site is <uri

3495

link="http://groups.google.com/googlegroups/deja_announcement.html">Deja

3496

News</uri>.

3497

</p>

3498

3499

</body>

3500

</section>

3501

<section>

3502

<title>Vendor and third-party Web sites</title>

3503

<body>

3504

3505

<p>

3506

Web sites for the various Linux distributions often provide updated

3507

documentation, installation instructions, hardware

3508

compatibility/incompatibility statements, and other support such as a knowledge

3509

base search tool. For example:

3510

</p>

3511

3512

<ul>

3513

  <li><uri link="http://www.redhat.com/">Redhat Linux</uri></li>

3514

  <li><uri link="http://www.debian.org/">Debian Linux</uri></li>

3515

  <li><uri link="http://www.gentoo.org/">Gentoo Linux</uri></li>

3516

  <li><uri link="http://www.suse.com/">SuSE Linux</uri></li>

3517

  <li><uri link="http://www.caldera.com/">Caldera</uri></li>

3518

  <li><uri link="http://www.turbolinux.com/">Turbolinux</uri></li>

3519

</ul>

3520

3521

</body>

3522

</section>

3523

<section>

3524

<title>Hardware and software vendors</title>

3525

<body>

3526

3527

<p>

3528

Many hardware and software vendors have added Linux support to their products

3529

in recent years. At their sites, you can find information about which hardware

3530

supports Linux, software development tools, released sources, downloads of

3531

Linux drivers for specific hardware, and other special Linux projects. For

3532

example:

3533

</p>

3534

3535

<ul>

3536

  <li><uri link="http://www.ibm.com/linux/">IBM and Linux</uri></li>

3537

  <li>

3538

    <uri link="http://www.compaq.com/products/software/linux/">Compaq and

3539

    Linux</uri>

3540

  </li>

3541

  <li>

3542

    <uri link="http://www.sgi.com/developers/technology/linux/">SGI and

3543

    Linux</uri>

3544

  </li>

3545

  <li><uri link="http://www.hp.com/products1/linux/">HP and Linux</uri></li>

3546

  <li><uri link="http://www.sun.com/linux/">Sun and Linux</uri></li>

3547

  <li>

3548

    <uri link="http://technet.oracle.com/tech/linux/content.html">Oracle and

3549

    Linux</uri>.

3550

  </li>

3551

</ul>

3552

3553

</body>

3554

</section>

3555

<section>

3556

<title>Developer resources</title>

3557

<body>

3558

3559

<p>

3560

In addition, many hardware and software vendors have developed wonderful

3561

resources for Linux developers and administrators. At the risk of sounding

3562

self-promoting, one of the most valuable Linux resources run by a

3563

hardware/software vendor is the <uri

3564

link="http://www.ibm.com/developerworks/linux/">IBM developerWorks Linux

3565

zone</uri>.

3566

</p>

3567

3568

</body>

3569

</section>

3570

</chapter>

3571

3572

<chapter>

3573

<title>The Linux permissions model</title>

3574

<section>

3575

<title>One user, one group</title>

3576

<body>

3577

3578

<p>

3579

In this section, we'll take a look at the Linux permissions and ownership

3580

model. We've already seen that every file is owned by one user and one group.

3581

This is the very core of the permissions model in Linux. You can view the user

3582

and group of a file in a <c>ls -l</c> listing:

3583

</p>

3584

3585

<pre caption="Listing files">

3586

$ <i>ls -l /bin/bash</i>

3587

-rwxr-xr-x    1 root     wheel      430540 Dec 23 18:27 /bin/bash

3588

</pre>

3589

3590

<p>

3591

In this particular example, the <path>/bin/bash</path> executable is owned by

3592

root and is in the wheel group. The Linux permissions model works by allowing

3593

three independent levels of permission to be set for each filesystem object --

3594

those for the file's owner, the file's group, and all other users.

3595

</p>

3596

3597

</body>

3598

</section>

3599

<section>

3600

<title>Understanding "ls -l"</title>

3601

<body>

3602

3603

<p>

3604

Let's take a look at our <c>ls -l</c> output and inspect the first column of

3605

the listing:

3606

</p>

3607

3608

<pre caption="Inspecting ls -l command">

3609

$ <i>ls -l /bin/bash</i>

3610

-rwxr-xr-x    1 root     wheel      430540 Dec 23 18:27 /bin/bash

3611

</pre>

3612

3613

<p>

3614

This first field <e>-rwxr-xr-</e> contains a symbolic representation of this

3615

particular files' permissions. The first character (-) in this field specifies

3616

the type of this file, which in this case is a regular file. Other possible

3617

first characters:

3618

</p>

3619

3620

<pre caption="First characters">

3621

'd' directory

3622

'l' symbolic link

3623

'c' character special device 

3624

'b' block special device

3625

'p' fifo

3626

's' socket

3627

</pre>

3628

3629

</body>

3630

</section>

3631

<section>

3632

<title>Three triplets</title>

3633

<body>

3634

3635

<pre caption="ls -l /bin/bash">

3636

$ <i>ls -l /bin/bash</i>

3637

-rwxr-xr-x    1 root     wheel      430540 Dec 23 18:27 /bin/bash

3638

</pre>

3639

3640

<p>

3641

The rest of the field consists of three character triplets. The first triplet

3642

represents permissions for the owner of the file, the second represents

3643

permissions for the file's group, and the third represents permissions for all

3644

other users:

3645

</p>

3646

3647

<pre caption="Triplets in ls -l command">

3648

"rwx"

3649

"r-x"

3650

"r-x"

3651

</pre>

3652

3653

<p>

3654

Above, the r means that reading (looking at the data in the file) is allowed,

3655

the w means that writing (modifying the file, as well as deletion) is allowed,

3656

and the x means that "execute" (running the program) is allowed. Putting

3657

together all this information, we can see that everyone is able to read the

3658

contents of and execute this file, but only the owner (root) is allowed to

3659

modify this file in any way. So, while normal users can copy this file, only

3660

root is allowed to update it or delete it.

3661

</p>

3662

3663

<p>

3664

Above, the r means that reading (looking at the data in the file) is allowed,

3665

the w means that writing (modifying the file, as well as deletion) is allowed,

3666

and the x means that "execute" (running the program) is allowed. Putting

3667

together all this information, we can see that everyone is able to read the

3668

contents of and execute this file, but only the owner (root) is allowed to

3669

modify this file in any way. So, while normal users can copy this file, only

3670

root is allowed to update it or delete it.

3671

</p>

3672

3673

</body>

3674

</section>

3675

<section>

3676

<title>Who am I?</title>

3677

<body>

3678

3679

<p>

3680

Before we take a look at how to change the user and group ownership of a file,

3681

let's first take a look at how to learn your current user id and group

3682

membership. Unless you've used the <c>su</c> command recently, your current

3683

user id is the one you used to log in to the system. If you use <c>su</c>

3684

frequently, however, you may not remember your current effective user id. To

3685

view it, type <c>whoami</c>:

3686

</p>

3687

3688

<pre caption="Using whoami command">

3689

# <i>whoami</i>

3690

root

3691

# <i>su drobbins</i>

3692

$ <i>whoami</i>

3693

drobbins

3694

</pre>

3695

3696

</body>

3697

</section>

3698

<section>

3699

<title>What groups am I in?</title>

3700

<body>

3701

3702

<p>

3703

To see what groups you belong to, use the <c>groups</c> command:

3704

</p>

3705

3706

<pre caption="Using groups command">

3707

$ <i>groups</i>

3708

drobbins wheel audio

3709

</pre>

3710

3711

<p>

3712

In the above example, I'm a member of the drobbins, wheel, and audio groups.

3713

If you want to see what groups other user(s) are in, specify their usernames as

3714

arguments:

3715

</p>

3716

3717

<pre caption="Specifying user argument">

3718

$ <i>groups root daemon</i>

3719

root : root bin daemon sys adm disk wheel floppy dialout tape video

3720

daemon : daemon bin adm

3721

</pre>

3722

3723

</body>

3724

</section>

3725

<section>

3726

<title>Changing user and group ownership</title>

3727

<body>

3728

3729

<p>

3730

To change the owner or group of a file or other filesystem object, use

3731

<c>chown</c> or <c>chgrp</c>, respectively. Each of these commands takes a name

3732

followed by one or more filenames.

3733

</p>

3734

3735

<pre caption="Using chown and chgrp commands">

3736

# <i>chown root /etc/passwd</i>

3737

# <i>chgrp wheel /etc/passwd</i>

3738

</pre>

3739

3740

<p>

3741

You can also set the owner and group simultaneously with an alternate form of

3742

the <c>chown</c> command:

3743

</p>

3744

3745

<pre caption="Setting owner and group simultaneously">

3746

# <i>chown root:wheel /etc/passwd</i>

3747

</pre>

3748

3749

<p>

3750

You may not use <c>chown</c> unless you are the superuser, but <c>chgrp</c> can

3751

be used by anyone to change the group ownership of a file to a group to which

3752

they belong.

3753

</p>

3754

3755

</body>

3756

</section>

3757

<section>

3758

<title>Recursive ownership changes</title>

3759

<body>

3760

3761

<p>

3762

Both <c>chown</c> and <c>chgrp</c> have a -R option that can be used to tell

3763

them to recursively apply ownership and group changes to an entire directory

3764

tree. For example:

3765

</p>

3766

3767

<pre caption="Using chown and chgrp with -R option">

3768

# <i>chown -R drobbins /home/drobbins</i>

3769

</pre>

3770

3771

</body>

3772

</section>

3773

<section>

3774

<title>Introducing chmod</title>

3775

<body>

3776

3777

<p>

3778

<c>chown</c> and <c>chgrp</c> can be used to change the owner and group of a

3779

filesystem object, but another program -- called <c>chmod</c> -- is used to

3780

change the rwx permissions that we can see in an <c>ls -l</c> listing.

3781

<c>chmod</c> takes two or more arguments: a "mode", describing how the

3782

permissions should be changed, followed by a file or list of files that should

3783

be affected:

3784

</p>

3785

3786

<pre caption="Adding x permission with chmod">

3787

$ <i>chmod +x scriptfile.sh</i>

3788

</pre>

3789

3790

<p>

3791

In the above example, our "mode" is +x. As you might guess, a +x mode tells

3792

<c>chmod</c> to make this particular file executable for both the user and

3793

group and for anyone else.

3794

</p>

3795

3796

<p>

3797

If we wanted to remove all execute permissions of a file, we'd do this:

3798

</p>

3799

3800

<pre caption="Removing x permission with chmod">

3801

$ <i>chmod -x scriptfile.sh</i>

3802

</pre>

3803

3804

</body>

3805

</section>

3806

<section>

3807

<title>User/group/other granularity</title>

3808

<body>

3809

3810

<p>

3811

So far, our <c>chmod</c> examples have affected permissions for all three

3812

triplets -- the user, the group, and all others. Often, it's handy to modify

3813

only one or two triplets at a time. To do this, simply specify the symbolic

3814

character for the particular triplets you'd like to modify before the + or -

3815

sign. Use u for the "user" triplet, g for the "group" triplet, and o for the

3816

"other/everyone" triplet:

3817

</p>

3818

3819

<pre caption="Using triplets">

3820

$ <i>chmod go-w scriptfile.sh</i>

3821

</pre>

3822

3823

<p>

3824

We just removed write permissions for the group and all other users, but left

3825

"owner" permissions untouched.

3826

</p>

3827

3828

</body>

3829

</section>

3830

<section>

3831

<title>Resetting permissions</title>

3832

<body>

3833

3834

<p>

3835

In addition to flipping permission bits on and off, we can also reset them

3836

altogether. By using the = operator, we can tell <c>chmod</c> that we want the

3837

specified permissions and no others:

3838

</p>

3839

3840

<pre caption="Flipping permission bits">

3841

$ <i>chmod =rx scriptfile.sh</i>

3842

</pre>

3843

3844

<p>

3845

Above, we just set all "read" and "execute" bits, and unset all "write" bits.

3846

If you just want to reset a particular triplet, you can specify the symbolic

3847

name for the triplet before the = as follows:

3848

</p>

3849

3850

<pre caption="Reseting triplet">

3851

$ <i>chmod u=rx scriptfile.sh</i>

3852

</pre>

3853

3854

</body>

3855

</section>

3856

<section>

3857

<title>Numeric modes</title>

3858

<body>

3859

3860

<p>

3861

Up until now, we've used what are called symbolic modes to specify permission

3862

changes to <c>chmod</c>. However, there's another common way of specifying

3863

permissions: using a 4-digit octal number. Using this syntax, called numeric

3864

permissions syntax, each digit represents a permissions triplet. For example,

3865

in 1777, the 777 sets the "owner", "group", and "other" flags that we've been

3866

discussing in this section. The 1 is used to set the special permissions bits,

3867

which we'll cover later (see "<uri

3868

link="https://www6.software.ibm.com/developerworks/education/l-lpir23/l-lpir23-3-23.html">The

3869

elusive first digit</uri>" at the end of this section). This chart shows how

3870

the second through fourth digits (777) are interpreted:

3871

</p>

3872

3873

<table>

3874

<tr>

3875

  <th>Mode</th>

3876

  <th>Digit</th>

3877

</tr>

3878

<tr>

3879

  <ti>rwx</ti>

3880

  <ti>7</ti>

3881

</tr>

3882

<tr>

3883

  <ti>rw-</ti>

3884

  <ti>6</ti>

3885

</tr>

3886

<tr>

3887

  <ti>r-x</ti>

3888

  <ti>5</ti>

3889

</tr>

3890

<tr>

3891

  <ti>r--</ti>

3892

  <ti>4</ti>

3893

</tr>

3894

<tr>

3895

  <ti>-wx</ti>

3896

  <ti>3</ti>

3897

</tr>

3898

<tr>

3899

  <ti>-w-</ti>

3900

  <ti>2</ti>

3901

</tr>

3902

<tr>

3903

  <ti>--x</ti>

3904

  <ti>1</ti>

3905

</tr>

3906

<tr>

3907

  <ti>---</ti>

3908

  <ti>0</ti>

3909

</tr>

3910

</table>

3911

3912

</body>

3913

</section>

3914

<section>

3915

<title>Numeric permission syntax</title>

3916

<body>

3917

3918

<p>

3919

Numeric permission syntax is especially useful when you need to specify all

3920

permissions for a file, such as in the following example:

3921

</p>

3922

3923

<pre caption="Adding numeric permission">

3924

$ <i>chmod 0755 scriptfile.sh</i>

3925

$ <i>ls -l scriptfile.sh</i>

3926

-rwxr-xr-x    1 drobbins drobbins        0 Jan  9 17:44 scriptfile.sh

3927

</pre>

3928

3929

<p>

3930

In this example, we used a mode of 0755, which expands to a complete

3931

permissions setting of -rwxr-xr-x.

3932

</p>

3933

3934

</body>

3935

</section>

3936

<section>

3937

<title>The umask</title>

3938

<body>

3939

3940

<p>

3941

When a process creates a new file, it specifies the permissions that it would

3942

like the new file to have. Often, the mode requested is 0666 (readable and

3943

writable by everyone), which is more permissive that we would like.

3944

Fortunately, Linux consults something called a "umask" whenever a new file is

3945

created. The system uses the umask value to reduce the originally specified

3946

permissions to something more reasonable and secure. You can view your current

3947

umask setting by typing umask at the command line:

3948

</p>

3949

3950

<pre caption="Viewing current umask">

3951

$ <i>umask</i>

3952

0022

3953

</pre>

3954

3955

<p>

3956

On Linux systems, the umask normally defaults to 0022, which allows others to

3957

read your new files (if they can get to them) but not modify them.

3958

</p>

3959

3960

<p>

3961

To make new files more secure by default, you can change the umask setting:

3962

</p>

3963

3964

<pre caption="Changing umask setting">

3965

$ <i>umask 0077</i>

3966

</pre>

3967

3968

<p>

3969

This umask will make sure that the group and others will have absolutely no

3970

permissions for any newly created files. So, how does the umask work? Unlike

3971

"regular" permissions on files, the umask specifies which permissions should be

3972

turned off. Let's consult our mode-to-digit mapping table so that we can

3973

understand what a umask of 0077 means:

3974

</p>

3975

3976

<table>

3977

<tr>

3978

  <th>Mode</th>

3979

  <th>Digit</th>

3980

</tr>

3981

<tr>

3982

  <ti>rwx</ti>

3983

  <ti>7</ti>

3984

</tr>

3985

<tr>

3986

  <ti>rw-</ti>

3987

  <ti>6</ti>

3988

</tr>

3989

<tr>

3990

  <ti>r-x</ti>

3991

  <ti>5</ti>

3992

</tr>

3993

<tr>

3994

  <ti>r--</ti>

3995

  <ti>4</ti>

3996

</tr>

3997

<tr>

3998

  <ti>-wx</ti>

3999

  <ti>3</ti>

4000

</tr>

4001

<tr>

4002

  <ti>-w-</ti>

4003

  <ti>2</ti>

4004

</tr>

4005

<tr>

4006

  <ti>--x</ti>

4007

  <ti>1</ti>

4008

</tr>

4009

<tr>

4010

  <ti>---</ti>

4011

  <ti>0</ti>

4012

</tr>

4013

</table>

4014

4015

<p>

4016

Using our table, the last three digits of 0077 expand to ---rwxrwx. Now,

4017

remember that the <c>umask</c> tells the system which permissions to disable.

4018

Putting two and two together, we can see that all "group" and "other"

4019

permissions will be turned off, while "user" permissions will remain untouched.

4020

</p>

4021

4022

</body>

4023

</section>

4024

<section>

4025

<title>Introducing suid and sgid</title>

4026

<body>

4027

4028

<p>

4029

When you initially log in, a new shell process is started. You already know

4030

that, but you may not know that this new shell process (typically bash) runs

4031

using your user id. As such, the bash program can access all files and

4032

directories that you own. In fact, we as users are totally dependent on other

4033

programs to perform operations on our behalf. Because the programs you start

4034

inherit your user id, they cannot access any filesystem objects for which you

4035

haven't been granted access.

4036

</p>

4037

4038

<p>

4039

For example, the passwd file cannot be changed by normal users directly,

4040

because the "write" flag is off for every user except root:

4041

</p>

4042

4043

<pre caption="ls -l /etc/passwd">

4044

$ <i>ls -l /etc/passwd</i>

4045

-rw-r--r--    1 root     wheel        1355 Nov  1 21:16 /etc/passwd

4046

</pre>

4047

4048

<p>

4049

However, normal users do need to be able to modify /etc/passwd (at least

4050

indirectly) whenever they need to change their password. But, if the user is

4051

unable to modify this file, how exactly does this work?

4052

</p>

4053

4054

</body>

4055

</section>

4056

<section>

4057

<title>suid</title>

4058

<body>

4059

4060

<p>

4061

Thankfully, the Linux permissions model has two special bits called <c>suid</c>

4062

and <c>sgid</c>. When an executable program has the <c>suid</c> bit set, it

4063

will run on behalf of the owner of the executable, rather than on behalf of the

4064

person who started the program.

4065

</p>

4066

4067

<p>

4068

Now, back to the <path>/etc/passwd</path> problem. If we take a look at the

4069

<c>passwd</c> executable, we can see that it's owned by root:

4070

</p>

4071

4072

<pre caption="Checking owner of /usr/bin/passwd file">

4073

$ <i>ls -l /usr/bin/passwd</i>

4074

-rwsr-xr-x    1 root     wheel       17588 Sep 24 00:53 /usr/bin/passwd

4075

</pre>

4076

4077

<p>

4078

You'll also note that in place of an x in the user's permission triplet,

4079

there's an s. This indicates that, for this particular program, the <c>suid</c>

4080

and executable bits are set. Because of this, when <c>passwd</c> runs, it will

4081

execute on behalf of the root user (with full superuser access) rather than

4082

that of the user who ran it. And because <c>passwd</c> runs with root access,

4083

it's able to modify the <path>/etc/passwd</path> file with no problem.

4084

</p>

4085

4086

</body>

4087

</section>

4088

<section>

4089

<title>suid/sgid caveats</title>

4090

<body>

4091

4092

<p>

4093

We've seen how <c>suid</c> works, and <c>sgid</c> works in a similar way. It

4094

allows programs to inherit the group ownership of the program rather than that

4095

of the current user.

4096

</p>

4097

4098

<impo>

4099

Here's some miscellaneous yet important information about <c>suid</c> and

4100

<c>sgid</c>. First, <c>suid</c> and <c>sgid</c> bits occupy the same space as

4101

the x bits in a ls -l listing. If the x bit is also set, the respective bits

4102

will show up as s (lowercase). However, if the x bit is not set, it will show

4103

up as a S (uppercase).

4104

</impo>

4105

4106

<impo>

4107

Another important note: suid and sgid come in handy in many circumstances, but

4108

improper use of these bits can allow the security of a system to be breached.

4109

It's best to have as few suid programs as possible. The passwd command is one

4110

of the few that must be suid.

4111

</impo>

4112

4113

</body>

4114

</section>

4115

<section>

4116

<title>Changing suid and sgid</title>

4117

<body>

4118

4119

<p>

4120

Setting and removing the <c>suid</c> and <c>sgid</c> bits is fairly

4121

straightforward. Here, we set the suid bit:

4122

</p>

4123

4124

<pre caption="Setting suid bit">

4125

# <i>chmod u+s /usr/bin/myapp</i>

4126

</pre>

4127

4128

<p>

4129

And here, we remove the <c>sgid</c> bit from a directory. We'll see how the

4130

<c>sgid</c> bit affects directories in just a few panels:

4131

</p>

4132

4133

<pre caption="Removing sgid bit">

4134

# <i>chmod g-s /home/drobbins</i>

4135

</pre>

4136

4137

</body>

4138

</section>

4139

<section>

4140

<title>Permissions and directories</title>

4141

<body>

4142

4143

<p>

4144

So far, we've been looking at permissions from the perspective of regular

4145

files. When it comes to directories, things are a bit different. Directories

4146

use the same permissions flags, but they are interpreted to mean slightly

4147

different things.

4148

</p>

4149

4150

<p>

4151

For a directory, if the "read" flag is set, you may list the contents of the

4152

directory; "write" means you may create files in the directory; and "execute"

4153

means you may enter the directory and access any sub-directories inside.

4154

Without the "execute" flag, the filesystem objects inside a directory aren't

4155

accessible. Without a "read" flag, the filesystem objects inside a directory

4156

aren't viewable, but objects inside the directory can still be accessed as long

4157

as someone knows the full path to the object on disk.

4158

</p>

4159

4160

</body>

4161

</section>

4162

<section>

4163

<title>Directories and sgid</title>

4164

<body>

4165

4166

<p>

4167

And, if a directory has the "sgid" flag enabled, any filesystem objects created

4168

inside it will inherit the group of the directory. This particular feature

4169

comes in handy when you need to create a directory tree to be used by a group

4170

of people that all belong to the same group. Simply do this:

4171

</p>

4172

4173

<pre caption="Creating directory for a group of people">

4174

# <i>mkdir /home/groupspace</i>

4175

# <i>chgrp mygroup /home/groupspace</i>

4176

# <i>chmod g+s /home/groupspace</i>

4177

</pre>

4178

4179

<p>

4180

Now, any users in the group mygroup can create files or directories inside

4181

<path>/home/groupspace</path>, and they will be automatically assigned a group

4182

ownership of mygroup as well. Depending on the users' umask setting, new

4183

filesystem objects may or may not be readable, writable, or executable by other

4184

members of the mygroup group.

4185

</p>

4186

4187

</body>

4188

</section>

4189

<section>

4190

<title>Directories and deletion</title>

4191

<body>

4192

4193

<p>

4194

By default, Linux directories behave in a way that may not be ideal in all

4195

situations. Normally, anyone can rename or delete a file inside a directory, as

4196

long as they have write access to that directory. For directories used by

4197

individual users, this behavior is usually just fine.

4198

</p>

4199

4200

<p>

4201

However, for directories that are used by many users, especially

4202

<path>/tmp</path> and <path>/var/tmp</path>, this behavior can be bad news.

4203

Since anyone can write to these directories, anyone can delete or rename anyone

4204

else's files -- even if they don't own them! Obviously, it's hard to use

4205

<path>/tmp</path> for anything meaningful when any other user can type <c>rm

4206

-rf /tmp/*</c> at any time and destroy everyone's files.

4207

</p>

4208

4209

<p>

4210

Thankfully, Linux has something called the sticky bit. When <path>/tmp</path>

4211

has the sticky bit set (with a <c>chmod +t</c>), the only people who are able

4212

to delete or rename files in <path>/tmp</path> are the directory's owner

4213

(typically root), the file's owner, or root. Virtually all Linux distributions

4214

enable <path>/tmp</path>'s sticky bit by default, but you may find that the

4215

sticky bit comes in handy in other situations.

4216

</p>

4217

4218

</body>

4219

</section>

4220

<section>

4221

<title>The elusive first digit</title>

4222

<body>

4223

4224

<p>

4225

And to conclude this section, we finally take a look at the elusive first digit

4226

of a numeric mode. As you can see, this first digit is used for setting the

4227

sticky, <c>suid</c>, and <c>sgid</c> bits:

4228

</p>

4229

4230

<table>

4231

<tr>

4232

  <th>suid</th>

4233

  <th>sgid</th>

4234

  <th>sticky</th>

4235

  <th>mode digit</th>

4236

</tr>

4237

<tr>

4238

  <ti>on</ti>

4239

  <ti>on</ti>

4240

  <ti>on</ti>

4241

  <ti>7</ti>

4242

</tr>

4243

<tr>

4244

  <ti>on</ti>

4245

  <ti>on</ti>

4246

  <ti>off</ti>

4247

  <ti>6</ti>

4248

</tr>

4249

<tr>

4250

  <ti>on</ti>

4251

  <ti>off</ti>

4252

  <ti>on</ti>

4253

  <ti>5</ti>

4254

</tr>

4255

<tr>

4256

  <ti>on</ti>

4257

  <ti>off</ti>

4258

  <ti>off</ti>

4259

  <ti>4</ti>

4260

</tr>

4261

<tr>

4262

  <ti>off</ti>

4263

  <ti>on</ti>

4264

  <ti>on</ti>

4265

  <ti>3</ti>

4266

</tr>

4267

<tr>

4268

  <ti>off</ti>

4269

  <ti>on</ti>

4270

  <ti>off</ti>

4271

  <ti>2</ti>

4272

</tr>

4273

<tr>

4274

  <ti>off</ti>

4275

  <ti>off</ti>

4276

  <ti>on</ti>

4277

  <ti>1</ti>

4278

</tr>

4279

<tr>

4280

  <ti>off</ti>

4281

  <ti>off</ti>

4282

  <ti>off</ti>

4283

  <ti>0</ti>

4284

</tr>

4285

</table>

4286

4287

<p>

4288

Here's an example of how to use a 4-digit numeric mode to set permissions for a

4289

directory that will be used by a workgroup:

4290

</p>

4291

4292

<pre caption="Setting numeric permissions">

4293

# <i>chmod 1775 /home/groupfiles</i>

4294

</pre>

4295

4296

<p>

4297

As homework, figure out the meaning of the 1755 numeric permissions setting. :)

4298

</p>

4299

4300

</body>

4301

</section>

4302

</chapter>

4303

4304

<chapter>

4305

<title>Linux account managment</title>

4306

<section>

4307

<title>Introducing /etc/passwd</title>

4308

<body>

4309

4310

<p>

4311

In this section, we'll look at the Linux account management mechanism, starting

4312

with the <path>/etc/passwd</path> file, which defines all the users that exist

4313

on a Linux system. You can view your own <path>/etc/passwd</path> file by

4314

typing less <path>/etc/passwd</path>.

4315

</p>

4316

4317

<p>

4318

Each line in <path>/etc/passwd</path> defines a user account. Here's an example

4319

line from my <path>/etc/passwd</path> file:

4320

</p>

4321

4322

<pre caption="/etc/passwd">

4323

drobbins:x:1000:1000:Daniel Robbins:/home/drobbins:/bin/bash

4324

</pre>

4325

4326

<p>

4327

As you can see, there is quite a bit of information on this line. In fact, each

4328

<path>/etc/passwd</path> line consists of multiple fields, each separated by a

4329

:.

4330

</p>

4331

4332

<p>

4333

The first field defines the username (drobbins)), and the second field contains

4334

an x. On ancient Linux systems, this field contained an encrypted password to

4335

be used for authentication, but virtually all Linux systems now store this

4336

password information in another file.

4337

</p>

4338

4339

<p>

4340

The third field (1000) defines the numeric user id associated with this

4341

particular user, and the fourth field (1000) associates this user with a

4342

particular group; in a few panels, we'll see where group 1000 is defined.

4343

</p>

4344

4345

<p>

4346

The fifth field contains a textual description of this account -- in this case,

4347

the user's name. The sixth field defines this user's home directory, and the

4348

seventh field specifies the user's default shell -- the one that will be

4349

automatically started when this user logs in.

4350

</p>

4351

4352

</body>

4353

</section>

4354

<section>

4355

<title>/etc/passwd tips and tricks</title>

4356

<body>

4357

4358

<p>

4359

You've probably noticed that there are many more user accounts defined in

4360

<path>/etc/passwd</path> than actually log in to your system. This is because

4361

various Linux components use user accounts to enhance security. Typically,

4362

these system accounts have a user id ("uid") of under 100, and many of them

4363

will have something like /bin/false listed as a default shell. Since the

4364

<path>/bin/false</path> program does nothing but exit with an error code, this

4365

effectively prevents these accounts from being used as login accounts -- they

4366

are for internal use only.

4367

</p>

4368

4369

</body>

4370

</section>

4371

<section>

4372

<title>/etc/shadow</title>

4373

<body>

4374

4375

<p>

4376

So, user accounts themselves are defined in <path>/etc/passwd</path>. Linux

4377

systems contain a companion file to <path>/etc/passwd</path> that's called

4378

<path>/etc/shadow</path>. This file, unlike <path>/etc/passwd</path>, is

4379

readable only by root and contains encrypted password information. Let's look

4380

at a sample line from <path>/etc/shadow</path>:

4381

</p>

4382

4383

<pre caption="/etc/shadow">

4384

drobbins:$1$1234567890123456789012345678901:11664:0:-1:-1:-1:-1:0

4385

</pre>

4386

4387

<p>

4388

Each line defines password information for a particular account, and again,

4389

each field is separated by a :. The first field defines the particular user

4390

account with which this shadow entry is associated. The second field contains

4391

an encrypted password. The remaining fields are described in the following

4392

table:

4393

</p>

4394

4395

<table>

4396

<tr>

4397

  <ti>field 3</ti>

4398

  <ti># of days since 1/1/1970 that the password was modified</ti>

4399

</tr>

4400

<tr>

4401

  <ti>field 4</ti>

4402

  <ti>

4403

    # of days before password will be allowed to be changed (0 for "change

4404

    anytime")

4405

  </ti>

4406

</tr>

4407

<tr>

4408

  <ti>field 5</ti>

4409

  <ti>

4410

    # of days before system will force user to change to a new password (-1

4411

    for "never")

4412

  </ti>

4413

</tr>

4414

<tr>

4415

  <ti>field 6</ti>

4416

  <ti>

4417

    # of days before password expires that user will be warned about

4418

    expiration (-1 for "no warning")

4419

  </ti>

4420

</tr>

4421

<tr>

4422

  <ti>field 7</ti>

4423

  <ti>

4424

    # of days after password expiration that this account is automatically

4425

    # disabled by the system (-1 for "never disable")

4426

  </ti>

4427

</tr>

4428

<tr>

4429

  <ti>field 8</ti>

4430

  <ti>

4431

    # of days that this account has been disabled (-1 for "this account is

4432

    enabled")

4433

  </ti>

4434

</tr>

4435

<tr>

4436

  <ti>field 9</ti>

4437

  <ti>Reserved for future use</ti>

4438

</tr>

4439

</table>

4440

4441

</body>

4442

</section>

4443

<section>

4444

<title>/etc/group</title>

4445

<body>

4446

4447

<p>

4448

Next, we take a look at the <path>/etc/group</path> file, which defines all the

4449

groups on a Linux system. Here's a sample line:

4450

</p>

4451

4452

<pre caption="/etc/group">

4453

drobbins:x:1000:

4454

</pre>

4455

4456

<p>

4457

The <path>/etc/group</path> field format is as follows. The first field defines

4458

the name of the group; the second field is a vestigial password field that now

4459

simply holds an x, and the third field defines the numeric group id of this

4460

particular group. The fourth field (empty in the above example) defines any

4461

users that are members of this group.

4462

</p>

4463

4464

<p>

4465

You'll recall that our sample <path>/etc/passwd</path> line referenced a group

4466

id of 1000. This has the effect of placing the drobbins user in the drobbins

4467

group, even though the drobbins username isn't listed in the fourth field of

4468

<path>/etc/group</path>. 

4469

</p>

4470

4471

</body>

4472

</section>

4473

<section>

4474

<title>Group notes</title>

4475

<body>

4476

4477

<p>

4478

A note about associating users with groups: on some systems, you'll find that

4479

every new login account is associated with an identically named (and usually

4480

identically numbered) group. On other systems, all login accounts will belong

4481

to a single users group. The approach that you use on the system(s) you

4482

administrate is up to you. Creating matching groups for each user has the

4483

advantage of allowing users to more easily control access to their own files by

4484

placing trusted friends in their personal group.

4485

</p>

4486

4487

</body>

4488

</section>

4489

<section>

4490

<title>Adding a user and group by hand</title>

4491

<body>

4492

4493

<p>

4494

Now, I'll show you how to create your own user and group account. The best way

4495

to learn how to do this is to add a new user to the system manually. To begin,

4496

first make sure that your EDITOR environment variable is set to your favorite

4497

text editor:

4498

</p>

4499

4500

<pre caption="Checking favorite text editor variable">

4501

# <i>echo $EDITOR</i>

4502

vim

4503

</pre>

4504

4505

<p>

4506

If it isn't, you can set EDITOR by typing something like:

4507

</p>

4508

4509

<pre caption="Setting EDITOR variable">

4510

# <i>export EDITOR=/usr/bin/emacs</i>

4511

# <i>vipw</i>

4512

</pre>

4513

4514

<p>

4515

You should now find yourself in your favorite text editor with the

4516

<path>/etc/passwd</path> file loaded up on the screen. When modifying system

4517

<path>passwd</path> and <path>group</path> files, it's very important to use

4518

the <c>vipw</c> and <c>vigr</c> commands. They take extra precautions to ensure

4519

that your critical <path>passwd</path> and <path>group</path> files are locked

4520

properly so they don't become corrupted.

4521

</p>

4522

4523

</body>

4524

</section>

4525

<section>

4526

<title>Editing /etc/passwd</title>

4527

<body>

4528

4529

<p>

4530

Now that you have the <path>/etc/passwd</path> file up, go ahead and add the

4531

following line:

4532

</p>

4533

4534

<pre caption="/etc/passwd">

4535

testuser:x:3000:3000:LPI tutorial test user:/home/testuser:/bin/false

4536

</pre>

4537

4538

<p>

4539

We've just added a "testuser" user with a UID of 3000. We've added him to a

4540

group with a GID of 3000, which we haven't created just yet. Alternatively, we

4541

could have assigned this user to the GID of the users group if we wanted. This

4542

new user has a comment that reads LPI tutorial test user; the user's home

4543

directory is set to <path>/home/testuser</path>, and the user's shell is set to

4544

<path>/bin/false</path> for security purposes. If we were creating an non-test

4545

account, we would set the shell to <path>/bin/bash</path>. OK, go ahead and

4546

save your changes and exit.

4547

</p>

4548

4549

</body>

4550

</section>

4551

<section>

4552

<title>Editing /etc/shadow</title>

4553

<body>

4554

4555

<p>

4556

Now, we need to add an entry in <path>/etc/shadow</path> for this particular

4557

user. To do this, type <c>vipw -s</c>. You'll be greeted with your favorite

4558

editor, which now contains the <path>/etc/shadow</path> file. Now, go ahead and

4559

copy the line of an existing user account (one that has a password and is

4560

longer than the standard system account entries):

4561

</p>

4562

4563

<pre caption="/etc/shadow">

4564

drobbins:$1$1234567890123456789012345678901:11664:0:-1:-1:-1:-1:0

4565

</pre>

4566

4567

<p>

4568

Now, change the username on the copied line to the name of your new user, and

4569

ensure that all fields (particularly the password aging ones) are set to your

4570

liking:

4571

</p>

4572

4573

<pre caption="Modifed /etc/shadow">

4574

testuser:$1$1234567890123456789012345678901:11664:0:-1:-1:-1:-1:0

4575

</pre>

4576

4577

<p>

4578

Now, save and exit.

4579

</p>

4580

4581

</body>

4582

</section>

4583

<section>

4584

<title>Setting a password</title>

4585

<body>

4586

4587

<p>

4588

You'll be back at the prompt. Now, it's time to set a password for your new

4589

user:

4590

</p>

4591

4592

<pre caption="Setting password for new user">

4593

# <i>passwd testuser</i>

4594

Enter new UNIX password: <comment>(enter a password for testuser)</comment>

4595

Retype new UNIX password: <comment>(enter testuser's new password again)</comment>

4596

</pre>

4597

4598

</body>

4599

</section>

4600

<section>

4601

<title>Editing /etc/group</title>

4602

<body>

4603

4604

<p>

4605

Now that <path>/etc/passwd</path> and <path>/etc/shadow</path> are set up, it's

4606

now time to get <path>/etc/group</path> configured properly. To do this, type:

4607

</p>

4608

4609

<pre caption="Configuring /etc/group">

4610

# <i>vigr</i>

4611

</pre>

4612

4613

<p>

4614

Your <path>/etc/group</path> file will appear in front of you, ready for

4615

editing. Now, if you chose to assign a default group of users for your

4616

particular test user, you do not need to add any groups to

4617

<path>/etc/groups</path>. However, if you chose to create a new group for this

4618

user, go ahead and add the following line:

4619

</p>

4620

4621

<pre caption="Adding new group manually">

4622

testuser:x:3000:

4623

</pre>

4624

4625

<p>

4626

Now save and exit.

4627

</p>

4628

4629

</body>

4630

</section>

4631

<section>

4632

<title>Creating a home directory</title>

4633

<body>

4634

4635

<p>

4636

We're nearly done. Type the following commands to create testuser's home

4637

directory:

4638

</p>

4639

4640

<pre caption="Creating home directory">

4641

# <i>cd /home</i>

4642

# <i>mkdir testuser</i>

4643

# <i>chown testuser.testuser testuser</i>

4644

# <i>chmod o-rwx testuser</i>

4645

</pre>

4646

4647

<p>

4648

Our user's home directory is now in place and the account is ready for use.

4649

Well, almost ready. If you'd like to use this account, you'll need to use vipw

4650

to change testuser's default shell to <path>/bin/bash</path> so that the user

4651

can log in.

4652

</p>

4653

4654

</body>

4655

</section>

4656

<section>

4657

<title>Account admin utils</title>

4658

<body>

4659

4660

<p>

4661

Now that you know how to add a new account and group by hand, let's review the

4662

various time-saving account administration utilities available under Linux. Due

4663

to space constraints, we won't cover a lot of detail describing these commands.

4664

Remember that you can always get more information about a command by viewing

4665

the command's man page. If you are planning to take the LPIC 101 exam, you

4666

should spend some time getting familiar with each of these commands.

4667

</p>

4668

4669

<p>

4670

newgrp

4671

</p>

4672

4673

<p>

4674

By default, any files that a user creates are assigned to the user's group

4675

specified in <path>/etc/passwd</path>. If the user belongs to other groups, he

4676

or she can type newgrp thisgroup to set current default group membership to the

4677

group thisgroup. Then, any new files created will inherit thisgroup membership.

4678

</p>

4679

4680

<table>

4681

<tr>

4682

  <ti><c>chage</c></ti>

4683

  <ti>

4684

    The <c>chage</c> command is used to view and change the password aging

4685

    setting stored in <path>/etc/shadow</path>.

4686

  </ti>

4687

</tr>

4688

<tr>

4689

  <ti><c>gpasswd</c></ti>

4690

  <ti>A general-purpose group administration tool.</ti>

4691

</tr>

4692

<tr>

4693

  <ti><c>groupadd</c>/<c>groupdel</c>/<c>groupmod</c></ti>

4694

  <ti>Used to add/delete/modify groups in <path>/etc/group</path></ti>

4695

</tr>

4696

<tr>

4697

  <ti><c>useradd</c>/<c>userdel</c>/<c>usermod</c></ti>

4698

  <ti>

4699

    Used to add/delete/modify users in <path>/etc/passwd</path>. These commands

4700

    also perform various other convenience functions. See the man pages for

4701

    more information.

4702

  </ti>

4703

</tr>

4704

<tr>

4705

  <ti><c>pwconv</c>/<c>grpconv</c></ti>

4706

  <ti>

4707

    Used to convert <path>passwd</path> and <path>group</path> files to

4708

    "new-style" shadow passwords.  Virtually all Linux systems already use

4709

    shadow passwords, so you should never need to use these commands.

4710

  </ti>

4711

</tr>

4712

</table>

4713

4714

</body>

4715

</section>

4716

</chapter>

4717

4718

<chapter>

4719

<title>Tuning the user environment</title>

4720

<section>

4721

<title>Introducing "fortune"</title>

4722

<body>

4723

4724

<p>

4725

Your shell has many useful options that you can set to fit your personal

4726

preferences. So far, however, we haven't discussed any way to have these

4727

settings set up automatically every time you log in, except for re-typing them

4728

each time. In this section we will look at tuning your login environment by

4729

modifying startup files.

4730

</p>

4731

4732

<p>

4733

First, let's add a friendly message for when you first log in. To see an

4734

example message, run <c>fortune</c>:

4735

</p>

4736

4737

<pre caption="Running fortune command">

4738

$ <i>fortune</i>

4739

No amount of careful planning will ever replace dumb luck.

4740

</pre>

4741

4742

</body>

4743

</section>

4744

<section>

4745

<title>.bash_profile</title>

4746

<body>

4747

4748

<p>

4749

Now, let's set up <c>fortune</c> so that it gets run every time you log in. Use

4750

your favorite text editor to edit a file named <path>.bash_profile</path> in

4751

your home directory. If the file doesn't exist already, go ahead and create it.

4752

Insert a line at the top:

4753

</p>

4754

4755

<pre caption="~/.bash_profile">

4756

fortune

4757

</pre>

4758

4759

<p>

4760

Try logging out and back in. Unless you're running a display manager like xdm,

4761

gdm, or kdm, you should be greeted cheerfully when you log in:

4762

</p>

4763

4764

<pre caption="Results of fortune command in .bash_profile file">

4765

mycroft.flatmonk.org login: chouser

4766

Password:

4767

Freedom from incrustations of grime is contiguous to rectitude.

4768

$

4769

</pre>

4770

4771

</body>

4772

</section>

4773

<section>

4774

<title>The login shell</title>

4775

<body>

4776

4777

<p>

4778

When bash started, it walked through the <path>.bash_profile</path> file in

4779

your home directory, running each line as though it had been typed at a bash

4780

prompt. This is called sourcing the file.

4781

</p>

4782

4783

<p>

4784

Bash acts somewhat differently depending on how it is started. If it is started

4785

as a login shell, it will act as it did above -- first sourcing the system-wide

4786

<path>/etc/profile</path>, and then your personal <path>~/.bash_profile</path>.

4787

</p>

4788

4789

<p>

4790

There are two ways to tell bash to run as a login shell. One way is used when

4791

you first log in: bash is started with a process name of -bash. You can see

4792

this in your process listing:

4793

</p>

4794

4795

<pre caption="Process listing">

4796

$ <i>ps u</i>

4797

USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND

4798

chouser    404  0.0  0.0  2508  156 tty2     S     2001   0:00 -bash

4799

</pre>

4800

4801

<p>

4802

You will probably see a much longer listing, but you should have at least one

4803

COMMAND with a dash before the name of your shell, like -bash in the example

4804

above. This dash is used by the shell to determine if it's being run as a login

4805

shell.

4806

</p>

4807

4808

</body>

4809

</section>

4810

<section>

4811

<title>Understanding --login</title>

4812

<body>

4813

4814

<p>

4815

The second way to tell bash to run as a login shell is with the <c>--login</c>

4816

command-line option. This is sometimes used by terminal emulators (like xterm)

4817

to make their bash sessions act like initial login sessions.

4818

</p>

4819

4820

<p>

4821

After you have logged in, more copies of your shell will be run. Unless they

4822

are started with <c>--login</c> or have a dash in the process name, these

4823

sessions will not be login shells. If they give you a prompt, however, they are

4824

called interactive shells. If bash is started as interactive, but not login, it

4825

will ignore <path>/etc/profile</path> and <path>~/.bash_profile</path> and will

4826

instead source <path>~/.bashrc</path>.

4827

</p>

4828

4829

<table>

4830

<tr>

4831

  <th>interactive</th>

4832

  <th>login</th>

4833

  <th>profile</th>

4834

  <th>rc</th>

4835

</tr>

4836

<tr>

4837

  <ti>yes</ti>

4838

  <ti>yes</ti>

4839

  <ti>source</ti>

4840

  <ti>ignore</ti>

4841

</tr>

4842

<tr>

4843

  <ti>yes</ti>

4844

  <ti>no</ti>

4845

  <ti>ignore</ti>

4846

  <ti>source</ti>

4847

</tr>

4848

<tr>

4849

  <ti>no</ti>

4850

  <ti>yes</ti>

4851

  <ti>source</ti>

4852

  <ti>ignore</ti>

4853

</tr>

4854

<tr>

4855

  <ti>no</ti>

4856

  <ti>no</ti>

4857

  <ti>ignore</ti>

4858

  <ti>ignore</ti>

4859

</tr>

4860

</table>

4861

4862

</body>

4863

</section>

4864

<section>

4865

<title>Testing for interactivity</title>

4866

<body>

4867

4868

<p>

4869

Sometimes bash sources your <path>~/.bashrc</path>, even though it isn't really

4870

interactive, such as when using commands like rsh and scp. This is important to

4871

keep in mind because printing out text, like we did with the fortune command

4872

earlier, can really mess up these non-interactive bash sessions. It's a good

4873

idea to use the PS1 variable to detect whether the current shell is truly

4874

interactive before printing text from a startup file:

4875

</p>

4876

4877

<pre caption="Testing PS1 varibale">

4878

if [ -n "$PS1" ]; then

4879

fortune

4880

fi

4881

</pre>

4882

4883

</body>

4884

</section>

4885

<section>

4886

<title>/etc/profile and /etc/skel</title>

4887

<body>

4888

4889

<p>

4890

As a system administrator, you are in charge of <path>/etc/profile</path>.

4891

Since it is sourced by everyone when they first log in, it is important to keep

4892

it in working order. It is also a powerful tool in making things work correctly

4893

for new users as soon as they log into their new account.

4894

</p>

4895

4896

<p>

4897

However, there are some settings that you may want new users to have as

4898

defaults, but also allow them to change easily. This is where the

4899

<path>/etc/skel</path> directory comes in. When you use the <c>useradd</c>

4900

command to create a new user account, it copies all the files from

4901

<path>/etc/skel</path> into the user's new home directory. That means you can

4902

put helpful <path>.bash_profile</path> and <path>.bashrc</path> files in

4903

<path>/etc/skel</path> to get new users off to a good start.

4904

</p>

4905

4906

</body>

4907

</section>

4908

<section>

4909

<title>export</title>

4910

<body>

4911

4912

<p>

4913

Variables in bash can be marked so that they are set the same in any new shells

4914

that it starts; this is called being marked for export. You can have bash list

4915

all of the variables that are currently marked for export in your shell

4916

session:

4917

</p>

4918

4919

<pre caption="results of export command">

4920

$ <i>export</i>

4921

declare -x EDITOR="vim"

4922

declare -x HOME="/home/chouser"

4923

declare -x MAIL="/var/spool/mail/chouser"

4924

declare -x PAGER="/usr/bin/less"

4925

declare -x PATH="/bin:/usr/bin:/usr/local/bin:/home/chouser/bin"

4926

declare -x PWD="/home/chouser"

4927

declare -x TERM="xterm"

4928

declare -x USER="chouser"

4929

</pre>

4930

4931

</body>

4932

</section>

4933

<section>

4934

<title>Marking variables for export</title>

4935

<body>

4936

4937

<p>

4938

If a variable is not marked for export, any new shells that it starts will not

4939

have that variable set. However, you can mark a variable for export by passing

4940

it to the <c>export</c> built-in:

4941

</p>

4942

4943

<pre caption="Marking variable for export">

4944

$ <i>FOO=foo</i>

4945

$ <i>BAR=bar</i>

4946

$ <i>export BAR</i>

4947

$ <i>echo $FOO $BAR</i>

4948

foo bar

4949

$ <i>bash</i>

4950

$ <i>echo $FOO $BAR</i>

4951

bar

4952

</pre>

4953

4954

<p>

4955

In this example, the variables FOO and BAR were both set, but only BAR was

4956

marked for export. When a new bash was started, it had lost the value for FOO.

4957

If you exit this new bash, you can see that the original one still has values

4958

for both FOO and BAR:

4959

</p>

4960

4961

<pre caption="Checking settings in original bash">

4962

$ <i>exit</i>

4963

$ <i>echo $FOO $BAR</i>

4964

foo bar

4965

</pre>

4966

4967

</body>

4968

</section>

4969

<section>

4970

<title>Export and set -x</title>

4971

<body>

4972

4973

<p>

4974

Because of this behavior, variables can be set in <path>~/.bash_profile</path>

4975

or <path>/etc/profile</path> and marked for export, and then never need to be

4976

set again. There are some options that cannot be exported, however, and so they

4977

must be put in put in your <path>~/.bashrc</path> and your <e>profile</e> in

4978

order to be set consistently. These options are adjusted with the set built-in:

4979

</p>

4980

4981

<pre caption="Using set command">

4982

$ <i>set -x</i>

4983

</pre>

4984

4985

<p>

4986

The <c>-x</c> option causes bash to print out each command it is about to run:

4987

</p>

4988

4989

<pre caption="Checking results of -x option">

4990

$ <i>echo $FOO</i>

4991

$ <i>echo foo</i>

4992

foo

4993

</pre>

4994

4995

<p>

4996

This can be very useful for understanding unexpected quoting behavior or

4997

similar strangeness. To turn off the <c>-x</c> option, do <c>set +x</c>. See

4998

the bash man page for all of the options to the set built-in.

4999

</p>

5000

5001

</body>

5002

</section>

5003

<section>

5004

<title>Setting variables with "set"</title>

5005

<body>

5006

5007

<p>

5008

The <c>set</c> built-in can also be used for setting variables, but when used

5009

that way, it is optional. The bash command <c>set FOO=foo</c> means exactly the

5010

same as <c>FOO=foo</c>. Un-setting a variable is done with the <c>unset</c>

5011

built-in:

5012

</p>

5013

5014

<pre caption="Un-setting variable">

5015

$ <i>FOO=bar</i>

5016

$ <i>echo $FOO</i>

5017

bar

5018

$ <i>unset FOO</i>

5019

$ <i>echo $FOO</i>

5020

</pre>

5021

5022

</body>

5023

</section>

5024

<section>

5025

<title>Unset vs. FOO=</title>

5026

<body>

5027

5028

<p>

5029

This is <e>not</e> the same as setting a variable to nothing, although it is

5030

sometimes hard to tell the difference. One way to tell is to use the <c>set</c>

5031

built-in with no parameters to list all current variables:

5032

</p>

5033

5034

<pre caption="Comparison of unset and FOO=">

5035

$ <i>FOO=bar</i>

5036

$ <i>set | grep ^FOO</i>

5037

FOO=bar

5038

$ <i>FOO=</i>

5039

$ <i>set | grep ^FOO</i>

5040

FOO=

5041

$ <i>unset FOO</i>

5042

$ <i>set | grep ^FOO</i>

5043

</pre>

5044

5045

<p>

5046

Using <c>set</c> with no parameters like this is similar to using the

5047

<c>export</c> built-in, except that <c>set</c> lists all variables instead of

5048

just those marked for export.

5049

</p>

5050

5051

</body>

5052

</section>

5053

<section>

5054

<title>Exporting to change command behavior</title>

5055

<body>

5056

5057

<p>

5058

Often, the behavior of commands can be altered by setting environment

5059

variables. Just as with new bash sessions, other programs that are started from

5060

your bash prompt will only be able to see variables that are marked for export.

5061

For example, the command <c>man</c> checks the variable PAGER to see what

5062

program to use to step through the text one page at a time.

5063

</p>

5064

5065

<pre caption="Exporting PAGER variable">

5066

$ <i>PAGER=less</i>

5067

$ <i>export PAGER</i>

5068

$ <i>man man</i>

5069

</pre>

5070

5071

<p>

5072

With PAGER set to <c>less</c>, you will see one page at a time, and pressing

5073

the space bar moves on to the next page. If you change PAGER to <c>cat</c>, the

5074

text will be displayed all at once, without stopping.

5075

</p>

5076

5077

<pre caption="Setting PAGER variable to cat">

5078

$ <i>PAGER=cat</i>

5079

$ <i>man man</i>

5080

</pre>

5081

5082

</body>

5083

</section>

5084

<section>

5085

<title>Using "env"</title>

5086

<body>

5087

5088

<p>

5089

Unfortunately, if you forget to set PAGER back to <c>less</c>, <c>man</c> (as

5090

well as some other commands) will continue to display all their text without

5091

stopping. If you wanted to have PAGER set to <c>cat</c> just once, you could

5092

use the <c>env</c> command:

5093

</p>

5094

5095

<pre caption="Using env command to set variable">

5096

$ <i>PAGER=less</i>

5097

$ <i>env PAGER=cat man man</i>

5098

$ <i>echo $PAGER</i>

5099

less

5100

</pre>

5101

5102

<p>

5103

This time, PAGER was exported to <c>man</c> with a value of <c>cat</c>, but the

5104

PAGER variable itself remained unchanged in the bash session.

5105

</p>

5106

5107

</body>

5108

</section>

5109

</chapter>

5110

5111

<chapter>

5112

<title>Summary and resources</title>

5113

<section>

5114

<title>Summary</title>

5115

<body>

5116

5117

<p>

5118

Congratulations on finishing Part 3 of this tutorial series! At this point, you

5119

should know how to locate information in system and Internet documentation, and

5120

you should have a good grasp of the Linux permissions model, user account

5121

management, and login environment tuning.

5122

</p>

5123

5124

</body>

5125

</section>

5126

<section id="resources">

5127

<title>Resources</title>

5128

<body>

5129

5130

<p>

5131

Be sure to check out the various Linux documentation resources covered in this

5132

tutorial -- particularly the <uri link="http://www.tldp.org/">Linux

5133

Documentation Project</uri>. You'll find its collection of guides, HOWTOs,

5134

FAQs, and man pages to be invaluable. Be sure to check out <uri

5135

link="http://www.tldp.org/LDP/LG/current/">Linux Gazette</uri> and <uri

5136

link="http://www.tldp.org/linuxfocus/index.html">LinuxFocus</uri> as well.

5137

</p>

5138

5139

<p>

5140

The <uri link="http://www.tldp.org/guides.html">Linux System Administrators

5141

guide</uri> (available from the "Guides" section at www.tldp.org) is a good

5142

complement to this series of tutorials -- give it a read! You may also find

5143

Eric S. Raymond's <uri

5144

link="http://www.tldp.org/HOWTO/Unix-and-Internet-Fundamentals-HOWTO/">Unix and

5145

Internet Fundamentals HOWTO</uri> to be helpful.

5146

</p>

5147

5148

<p>

5149

You can read the GNU Project's online documentation for the GNU info system

5150

(also called "texinfo") at <uri

5151

link="http://www.gnu.org/manual/texinfo/index.html">GNU's texinfo documentation

5152

page</uri>.

5153

</p>

5154

5155

<p>

5156

Browse the <uri link="http://www.tldp.org/links/#ng">Linux newsgroup list</uri>

5157

on the LDP site, and the newsgroup archives at <uri

5158

link="http://groups.google.com/googlegroups/deja_announcement.html">Deja

5159

News</uri>.

5160

</p>

5161

5162

<p>

5163

In the Bash by example article series on developerWorks, Daniel shows you how

5164

to use bash programming constructs to write your own bash scripts. This bash

5165

series (particularly Parts 1 and 2) is good preparation for the LPIC Level 1

5166

exam and reinforces the concepts covered in this tutorial's "Tuning the user

5167

environment" section:

5168

</p>

5169

5170

<ul>

5171

  <li>

5172

    <uri link="/doc/en/articles/bash-by-example-p1.xml">Bash by example, Part

5173

    1: Fundamental programming in the Bourne-again shell</uri>

5174

  </li>

5175

  <li>

5176

    <uri link="/doc/en/articles/bash-by-example-p2.xml">Bash by example, Part

5177

    2: More bash programming fundamentals</uri>

5178

  </li>

5179

  <li>

5180

    <uri link="/doc/en/articles/bash-by-example-p3.xml">Bash by example, Part

5181

    3: Exploring the ebuild system.</uri>

5182

  </li>

5183

</ul>

5184

5185

<p>

5186

We highly recommend the <uri

5187

link="http://www-106.ibm.com/developerworks/linux/library/l-faq/">Technical FAQ

5188

by Linux Users</uri> by Mark Chapman, a 50-page in-depth list of

5189

frequently-asked Linux questions, along with detailed answers. The FAQ itself

5190

is in PDF (Adobe Acrobat) format. If you're a beginning or intermediate Linux

5191

user, you really owe it to yourself to check this FAQ out. We also recommend

5192

the <uri

5193

link="http://www-106.ibm.com/developerworks/linux/library/l-gloss/index.html">Linux

5194

glossary for Linux users</uri>, also from Mark.

5195

</p>

5196

5197

<p>

5198

If you're not familiar with the vi editor, check out Daniel's <uri

5199

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxvi-i.html">Vi intro

5200

-- the cheat sheet method tutorial</uri>. This tutorial will give you a gentle

5201

yet fast-paced introduction to this powerful text editor. Consider this

5202

must-read material if you don't know how to use vi.

5203

</p>

5204

5205

<p>

5206

For an intro to the Emacs editor, see the developerWorks tutorial, <uri

5207

link="http://www-106.ibm.com/developerworks/edu/l-dw-linuxemacs-i.html">Living

5208

in Emacs</uri>.

5209

</p>

5210

5211

</body>

5212

</section>

5213

<section>

5214

<title>Feedback</title>

5215

<body>

5216

5217

<p>

5218

Please let us know whether this tutorial was helpful to you and how we could

5219

make it better. We'd also like to hear about other tutorial topics you'd like

5220

to see covered in developerWorks tutorials.

5221

</p>

5222

5223

<p>

5224

For questions about the content of this tutorial, contact the authors:

5225

</p>

5226

5227

<ul>

5228

  <li>Daniel Robbins, at <mail>drobbins@g.o</mail></li>

5229

  <li>Chris Houser, at <mail>chouser@g.o</mail></li>

5230

  <li>Aron Griffis, at <mail>agriffis@g.o</mail>.</li>

5231

</ul>

5232

5233

</body>

5234

</section>

5235

</chapter>

5236

</guide>

--

5241

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