Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION... User manual

Red Hat Linux 7.2
The Official Red Hat Linux Reference Guide

ISBN: N/A
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Contents
Red Hat Linux 7.2
Introduction................................................................................... ix
Finding Appropriate Documentation ..................................................... ix
Document Conventions.................................................................... xiii
Using the Mouse ........................................................................... xvi
Copying and Pasting Text With X......................................................... xvi
MoretoCome.............................................................................. xvi
Sign Up for Support........................................................................ xvii
Part I System Reference............................................................ 19
Chapter 1 Filesystem Structure.............................................. 21
1.1 Why Share a Common Structure?.............................................. 21
1.2 Overview of Filesystem Hierarchy Standard (FHS)........................... 21
1.3 Special Red Hat Linux File Locations .......................................... 26
Chapter 2 Users and Groups .................................................. 27
2.1 Tools for User and Group Administration....................................... 27
2.2 Standard Users ................................................................... 27
2.3 Standard Groups ................................................................. 29
2.4 User Private Groups.............................................................. 31
2.5 Shadow Utilities................................................................... 33
Chapter 3 Boot Process, Init, and Shutdown ....................... 35
3.1 Introduction........................................................................ 35
3.2 Behind the Scenes of the Boot Process ....................................... 35
3.3 Sysconfig Information............................................................ 43
3.4 Init Runlevels...................................................................... 54
3.5 Running Programs at Boot Time................................................ 56
3.6 Shutting Down .................................................................... 56
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3.7 Differences in the Boot Process of Other Architectures ...................... 57
Chapter 4 The /proc Filesystem.............................................. 59
4.1 A Virtual Filesystem.............................................................. 59
4.2 Top-Level Files in /proc .......................................................... 62
4.3 Directories in /proc ............................................................... 78
4.4 Using sysctl ....................................................................... 98
4.5 Additional Resources ............................................................ 98
Chapter 5 GRUB ....................................................................... 101
5.1 Defining GRUB ................................................................... 101
5.2 Terminology ....................................................................... 104
5.3 Interfaces.......................................................................... 106
5.4 Commands........................................................................ 107
5.5 The Menu Configuration File .................................................... 109
5.6 Additional Resources ............................................................ 110
Chapter 6 X Servers and Clients ............................................ 113
6.1 ThePowerofX ................................................................... 113
6.2 The XFree86 Server.............................................................. 114
6.3 Desktop Environments and Window Managers ............................... 120
6.4 Runlevels.......................................................................... 121
6.5 Fonts............................................................................... 124
6.6 Additional Resources ............................................................ 126
Part II Security Reference .......................................................... 129
Chapter 7 Pluggable Authentication Modules (PAM) .......... 131
7.1 Advantages of PAM .............................................................. 131
7.2 PAM Configuration Files ......................................................... 131
7.3 Shadow Passwords .............................................................. 137
7.4 Using rlogin, rsh, and rexec with PAM.......................................... 137
7.5 Additional Resources ............................................................ 138
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Chapter 8 Using Kerberos 5 on Red Hat Linux .................... 139
8.1 Why Use Kerberos?.............................................................. 139
8.2 Why Not Use Kerberos? ......................................................... 139
8.3 Kerberos Terminology............................................................ 140
8.4 How Kerberos Works............................................................. 141
8.5 Kerberos and PAM................................................................ 143
8.6 Additional Resources ............................................................ 143
Chapter 9 TCP Wrappers and xinetd ..................................... 145
9.1 Purpose of TCP Wrappers ...................................................... 145
9.2 Host-Based Access Control Lists............................................... 146
9.3 Access Control Using xinetd .................................................... 150
9.4 Additional Resources ............................................................ 155
Chapter 10 SSH Protocol........................................................... 157
10.1 Introduction........................................................................ 157
10.2 Event Sequence of an SSH Connection ....................................... 158
10.3 Layers of SSH Security .......................................................... 160
10.4 OpenSSH Configuration Files................................................... 162
10.5 More Than a Secure Shell....................................................... 163
10.6 Requiring SSH for Remote Connections....................................... 165
Chapter 11 Installing and Configuring Tripwire ..................... 167
11.1 How to Use Tripwire.............................................................. 167
11.2 Installation Instructions........................................................... 169
11.3 File Locations ..................................................................... 171
11.4 Tripwire Components............................................................. 172
11.5 Modifying the Policy File ......................................................... 172
11.6 Selecting Passphrases........................................................... 173
11.7 Initializing the Database ......................................................... 174
11.8 Running an Integrity Check...................................................... 174
11.9 Printing Reports .................................................................. 174
11.10 Updating the Database after an Integrity Check .............................. 177
11.11 Updating the Policy File.......................................................... 178
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11.12 Tripwire and Email................................................................ 179
11.13 Additional Resources ............................................................ 180
Part III Network Services Reference.......................................... 181
Chapter 12 Network Scripts...................................................... 183
12.1 Interface Configuration Files .................................................... 183
12.2 Interface Control Scripts ......................................................... 187
12.3 Network Functions................................................................ 189
Chapter 13 Apache..................................................................... 191
13.1 Default Modules .................................................................. 192
13.2 Starting and Stopping httpd ..................................................... 193
13.3 Configuration Directives in httpd.conf .......................................... 194
13.4 Adding Modules to Your Server................................................. 215
13.5 Using Virtual Hosts............................................................... 218
13.6 Additional Resources ............................................................ 221
Chapter 14 Berkeley Internet Name Domain (BIND).............. 223
14.1 Introduction to DNS and BIND .................................................. 223
14.2 BIND Configuration Files ........................................................ 225
14.3 Using rndc......................................................................... 238
14.4 BIND Advanced Features........................................................ 241
14.5 Common Mistakes to Avoid ..................................................... 243
14.6 Additional Resources ............................................................ 244
Chapter 15 Lightweight Directory Access Protocol (LDAP). 247
15.1 What is LDAP?.................................................................... 247
15.2 Pros and Cons of LDAP ......................................................... 247
15.3 Uses for LDAP .................................................................... 248
15.4 LDAP Terminology................................................................ 249
15.5 OpenLDAP 2.0 Enhancements ................................................. 249
15.6 OpenLDAP Files.................................................................. 250
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15.7 OpenLDAP Daemons and Utilities.............................................. 252
15.8 Modules for Adding Extra Functionality to LDAP.............................. 253
15.9 LDAP How To: A Quick Overview............................................... 254
15.10 Configuring Your System to Authenticate Using OpenLDAP................. 254
15.11 Additional Resources ............................................................ 257
Chapter 16 Email ........................................................................ 259
16.1 Protocols .......................................................................... 259
16.2 Different Types of Email Programs ............................................. 262
16.3 Sendmail .......................................................................... 263
16.4 Fetchmail .......................................................................... 268
16.5 Procmail ........................................................................... 273
16.6 Security............................................................................ 280
16.7 Additional Resources ............................................................ 282
Chapter 17 Network File System (NFS) ................................... 285
17.1 Methodology ...................................................................... 285
17.2 NFS Server Configuration Files................................................. 287
17.3 NFS Client Configuration Files.................................................. 291
17.4 Securing NFS..................................................................... 293
17.5 Additional Resources ............................................................ 295
Chapter 18 Firewalling with iptables........................................ 297
18.1 Packet Filtering ................................................................... 297
18.2 Differences between iptables and ipchains .................................... 298
18.3 Options Used in iptables Commands........................................... 299
18.4 Storing iptables Information ..................................................... 307
18.5 Additional Resources ............................................................ 308
Part IV Appendixes....................................................................... 309
Appendix A General Parameters and Modules........................ 311
A.1 Specifying Module Parameters.................................................. 312
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A.2 CD-ROM Module Parameters................................................... 312
A.3 SCSI parameters ................................................................. 315
A.4 Ethernet parameters ............................................................. 319
viii

Section 0.1:Finding Appropriate Documentation ix
Introduction
Welcome to the Official Red Hat Linux Reference Guide.
The Official Red Hat Linux Reference Guide contains useful information about your Red Hat Linux
system. From fundamental concepts, such as the structure of the Red Hat Linux filesystem, to the finer
points of system security and authentication control, we hope you will find this book to be a valuable
resource.
This guide is for you if you want to learn a bit more about how your Red Hat Linux system works.
Topics that you will explore include the following:
•Booting Red Hat Linux — Information about runlevels, rc.d directories, and how to start your
favorite applications at boot time.
•The
/proc filesystem — Provides you with the kernel’s view of the system.
•The GRUB boot loader — A behind the scenes look at GRUB and how it boots your system.
•System and network security — Find out the most common methods used by attackers to com-
promise your system and how to prevent security problems.
•Apache directives — A look at the default Apache configuration and the options available.
Before reading this guide, you should be familiar with the contents of the Official Red Hat Linux
Installation Guide concerning installation issues, the Official Red Hat Linux Getting Started Guide for
basic Linux concepts and the Official Red Hat Linux Customization Guide for general customization
instructions. The Official Red Hat Linux Reference Guide contains information about advanced topics
that may not affect every user, depending upon how they use their Red Hat Linux system.
HTML and PDF versions of all Official Red HatLinux manuals are available onlineat http://www.red-
hat.com/support/manuals.
Finding Appropriate Documentation
You need documentation that is appropriate to your level of Linux expertise. Otherwise, you might
feel overwhelmed or not find the necessary information to answer your questions. The Official Red
Hat Linux Reference Guide deals with the more technical aspects and options of your Red Hat Linux
system. This section will help you decide whether to look in this manual for the information you need
or consider other Red Hat Linux manuals, including online sources, in your search.
Three different categories of people use Red Hat Linux, and each of these categories require differ-
ent sets of documentation and informatative sources. To help you figure out where you should start,
determine your own experience level:
New to Linux

x Introduction
This type of user has never used any Linux (or Linux-like) operating system before or has had
only limited exposure to Linux. They may or may not have experience using other operating
systems (such as Windows). Is this you? If so, skip ahead to Documentation For First-Time
Linux Users.
Some Linux Experience
This type of user has installed and successfully used Linux (but not Red Hat Linux) before or
may have equivalent experience with other Linux-like operating systems. Does this describe
you? If so, turn to For the More Experienced.
Experienced User
This type of user has installed and successfully used Red Hat Linux before. If this describes
you, turn to Documentation for Linux Gurus.
Documentation For First-Time Linux Users
For someone new to Linux, the amount of information available on any particular subject, such as
printing, starting up the system or partitioning your hard drive, can be overwhelming. It helps to
initially step back and gain a decent base of information centered around how Linux works before
tackling these kinds of advanced issues.
Your first goal should be to obtain some useful documentation. This cannot be stressed enough. With-
out documentation, you will only become frustrated at your inability to get your Red Hat Linux system
working the way you want.
You should acquire the following types of Linux documentation:
•A brief history of Linux — Many aspects of Linux are the way they are because of historical prece-
dent. The Linux culture is also based on past events, needs or requirements. A basic understanding
of the history of Linux will help you figure out how to solve many potential problems before you
actually see them.
•An explanation of how Linux works — While delving into the most arcane aspects of the Linux
kernel is not necessary, it is a good idea to know something about how Linux is put together. This
is particularly important if you have been working with other operating systems, as some of the
assumptions you currently hold about how computers work may not transfer from that operating
system to Linux.
•An introductory command overview (with examples) — This is probably the most important thing
to look for in Linux documentation. The underlying design philosophy for Linux is that it’s better
to use many small commands connected together in different ways than it is to have a few large
(and complex) commands that do the whole job themselves. Without examples that illustrate this