Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION... Manuale utente

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

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

iii

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

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

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

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

vii

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

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