UNIX Administration A Comprehensive Sourcebook for Effective Systems and Network Management

Contents

Section I UNIX Administration
1 UNIX — Introductory Notes
1.1 UNIX Operating System
1.2 User’s View of UNIX
1.3 The History of UNIX
1.3.1 Berkeley Standard Distribution — BSD UNIX
1.3.2 System V or ATT UNIX
1.4 UNIX System and Network Administration
1.4.1 System Administrator’s Job
1.4.2 Computing Policies
1.4.3 Administration Guidelines
1.4.3.1 Legal Acts
1.4.3.2 Code of Ethics
1.4.3.3 Organizations
1.4.3.4 Standardization
1.4.4 In This Book

2 The UNIX Model — Selected Topics
2.1 Introduction
2.2 Files
2.2.1 File Ownership
2.2.2 File Protection/File Access
2.2.2.1 Access Classes
2.2.2.2 Setting a File Protection
2.2.2.3 Default File Mode
2.2.2.4 Additional Access Modes
2.2.3 Access Control Lists (ACLs)
2.2.4 File Types
2.2.4.1 Plain (Regular) File
2.2.4.2 Directory
2.2.4.3 Special Device File
2.2.4.4 Link
2.2.4.5 Socket
2.2.4.6 Named Pipe
2.2.4.7 Conclusion
2.3 Devices and Special Device Files
2.3.1 Special File Names
2.3.2 Special File Creation
2.4 Processes
2.4.1 Process Parameters
2.4.1.1 Process Types
2.4.1.2 Process Attributes
2.4.1.3 File Descriptors
2.4.1.4 Process States
2.4.2 Process Life Cycles
2.4.2.1 Process Creation
2.4.2.2 Process Termination
2.4.3 Process Handling
2.4.3.1 Monitoring Process Activities
2.4.3.2 Destroying Processes
2.4.3.3 Job Control

3 UNIX Administration Starters
3.1 Superuser and Users
3.1.1 Becoming a Superuser
3.1.2 Communicating with Other Users
3.1.3 The su Command
3.2 UNIX Online Documentation
3.2.1 The man Command
3.2.2 The whatis Database
3.3 System Information
3.3.1 System Status Information
3.3.1.1 The uname Command
3.3.1.2 The uptime Command
3.3.1.3 The dmesg Command
3.3.2 Hardware Information
3.3.2.1 The HP-UX ioscan Command
3.3.2.2 The Solaris prtconf Command
3.3.2.3 The Solaris sysdef Command
3.4 Personal Documentation
3.5 Shell Script Programming
3.5.1 UNIX User Shell
3.5.2 UNIX Shell Scripts
3.5.2.1 Shell Script Execution
3.5.2.2 Shell Variables
3.5.2.3 Double Command-Line Scanning
3.5.2.4 Here Document
3.5.2.5 Few Tips

4 System Startup and Shutdown
4.1 Introductory Notes
4.2 System Startup
4.2.1 The Bootstrap Program
4.2.2 The Kernel Execution
4.2.3 The Overall System Initialization
4.2.3.1 rc Initialization Scripts
4.2.3.2 Terminal Line Initialization
4.2.4 System States
4.2.5 The Outlook of a Startup Procedure
4.2.6 Initialization Scripts
4.3 BSD Initialization
4.3.1 The BSD rc Scripts
4.3.2 BSD Initialization Sequence
4.4 System V Initialization
4.4.1 The Configuration File /etc/inittab
4.4.2 System V rc Initialization Scripts
4.4.3 BSD-Like Initialization
4.5 Shutdown Procedures
4.5.1 The BSD shutdown Command
4.5.2 The System V shutdown Command
4.5.3 An Example

5 UNIX Filesystem Management
5.1 Introduction to the UNIX Filesystem
5.2 UNIX Filesystem Directory Organization
5.2.1 BSD Filesystem Directory Organization
5.2.2 System V Filesystem Directory Organization
5.3 Mounting and Dismounting Filesystems
5.3.1 Mounting a Filesystem
5.3.1.1 The mount Command
5.3.2 Dismounting a Filesystem
5.3.3 Automatic Filesystem Mounting
5.3.4 Removable Media Management
5.4 Filesystem Configuration
5.4.1 BSD Filesystem Configuration File
5.4.2 System V Filesystem Configuration File
5.4.3 AIX Filesystem Configuration File
5.4.4 The Filesystem Status File
5.5 A Few Other Filesystem Issues
5.5.1 Filesystem Types
5.5.2 Swap Space — Paging and Swapping
5.5.3 Loopback Virtual Filesystem
5.6 Managing Filesystem Usage
5.6.1 Display Filesystem Statistics: The df Command
5.6.2 Report on Disk Usage: The du Command
5.6.3 Report on Disk Usage by Users: The quot Command
5.6.4 Checking Filesystems: The fsck Command

6 UNIX Filesystem Layout
6.1 Introduction
6.2 Physical Filesystem Layout
6.2.1 Disk Partitions
6.2.2 Filesystem Structures
6.2.3 Filesystem Creation
6.2.3.1 The mkfs Command
6.2.3.2 The newfs Command
6.2.3.3 The tunefs Command
6.2.4 File Identification and Allocation
6.2.4.1 Index Node (inode)
6.2.4.2 File Allocation
6.2.5 Filesystem Performance Issues
6.2.5.1 File Storage vs. File Transfer
6.2.5.2 Reserved Free Space
6.3 Logical Filesystem Layout
6.3.1 Logical Volume Manager — AIX Flavor
6.3.2 Logical Volume Manager — HP-UX Flavor
6.3.3 Logical Volume Manager — Solaris Flavor
6.3.4 Redundant Array of Inexpensive Disks (RAID)
6.3.5 Snapshot
6.3.5.1 The Volume Snapshot
6.3.5.2 The Filesystem Snapshot
6.3.6 Virtual UNIX Filesystem
6.4 Disk Space Upgrade

7 User Account Management
7.1 Users and Groups
7.1.1 Creation of User Accounts
7.1.2 User Database — File /etc/passwd
7.1.3 Group Database — File /etc/group
7.1.4 Creating User Home Directories
7.1.5 UNIX Login Initialization
7.1.5.1 Intialization Template Files
7.1.5.2 User Login Initialization Files
7.1.5.3 Systemwide Login Initialization Files
7.1.5.4 Shell Initialization Files
7.1.5.5 Setting the Proper Ownership
7.1.6 Utilities to Create User Accounts
7.2 Maintenance of User Accounts
7.2.1 Restricted User Accounts
7.2.2 Users and Secondary Groups
7.2.3 Assigning User Passwords
7.2.4 Standard UNIX Users and Groups
7.2.5 Removing User Accounts
7.3 Disk Quotas
7.3.1 Managing Disk Usage by Users
7.4 Accounting
7.4.1 BSD Accounting
7.4.2 System V Accounting
7.4.3 AIX-Flavored Accounting

8 UNIX System Security
8.1 UNIX Lines of Defense
8.1.1 Physical Security
8.1.2 Passwords
8.1.3 File Permissions
8.1.4 Encryption
8.1.5 Backups
8.2 Password Issues
8.2.1 Password Encryption
8.2.2 Choosing a Password
8.2.3 Setting Password Restrictions
8.2.4 A Shadowed Password
8.2.4.1 Usual Approach
8.2.4.2 Other Approaches
8.3 Secure Console and Terminals
8.3.1 Traditional BSD Approach
8.3.2 The Wheel Group
8.3.3 Secure Terminals — Other Approaches
8.4 Monitoring and Detecting Security Problems
8.4.1 Important Files for System Security
8.4.2 Monitoring System Activities
8.4.3 Monitoring Login Attempts
8.4.3.1 The su Log File
8.4.3.2 History of the Root Account
8.4.3.3 Tracking User Activities

And Many More 

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Dictionary of Networking

Introduction

Networks are currently one of the fastest growing and most important developments in
the computer industry. Not only are more and more PCs becoming parts of networks, but
networked PCs are being incorporated into larger enterprise-wide applications so that everyone
in a company can access and share data.
With the expanding technology of networking comes the terminology to describe it.
This
Dictionary of Networking
provides definitions for all the terms you will encounter
when dealing with networks of any type.

Who Should Use This Book?

This book is designed to meet the needs of people who work with networks, communications,
and mobile computing systems. Whether you are networking previously unconnected
computers or downsizing from a mainframe, this book is for you. And if you are
studying for one of the network certification exams, you will find this book to be an essential
reference.
Network users of all levels are barraged with an almost bewildering array of terms, abbreviations,
and acronyms in books, magazine and newspaper articles, advertisements,
and their day-to-day conversations. Jargon is a useful shorthand, but it can easily become
incomprehensible and unmanageable, even to the most seasoned network administrator.

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Linux Network Administrators Guide

2. Sources of Information...................................................................................................................................2
2.1. Documentation Available via FTP....................................................................................................3
2.2. Documentation Available via WWW...............................................................................................3
2.3. Documentation Available Commercially.........................................................................................3
2.4. Linux Journal and Linux Magazine..................................................................................................4
2.5. Linux Usenet Newsgroups................................................................................................................4
2.6. Linux Mailing Lists..........................................................................................................................5
2.7. Online Linux Support.......................................................................................................................6
2.8. Linux User Groups............................................................................................................................6
2.9. Obtaining Linux................................................................................................................................7
3. File System Standards........................................................................................9
4. Standard Linux Base...............................................................................................10
5. About This Book.................................................................................................11
6. The Official Printed Version................................................................................................13
7. Overview..........................................................................................................................15
8. Conventions Used in This Book...................................................................................................................17
9. Submitting Changes......................................................................................................................................18
10. Acknowledgments..........................................................................................................19
10.1. The Hall of Fame................................................................................................19
Chapter 1. Introduction to Networking..........................................................................................................21
1.1. History........................................................................................................................22
1.2. TCP/IP Networks.................................................................................................23
1.2.1. Introduction to TCP/IP Networks................................................................................23
1.2.2. Ethernets................................................................................................................24
1.2.3. Other Types of Hardware.............................................................................................25
1.2.4. The Internet Protocol......................................................................................................27
1.2.5. IP Over Serial Lines........................................................................................................28
1.2.6. The Transmission Control Protocol.....................................................................................28
1.2.7. The User Datagram Protocol........................................................................................29
1.2.8. More on Ports...................................................................................................................29
1.2.9. The Socket Library....................................................................................................30
1.3. UUCP Networks.....................................................................................................31
1.4. Linux Networking......................................................................................................................................32

And Many More . . . .
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Network Security using Linux

Table of Contents

Network Security using Linux.........................................................
Credits.............................................................................................X
Preface............................................................................................xii
Who is this book for?......................................................................................xiii
How the book was written..............................................................................xiii

Chapter 1..........................................................................................1
TCP/IP Fundamentals.........................................................................................1
Layers.................................................................................................................2
TCP/IP Addressing.............................................................................................3
Subnetting with CIDR...................................................................................6
Subnetting with VLSM..................................................................................7
TCP/IP Version 6...............................................................................................8
IPv6 and the Kernel.....................................................................................11
Constructing Packets........................................................................................14
TCP Communication........................................................................................16
Any port will do...........................................................................................18
What does a router really do?...........................................................................18
Open Source Linux Routers........................................................................20
Is a Linux router secure?..................................................................................22
Shutting off the unwanted services.............................................................22

Chapter 2........................................................................................24
Firewalling the Network...................................................................................24
Isn’t a router a firewall?...................................................................................26
IP v6 and IPTables...........................................................................................28
Patch-O-Matic.............................................................................................29
Firewalling 101................................................................................................31
Papers Please....................................................................................................34
The Penguin Builds a Wall...............................................................................34
TOC p:v
Bastille Linux...................................................................................................36
Free is good......................................................................................................37
IPCOP..........................................................................................................38
Firestarter.....................................................................................................40
Shorewall.....................................................................................................41
Web Based Tools.........................................................................................43
Commercial Firewalls......................................................................................44
Astaro..........................................................................................................44
Smoothwall..................................................................................................46
Gibraltar.......................................................................................................47
Resources.....................................................................................................50

Chapter 3........................................................................................52
IP Tables, Rules and Filters..............................................................................52
Chain Syntax...........................................................................................53
Rules.......................................................................................................53
Building of a Basic Rule..............................................................................54
Demonstrating rules................................................................................55
Advanced Rules...........................................................................................56
Matching Connection States...................................................................56
Configuring NAT...................................................................................57
Defending Against Basic Attacks ..........................................................59
Examing The Rules ................................................................................60
Strengthen Your Rules with ROPE .......................................................60
Your Basic Firewall.....................................................................................62
Firewall Testing...........................................................................................63
Firewall Script........................................................................................65
Resources.....................................................................................................72

Chapter 4........................................................................................73
Updating Linux................................................................................................73
RPMs................................................................................................................73
Red Hat Up2date..............................................................................................81
TOC p:vi
YUM.................................................................................................................84
APT..................................................................................................................86
What is a kernel update?..................................................................................87
How do I tell which kernel I have installed?...................................................88
How do I update the kernel?............................................................................88
Alternative Security Kernels............................................................................90
Keeping the LID on.....................................................................................91
Resources.....................................................................................................92

Chapter 5........................................................................................93
Encryption or protecting your Data..................................................................93
What is encryption?..........................................................................................93
What is this alphabet soup?..............................................................................94
How does encryption work?............................................................................95
What are keys all about?..................................................................................96
Why do I need encryption?..............................................................................98
How do I use GPG?..........................................................................................98
Managing keys...........................................................................................106
Revoking a Key....................................................................................106
Key Signing Parties..............................................................................107
Additional Notes About GnuPG................................................................108
Securing Data with SSH.................................................................................109
What is OpenSSH?.........................................................................................109
The basics of SSH..........................................................................................111
What else can SSH do?.............................................................................112
SSH Port Forwarding ...............................................................................115
What is a X.509 Certificate?..........................................................................118
Make Your Own Certificates.....................................................................118
Are You Certified?....................................................................................119
How to use the Certificate.........................................................................125
Secure Socket Layer.......................................................................................128
SSL and Apache.............................................................................................128
TOC p:vii
Resources...................................................................................................129

Chapter 6......................................................................................130
Detecting Intruders.........................................................................................130
Deploying an IDS...........................................................................................131
What is Snort..................................................................................................132
Building a Sensor...........................................................................................133
Secure Communications.................................................................................138
Making the Pig Fly.........................................................................................139
Installing MySQL......................................................................................139
Installing Snort..........................................................................................144
Snort Configuration...................................................................................146
Syslog Notes..............................................................................................147
Configuring Snort’s New Database...........................................................149
Starting the Pig..........................................................................................152
Apache.......................................................................................................153
Installing PHP............................................................................................154
Snort on ACID...........................................................................................156
Securing the Pig.........................................................................................160
Multiple NIC cards...............................................................................161
Rules? What Rules?.......................................................................................162
Updating the Rules...............................................................................166
Deploying Snort.............................................................................................167
Tapping the network..................................................................................168
Where to place Snort.................................................................................171
Managing Snort..............................................................................................171
Webmin.....................................................................................................171
Snort Center...............................................................................................173
Resources:..................................................................................................173

Chapter 7......................................................................................174
Virtual Private Networks................................................................................174
IPsec...........................................................................................................174
TOC p:viii
L2TP..........................................................................................................176
PPTP..........................................................................................................177
VPN Utilities..................................................................................................177
PPTP Client...............................................................................................177
OpenSwan..................................................................................................181
Installing and Configuring Openswan.......................................................183
Certificates and Keys............................................................................184
Configuration........................................................................................186
Resources...................................................................................................188

Chapter 8......................................................................................190
Logging for Fun and Profit............................................................................190
NTP for Linux...........................................................................................192
Monitoring and Analyzing the Logs.........................................................195
What to Look for..................................................................................202
Tuning Syslog.......................................................................................202
Rotating Logs........................................................................................204
Syslog Improved...................................................................................206
Securing Syslog Traffic........................................................................208
Windows to Syslog Converters............................................................208
Configuration Guides...........................................................................208
Sawmill.................................................................................................209
Logwatch..............................................................................................211
Swatch...................................................................................................213
LogSurfer..............................................................................................216
Nagios...................................................................................................217
Resources...................................................................................................219

Chapter 9......................................................................................220
Summary........................................................................................................220
Appendix 1...................................................................................223
INDEX..........................................................................................226

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A Beginner’s Guide to Network Security

An Introduction to the Key Security Issues for the E-Business Economy
With the explosion of the public Internet and e-commerce, private computers, and computer networks, if not
adequately secured, are increasingly vulnerable to damaging attacks. Hackers, viruses, vindictive employees
and even human error all represent clear and present dangers to networks. And all computer users, from the
most casual Internet surfers to large enterprises, could be affected by network security breaches. However,
security breaches can often be easily prevented. How? This guide provides you with a general overview of the
most common network security threats and the steps you and your organization can take to protect
yourselves from threats and ensure that the data traveling across your networks is safe.

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