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Red Hat Enterprise Linux 9 Essentials Book now available.

Purchase a copy of Red Hat Enterprise Linux 9 (RHEL 9) Essentials

Red Hat Enterprise Linux 9 Essentials Print and eBook (PDF) editions contain 34 chapters and 298 pages

Preview Book

Red Hat Enterprise Linux 6

Security Guide

A Guide to Securing Red Hat Enterprise Linux

Edition 1.5


Red Hat Engineering Content Services

Legal Notice

Copyright © 2010 Red Hat, Inc.
The text of and illustrations in this document are licensed by Red Hat under a Creative Commons Attribution–Share Alike 3.0 Unported license ("CC-BY-SA"). An explanation of CC-BY-SA is available at In accordance with CC-BY-SA, if you distribute this document or an adaptation of it, you must provide the URL for the original version.
Red Hat, as the licensor of this document, waives the right to enforce, and agrees not to assert, Section 4d of CC-BY-SA to the fullest extent permitted by applicable law.
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The Red Hat Enterprise Linux Security Guide is designed to assist users and administrators in learning the processes and practices of securing workstations and servers against local and remote intrusion, exploitation and malicious activity.
Focused on Red Hat Enterprise Linux but detailing concepts and techniques valid for all Linux systems, this guide details the planning and the tools involved in creating a secured computing environment for the data center, workplace, and home.
With proper administrative knowledge, vigilance, and tools, systems running Linux can be both fully functional and secured from most common intrusion and exploit methods.

1. Document Conventions
1.1. Typographic Conventions
1.2. Pull-quote Conventions
1.3. Notes and Warnings
2. We Need Feedback!
1. Security Overview
1.1. Introduction to Security
1.1.1. What is Computer Security?
1.1.2. SELinux
1.1.3. Security Controls
1.1.4. Conclusion
1.2. Vulnerability Assessment
1.2.1. Thinking Like the Enemy
1.2.2. Defining Assessment and Testing
1.2.3. Evaluating the Tools
1.3. Attackers and Vulnerabilities
1.3.1. A Quick History of Hackers
1.3.2. Threats to Network Security
1.3.3. Threats to Server Security
1.3.4. Threats to Workstation and Home PC Security
1.4. Common Exploits and Attacks
1.5. Security Updates
1.5.1. Updating Packages
1.5.2. Verifying Signed Packages
1.5.3. Installing Signed Packages
1.5.4. Applying the Changes
2. Securing Your Network
2.1. Workstation Security
2.1.1. Evaluating Workstation Security
2.1.2. BIOS and Boot Loader Security
2.1.3. Password Security
2.1.4. Administrative Controls
2.1.5. Available Network Services
2.1.6. Personal Firewalls
2.1.7. Security Enhanced Communication Tools
2.2. Server Security
2.2.1. Securing Services With TCP Wrappers and xinetd
2.2.2. Securing Portmap
2.2.3. Securing NIS
2.2.4. Securing NFS
2.2.5. Securing the Apache HTTP Server
2.2.6. Securing FTP
2.2.7. Securing Sendmail
2.2.8. Verifying Which Ports Are Listening
2.3. TCP Wrappers and xinetd
2.3.1. TCP Wrappers
2.3.2. TCP Wrappers Configuration Files
2.3.3. xinetd
2.3.4. xinetd Configuration Files
2.3.5. Additional Resources
2.4. Virtual Private Networks (VPNs)
2.4.1. How Does a VPN Work?
2.4.2. Openswan
2.5. Firewalls
2.5.1. Netfilter and IPTables
2.5.2. Basic Firewall Configuration
2.5.3. Using IPTables
2.5.4. Common IPTables Filtering
2.5.5. FORWARD and NAT Rules
2.5.6. Malicious Software and Spoofed IP Addresses
2.5.7. IPTables and Connection Tracking
2.5.8. IPv6
2.5.9. Additional Resources
2.6. IPTables
2.6.1. Packet Filtering
2.6.2. Command Options for IPTables
2.6.3. Saving IPTables Rules
2.6.4. IPTables Control Scripts
2.6.5. IPTables and IPv6
2.6.6. Additional Resources
3. Encryption
3.1. Data at Rest
3.2. Full Disk Encryption
3.3. File Based Encryption
3.4. Data in Motion
3.5. Virtual Private Networks
3.6. Secure Shell
3.7. OpenSSL PadLock Engine
3.8. LUKS Disk Encryption
3.8.1. LUKS Implementation in Red Hat Enterprise Linux
3.8.2. Manually Encrypting Directories
3.8.3. Step-by-Step Instructions
3.8.4. What you have just accomplished.
3.8.5. Links of Interest
3.9. Using GNU Privacy Guard (GnuPG)
3.9.1. Creating GPG Keys in GNOME
3.9.2. Creating GPG Keys in KDE
3.9.3. Creating GPG Keys Using the Command Line
3.9.4. About Public Key Encryption
4. General Principles of Information Security
4.1. Tips, Guides, and Tools
5. Secure Installation
5.1. Disk Partitions
5.2. Utilize LUKS Partition Encryption
6. Software Maintenance
6.1. Install Minimal Software
6.2. Plan and Configure Security Updates
6.3. Adjusting Automatic Updates
6.4. Install Signed Packages from Well Known Repositories
7. Federal Standards and Regulations
7.1. Introduction
7.2. Federal Information Processing Standard (FIPS)
7.3. National Industrial Security Program Operating Manual (NISPOM)
7.4. Payment Card Industry Data Security Standard (PCI DSS)
7.5. Security Technical Implementation Guide
8. References
A. Encryption Standards
A.1. Synchronous Encryption
A.1.1. Advanced Encryption Standard - AES
A.1.2. Data Encryption Standard - DES
A.2. Public-key Encryption
A.2.1. Diffie-Hellman
A.2.2. RSA
A.2.3. DSA
A.2.4. SSL/TLS
A.2.5. Cramer-Shoup Cryptosystem
A.2.6. ElGamal Encryption
B. Revision History

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