GL550 - Enterprise Linux Security Administration

This course offers an extensive exploration into the security features and protocols necessary for maintaining robust security on Enterprise Linux systems. Designed for system administrators, security professionals, and IT personnel responsible for Linux systems, the course covers a variety of topics aimed at enhancing the security infrastructure of organizations.

The course begins with fundamental security concepts where participants learn about essential security principles such as minimization, hardening, and simplification of systems. It progresses through detailed explanations of tools and methods for scanning, probing, and mapping vulnerabilities, thus equipping attendees with the skills needed to identify and mitigate potential security threats. Each module is structured to provide both theoretical knowledge and practical skills through hands-on labs, ensuring that participants can apply what they've learned in real-world scenarios.

In more advanced sections, the course delves into specific security protocols and configurations, such as Kerberos for secure network authentication and SELinux for enforcing security policies. These modules are particularly crucial as they address complex security challenges and provide the tools to configure, manage, and troubleshoot advanced security settings on Linux systems. Through structured labs and detailed guides, participants gain proficiency in securing file systems, managing user authentication, and securing network services like Apache and PostgreSQL, all within the security frameworks provided by Enterprise Linux environments.


  1. System Administrators: Individuals responsible for the daily management of Linux-based servers and systems, who need to ensure these are secure from unauthorized access and vulnerabilities.
  2. Security Professionals: Those specializing in cybersecurity who are looking to deepen their understanding of security practices specifically tailored to Linux environments.
  3. IT Professionals: General IT staff who require a comprehensive knowledge of Linux security to support and safeguard their organization's technology infrastructure.
  4. Network Administrators: Professionals in charge of managing and securing network communications and services on Linux systems.
  5. Technical Support Staff: Support personnel who need to understand security configurations and vulnerabilities to effectively troubleshoot and maintain Linux systems within their organizations.


  1. Enhanced Security Skills: Participants will gain a deep understanding of the latest security protocols and techniques for securing Linux systems. This knowledge is crucial for protecting organizational infrastructure from potential threats and vulnerabilities.
  2. Hands-on Experience: The course includes practical labs that provide hands-on experience with real-world security scenarios. This experiential learning helps solidify theoretical knowledge and builds confidence in handling security tasks on Linux systems.
  3. Advanced Tools and Technologies: Attendees will learn to use advanced tools and technologies such as SELinux, Kerberos, and various network security measures. Mastery of these tools is vital for administering secure and robust Linux environments.
  4. Professional Development: Completing the course can significantly enhance a professional's credentials and expertise in Linux security, making them more valuable to current or prospective employers and potentially opening up new career opportunities.
  5. Network Security Management: The course covers critical aspects of network security management, including securing network services and protocols. This is essential for ensuring that all communication within the network is safeguarded against unauthorized access and data breaches.

Current Version: F05


This class covers advanced security topics and is intended for experienced systems administrators. Candidates should have current Linux or UNIX systems administration experience equivalent to the GL120 "Linux Fundamentals", GL250 "Enterprise Linux Systems Administration", and GL275 "Enterprise Linux Network Services"

Supported Distributions:
Red Hat Enterprise Linux 7
SUSE Linux Enterprise 12
Course Outline:
  1. Security Concepts
    1. Basic Security Principles
    2. RHEL7 Default Install
    3. RHEL7 Firewall
    4. SLES12 Default Install
    5. SUSE Basic Firewall Configuration
    6. SLES12: File Security
    7. Minimization – Discovery
    8. Service Discovery
    9. Hardening
    10. Security Concepts
    Lab Tasks
    1. Removing Packages Using RPM
    2. Firewall Configuration
    3. Process Discovery
    4. Operation of the setuid() and capset() System Calls
    5. Operation of the chroot() System Call
  2. Scanning, Probing, and Mapping Vulnerabilities
    1. The Security Environment
    2. Stealth Reconnaissance
    3. The WHOIS database
    4. Interrogating DNS
    5. Discovering Hosts
    6. Discovering Reachable Services
    7. Reconnaissance with SNMP
    8. Discovery of RPC Services
    9. Enumerating NFS Shares
    10. Nessus/OpenVAS Insecurity Scanner
    11. Configuring OpenVAS
    12. Intrusion Detection Systems
    13. Snort Rules
    14. Writing Snort Rules
    Lab Tasks
    1. NMAP
    2. OpenVAS
    3. Advanced nmap Options
  3. Password Security and PAM
    1. Unix Passwords
    2. Password Aging
    3. Auditing Passwords
    4. PAM Overview
    5. PAM Module Types
    6. PAM Order of Processing
    7. PAM Control Statements
    8. PAM Modules
    9. pam_unix
    Lab Tasks
    1. John the Ripper
    2. Cracklib
    3. Using pam_listfile to Implement Arbitrary ACLs
    4. Using pam_limits to Restrict Simultaneous Logins
    5. Using pam_nologin to Restrict Logins
    6. Using pam_access to Restrict Logins
    7. su & pam
  4. Secure Network Time Protocol (NTP)
    1. The Importance of Time
    2. Hardware and System Clock
    3. Time Measurements
    4. NTP Terms and Definitions
    5. Synchronization Methods
    6. NTP Evolution
    7. Time Server Hierarchy
    8. Operational Modes
    9. NTP Clients
    10. Configuring NTP Clients
    11. Configuring NTP Servers
    12. Securing NTP
    13. NTP Packet Integrity
    14. Useful NTP Commands
    Lab Tasks
    1. Configuring and Securing NTP
    2. Peering NTP with Multiple Systems
  5. Kerberos Concepts and Components
    1. Common Security Problems
    2. Account Proliferation
    3. The Kerberos Solution
    4. Kerberos History
    5. Kerberos Implementations
    6. Kerberos Concepts
    7. Kerberos Principals
    8. Kerberos Safeguards
    9. Kerberos Components
    10. Authentication Process
    11. Identification Types
    12. Logging In
    13. Gaining Privileges
    14. Using Privileges
    15. Kerberos Components and the KDC
    16. Kerberized Services Review
    17. KDC Server Daemons
    18. Configuration Files
    19. Utilities Overview
  6. Implementing Kerberos
    1. Plan Topology and Implementation
    2. Kerberos 5 Client Software
    3. Kerberos 5 Server Software
    4. Synchronize Clocks
    5. Create Master KDC
    6. Configuring the Master KDC
    7. KDC Logging
    8. Kerberos Realm Defaults
    9. Specifying [realms]
    10. Specifying [domain_realm]
    11. Allow Administrative Access
    12. Create KDC Databases
    13. Create Administrators
    14. Install Keys for Services
    15. Start Services
    16. Add Host Principals
    17. Add Common Service Principals
    18. Configure Slave KDCs
    19. Create Principals for Slaves
    20. Define Slaves as KDCs
    21. Copy Configuration to Slaves
    22. Install Principals on Slaves
    23. Synchronization of Database
    24. Propagate Data to Slaves
    25. Create Stash on Slaves
    26. Start Slave Daemons
    27. Client Configuration
    28. Install krb5.conf on Clients
    29. Client PAM Configuration
    30. Install Client Host Keys
    Lab Tasks
    1. Implementing Kerberos
  7. Administering and Using Kerberos
    1. Administrative Tasks
    2. Key Tables
    3. Managing Keytabs
    4. Managing Principals
    5. Viewing Principals
    6. Adding, Deleting, and Modifying Principals
    7. Principal Policy
    8. Overall Goals for Users
    9. Signing In to Kerberos
    10. Ticket types
    11. Viewing Tickets
    12. Removing Tickets
    13. Passwords
    14. Changing Passwords
    15. Giving Others Access
    16. Using Kerberized Services
    17. Kerberized FTP
    18. Enabling Kerberized Services
    19. OpenSSH and Kerberos
    Lab Tasks
    1. Using Kerberized Clients
    2. Forwarding Kerberos Tickets
    3. OpenSSH with Kerberos
    4. Wireshark and Kerberos
  8. Securing the Filesystem
    1. Filesystem Mount Options
    2. NFS Properties
    3. NFS Export Option
    4. NFSv4 and GSSAPI Auth
    5. Implementing NFSv4
    6. Implementing Kerberos with NFS
    7. GPG – GNU Privacy Guard
    8. File Encryption with OpenSSL
    9. File Encryption With encfs
    10. Linux Unified Key Setup (LUKS)
    Lab Tasks
    1. Securing Filesystems
    2. Securing NFS
    3. Implementing NFSv4
    4. File Encryption with GPG
    5. File Encryption With OpenSSL
    6. LUKS-on-disk format Encrypted Filesystem
  9. AIDE
    1. Host Intrusion Detection Systems
    2. Using RPM as a HIDS
    3. Introduction to AIDE
    4. AIDE Installation
    5. AIDE Policies
    6. AIDE Usage
    Lab Tasks
    1. File Integrity Checking with RPM
    2. File Integrity Checking with AIDE
  10. Accountability with Kernel Auditd
    1. Accountability and Auditing
    2. Simple Session Auditing
    3. Simple Process Accounting & Command History
    4. Kernel-Level Auditing
    5. Configuring the Audit Daemon
    6. Controlling Kernel Audit System
    7. Creating Audit Rules
    8. Searching Audit Logs
    9. Generating Audit Log Reports
    10. Audit Log Analysis
    Lab Tasks
    1. Auditing Login/Logout
    2. Auditing File Access
    3. Auditing Command Execution
  11. SELinux
    1. DAC vs. MAC
    2. Shortcomings of Traditional Unix Security
    3. AppArmor
    4. SELinux Goals
    5. SELinux Evolution
    6. SELinux Modes
    7. Gathering SELinux Information
    8. SELinux Virtual Filesystem
    9. SELinux Contexts
    10. Managing Contexts
    11. The SELinux Policy
    12. Choosing an SELinux Policy
    13. Policy Layout
    14. Tuning and Adapting Policy
    15. Booleans
    16. Permissive Domains
    17. Managing File Context Database
    18. Managing Port Contexts
    19. SELinux Policy Tools
    20. Examining Policy
    21. SELinux Troubleshooting
    22. SELinux Troubleshooting Continued
    Lab Tasks
    1. Exploring SELinux Modes
    2. Exploring AppArmor Modes
    3. SELinux Contexts in Action
    4. Exploring AppArmor
    5. Managing SELinux Booleans
    6. Creating Policy with Audit2allow
    7. Creating & Compiling Policy from Source
  12. Securing Apache
    1. Apache Overview
    2. httpd.conf – Server Settings
    3. Configuring CGI
    4. Turning Off Unneeded Modules
    5. Delegating Administration
    6. Apache Access Controls (mod_access)
    7. HTTP User Authentication
    8. Standard Auth Modules
    9. HTTP Digest Authentication
    10. TLS Using
    11. Authentication via SQL
    12. Authentication via LDAP
    13. Authentication via Kerberos
    14. Scrubbing HTTP Headers
    15. Metering HTTP Bandwidth
    Lab Tasks
    1. Hardening Apache by Minimizing Loaded Modules
    2. Scrubbing Apache & PHP Version Headers
    3. Protecting Web Content
    4. Protecting Web Content
    5. Using the suexec Mechanism
    6. Create a TLS CA key pair
    7. Using SSL CA Certificates with Apache
    8. Enable Apache SSL Client Certificate Authentication
    9. Enabling SSO in Apache with mod_auth_kerb
  13. Securing PostgreSQL
    1. PostgreSQL Overview
    2. PostgreSQL Default Config
    3. Configuring TLS
    4. Client Authentication Basics
    5. Advanced Authentication
    6. Ident-based Authentication
    Lab Tasks
    1. Configure PostgreSQL
    2. PostgreSQL with TLS
    3. PostgreSQL with Kerberos Authentication
    4. Securing PostgreSQL with Web Based Applications
  1. Securing Email Systems
    1. SMTP Implementations
    2. Security Considerations
    3. chrooting Postfix
    4. Email with GSSAPI/Kerberos Auth
    Lab Tasks
    1. Postfix In a Change Root Environment
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