Linux Security

  1. User and Group Management
    1. User Account Administration
      1. Creating Users
        1. useradd Command
          1. Default Settings Configuration
            1. Customizing User Creation
              1. Home Directory Setup
                1. Shell Assignment
                2. Modifying Users
                  1. usermod Command
                    1. Changing User Information
                      1. Managing User Groups
                        1. Account Status Management
                          1. Locking and Unlocking Accounts
                          2. Deleting Users
                            1. userdel Command
                              1. Removing User Files
                                1. Handling Orphaned Files
                                  1. Backup Considerations
                                  2. User Account Files
                                    1. /etc/passwd Structure
                                      1. /etc/shadow Structure
                                        1. Password Field Formats
                                          1. Security of Account Files
                                            1. File Permissions and Ownership
                                            2. User Environment Security
                                              1. Shell Configuration Files
                                                1. Environment Variable Security
                                                  1. PATH Security
                                                    1. Startup Script Security
                                                  2. Group Account Administration
                                                    1. Creating Groups
                                                      1. groupadd Command
                                                        1. Primary vs Secondary Groups
                                                          1. Group ID Assignment
                                                          2. Modifying Groups
                                                            1. groupmod Command
                                                              1. Renaming Groups
                                                                1. Changing Group IDs
                                                                  1. Group Membership Management
                                                                  2. Deleting Groups
                                                                    1. groupdel Command
                                                                      1. Impact on User Accounts
                                                                        1. File Ownership Considerations
                                                                        2. Group Files
                                                                          1. /etc/group Structure
                                                                            1. /etc/gshadow Structure
                                                                              1. Group Password Security
                                                                            2. Password Security
                                                                              1. Password Policies
                                                                                1. chage Command
                                                                                  1. Minimum and Maximum Age
                                                                                    1. Expiration Warnings
                                                                                      1. Forced Password Changes
                                                                                        1. Account Expiration
                                                                                        2. Password Hashing
                                                                                          1. DES Algorithm
                                                                                            1. MD5 Algorithm
                                                                                              1. SHA-256 Algorithm
                                                                                                1. SHA-512 Algorithm
                                                                                                  1. bcrypt Algorithm
                                                                                                    1. scrypt Algorithm
                                                                                                      1. Argon2 Algorithm
                                                                                                      2. Password Strength Enforcement
                                                                                                        1. Complexity Requirements
                                                                                                          1. Dictionary Attack Prevention
                                                                                                            1. Password History
                                                                                                              1. Reuse Prevention
                                                                                                                1. Account Lockout Policies
                                                                                                                2. Password Storage Security
                                                                                                                  1. Shadow File Protection
                                                                                                                    1. Hash Salt Usage
                                                                                                                      1. Timing Attack Prevention
                                                                                                                    2. Privileged Access Management
                                                                                                                      1. Root User Security
                                                                                                                        1. Risks of Root Access
                                                                                                                          1. Limiting Root Login
                                                                                                                            1. Root Password Management
                                                                                                                              1. Emergency Access Procedures
                                                                                                                              2. User Switching
                                                                                                                                1. su Command
                                                                                                                                  1. Security Implications
                                                                                                                                    1. Configuration Options
                                                                                                                                      1. Logging and Auditing
                                                                                                                                      2. Sudo Configuration
                                                                                                                                        1. sudo Command Usage
                                                                                                                                          1. Sudoers File Syntax
                                                                                                                                            1. User and Group Specifications
                                                                                                                                              1. Command Restrictions
                                                                                                                                                1. Environment Control
                                                                                                                                                  1. Logging Configuration
                                                                                                                                                  2. Advanced Sudo Features
                                                                                                                                                    1. User Aliases
                                                                                                                                                      1. Group Aliases
                                                                                                                                                        1. Command Aliases
                                                                                                                                                          1. Host Aliases
                                                                                                                                                            1. Defaults Configuration
                                                                                                                                                              1. Timestamp Management
                                                                                                                                                            2. Pluggable Authentication Modules (PAM)
                                                                                                                                                              1. PAM Architecture
                                                                                                                                                                1. Module Types
                                                                                                                                                                  1. Control Flags
                                                                                                                                                                    1. Stacking Behavior
                                                                                                                                                                      1. Return Value Handling
                                                                                                                                                                      2. PAM Configuration
                                                                                                                                                                        1. /etc/pam.d/ Directory
                                                                                                                                                                          1. Service Configuration Files
                                                                                                                                                                            1. Module Arguments
                                                                                                                                                                              1. Include Directives
                                                                                                                                                                              2. Common PAM Modules
                                                                                                                                                                                1. pam_unix
                                                                                                                                                                                  1. pam_tally2
                                                                                                                                                                                    1. pam_faillock
                                                                                                                                                                                      1. pam_cracklib
                                                                                                                                                                                        1. pam_pwquality
                                                                                                                                                                                          1. pam_limits
                                                                                                                                                                                            1. pam_time
                                                                                                                                                                                              1. pam_access
                                                                                                                                                                                              2. PAM Security Considerations
                                                                                                                                                                                                1. Module Ordering
                                                                                                                                                                                                  1. Bypass Prevention
                                                                                                                                                                                                    1. Error Handling
                                                                                                                                                                                                      1. Logging Configuration

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                                                                                                                                                                                                  3. Filesystem and Data Security