Linux AAA
Linux AAA Authentication What it means: Authentication verifies who the user is . How it works in Linux: When you log in, Linux checks your credentials (usually username + password) against /etc/passwd and /etc/shadow . /etc/passwd stores user information (username, UID, GID, shell, home directory). /etc/shadow stores hashed passwords and password expiration info, readable only by root. Common authentication methods: Local authentication: Using /etc/passwd and /etc/shadow . Remote authentication: Using services like: LDAP (Lightweight Directory Access Protocol) – centralized user management. Kerberos – provides secure, ticket-based authentication. RADIUS – used in network access (VPNs, Wi-Fi, etc.). PAM (Pluggable Authentication Modules) – modular framework used by Linux for integrating different authentication methods. Example PAM file location: /etc/pam.d/ Each service (like SSH, sudo, login) has its own PAM configuration file.