/etc/pam.d

The `/etc/pam.d` directory contains configuration files for PAM (Pluggable Authentication Modules), which manage user authentication on Linux systems. These files specify how the system verifies user identities when logging in or accessing services, enabling administrators to customize security policies like password requirements, session management, and access controls. By modularly organizing authentication methods, PAM allows flexible and consistent security configurations across various services, ensuring a centralized way to handle authentication processes securely and efficiently.