PAM - Pluggable Authentication Modules
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PAM (Pluggable Authentication Modules) acts as a security mechanism that verifies the identity of users attempting to access computer services, controlling their access based on various criteria. It's akin to a digital gatekeeper, ensuring that only authorized users can engage with specific services while potentially limiting their usage to prevent system overloads.
Solaris and UNIX-based systems typically utilize a central configuration file located at /etc/pam.conf.
Linux systems prefer a directory approach, storing service-specific configurations within /etc/pam.d. For instance, the configuration file for the login service is found at /etc/pam.d/login.
An example of a PAM configuration for the login service might look like this:
These realms, or management groups, include auth, account, password, and session, each responsible for different aspects of the authentication and session management process:
Auth: Validates user identity, often by prompting for a password.
Account: Handles account verification, checking for conditions like group membership or time-of-day restrictions.
Password: Manages password updates, including complexity checks or dictionary attacks prevention.
Session: Manages actions during the start or end of a service session, such as mounting directories or setting resource limits.
Controls dictate the module's response to success or failure, influencing the overall authentication process. These include:
Required: Failure of a required module results in eventual failure, but only after all subsequent modules are checked.
Requisite: Immediate termination of the process upon failure.
Sufficient: Success bypasses the rest of the same realm's checks unless a subsequent module fails.
Optional: Only causes failure if it's the sole module in the stack.
In a setup with multiple auth modules, the process follows a strict order. If the pam_securetty module finds the login terminal unauthorized, root logins are blocked, yet all modules are still processed due to its "required" status. The pam_env sets environment variables, potentially aiding in user experience. The pam_ldap and pam_unix modules work together to authenticate the user, with pam_unix attempting to use a previously supplied password, enhancing efficiency and flexibility in authentication methods.
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