Programs which grant users access to a system verify each user's identity through a process called authentication. Historically, each such program had its own way of performing the task of authentication. Under Red Hat Enterprise Linux, many such programs are configured to use a centralized authentication mechanism called Pluggable Authentication Modules or PAM.

PAM uses a pluggable, modular architecture, which affords the system administrator a great deal of flexibility in setting authentication policies for the system.

In most situations, the default PAM configuration file for a PAM-aware application is sufficient. However, sometimes it may become necessary to edit a PAM configuration file. Because misconfiguration of PAM can compromise system security, it is important to understand the structure of these files before making any modifications (refer to Section 16.3, “PAM Configuration File Format” for more information).