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Chapter 10. Using Pluggable Authentication Modules (PAM)

Pluggable authentication modules (PAMs) are a common framework for authentication and authorization. Most system applications in Red Hat Enterprise Linux depend on underlying PAM configuration for authentication and authorization.

10.1. About PAM

Pluggable Authentication Modules (PAMs) provide a centralized authentication mechanism which system application can use to relay authentication to a centrally configured framework.
PAM is pluggable because there is a PAM module for different types of authentication sources (such as Kerberos, SSSD, NIS, or the local file system). Different authentication sources can be prioritized.
This modular architecture offers administrators a great deal of flexibility in setting authentication policies for the system. PAM is a useful system for developers and administrators for several reasons:
  • PAM provides a common authentication scheme that can be used with a wide variety of applications.
  • PAM provides significant flexibility and control over authentication for system administrators.
  • PAM provides a single, fully-documented library which allows developers to write programs without having to create their own authentication schemes.

10.1.1. Other PAM Resources

PAM has an extensive documentation set with much more detail about both using PAM and writing modules to extend or integrate PAM with other applications. Almost all of the major modules and configuration files with PAM have their own man pages. Additionally, the /usr/share/doc/pam-version#/ directory contains a System Administrators' Guide, a Module Writers' Manual, and the Application Developers' Manual, as well as a copy of the PAM standard, DCE-RFC 86.0.
The libraries for PAM are available at This is the primary distribution website for the Linux-PAM project, containing information on various PAM modules, frequently asked questions, and additional PAM documentation.

10.1.2. Custom PAM Modules

New PAM modules can be created or added at any time for use by PAM-aware applications. PAM-aware programs can immediately use the new module and any methods it defines without being recompiled or otherwise modified. This allows developers and system administrators to use a selection of authentication modules, as well as tests, for different programs without recompiling them.
Documentation on writing modules is included in the /usr/share/doc/pam-devel-version#/ directory.