NAME

       PAM, pam - Pluggable Authentication Modules for Linux

DESCRIPTION

       This manual is intended to offer a quick introduction to Linux-PAM. For more information the reader is
       directed to the Linux-PAM system administrators' guide.

       Linux-PAM is a system of libraries that handle the authentication tasks of applications (services) on the
       system. The library provides a stable general interface (Application Programming Interface - API) that
       privilege granting programs (such as login(1) and su(1)) defer to to perform standard authentication
       tasks.

       The principal feature of the PAM approach is that the nature of the authentication is dynamically
       configurable. In other words, the system administrator is free to choose how individual service-providing
       applications will authenticate users. This dynamic configuration is set by the contents of the single
       Linux-PAM configuration file /etc/pam.conf. Alternatively and preferably, the configuration can be set by
       individual configuration files located in a pam.d directory. The presence of this directory will cause
       Linux-PAM to ignore /etc/pam.conf.

       Vendor-supplied PAM configuration files might be installed in the system directory /usr/lib/pam.d/ or a
       configurable vendor specific directory instead of the machine configuration directory /etc/pam.d/. If no
       machine configuration file is found, the vendor-supplied file is used. All files in /etc/pam.d/ override
       files with the same name in other directories.

       From the point of view of the system administrator, for whom this manual is provided, it is not of
       primary importance to understand the internal behavior of the Linux-PAM library. The important point to
       recognize is that the configuration file(s) define the connection between applications (services) and the
       pluggable authentication modules (PAMs) that perform the actual authentication tasks.

       Linux-PAM separates the tasks of authentication into four independent management groups: account
       management; authentication management; password management; and session management. (We highlight the
       abbreviations used for these groups in the configuration file.)

       Simply put, these groups take care of different aspects of a typical user's request for a restricted
       service:

       account - provide account verification types of service: has the user's password expired?; is this user
       permitted access to the requested service?

       authentication - authenticate a user and set up user credentials. Typically this is via some
       challenge-response request that the user must satisfy: if you are who you claim to be please enter your
       password. Not all authentications are of this type, there exist hardware based authentication schemes
       (such as the use of smart-cards and biometric devices), with suitable modules, these may be substituted
       seamlessly for more standard approaches to authentication - such is the flexibility of Linux-PAM.

       password - this group's responsibility is the task of updating authentication mechanisms. Typically, such
       services are strongly coupled to those of the auth group. Some authentication mechanisms lend themselves
       well to being updated with such a function. Standard UN*X password-based access is the obvious example:
       please enter a replacement password.

       session - this group of tasks cover things that should be done prior to a service being given and after
       it is withdrawn. Such tasks include the maintenance of audit trails and the mounting of the user's home
       directory. The session management group is important as it provides both an opening and closing hook for
       modules to affect the services available to a user.

FILES

       /etc/pam.conf
           the configuration file

       /etc/pam.d
           the Linux-PAM configuration directory. Generally, if this directory is present, the /etc/pam.conf
           file is ignored.

       /usr/lib/pam.d
           the Linux-PAM vendor configuration directory. Files in /etc/pam.d override files with the same name
           in this directory.

ERRORS

       Typically errors generated by the Linux-PAM system of libraries, will be written to syslog(3).

CONFORMING TO

       DCE-RFC 86.0, October 1995. Contains additional features, but remains backwardly compatible with this
       RFC.

SEE ALSO

       pam(3), pam_authenticate(3), pam_sm_setcred(3), pam_strerror(3), PAM(8)

Linux-PAM                                          09/15/2025                                             PAM(7)