pam(8) — Linux manual page


PAM(8)                        Linux-PAM Manual                        PAM(8)

NAME         top

       PAM, pam - Pluggable Authentication Modules for Linux

DESCRIPTION         top

       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, the configuration
       can be set by individual configuration files located in the
       /etc/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/ 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 /usr/lib/pam.d/.

       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         top

           the configuration file

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

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

ERRORS         top

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

CONFORMING TO         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the linux-pam (Pluggable Authentication Modules
       for Linux) project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for this manual
       page, see ⟨//⟩.  This page was obtained from the
       tarball Linux-PAM-1.3.0.tar.bz2 fetched from
       ⟨⟩ on 2020-11-01.  If you discover
       any rendering problems in this HTML version of the page, or you be‐
       lieve there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

Linux-PAM Manual                 04/01/2016                           PAM(8)

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