PAM, pam - Pluggable Authentication Modules for Linux


   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

   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

   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.


       the configuration file

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


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


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


   pam(3), pam_authenticate(3), pam_sm_setcred(3), pam_strerror(3), PAM(7)


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