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

       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 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

       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

       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

       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.

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

           the Linux-PAM vendor configuration directory. Files in /etc/pam.d and
           /usr/lib/pam.d override files with the same name in this directory.
           Only available if Linux-PAM was compiled with vendordir enabled.

       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(8)

Linux-PAM Manual                   11/25/2020                             PAM(8)