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



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, 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.

       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.