PAM(7)                                                         Linux-PAM Manual                                                         PAM(7)


       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.

       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.


           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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