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



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.

       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 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.

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

       <vendordir>/pam.d
           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.

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

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

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



Linux-PAM Manual                             06/08/2020                                       PAM(7)