$Id: pam.man 648 2013-03-05 17:54:27Z des $

.Sh DESCRIPTION The Pluggable Authentication Modules (PAM) library abstracts a number of common authentication-related operations and provides a framework for dynamically loaded modules that implement these operations in various ways. .Ss Terminology In PAM parlance, the application that uses PAM to authenticate a user is the server, and is identified for configuration purposes by a service name, which is often (but not necessarily) the program name.

p The user requesting authentication is called the applicant, while the user (usually, root) charged with verifying his identity and granting him the requested credentials is called the arbitrator.

p The sequence of operations the server goes through to authenticate a user and perform whatever task he requested is a PAM transaction; the context within which the server performs the requested task is called a session.

p The functionality embodied by PAM is divided into six primitives grouped into four facilities: authentication, account management, session management and password management. .Ss Conversation The PAM library expects the application to provide a conversation callback which it can use to communicate with the user. Some modules may use specialized conversation functions to communicate with special hardware such as cryptographic dongles or biometric devices. See .Xr pam_conv 3 for details. .Ss Initialization and Cleanup The .Fn pam_start function initializes the PAM library and returns a handle which must be provided in all subsequent function calls. The transaction state is contained entirely within the structure identified by this handle, so it is possible to conduct multiple transactions in parallel.

p The .Fn pam_end function releases all resources associated with the specified context, and can be called at any time to terminate a PAM transaction. .Ss Storage The .Fn pam_set_item and .Fn pam_get_item functions set and retrieve a number of predefined items, including the service name, the names of the requesting and target users, the conversation function, and prompts.

p The .Fn pam_set_data and .Fn pam_get_data functions manage named chunks of free-form data, generally used by modules to store state from one invocation to another. .Ss Authentication There are two authentication primitives: .Fn pam_authenticate and .Fn pam_setcred . The former authenticates the user, while the latter manages his credentials. .Ss Account Management The .Fn pam_acct_mgmt function enforces policies such as password expiry, account expiry, time-of-day restrictions, and so forth. .Ss Session Management The .Fn pam_open_session and .Fn pam_close_session functions handle session setup and teardown. .Ss Password Management The .Fn pam_chauthtok function allows the server to change the user's password, either at the user's request or because the password has expired. .Ss Miscellaneous The .Fn pam_putenv , .Fn pam_getenv and .Fn pam_getenvlist functions manage a private environment list in which modules can set environment variables they want the server to export during the session.

p The .Fn pam_strerror function returns a pointer to a string describing the specified PAM error code.