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Solitox Community Framework: libmsocket-0.4 release
10-17-2008
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pam(3) Library Functions Manual pam(3) NAME
PAM - Pluggable Authentication Module SYNOPSIS
[flag]... file..." [library]... DESCRIPTION
PAM gives system administrators the flexibility of choosing any authentication service available on the system to perform authentication. The framework also allows new authentication service modules to be plugged in and made available without modifying the applications. The PAM framework, consists of an interface library and multiple authentication service modules. The PAM interface library is the layer implementing the Application Programming Interface (API). The authentication service modules are a set of dynamically loadable objects invoked by the PAM API to provide a particular type of user authentication. Interface Overview The PAM library interface consists of functions which can be grouped into five categories. The names for all the authentication library functions start with The first category contains functions for establishing and terminating an authentication activity (pam_start(3) and pam_end(3)), functions to maintain module specific data (pam_get_data(3) and pam_set_data(3)), functions to maintain state information (pam_get_item(3) and pam_set_item(3)), and a function to return error status information (pam_strerror(3)). The second category contains functions to authenticate an individual user (pam_authenticate(3)) and to set the credentials of the user (pam_setcred(3)). The third category contains functions to do account management (pam_acct_mgmt(3)). This includes checking for password aging and access- hour restrictions. The fourth category contains functions to perform session management (pam_open_session(3) and pam_close_session(3)) after access to the system has been granted. The fifth category consists of functions to change authentication tokens pam_chauthtok(3). An authentication token is the object used to verify the identity of the user. In UNIX, an authentication token is a user's password, even when using a smart card, because the PAM Framework retrieves the password from the smart card. All the interfaces are implemented through the library For each of the categories listed above, excluding the first category and there exists a dynamically loadable shared module that provides the appropriate service layer functionality upon demand. The functional entry points in the service layer start with the prefix. The only difference between the interfaces and their corresponding interfaces is that all the interfaces require extra parameters to pass service specific options to the shared modules. Please refer to pam_sm(3) for an over- view of the PAM service module APIs. Stateful Interface A sequence of calls sharing a common set of state information is referred to as an authentication transaction. An authentication transac- tion begins with a call to allocates space, performs various initialization activities, and assigns a PAM authentication handle to be used for subsequent calls to the library. After initiating an authentication transaction, applications can invoke to authenticate a particular user, and to perform system entry man- agement (the application may want to determine if the user's password has expired). If the user has been successfully authenticated, applications call to set any user credentials associated with the authentication service. Within one authentication transaction (between and all calls to the PAM interface should be made with the same authentication handle returned by This is necessary because certain service modules may store module-specific data in the handle that is intended for use by other modules. For example, during the call to service modules may store data in the handle that is intended for use by To perform session management, applications call For example, the system may want to store the total time for the session. The function closes the current session. When necessary, applications can call and to access and update specific authentication information. Such information may include the cur- rent username. To terminate an authentication transaction, the application simply calls which frees previously allocated space used to store authentica- tion information. Application - Authentication Service Interactive Interface The authentication service in PAM does not communicate directly with the user; instead it relies on the application to perform all such interactions. The application passes a pointer to the function, along with any associated application data pointers, through a structure to the authentication service when it initiates an authentication transaction (via a call to The service will then use the function, to prompt the user for data, output error messages, and display text information. Refer to pam_start(3) for more information. Stacking Multiple Schemes The PAM architecture enables authentication by multiple authentication services through stacking. System entry applications, such as login(1), stack multiple service modules to authenticate users with multiple authentication services. The order in which authentication service modules are stacked is specified in the configuration file, pam.conf(4). A system administrator determines this ordering, and also determines whether the same password can be used for all authentication services. Administrative Interface Various authentication services are implemented by their own loadable modules whose paths are specified through the pam.conf(4) file. User configuration The system administrator can determine a policy by user. These are specified in the configuration files: pam.conf(4), pam_user.conf(4). APPLICATION USAGE
All the interfaces implemented in the PAM framework, are thread-safe. A cancellation point may occur while a thread is executing any of these interfaces. They are not cancel-safe, async-cancel-safe, nor async-signal-safe. However, system administrators should be aware that the and interfaces invoke the corresponding interfaces implemented in the dynamically loadable modules specified in the configuration file, pam.conf(4). Therefore, the thread-safety of these interfaces depends on the implementation of the service module. Refer to module spe- cific man pages such as pam_unix(5) for this information. RETURN VALUE
The PAM functions may return one of the following generic values, or one of the values defined in the specific man pages: Successful function return. Failure in dynamically loading a service module. Symbol not found. Error in service module. System error. Memory buffer error. Conversation failure. Permission denied. WARNINGS
Please note that all the PAM APIs and the data structures are subject to change without notice. SEE ALSO
pam_authenticate(3), pam_open_session(3), pam_chauthtok(3), pam_set_item(3), pam_setcred(3), pam_sm(3), pam_start(3), pam_strerror(3), pam.conf(4), pam_user.conf(4). pam(3)