# PAM

## 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 (**PAM** s) that perform the actual
           authentication tasks.
    
           **Linux-PAM** separates the tasks of _authentication_ into four
           independent management groups: **account** management; **auth** entication
           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?
    
           **auth** entication - 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.
    


## 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.
    


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