1PAM(8)                         Linux-PAM Manual                         PAM(8)


6       PAM, pam - Pluggable Authentication Modules for Linux


9       This manual is intended to offer a quick introduction to Linux-PAM. For
10       more information the reader is directed to the Linux-PAM system
11       administrators' guide.
13       Linux-PAM is a system of libraries that handle the authentication tasks
14       of applications (services) on the system. The library provides a stable
15       general interface (Application Programming Interface - API) that
16       privilege granting programs (such as login(1) and su(1)) defer to to
17       perform standard authentication tasks.
19       The principal feature of the PAM approach is that the nature of the
20       authentication is dynamically configurable. In other words, the system
21       administrator is free to choose how individual service-providing
22       applications will authenticate users. This dynamic configuration is set
23       by the contents of the single Linux-PAM configuration file
24       /etc/pam.conf. Alternatively, the configuration can be set by
25       individual configuration files located in the /etc/pam.d/ directory.
26       The presence of this directory will cause Linux-PAM to
27       ignore/etc/pam.conf.
29       Vendor-supplied PAM configuration files might be installed in the
30       system directory /usr/lib/pam.d/ instead of the machine configuration
31       directory /etc/pam.d/. If no machine configuration file is found, the
32       vendor-supplied file is used. All files in /etc/pam.d/ override files
33       with the same name in /usr/lib/pam.d/.
35       From the point of view of the system administrator, for whom this
36       manual is provided, it is not of primary importance to understand the
37       internal behavior of the Linux-PAM library. The important point to
38       recognize is that the configuration file(s) define the connection
39       between applications (services) and the pluggable authentication
40       modules (PAMs) that perform the actual authentication tasks.
42       Linux-PAM separates the tasks of authentication into four independent
43       management groups: account management; authentication management;
44       password management; and session management. (We highlight the
45       abbreviations used for these groups in the configuration file.)
47       Simply put, these groups take care of different aspects of a typical
48       user's request for a restricted service:
50       account - provide account verification types of service: has the user's
51       password expired?; is this user permitted access to the requested
52       service?
54       authentication - authenticate a user and set up user credentials.
55       Typically this is via some challenge-response request that the user
56       must satisfy: if you are who you claim to be please enter your
57       password. Not all authentications are of this type, there exist
58       hardware based authentication schemes (such as the use of smart-cards
59       and biometric devices), with suitable modules, these may be substituted
60       seamlessly for more standard approaches to authentication - such is the
61       flexibility of Linux-PAM.
63       password - this group's responsibility is the task of updating
64       authentication mechanisms. Typically, such services are strongly
65       coupled to those of the auth group. Some authentication mechanisms lend
66       themselves well to being updated with such a function. Standard UN*X
67       password-based access is the obvious example: please enter a
68       replacement password.
70       session - this group of tasks cover things that should be done prior to
71       a service being given and after it is withdrawn. Such tasks include the
72       maintenance of audit trails and the mounting of the user's home
73       directory. The session management group is important as it provides
74       both an opening and closing hook for modules to affect the services
75       available to a user.


78       /etc/pam.conf
79           the configuration file
81       /etc/pam.d
82           the Linux-PAM configuration directory. Generally, if this directory
83           is present, the /etc/pam.conf file is ignored.
85       /usr/lib/pam.d
86           the Linux-PAM vendor configuration directory. Files in /etc/pam.d
87           override files with the same name in this directory.


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


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


98       pam(3), pam_authenticate(3), pam_sm_setcred(3), pam_strerror(3), PAM(8)
102Linux-PAM Manual                  05/18/2018                            PAM(8)