1PAM(8) Linux-PAM Manual PAM(8)
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6 PAM, pam - Pluggable Authentication Modules for Linux
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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.
12 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.
18 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 ignore
27 /etc/pam.conf.
28 From the point of view of the system administrator, for whom this
30 manual is provided, it is not of primary importance to understand the
31 internal behavior of the Linux-PAM library. The important point to
32 recognize is that the configuration file(s) define the connection
33 between applications (services) and the pluggable authentication
34 modules (PAMs) that perform the actual authentication tasks.
35 Linux-PAM separates the tasks of authentication into four independent
37 management groups: account management; authentication management;
38 password management; and session management. (We highlight the
39 abbreviations used for these groups in the configuration file.)
40 Simply put, these groups take care of different aspects of a typical
42 user's request for a restricted service:
43 account - provide account verification types of service: has the user's
45 password expired?; is this user permitted access to the requested
46 service?
47 authentication - authenticate a user and set up user credentials.
49 Typically this is via some challenge-response request that the user
50 must satisfy: if you are who you claim to be please enter your
51 password. Not all authentications are of this type, there exist
52 hardware based authentication schemes (such as the use of smart-cards
53 and biometric devices), with suitable modules, these may be substituted
54 seamlessly for more standard approaches to authentication - such is the
55 flexibility of Linux-PAM.
56 password - this group's responsibility is the task of updating
58 authentication mechanisms. Typically, such services are strongly
59 coupled to those of the auth group. Some authentication mechanisms lend
60 themselves well to being updated with such a function. Standard UN*X
61 password-based access is the obvious example: please enter a
62 replacement password.
63 session - this group of tasks cover things that should be done prior to
65 a service being given and after it is withdrawn. Such tasks include the
66 maintenance of audit trails and the mounting of the user's home
67 directory. The session management group is important as it provides
68 both an opening and closing hook for modules to affect the services
69 available to a user.
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72 /etc/pam.conf
73 the configuration file
74 /etc/pam.d
76 the Linux-PAM configuration directory. Generally, if this directory
77 is present, the /etc/pam.conf file is ignored.
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80 Typically errors generated by the Linux-PAM system of libraries, will
81 be written to syslog(3).
82
84 DCE-RFC 86.0, October 1995. Contains additional features, but remains
85 backwardly compatible with this RFC.
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88 pam(3), pam_authenticate(3), pam_sm_setcred(3), pam_strerror(3), PAM(8)
89Linux-PAM Manual 06/27/2006 PAM(8)