PAM
Section: Linux-PAM Manual (8)
Updated: 04/01/2016
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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/
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
/usr/lib/pam.d/.
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
(PAMs) that perform the actual authentication tasks.
Linux-PAM
separates the tasks of
authentication
into four independent management groups:
account
management;
authentication 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?
authentication - 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.
SEE ALSO
pam(3),
pam_authenticate(3),
pam_sm_setcred(3),
pam_strerror(3),
PAM(8)
Index
- NAME
-
- DESCRIPTION
-
- FILES
-
- ERRORS
-
- CONFORMING TO
-
- SEE ALSO
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