This manual is intended to offer a quick introduction to Linux-PAM.
For more information the reader is directed to the Linux-PAM systemadministrators' 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
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
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.
the configuration file
the Linux-PAM configuration directory. Generally, if this
directory is present, the /etc/pam.conf file is ignored.
the Linux-PAM vendor configuration directory. Files in /etc/pam.d
override files with the same name in this directory.
This page is part of the linux-pam (Pluggable Authentication Modules
for Linux) project. Information about the project can be found at
⟨https://fedorahosted.org/linux-pam/⟩. If you have a bug report for
this manual page, see ⟨https://fedorahosted.org/linux-pam/report⟩.
This page was obtained from the tarball Linux-PAM-1.3.0.tar.gz
fetched from ⟨http://www.linux-pam.org/library/⟩ on 2016-10-04. If
you discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information in
this COLOPHON (which is not part of the original manual page), send a
mail to firstname.lastname@example.org
Linux-PAM Manual 04/01/2016 PAM(8)