pam
8
Linux-PAM Manual
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
login1
and
su1)
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.
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.
/lib/libpam.so.X - the dynamic library
/lib/security/*.so - the PAMs
ERRORS
Typically errors generated by the
Linux-PAM
system of libraries, will be written to
syslog3.
CONFORMING TO
DCE-RFC 86.0, October 1995.
Contains additional features, but remains backwardly compatible with
this RFC.
BUGS
None known.
SEE ALSO
The three
Linux-PAM
Guides, for
system administrators,
module developers,
and
application developers.