'\" t
.\"     Title: pam
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 09/03/2021
.\"    Manual: Linux-PAM Manual
.\"    Source: Linux-PAM Manual
.\"  Language: English
.\"
.TH "PAM" "7" "09/03/2021" "Linux-PAM Manual" "Linux-PAM Manual"
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.SH "NAME"
PAM, pam \- Pluggable Authentication Modules for Linux
.SH "DESCRIPTION"
.PP
This manual is intended to offer a quick introduction to
\fBLinux\-PAM\fR\&. For more information the reader is directed to the
\fBLinux\-PAM system administrators\*(Aq guide\fR\&.
.PP
\fBLinux\-PAM\fR
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
\fBlogin\fR(1)
and
\fBsu\fR(1)) defer to to perform standard authentication tasks\&.
.PP
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
\fBLinux\-PAM\fR
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
\fBLinux\-PAM\fR
to
\fIignore\fR
/etc/pam\&.conf\&.
.PP
Vendor\-supplied PAM configuration files might be installed in the system directory
/usr/lib/pam\&.d/
or a configurable vendor specific directory 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 other directories\&.
.PP
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
\fBLinux\-PAM\fR
library\&. The important point to recognize is that the configuration file(s)
\fIdefine\fR
the connection between applications
(\fBservices\fR) and the pluggable authentication modules
(\fBPAM\fRs) that perform the actual authentication tasks\&.
.PP
\fBLinux\-PAM\fR
separates the tasks of
\fIauthentication\fR
into four independent management groups:
\fBaccount\fR
management;
\fBauth\fRentication management;
\fBpassword\fR
management; and
\fBsession\fR
management\&. (We highlight the abbreviations used for these groups in the configuration file\&.)
.PP
Simply put, these groups take care of different aspects of a typical user\*(Aqs request for a restricted service:
.PP
\fBaccount\fR
\- provide account verification types of service: has the user\*(Aqs password expired?; is this user permitted access to the requested service?
.PP
\fBauth\fRentication \- 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
\fBLinux\-PAM\fR\&.
.PP
\fBpassword\fR
\- this group\*(Aqs responsibility is the task of updating authentication mechanisms\&. Typically, such services are strongly coupled to those of the
\fBauth\fR
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\&.
.PP
\fBsession\fR
\- 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\*(Aqs home directory\&. The
\fBsession\fR
management group is important as it provides both an opening and closing hook for modules to affect the services available to a user\&.
.SH "FILES"
.PP
/etc/pam\&.conf
.RS 4
the configuration file
.RE
.PP
/etc/pam\&.d
.RS 4
the
\fBLinux\-PAM\fR
configuration directory\&. Generally, if this directory is present, the
/etc/pam\&.conf
file is ignored\&.
.RE
.PP
/usr/lib/pam\&.d
.RS 4
the
\fBLinux\-PAM\fR
vendor configuration directory\&. Files in
/etc/pam\&.d
override files with the same name in this directory\&.
.RE
.PP
<vendordir>/pam\&.d
.RS 4
the
\fBLinux\-PAM\fR
vendor configuration directory\&. Files in
/etc/pam\&.d
and
/usr/lib/pam\&.d
override files with the same name in this directory\&. Only available if Linux\-PAM was compiled with vendordir enabled\&.
.RE
.SH "ERRORS"
.PP
Typically errors generated by the
\fBLinux\-PAM\fR
system of libraries, will be written to
\fBsyslog\fR(3)\&.
.SH "CONFORMING TO"
.PP
DCE\-RFC 86\&.0, October 1995\&. Contains additional features, but remains backwardly compatible with this RFC\&.
.SH "SEE ALSO"
.PP
\fBpam\fR(3),
\fBpam_authenticate\fR(3),
\fBpam_sm_setcred\fR(3),
\fBpam_strerror\fR(3),
\fBPAM\fR(7)