freebsd-dev/contrib/libpam/doc/man/pam.8

.\" Hey Emacs! This file is -*- nroff -*- source.
.\" $Id: pam.8,v 1.2 2001/01/20 23:47:07 agmorgan Exp $
.\" Copyright (c) Andrew G. Morgan 1996-7,2001 <morgan@kernel.org>
.\" $FreeBSD$
.TH PAM 8 "2001 Jan 20" "PAM 0.74" "PAM Manual"
.SH NAME

PAM \- Pluggable Authentication Modules

.SH SYNOPSIS
.B /etc/pam.conf
.sp 2
.SH DESCRIPTION

This manual is intended to offer a quick introduction to
.BR PAM ". "
For more information the reader is directed to the
.BR "PAM system administrators' guide".

.sp
.BR 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
.BR login "(1) "
and
.BR su "(1)) "
defer to to perform standard authentication tasks.

.sp
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
.BR PAM
configuration file
.BR /etc/pam.conf "."
Alternatively, the configuration can be set by individual
configuration files located in the
.B /etc/pam.d/
directory.
.IB "The presence of this directory will cause " PAM " to ignore"
.BI /etc/pam.conf "."

.sp
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
.BR PAM
library.  The important point to recognize is that the configuration
file(s)
.I define
the connection between applications
.BR "" "(" services ")"
and the pluggable authentication modules
.BR "" "(" PAM "s)"
that perform the actual authentication tasks.

.sp
.BR PAM
separates the tasks of
.I authentication
into four independent management groups:
.BR "account" " management; "
.BR "auth" "entication management; "
.BR "password" " management; "
and
.BR "session" " management."
(We highlight the abbreviations used for these groups in the
configuration file.)

.sp
Simply put, these groups take care of different aspects of a typical
user's request for a restricted service:

.sp
.BR account " - "
provide account verification types of service: has the user's password
expired?; is this user permitted access to the requested service?

.br
.BR auth "entication - "
establish the user is who they claim to be. 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
.BR PAM "."

.br
.BR password " - "
this group's responsibility is the task of updating authentication
mechanisms. Typically, such services are strongly coupled to those of
the
.BR 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.

.br
.BR 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
.BR session
management group is important as it provides both an opening and
closing hook for modules to affect the services available to a user.

.SH The configuration file(s)

When a
.BR PAM
aware privilege granting application is started, it activates its
attachment to the PAM-API.  This activation performs a number of
tasks, the most important being the reading of the configuration file(s):
.BR /etc/pam.conf "."
Alternatively, this may be the contents of the
.BR /etc/pam.d/
directory.

These files list the
.BR PAM "s"
that will do the authentication tasks required by this service, and
the appropriate behavior of the PAM-API in the event that individual
.BR PAM "s "
fail.

.sp
The syntax of the
.B /etc/pam.conf
configuration file is as follows. The file is made
up of a list of rules, each rule is typically placed on a single line,
but may be extended with an escaped end of line: `\\<LF>'. Comments
are preceded with `#' marks and extend to the next end of line.

.sp
The format of each rule is a space separated collection of tokens, the
first three being case-insensitive:

.sp
.br
.BR "   service  type  control  module-path  module-arguments"

.sp
The syntax of files contained in the
.B /etc/pam.d/
directory, are identical except for the absence of any
.I service 
field. In this case, the
.I service
is the name of the file in the
.B /etc/pam.d/
directory. This filename must be in lower case.

.sp
An important feature of
.BR PAM ", "
is that a number of rules may be
.I stacked
to combine the services of a number of PAMs for a given authentication
task.

.sp
The
.BR service
is typically the familiar name of the corresponding application:
.BR login
and 
.BR su
are good examples. The
.BR service "-name, " other ", "
is reserved for giving
.I default
rules.  Only lines that mention the current service (or in the absence
of such, the
.BR other
entries) will be associated with the given service-application.

.sp
The
.BR type
is the management group that the rule corresponds to. It is used to
specify which of the management groups the subsequent module is to
be associated with. Valid entries are:
.BR account "; "
.BR auth "; "
.BR password "; "
and
.BR session "."
The meaning of each of these tokens was explained above.

.sp
The third field,
.BR control ", "
indicates the behavior of the PAM-API should the module fail to
succeed in its authentication task. There are two types of syntax for
this control field: the simple one has a single simple keyword; the
more complicated one involves a square-bracketed selection of
.B value=action
pairs.

.sp
For the simple (historical) syntax valid
.BR control
values are:
.BR requisite
- failure of such a PAM results in the immediate termination of the
authentication process;
.BR required
- failure of such a PAM will ultimately lead to the PAM-API returning
failure but only after the remaining
.I stacked
modules (for this
.BR service
and
.BR type ")"
have been invoked;
.BR sufficient
- success of such a module is enough to satisfy the authentication
requirements of the stack of modules (if a prior
.BR required
module has failed the success of this one is
.IR ignored "); "
.BR optional
- the success or failure of this module is only important if it is the
only module in the stack associated with this
.BR service "+" type "."

.sp
For the more complicated syntax valid
.B control
values have the following form:
.sp
.RB  [value1=action1 value2=action2 ...]
.sp
Where
.B valueN
corresponds to the return code from the function invoked in the module
for which the line is defined. It is selected from one of these:
.BR success ;
.BR open_err ;
.BR symbol_err ;
.BR service_err ;
.BR system_err ;
.BR buf_err ;
.BR perm_denied ;
.BR auth_err ;
.BR cred_insufficient ;
.BR authinfo_unavail ;
.BR user_unknown ;
.BR maxtries ;
.BR new_authtok_reqd ;
.BR acct_expired ;
.BR session_err ;
.BR cred_unavail ;
.BR cred_expired ;
.BR cred_err ;
.BR no_module_data ;
.BR conv_err ;
.BR authtok_err ;
.BR authtok_recover_err ;
.BR authtok_lock_busy ;
.BR authtok_disable_aging ;
.BR try_again ;
.BR ignore ;
.BR abort ;
.BR authtok_expired ;
.BR module_unknown ;
.BR bad_item "; and"
.BR default .
The last of these,
.BR default ,
implies 'all
.BR valueN 's
not mentioned explicitly. Note, the full list of PAM errors is
available in /usr/include/security/_pam_types.h . The
.B actionN
can be: an unsigned integer, 
.BR J ,
signifying an action of 'jump over the next J modules in the stack';
or take one of the following forms:
.br
.B ignore
- when used with a stack of modules, the module's return status will
not contribute to the return code the application obtains;
.br
.B bad 
- this action indicates that the return code should be thought of as
indicative of the module failing. If this module is the first in the
stack to fail, its status value will be used for that of the whole
stack.
.br
.B die
- equivalent to bad with the side effect of terminating the module
stack and PAM immediately returning to the application.
.br
.B ok
- this tells PAM that the administrator thinks this return code
should contribute directly to the return code of the full stack of
modules. In other words, if the former state of the stack would lead
to a return of
.BR PAM_SUCCESS ,
the module's return code will override this value. Note, if the former
state of the stack holds some value that is indicative of a modules
failure, this 'ok' value will not be used to override that value.
.br
.B done
- equivalent to ok with the side effect of terminating the module
stack and PAM immediately returning to the application.
.br
.B reset
- clear all memory of the state of the module stack and start again
with the next stacked module.

.sp
.BR module-path
- this is either the full filename of the PAM to be used by the
application (it begins with a '/'), or a relative pathname from the
default module location:
.BR /usr/lib/ .

.sp
.BR module-arguments
- these are a space separated list of tokens that can be used to
modify the specific behavior of the given PAM. Such arguments will be
documented for each individual module.

.SH "FILES"
.BR /etc/pam.conf " - the configuration file"
.br
.BR /etc/pam.d/ " - the"
.BR PAM
configuration directory. Generally, if this directory is present, the
.B /etc/pam.conf
file is ignored.
.br
.BR /usr/lib/libpam.so.X " - the dynamic library"
.br
.BR /usr/lib/pam_*.so " - the PAMs

.SH ERRORS
Typically errors generated by the
.BR PAM
system of libraries, will be written to
.BR syslog "(3)."

.SH "CONFORMING TO"
DCE-RFC 86.0, October 1995.
.br
Contains additional features, but remains backwardly compatible with
this RFC.

.SH BUGS
.sp 2
None known.

.SH "SEE ALSO"

The three
.BR PAM
Guides, for
.BR "system administrators" ", "
.BR "module developers" ", "
and
.BR "application developers" ". "