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2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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8 <refentrytitle>pam</refentrytitle>
9 <manvolnum>8</manvolnum>
10 <refmiscinfo class='setdesc'>Linux-PAM Manual</refmiscinfo>
13 <refnamediv id='pam8-name'>
14 <refname>PAM</refname>
15 <refname>pam</refname>
16 <refpurpose>Pluggable Authentication Modules for Linux</refpurpose>
19 <refsect1 id='pam8-description'>
20 <title>DESCRIPTION</title>
22 This manual is intended to offer a quick introduction to
23 <emphasis remap='B'>Linux-PAM</emphasis>. For more information
24 the reader is directed to the
25 <emphasis remap='B'>Linux-PAM system administrators' guide</emphasis>.
29 <emphasis remap='B'>Linux-PAM</emphasis> is a system of libraries
30 that handle the authentication tasks of applications (services) on
31 the system. The library provides a stable general interface
32 (Application Programming Interface - API) that privilege granting
33 programs (such as <citerefentry>
34 <refentrytitle>login</refentrytitle><manvolnum>1</manvolnum>
35 </citerefentry> and <citerefentry>
36 <refentrytitle>su</refentrytitle><manvolnum>1</manvolnum>
37 </citerefentry>) defer to to perform standard authentication tasks.
41 The principal feature of the PAM approach is that the nature of the
42 authentication is dynamically configurable. In other words, the
43 system administrator is free to choose how individual
44 service-providing applications will authenticate users. This dynamic
45 configuration is set by the contents of the single
46 <emphasis remap='B'>Linux-PAM</emphasis> configuration file
47 <filename>/etc/pam.conf</filename>. Alternatively, the configuration
48 can be set by individual configuration files located in the
49 <filename>/etc/pam.d/</filename> directory. The presence of this
50 directory will cause <emphasis remap='B'>Linux-PAM</emphasis> to
51 <emphasis remap='I'>ignore</emphasis>
52 <filename>/etc/pam.conf</filename>.
56 <para>From the point of view of the system administrator, for whom this
57 manual is provided, it is not of primary importance to understand the
58 internal behavior of the
59 <emphasis remap='B'>Linux-PAM</emphasis>
60 library. The important point to recognize is that the configuration
62 <emphasis remap='I'>define</emphasis>
63 the connection between applications
64 <emphasis remap='B'></emphasis>(<emphasis remap='B'>services</emphasis>)
65 and the pluggable authentication modules
66 <emphasis remap='B'></emphasis>(<emphasis remap='B'>PAM</emphasis>s)
67 that perform the actual authentication tasks.</para>
70 <para><emphasis remap='B'>Linux-PAM</emphasis>
71 separates the tasks of
72 <emphasis remap='I'>authentication</emphasis>
73 into four independent management groups:
74 <emphasis remap='B'>account</emphasis> management;
75 <emphasis remap='B'>auth</emphasis>entication management;
76 <emphasis remap='B'>password</emphasis> management;
78 <emphasis remap='B'>session</emphasis> management.
79 (We highlight the abbreviations used for these groups in the
80 configuration file.)</para>
83 <para>Simply put, these groups take care of different aspects of a typical
84 user's request for a restricted service:</para>
87 <para><emphasis remap='B'>account</emphasis> -
88 provide account verification types of service: has the user's password
89 expired?; is this user permitted access to the requested service?</para>
92 <para><emphasis remap='B'>auth</emphasis>entication -
93 authenticate a user and set up user credentials. Typically this is via
94 some challenge-response request that the user must satisfy: if you are
95 who you claim to be please enter your password. Not all authentications
96 are of this type, there exist hardware based authentication schemes
97 (such as the use of smart-cards and biometric devices), with suitable
98 modules, these may be substituted seamlessly for more standard
99 approaches to authentication - such is the flexibility of
100 <emphasis remap='B'>Linux-PAM</emphasis>.</para>
103 <para><emphasis remap='B'>password</emphasis> -
104 this group's responsibility is the task of updating authentication
105 mechanisms. Typically, such services are strongly coupled to those of
107 <emphasis remap='B'>auth</emphasis>
108 group. Some authentication mechanisms lend themselves well to being
109 updated with such a function. Standard UN*X password-based access is
110 the obvious example: please enter a replacement password.</para>
113 <para><emphasis remap='B'>session</emphasis> -
114 this group of tasks cover things that should be done prior to a
115 service being given and after it is withdrawn. Such tasks include the
116 maintenance of audit trails and the mounting of the user's home
118 <emphasis remap='B'>session</emphasis>
119 management group is important as it provides both an opening and
120 closing hook for modules to affect the services available to a user.</para>
124 <refsect1 id='pam8-files'>
128 <term><filename>/etc/pam.conf</filename></term>
130 <para>the configuration file</para>
134 <term><filename>/etc/pam.d</filename></term>
137 the <emphasis remap='B'>Linux-PAM</emphasis> configuration
138 directory. Generally, if this directory is present, the
139 <filename>/etc/pam.conf</filename> file is ignored.
146 <refsect1 id='pam8-errors'>
147 <title>ERRORS</title>
149 Typically errors generated by the
150 <emphasis remap='B'>Linux-PAM</emphasis> system of libraries, will
151 be written to <citerefentry>
152 <refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum>
157 <refsect1 id='pam8-conforming_to'>
158 <title>CONFORMING TO</title>
160 DCE-RFC 86.0, October 1995.
161 Contains additional features, but remains backwardly compatible
166 <refsect1 id='pam8-see_also'>
167 <title>SEE ALSO</title>
170 <refentrytitle>pam</refentrytitle><manvolnum>3</manvolnum>
173 <refentrytitle>pam_authenticate</refentrytitle><manvolnum>3</manvolnum>
176 <refentrytitle>pam_sm_setcred</refentrytitle><manvolnum>3</manvolnum>
179 <refentrytitle>pam_strerror</refentrytitle><manvolnum>3</manvolnum>
182 <refentrytitle>PAM</refentrytitle><manvolnum>8</manvolnum>