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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>4.1. Configuration file syntax</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="Linux-PAM_SAG.html" title="The Linux-PAM System Administrators' Guide"><link rel="up" href="sag-configuration.html" title="Chapter 4. The Linux-PAM configuration file"><link rel="prev" href="sag-configuration.html" title="Chapter 4. The Linux-PAM configuration file"><link rel="next" href="sag-configuration-directory.html" title="4.2. Directory based configuration"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">4.1. Configuration file syntax</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sag-configuration.html">Prev</a> </td><th width="60%" align="center">Chapter 4. The Linux-PAM configuration file</th><td width="20%" align="right"> <a accesskey="n" href="sag-configuration-directory.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sag-configuration-file"></a>4.1. Configuration file syntax</h2></div></div></div>
 The syntax of the <code class="filename">/etc/pam.conf</code>
 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: `\&lt;LF&gt;'.
 Comments are preceded with `#' marks and extend to the next end of
 line.
 
 The format of each rule is a space separated collection of tokens,
 the first three being case-insensitive:
 
 service type control module-path module-arguments
 
 The syntax of files contained in the <code class="filename">/etc/pam.d/</code>
 directory, are identical except for the absence of any
 service field. In this case, the
 service is the name of the file in the
 <code class="filename">/etc/pam.d/</code> directory. This filename must be
 in lower case.
 
 An important feature of PAM, is that a
 number of rules may be stacked to combine
 the services of a number of PAMs for a given authentication task.
 
 The service is typically the familiar name of
 the corresponding application: login and
 su are good examples. The
 service-name, other,
 is reserved for giving default rules.
 Only lines that mention the current service (or in the absence
 of such, the other entries) will be associated
 with the given service-application.
 
 The 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:
 <div class="variablelist"><dl class="variablelist"><dt>account</dt><dd>
 this module type performs non-authentication based account
 management. It is typically used to restrict/permit access
 to a service based on the time of day, currently available
 system resources (maximum number of users) or perhaps the
 location of the applicant user -- 'root' login only on the
 console.
 </dd><dt>auth</dt><dd>
 this module type provides two aspects of authenticating
 the user. Firstly, it establishes that the user is who they
 claim to be, by instructing the application to prompt the user
 for a password or other means of identification. Secondly, the
 module can grant group membership or other privileges through
 its credential granting properties.
 </dd><dt>password</dt><dd>
 this module type is required for updating the authentication
 token associated with the user. Typically, there is one module
 for each 'challenge/response' based authentication (auth) type.
 </dd><dt>session</dt><dd>
 this module type is associated with doing things that need to
 be done for the user before/after they can be given service.
 Such things include the logging of information concerning the
 opening/closing of some data exchange with a user, mounting
 directories, etc.
 </dd></dl></div>
 If the type value from the list above is prepended
 with a - character the PAM library will not log to
 the system log if it is not possible to load the module because it is
 missing in the system. This can be useful especially for modules which
 are not always installed on the system and are not required for correct
 authentication and authorization of the login session.
 
 The third field, 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
 value=action pairs.
 
 For the simple (historical) syntax valid control
 values are:
 <div class="variablelist"><dl class="variablelist"><dt>required</dt><dd>
 failure of such a PAM will ultimately lead to the PAM-API
 returning failure but only after the remaining
 stacked modules (for this
 service and type)
 have been invoked.
 </dd><dt>requisite</dt><dd>
 like required, however, in the case that
 such a module returns a failure, control is directly returned
 to the application or to the superior PAM stack.
 The return value is that associated with
 the first required or requisite module to fail. Note, this flag
 can be used to protect against the possibility of a user getting
 the opportunity to enter a password over an unsafe medium. It is
 conceivable that such behavior might inform an attacker of valid
 accounts on a system. This possibility should be weighed against
 the not insignificant concerns of exposing a sensitive password
 in a hostile environment.
 </dd><dt>sufficient</dt><dd>
 if such a module succeeds and no prior required
 module has failed the PAM framework returns success to
 the application or to the superior PAM stack immediately without
 calling any further modules in the stack. A failure of a
 sufficient module is ignored and processing
 of the PAM module stack continues unaffected.
 </dd><dt>optional</dt><dd>
 the success or failure of this module is only important if
 it is the only module in the stack associated with this
 service+type.
 </dd><dt>include</dt><dd>
 include all lines of given type from the configuration
 file specified as an argument to this control.
 </dd><dt>substack</dt><dd>
 include all lines of given type from the configuration
 file specified as an argument to this control. This differs from
 include in that evaluation of the
 done and die actions
 in a substack does not cause skipping the rest of the complete
 module stack, but only of the substack. Jumps in a substack
 also can not make evaluation jump out of it, and the whole substack
 is counted as one module when the jump is done in a parent stack.
 The reset action will reset the state of a
 module stack to the state it was in as of beginning of the substack
 evaluation.
 </dd></dl></div>
 For the more complicated syntax valid control
 values have the following form:
 <pre class="programlisting">
 [value1=action1 value2=action2 ...]
 </pre>
 Where 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:
 success, open_err,
 symbol_err, service_err,
 system_err, buf_err,
 perm_denied, auth_err,
 cred_insufficient,
 authinfo_unavail,
 user_unknown, maxtries,
 new_authtok_reqd,
 acct_expired, session_err,
 cred_unavail, cred_expired,
 cred_err, no_module_data,
 conv_err, authtok_err,
 authtok_recover_err,
 authtok_lock_busy,
 authtok_disable_aging,
 try_again, ignore,
 abort, authtok_expired,
 module_unknown, bad_item,
 conv_again, incomplete,
 and default.
 
 The last of these, default, implies 'all
 valueN's not mentioned explicitly. Note, the
 full list of PAM errors is available in
 <code class="filename">/usr/include/security/_pam_types.h</code>. The
 actionN can take one of the following forms:
 <div class="variablelist"><dl class="variablelist"><dt>ignore</dt><dd>
 when used with a stack of modules, the module's return
 status will not contribute to the return code the application
 obtains.
 </dd><dt>bad</dt><dd>
 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.
 </dd><dt>die</dt><dd>
 equivalent to bad with the side effect of terminating the
 module stack and PAM immediately returning to the application.
 </dd><dt>ok</dt><dd>
 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 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.
 </dd><dt>done</dt><dd>
 equivalent to ok with the side effect of terminating the module
 stack and PAM immediately returning to the application.
 </dd><dt>N (an unsigned integer)</dt><dd>
	 equivalent to ok with the side effect of jumping over the
	 next N modules in the stack. Note that N equal to 0 is not
	 allowed (and it would be identical to ok in such case).
 </dd><dt>reset</dt><dd>
 clear all memory of the state of the module stack and
 start again with the next stacked module.
 </dd></dl></div>
 Each of the four keywords: required; requisite; sufficient; and
 optional, have an equivalent expression in terms of the [...]
 syntax. They are as follows:
 <div class="variablelist"><dl class="variablelist"><dt>required</dt><dd>
 [success=ok new_authtok_reqd=ok ignore=ignore default=bad]
 </dd><dt>requisite</dt><dd>
 [success=ok new_authtok_reqd=ok ignore=ignore default=die]
 </dd><dt>sufficient</dt><dd>
 [success=done new_authtok_reqd=done default=ignore]
 </dd><dt>optional</dt><dd>
 [success=ok new_authtok_reqd=ok default=ignore]
 </dd></dl></div>
 module-path 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:
 <code class="filename">/lib/security/</code> or
 <code class="filename">/lib64/security/</code>, depending on the architecture.
 
 module-arguments 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. Note, if you wish to include spaces in an argument, you
 should surround that argument with square brackets.
 <pre class="programlisting">
 squid auth required pam_mysql.so user=passwd_query passwd=mada \
 db=eminence [query=select user_name from internet_service \
 where user_name='%u' and password=PASSWORD('%p') and \
 service='web_proxy']
 </pre>
 When using this convention, you can include `[' characters
 inside the string, and if you wish to include a `]' character
 inside the string that will survive the argument parsing, you
 should use `\]'. In other words:
 <pre class="programlisting">
 [..[..\]..] --&gt; ..[..]..
 </pre>
 Any line in (one of) the configuration file(s), that is not formatted
 correctly, will generally tend (erring on the side of caution) to make
 the authentication process fail. A corresponding error is written to
 the system log files with a call to
 syslog(3).
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