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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><p>
    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.
  </p><p>
      The format of each rule is a space separated collection of tokens,
      the first three being case-insensitive:
    </p><p>
      <span class="emphasis"><em> service  type  control  module-path  module-arguments</em></span>
    </p><p>
      The syntax of files contained in the <code class="filename">/etc/pam.d/</code>
      directory, are identical except for the absence of any
      <span class="emphasis"><em>service</em></span> field. In this case, the
      <span class="emphasis"><em>service</em></span> is the name of the file in the
      <code class="filename">/etc/pam.d/</code> directory. This filename must be
      in lower case.
    </p><p>
      An important feature of <span class="emphasis"><em>PAM</em></span>, is that a
      number of rules may be <span class="emphasis"><em>stacked</em></span> to combine
      the services of a number of PAMs for a given authentication task.
    </p><p>
      The <span class="emphasis"><em>service</em></span> is typically the familiar name of
      the corresponding application: <span class="emphasis"><em>login</em></span> and
      <span class="emphasis"><em>su</em></span> are good examples. The
      <span class="emphasis"><em>service</em></span>-name, <span class="emphasis"><em>other</em></span>,
      is reserved for giving <span class="emphasis"><em>default</em></span> rules.
      Only lines that mention the current service (or in the absence
      of such, the <span class="emphasis"><em>other</em></span> entries) will be associated
      with the given service-application.
    </p><p>
      The <span class="emphasis"><em>type</em></span> 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:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">account</span></dt><dd><p>
            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.
          </p></dd><dt><span class="term">auth</span></dt><dd><p>
            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.
          </p></dd><dt><span class="term">password</span></dt><dd><p>
            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.
          </p></dd><dt><span class="term">session</span></dt><dd><p>
            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.
          </p></dd></dl></div><p>
      If the <span class="emphasis"><em>type</em></span> value from the list above is prepended
      with a <span class="emphasis"><em>-</em></span> 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.
    </p><p>
      The third field, <span class="emphasis"><em>control</em></span>, 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
      <span class="emphasis"><em>value=action</em></span> pairs.
    </p><p>
      For the simple (historical) syntax valid <span class="emphasis"><em>control</em></span>
      values are:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">required</span></dt><dd><p>
            failure of such a PAM will ultimately lead to the PAM-API
            returning failure but only after the remaining
            <span class="emphasis"><em>stacked</em></span> modules (for this
            <span class="emphasis"><em>service</em></span> and <span class="emphasis"><em>type</em></span>)
            have been invoked.
          </p></dd><dt><span class="term">requisite</span></dt><dd><p>
            like <span class="emphasis"><em>required</em></span>, 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.
          </p></dd><dt><span class="term">sufficient</span></dt><dd><p>
            if such a module succeeds and no prior <span class="emphasis"><em>required</em></span>
            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
            <span class="emphasis"><em>sufficient</em></span> module is ignored and processing
            of the PAM module stack continues unaffected.
          </p></dd><dt><span class="term">optional</span></dt><dd><p>
            the success or failure of this module is only important if
            it is the only module in the stack associated with this
            <span class="emphasis"><em>service</em></span>+<span class="emphasis"><em>type</em></span>.
          </p></dd><dt><span class="term">include</span></dt><dd><p>
            include all lines of given type from the configuration
            file specified as an argument to this control.
          </p></dd><dt><span class="term">substack</span></dt><dd><p>
            include all lines of given type from the configuration
            file specified as an argument to this control. This differs from
            <span class="emphasis"><em>include</em></span> in that evaluation of the
            <span class="emphasis"><em>done</em></span> and <span class="emphasis"><em>die</em></span> 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 <span class="emphasis"><em>reset</em></span> action will reset the state of a
            module stack to the state it was in as of beginning of the substack
            evaluation.
          </p></dd></dl></div><p>
      For the more complicated syntax valid <span class="emphasis"><em>control</em></span>
      values have the following form:
    </p><pre class="programlisting">
      [value1=action1 value2=action2 ...]
    </pre><p>
      Where <span class="emphasis"><em>valueN</em></span> 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:
      <span class="emphasis"><em>success</em></span>, <span class="emphasis"><em>open_err</em></span>,
      <span class="emphasis"><em>symbol_err</em></span>, <span class="emphasis"><em>service_err</em></span>,
      <span class="emphasis"><em>system_err</em></span>, <span class="emphasis"><em>buf_err</em></span>,
      <span class="emphasis"><em>perm_denied</em></span>, <span class="emphasis"><em>auth_err</em></span>,
      <span class="emphasis"><em>cred_insufficient</em></span>,
      <span class="emphasis"><em>authinfo_unavail</em></span>,
      <span class="emphasis"><em>user_unknown</em></span>, <span class="emphasis"><em>maxtries</em></span>,
      <span class="emphasis"><em>new_authtok_reqd</em></span>,
      <span class="emphasis"><em>acct_expired</em></span>, <span class="emphasis"><em>session_err</em></span>,
      <span class="emphasis"><em>cred_unavail</em></span>, <span class="emphasis"><em>cred_expired</em></span>,
      <span class="emphasis"><em>cred_err</em></span>, <span class="emphasis"><em>no_module_data</em></span>,
      <span class="emphasis"><em>conv_err</em></span>, <span class="emphasis"><em>authtok_err</em></span>,
      <span class="emphasis"><em>authtok_recover_err</em></span>,
      <span class="emphasis"><em>authtok_lock_busy</em></span>,
      <span class="emphasis"><em>authtok_disable_aging</em></span>,
      <span class="emphasis"><em>try_again</em></span>, <span class="emphasis"><em>ignore</em></span>,
      <span class="emphasis"><em>abort</em></span>, <span class="emphasis"><em>authtok_expired</em></span>,
      <span class="emphasis"><em>module_unknown</em></span>, <span class="emphasis"><em>bad_item</em></span>,
      <span class="emphasis"><em>conv_again</em></span>, <span class="emphasis"><em>incomplete</em></span>,
      and <span class="emphasis"><em>default</em></span>.
    </p><p>
      The last of these, <span class="emphasis"><em>default</em></span>, implies 'all
      <span class="emphasis"><em>valueN</em></span>'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
      <span class="emphasis"><em>actionN</em></span> can take one of the following forms:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">ignore</span></dt><dd><p>
             when used with a stack of modules, the module's return
             status will not contribute to the return code the application
             obtains.
          </p></dd><dt><span class="term">bad</span></dt><dd><p>
             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.
          </p></dd><dt><span class="term">die</span></dt><dd><p>
             equivalent to bad with the side effect of terminating the
             module stack and PAM immediately returning to the application.
          </p></dd><dt><span class="term">ok</span></dt><dd><p>
             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 <span class="emphasis"><em>PAM_SUCCESS</em></span>,
             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.
          </p></dd><dt><span class="term">done</span></dt><dd><p>
             equivalent to ok with the side effect of terminating the module
             stack and PAM immediately returning to the application.
          </p></dd><dt><span class="term">N (an unsigned integer)</span></dt><dd><p>
	     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).
          </p></dd><dt><span class="term">reset</span></dt><dd><p>
             clear all memory of the state of the module stack and
             start again with the next stacked module.
          </p></dd></dl></div><p>
      Each of the four keywords: required; requisite; sufficient; and
      optional, have an equivalent expression in terms of the [...]
      syntax. They are as follows:
    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">required</span></dt><dd><p>
             [success=ok new_authtok_reqd=ok ignore=ignore default=bad]
          </p></dd><dt><span class="term">requisite</span></dt><dd><p>
             [success=ok new_authtok_reqd=ok ignore=ignore default=die]
          </p></dd><dt><span class="term">sufficient</span></dt><dd><p>
             [success=done new_authtok_reqd=done default=ignore]
          </p></dd><dt><span class="term">optional</span></dt><dd><p>
             [success=ok new_authtok_reqd=ok default=ignore]
          </p></dd></dl></div><p>
      <span class="emphasis"><em>module-path</em></span> 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.
    </p><p>
      <span class="emphasis"><em>module-arguments</em></span> 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.
    </p><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><p>
      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:
    </p><pre class="programlisting">
    [..[..\]..]    --&gt;   ..[..]..
    </pre><p>
      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
      <span class="citerefentry"><span class="refentrytitle">syslog</span>(3)</span>.
    </p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sag-configuration.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sag-configuration.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sag-configuration-directory.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 4. The Linux-PAM configuration file </td><td width="20%" align="center"><a accesskey="h" href="Linux-PAM_SAG.html">Home</a></td><td width="40%" align="right" valign="top"> 4.2. Directory based configuration</td></tr></table></div></body></html>
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