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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>6.41. pam_xauth - forward xauth keys between users</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-module-reference.html" title="Chapter 6. A reference guide for available modules"><link rel="prev" href="sag-pam_wheel.html" title="6.40. pam_wheel - only permit root access to members of group wheel"><link rel="next" href="sag-see-also.html" title="Chapter 7. See also"></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">6.41. pam_xauth - forward xauth keys between users</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sag-pam_wheel.html">Prev</a> </td><th width="60%" align="center">Chapter 6. A reference guide for available modules</th><td width="20%" align="right"> <a accesskey="n" href="sag-see-also.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-pam_xauth"></a>6.41. pam_xauth - forward xauth keys between users</h2></div></div></div><div class="cmdsynopsis"><p><code class="command">pam_xauth.so</code>  [
	debug
      ] [
        xauthpath=<em class="replaceable"><code>/path/to/xauth</code></em>
      ] [
        systemuser=<em class="replaceable"><code>UID</code></em>
      ] [
        targetuser=<em class="replaceable"><code>UID</code></em>
      ]</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_xauth-description"></a>6.41.1. DESCRIPTION</h3></div></div></div><p>
      The pam_xauth PAM module is designed to forward xauth keys
      (sometimes referred to as "cookies") between users.
    </p><p>
      Without pam_xauth, when xauth is enabled and a user uses the
       <span class="citerefentry"><span class="refentrytitle">su</span>(1)</span> command to assume another user's privileges,
      that user is no longer able to access the original user's X display
      because the new user does not have the key needed to access the
      display. pam_xauth solves the problem by forwarding the key from
      the user running su (the source user) to the user whose identity the
      source user is assuming (the target user) when the session is created,
      and destroying the key when the session is torn down.
    </p><p>
      This means, for example, that when you run
       <span class="citerefentry"><span class="refentrytitle">su</span>(1)</span> from an xterm session, you will be able to run
      X programs without explicitly dealing with the
      <span class="citerefentry"><span class="refentrytitle">xauth</span>(1)</span> xauth command or ~/.Xauthority files.
    </p><p>
      pam_xauth will only forward keys if xauth can list a key connected
      to the $DISPLAY environment variable.
    </p><p>
      Primitive access control is provided by
      <code class="filename">~/.xauth/export</code> in the invoking user's home
      directory and <code class="filename">~/.xauth/import</code> in the target
      user's home directory.
    </p><p>
      If a user has a <code class="filename">~/.xauth/import</code> file, the user
      will only receive cookies from users listed in the file. If there is
      no <code class="filename">~/.xauth/import</code> file, the user will accept
      cookies from any other user.
    </p><p>
      If a user has a <code class="filename">.xauth/export</code> file, the user will
      only forward cookies to users listed in the file. If there is no
      <code class="filename">~/.xauth/export</code> file, and the invoking user is
      not <span class="emphasis"><em>root</em></span>, the user will forward cookies
      to any other user. If there is no <code class="filename">~/.xauth/export</code>
      file, and the invoking user is <span class="emphasis"><em>root</em></span>,
      the user will <span class="emphasis"><em>not</em></span> forward cookies to
      other users.
    </p><p>
      Both the import and export files support wildcards (such as
      <span class="emphasis"><em>*</em></span>). Both the import and export files
      can be empty, signifying that no users are allowed.
    </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_xauth-options"></a>6.41.2. OPTIONS</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">
          <code class="option">debug</code>
        </span></dt><dd><p>
	    Print debug information.
          </p></dd><dt><span class="term">
          <code class="option">xauthpath=<em class="replaceable"><code>/path/to/xauth</code></em></code>
        </span></dt><dd><p>
            Specify the path the xauth program (it is expected in
            <code class="filename">/usr/X11R6/bin/xauth</code>,
            <code class="filename">/usr/bin/xauth</code>, or
            <code class="filename">/usr/bin/X11/xauth</code> by default).
          </p></dd><dt><span class="term">
          <code class="option">systemuser=<em class="replaceable"><code>UID</code></em></code>
        </span></dt><dd><p>
            Specify the highest UID which will be assumed to belong to a
            "system" user. pam_xauth will refuse to forward credentials to
            users with UID less than or equal to this number, except for
            root and the "targetuser", if specified.
          </p></dd><dt><span class="term">
          <code class="option">targetuser=<em class="replaceable"><code>UID</code></em></code>
        </span></dt><dd><p>
            Specify  a single target UID which is exempt from the
            systemuser check.
          </p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_xauth-types"></a>6.41.3. MODULE TYPES PROVIDED</h3></div></div></div><p>
      Only the <span class="emphasis"><em>session</em></span> type is provided.
    </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_xauth-return_values"></a>6.41.4. RETURN VALUES</h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">PAM_BUF_ERR</span></dt><dd><p>
             Memory buffer error.
          </p></dd><dt><span class="term">PAM_PERM_DENIED</span></dt><dd><p>
            Permission denied by import/export file.
          </p></dd><dt><span class="term">PAM_SESSION_ERR</span></dt><dd><p>
	    Cannot determine user name, UID or access users home directory.
          </p></dd><dt><span class="term">PAM_SUCCESS</span></dt><dd><p>
            Success.
          </p></dd><dt><span class="term">PAM_USER_UNKNOWN</span></dt><dd><p>
            User not known.
          </p></dd></dl></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_xauth-examples"></a>6.41.5. EXAMPLES</h3></div></div></div><p>
      Add the following line to <code class="filename">/etc/pam.d/su</code> to
      forward xauth keys between users when calling su:
      </p><pre class="programlisting">
session  optional  pam_xauth.so
      </pre><p>
    </p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sag-pam_xauth-author"></a>6.41.6. AUTHOR</h3></div></div></div><p>
        pam_xauth was written by Nalin Dahyabhai &lt;nalin@redhat.com&gt;,
        based on original version by
        Michael K. Johnson &lt;johnsonm@redhat.com&gt;.
      </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sag-pam_wheel.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sag-module-reference.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sag-see-also.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">6.40. pam_wheel - only permit root access to members of group wheel </td><td width="20%" align="center"><a accesskey="h" href="Linux-PAM_SAG.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 7. See also</td></tr></table></div></body></html>

6.41. pam_xauth - forward xauth keys between users

6.41. pam_xauth - forward xauth keys between users
Prev	Chapter 6. A reference guide for available modules	Next

6.41. pam_xauth - forward xauth keys between users

pam_xauth.so [ debug ] [ xauthpath=/path/to/xauth ] [ systemuser=UID ] [ targetuser=UID ]

6.41.1. DESCRIPTION

The pam_xauth PAM module is designed to forward xauth keys (sometimes referred to as "cookies") between users.

Without pam_xauth, when xauth is enabled and a user uses the su(1) command to assume another user's privileges, that user is no longer able to access the original user's X display because the new user does not have the key needed to access the display. pam_xauth solves the problem by forwarding the key from the user running su (the source user) to the user whose identity the source user is assuming (the target user) when the session is created, and destroying the key when the session is torn down.

This means, for example, that when you run su(1) from an xterm session, you will be able to run X programs without explicitly dealing with the xauth(1) xauth command or ~/.Xauthority files.

pam_xauth will only forward keys if xauth can list a key connected to the $DISPLAY environment variable.

Primitive access control is provided by ~/.xauth/export in the invoking user's home directory and ~/.xauth/import in the target user's home directory.

If a user has a ~/.xauth/import file, the user will only receive cookies from users listed in the file. If there is no ~/.xauth/import file, the user will accept cookies from any other user.

If a user has a .xauth/export file, the user will only forward cookies to users listed in the file. If there is no ~/.xauth/export file, and the invoking user is not root, the user will forward cookies to any other user. If there is no ~/.xauth/export file, and the invoking user is root, the user will not forward cookies to other users.

Both the import and export files support wildcards (such as *). Both the import and export files can be empty, signifying that no users are allowed.

6.41.2. OPTIONS

debug: Print debug information.
xauthpath=/path/to/xauth: Specify the path the xauth program (it is expected in /usr/X11R6/bin/xauth, /usr/bin/xauth, or /usr/bin/X11/xauth by default).
systemuser=UID: Specify the highest UID which will be assumed to belong to a "system" user. pam_xauth will refuse to forward credentials to users with UID less than or equal to this number, except for root and the "targetuser", if specified.
targetuser=UID: Specify a single target UID which is exempt from the systemuser check.

6.41.3. MODULE TYPES PROVIDED

Only the session type is provided.

6.41.4. RETURN VALUES

PAM_BUF_ERR: Memory buffer error.
PAM_PERM_DENIED: Permission denied by import/export file.
PAM_SESSION_ERR: Cannot determine user name, UID or access users home directory.
PAM_SUCCESS: Success.
PAM_USER_UNKNOWN: User not known.

6.41.5. EXAMPLES

Add the following line to /etc/pam.d/su to forward xauth keys between users when calling su:

session  optional  pam_xauth.so

6.41.6. AUTHOR

pam_xauth was written by Nalin Dahyabhai <nalin@redhat.com>, based on original version by Michael K. Johnson <johnsonm@redhat.com>.

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