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<div class="refentry">
<a name="pkexec.1"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
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<h2><span class="refentrytitle">pkexec</span></h2>
<p>pkexec — Execute a command as another user</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
</tr></table></div>
<div class="refsynopsisdiv">
<h2>Synopsis</h2>
<div class="cmdsynopsis"><p><code class="command">pkexec</code> [<code class="option">--version</code>] [<code class="option">--disable-internal-agent</code>] [<code class="option">--help</code>]</p></div>
<div class="cmdsynopsis"><p><code class="command">pkexec</code> [
<code class="option">--user</code>
<em class="replaceable"><code>username</code></em>
] <em class="replaceable"><code>PROGRAM</code></em> [ <em class="replaceable"><code>ARGUMENTS</code></em> ...]</p></div>
</div>
<div class="refsect1">
<a name="pkexec-description"></a><h2>DESCRIPTION</h2>
<p>
<span class="command"><strong>pkexec</strong></span> allows an authorized user to execute
<em class="replaceable"><code>PROGRAM</code></em> as another user. If
<em class="replaceable"><code>PROGRAM</code></em> is not specified, the default
shell will be run. If <em class="replaceable"><code>username</code></em> is
not specified, then the program will be executed as the
administrative super user, <span class="emphasis"><em>root</em></span>.
</p>
</div>
<div class="refsect1">
<a name="pkexec-return-value"></a><h2>RETURN VALUE</h2>
<p>
Upon successful completion, the return value is the return value
of <em class="replaceable"><code>PROGRAM</code></em>. If the calling process is
not authorized or an authorization could not be obtained through
authentication or an error occured, <span class="command"><strong>pkexec</strong></span>
exits with a return value of 127. If the authorization could not
be obtained because the user dismissed the authentication
dialog, <span class="command"><strong>pkexec</strong></span> exits with a return value of
126.
</p>
</div>
<div class="refsect1">
<a name="pkexec-auth-agent"></a><h2>AUTHENTICATION AGENT</h2>
<p>
<span class="command"><strong>pkexec</strong></span>, like any other polkit application,
will use the authentication agent registered for the calling
process or session. However, if no authentication agent is
available, then <span class="command"><strong>pkexec</strong></span> will register its own
textual authentication agent. This behavior can be turned off by
passing the <code class="option">--disable-internal-agent</code> option.
</p>
</div>
<div class="refsect1">
<a name="pkexec-security-notes"></a><h2>SECURITY NOTES</h2>
<p>
Executing a program as another user is a privileged
operation. By default the action to check for (see
<a class="xref" href="pkexec.1.html#pkexec-action" title="ACTION AND AUTHORIZATIONS">the section called “ACTION AND AUTHORIZATIONS”</a>) requires administrator
authentication. In addition, the authentication dialog presented
to the user will display the full path to the program to be
executed so the user is aware of what will happen.
</p>
<p>
The environment that <em class="replaceable"><code>PROGRAM</code></em> will run
it, will be set to a minimal known and safe environment in order
to avoid injecting code
through <code class="literal">LD_LIBRARY_PATH</code> or similar
mechanisms. In addition the <code class="literal">PKEXEC_UID</code>
environment variable is set to the user id of the process
invoking <span class="command"><strong>pkexec</strong></span>. As a
result, <span class="command"><strong>pkexec</strong></span> will not by default allow you to run
X11 applications as another user since
the <code class="literal">$DISPLAY</code> and <code class="literal">$XAUTHORITY</code>
environment variables are not set. These two variables will be retained
if the <span class="emphasis"><em>org.freedesktop.policykit.exec.allow_gui</em></span> annotation
on an action is set to a nonempty value; this is discouraged, though, and
should only be used for legacy programs.
</p>
<p>
Note that <span class="command"><strong>pkexec</strong></span> does no validation of
the <em class="replaceable"><code>ARGUMENTS</code></em> passed
to <em class="replaceable"><code>PROGRAM</code></em>. In the normal case (where
administrator authentication is required every
time <span class="command"><strong>pkexec</strong></span> is used), this is not a problem
since if the user is an administrator he might as well just
run <span class="command"><strong>pkexec bash</strong></span> to get root.
</p>
<p>
However, if an action is used for which the user can retain
authorization (or if the user is implicitly authorized) this
could be a security hole. Therefore, as a rule of thumb,
programs for which the default required authorization is
changed, should <span class="strong"><strong>never</strong></span> implicitly trust user input (e.g. like any
other well-written <span class="emphasis"><em>suid</em></span> program).
</p>
</div>
<div class="refsect1">
<a name="pkexec-action"></a><h2>ACTION AND AUTHORIZATIONS</h2>
<p>
By default, the
<span class="emphasis"><em>org.freedesktop.policykit.exec</em></span> action is
used. To use another action, use the
<span class="emphasis"><em>org.freedesktop.policykit.exec.path</em></span>
annotation on an action with the value set to the full path of
the program. In addition to specifying the program, the
authentication message, description, icon and defaults can be
specified. If the <span class="emphasis"><em>org.freedesktop.policykit.exec.argv1</em></span>
annotation is present, the action will only be picked if the
first argument to the program matches the value of the annotation.
</p>
<p>
Note that authentication messages may reference variables (see
<a class="xref" href="pkexec.1.html#pkexec-variables" title="VARIABLES">the section called “VARIABLES”</a>), for example
<code class="literal">$(user)</code> will be expanded to the value of the
<code class="literal">user</code> variable.
</p>
</div>
<div class="refsect1">
<a name="pkexec-wrapper"></a><h2>WRAPPER USAGE</h2>
<p>
To avoid modifying existing software to prefix their
command-line invocations with <span class="command"><strong>pkexec</strong></span>,
it's possible to use <span class="command"><strong>pkexec</strong></span> in a
<a class="ulink" href="http://en.wikipedia.org/wiki/Shebang_(Unix)" target="_top">she-bang wrapper</a>
like this:
</p>
<pre class="programlisting">
#!/usr/bin/pkexec /usr/bin/python
import os
import sys
print "Hello, I'm running as uid %d"%(os.getuid())
for n in range(len(sys.argv)):
print "arg[%d]=`%s'"%(n, sys.argv[n])
</pre>
<p>
If this script is installed into <code class="filename">/usr/bin/my-pk-test</code>,
then the following annotations
</p>
<pre class="programlisting">
[...]
<annotate key="org.freedesktop.policykit.exec.path">/usr/bin/python</annotate>
<annotate key="org.freedesktop.policykit.exec.argv1">/usr/bin/my-pk-test</annotate>
[...]
</pre>
<p>
can be used to select the appropriate polkit action. Be careful
to get the latter annotation right, otherwise it will match any
<span class="command"><strong>pkexec</strong></span> invocation of
<code class="filename">/usr/bin/python</code> scripts.
</p>
</div>
<div class="refsect1">
<a name="pkexec-variables"></a><h2>VARIABLES</h2>
<p>
The following variables are set by
<span class="command"><strong>pkexec</strong></span>. They can be used in authorization
rules and messages shown in authentication dialogs:
</p>
<div class="variablelist"><table border="0" class="variablelist">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><span class="emphasis"><em>program</em></span></span></p></td>
<td><p>
Fully qualified path to the program to be executed.
Example: <span class="quote">“<span class="quote">/bin/cat</span>”</span>
</p></td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>command_line</em></span></span></p></td>
<td><p>
The requested command-line (do not use this for any
security checks, it is not secure).
Example: <span class="quote">“<span class="quote">cat /srv/xyz/foobar</span>”</span>
</p></td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>user</em></span></span></p></td>
<td><p>
The user name of the user to execute the program as.
Example: <span class="quote">“<span class="quote">davidz</span>”</span>
</p></td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>user.gecos</em></span></span></p></td>
<td><p>
The full name of the user to execute the program as.
Example: <span class="quote">“<span class="quote">David Zeuthen</span>”</span>
</p></td>
</tr>
<tr>
<td><p><span class="term"><span class="emphasis"><em>user.display</em></span></span></p></td>
<td><p>
A representation of the user to execute the program as
that is suitable for display in an authentication dialog.
Is typically set to a combination of the user name and the
full name.
Example: <span class="quote">“<span class="quote">David Zeuthen (davidz)</span>”</span>
</p></td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="pkexec-author"></a><h2>AUTHOR</h2>
<p>
Written by David Zeuthen <code class="email"><<a class="email" href="mailto:davidz@redhat.com">davidz@redhat.com</a>></code> with
a lot of help from many others.
</p>
</div>
<div class="refsect1">
<a name="pkexec-bugs"></a><h2>BUGS</h2>
<p>
Please send bug reports to either the distribution or the
polkit-devel mailing list,
see the link <a class="ulink" href="http://lists.freedesktop.org/mailman/listinfo/polkit-devel" target="_top">http://lists.freedesktop.org/mailman/listinfo/polkit-devel</a>
on how to subscribe.
</p>
</div>
<div class="refsect1">
<a name="pkexec-see-also"></a><h2>SEE ALSO</h2>
<p>
<a class="link" href="polkit.8.html" title="polkit"><span class="citerefentry"><span class="refentrytitle">polkit</span>(8)</span></a>,
<a class="link" href="polkitd.8.html" title="polkitd"><span class="citerefentry"><span class="refentrytitle">polkitd</span>(8)</span></a>,
<a class="link" href="pkaction.1.html" title="pkaction"><span class="citerefentry"><span class="refentrytitle">pkaction</span>(1)</span></a>,
<a class="link" href="pkcheck.1.html" title="pkcheck"><span class="citerefentry"><span class="refentrytitle">pkcheck</span>(1)</span></a>,
<a class="link" href="pkttyagent.1.html" title="pkttyagent"><span class="citerefentry"><span class="refentrytitle">pkttyagent</span>(1)</span></a>
</p>
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