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<?xml version="1.0"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" [
<!ENTITY version SYSTEM "../version.xml">
]>
<refentry id="pkexec.1" xmlns:xi="http://www.w3.org/2003/XInclude">
<refentryinfo>
<title>pkexec</title>
<date>May 2009</date>
<productname>polkit</productname>
</refentryinfo>
<refmeta>
<refentrytitle>pkexec</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="version"></refmiscinfo>
</refmeta>
<refnamediv>
<refname>pkexec</refname>
<refpurpose>Execute a command as another user</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>pkexec</command>
<arg><option>--version</option></arg>
<arg><option>--disable-internal-agent</option></arg>
<arg><option>--help</option></arg>
</cmdsynopsis>
<cmdsynopsis>
<command>pkexec</command>
<arg choise="plain">
<option>--keep-cwd</option>
</arg>
<group>
<arg choice="plain">
<option>--user</option>
<replaceable>username</replaceable>
</arg>
</group>
<arg choice="plain"><replaceable>PROGRAM</replaceable></arg>
<group rep="repeat">
<arg choice="plain"><replaceable>ARGUMENTS</replaceable></arg>
</group>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1 id="pkexec-description"><title>DESCRIPTION</title>
<para>
<command>pkexec</command> allows an authorized user to execute
<replaceable>PROGRAM</replaceable> as another user. If
<replaceable>PROGRAM</replaceable> is not specified, the default
shell will be run. If <replaceable>username</replaceable> is
not specified, then the program will be executed as the
administrative super user, <emphasis>root</emphasis>.
</para>
</refsect1>
<refsect1 id="pkexec-return-value"><title>RETURN VALUE</title>
<para>
Upon successful completion, the return value is the return value
of <replaceable>PROGRAM</replaceable>. If the calling process is
not authorized or an authorization could not be obtained through
authentication or an error occurred, <command>pkexec</command>
exits with a return value of 127. If the authorization could not
be obtained because the user dismissed the authentication
dialog, <command>pkexec</command> exits with a return value of
126.
</para>
</refsect1>
<refsect1 id="pkexec-auth-agent"><title>AUTHENTICATION AGENT</title>
<para>
<command>pkexec</command>, 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 <command>pkexec</command> will register its own
textual authentication agent. This behavior can be turned off by
passing the <option>--disable-internal-agent</option> option.
</para>
</refsect1>
<refsect1 id="pkexec-security-notes"><title>SECURITY NOTES</title>
<para>
Executing a program as another user is a privileged
operation. By default the action to check for (see
<xref linkend="pkexec-action"/>) 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.
</para>
<para>
The environment that <replaceable>PROGRAM</replaceable> will run
it, will be set to a minimal known and safe environment in order
to avoid injecting code
through <literal>LD_LIBRARY_PATH</literal> or similar
mechanisms. In addition the <literal>PKEXEC_UID</literal>
environment variable is set to the user id of the process
invoking <command>pkexec</command>. As a
result, <command>pkexec</command> will not by default allow you to run
X11 applications as another user since
the <literal>$DISPLAY</literal> and <literal>$XAUTHORITY</literal>
environment variables are not set. These two variables will be retained
if the <emphasis>org.freedesktop.policykit.exec.allow_gui</emphasis> annotation
on an action is set to a nonempty value; this is discouraged, though, and
should only be used for legacy programs.
</para>
<para>
<command>pkexec</command> will run <replaceable>PROGRAM</replaceable>
in <replaceable>username</replaceable>'s home directory, unless
<option>--keep-cwd</option> is used to override this behavior
</para>
<para>
Note that <command>pkexec</command> does no validation of
the <replaceable>ARGUMENTS</replaceable> passed
to <replaceable>PROGRAM</replaceable>. In the normal case (where
administrator authentication is required every
time <command>pkexec</command> is used), this is not a problem
since if the user is an administrator he might as well just
run <command>pkexec bash</command> to get root.
</para>
<para>
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 <emphasis role='strong'>never</emphasis> implicitly trust user input (e.g. like any
other well-written <emphasis>suid</emphasis> program).
</para>
</refsect1>
<refsect1 id="pkexec-action"><title>ACTION AND AUTHORIZATIONS</title>
<para>
By default, the
<emphasis>org.freedesktop.policykit.exec</emphasis> action is
used. To use another action, use the
<emphasis>org.freedesktop.policykit.exec.path</emphasis>
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 <emphasis>org.freedesktop.policykit.exec.argv1</emphasis>
annotation is present, the action will only be picked if the
first argument to the program matches the value of the annotation.
</para>
<para>
Note that authentication messages may reference variables (see
<xref linkend="pkexec-variables"/>), for example
<literal>$(user)</literal> will be expanded to the value of the
<literal>user</literal> variable.
</para>
</refsect1>
<refsect1 id="pkexec-wrapper"><title>WRAPPER USAGE</title>
<para>
To avoid modifying existing software to prefix their
command-line invocations with <command>pkexec</command>,
it's possible to use <command>pkexec</command> in a
<ulink url="http://en.wikipedia.org/wiki/Shebang_(Unix)">she-bang wrapper</ulink>
like this:
</para>
<programlisting><![CDATA[
#!/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])
]]></programlisting>
<para>
If this script is installed into <filename>/usr/bin/my-pk-test</filename>,
then the following annotations
</para>
<programlisting><![CDATA[
[...]
<annotate key="org.freedesktop.policykit.exec.path">/usr/bin/python</annotate>
<annotate key="org.freedesktop.policykit.exec.argv1">/usr/bin/my-pk-test</annotate>
[...]
]]></programlisting>
<para>
can be used to select the appropriate polkit action. Be careful
to get the latter annotation right, otherwise it will match any
<command>pkexec</command> invocation of
<filename>/usr/bin/python</filename> scripts.
</para>
</refsect1>
<refsect1 id="pkexec-variables"><title>VARIABLES</title>
<para>
The following variables are set by
<command>pkexec</command>. They can be used in authorization
rules and messages shown in authentication dialogs:
</para>
<variablelist>
<varlistentry>
<term><emphasis>program</emphasis></term>
<listitem>
<para>
Fully qualified path to the program to be executed.
Example: <quote>/bin/cat</quote>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis>command_line</emphasis></term>
<listitem>
<para>
The requested command-line (do not use this for any
security checks, it is not secure).
Example: <quote>cat /srv/xyz/foobar</quote>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis>user</emphasis></term>
<listitem>
<para>
The user name of the user to execute the program as.
Example: <quote>davidz</quote>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis>user.gecos</emphasis></term>
<listitem>
<para>
The full name of the user to execute the program as.
Example: <quote>David Zeuthen</quote>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis>user.display</emphasis></term>
<listitem>
<para>
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: <quote>David Zeuthen (davidz)</quote>
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="pkexec-author"><title>AUTHOR</title>
<para>
Written by David Zeuthen <email>davidz@redhat.com</email> with
a lot of help from many others.
</para>
</refsect1>
<refsect1 id="pkexec-bugs">
<title>BUGS</title>
<para>
Please send bug reports to either the distribution or the
polkit-devel mailing list,
see <ulink url="https://github.com/polkit-org/polkit#bugs-and-development"/>.
</para>
</refsect1>
<refsect1 id="pkexec-see-also">
<title>SEE ALSO</title>
<para>
<link linkend="polkit.8"><citerefentry><refentrytitle>polkit</refentrytitle><manvolnum>8</manvolnum></citerefentry></link>,
<link linkend="polkitd.8"><citerefentry><refentrytitle>polkitd</refentrytitle><manvolnum>8</manvolnum></citerefentry></link>,
<link linkend="pkaction.1"><citerefentry><refentrytitle>pkaction</refentrytitle><manvolnum>1</manvolnum></citerefentry></link>,
<link linkend="pkcheck.1"><citerefentry><refentrytitle>pkcheck</refentrytitle><manvolnum>1</manvolnum></citerefentry></link>,
<link linkend="pkttyagent.1"><citerefentry><refentrytitle>pkttyagent</refentrytitle><manvolnum>1</manvolnum></citerefentry></link>
</para>
</refsect1>
</refentry>
|
