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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>
<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>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 occured, <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 PolicyKit application,
will use the authentication agent registered for the calling
process. 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 required authorization (See
<xref linkend="pkexec-required-authz"/>) 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>
<mediaobject id="pkexec-bash">
<imageobject>
<imagedata fileref="pkexec-bash.png" format="PNG"/>
</imageobject>
<textobject>
<programlisting><![CDATA[
+----------------------------------------------------------+
| Authenticate [X] |
+----------------------------------------------------------+
| |
| [Icon] Authentication is needed to run `/bin/bash' |
| as the super user |
| |
| An application is attempting to perform an |
| action that requires privileges. Authentication |
| as the super user is required to perform this |
| action. |
| |
| Password for root: [_________________________] |
| |
| [V] Details: |
| Command: /bin/bash |
| Run As: Super User (root) |
| Action: org.freedesktop.policykit.exec |
| Vendor: The PolicyKit Project |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
]]></programlisting>
</textobject>
</mediaobject>
<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 allow you to run
e.g. X11 applications as another user since
the <literal>$DISPLAY</literal> environment variable is not set.
</para>
</refsect1>
<refsect1 id="pkexec-required-authz"><title>REQUIRED AUTHORIZATIONS</title>
<para>
By default,
the <emphasis>org.freedesktop.policykit.exec</emphasis>
authorization is required unless an action definition file is
present for the program in question. To require another
authorization, it can be specified using the <emphasis>org.freedesktop.policykit.exec.path</emphasis> annotation on an action (See <xref linkend="pkexec-example"/> for details).
</para>
</refsect1>
<refsect1 id="pkexec-example"><title>EXAMPLE</title>
<para>
To specify what kind of authorization is needed to execute the
program <filename>/usr/bin/pk-example-frobnicate</filename> as
another user, simply write an action definition file like this
</para>
<programlisting>
<xi:include xmlns:xi="http://www.w3.org/2001/XInclude" parse="text" href="../../src/examples/org.freedesktop.policykit.examples.pkexec.policy"><xi:fallback>FIXME: MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
<para>
and drop it in
the <filename>/usr/share/polkit-1/actions</filename> directory
under a suitable name (e.g. matching the namespace of the
action). Note that in addition to specifying the program, the
authentication message, description, icon and defaults can be
specified. For example, for the action defined above, the following
authentication dialog will be shown:
</para>
<mediaobject id="pkexec-frobnicate">
<imageobject>
<imagedata fileref="pkexec-frobnicate.png" format="PNG"/>
</imageobject>
<textobject>
<programlisting><![CDATA[
+----------------------------------------------------------+
| Authenticate [X] |
+----------------------------------------------------------+
| |
| [Icon] Authentication is required to run the PolicyKit |
| example program Frobnicate |
| |
| An application is attempting to perform an |
| action that requires privileges. Authentication |
| is required to perform this action. |
| |
| Password: [__________________________________] |
| |
| [V] Details: |
| Command: /usr/bin/pk-example-frobnicate |
| Run As: Super User (root) |
| Action: org.fd.pk.example.pkexec.run-frobnicate |
| Vendor: Examples for the PolicyKit Project |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
]]></programlisting>
</textobject>
</mediaobject>
<para>
If the user is using the <literal>da_DK</literal> locale, the
dialog looks like this:
</para>
<mediaobject id="pkexec-frobnicate-da">
<imageobject>
<imagedata fileref="pkexec-frobnicate-da.png" format="PNG"/>
</imageobject>
<textobject>
<programlisting><![CDATA[
+----------------------------------------------------------+
| Autorisering [X] |
+----------------------------------------------------------+
| |
| [Icon] Autorisering er påkrævet for at afvikle |
| PolicyKit eksemplet Frobnicate |
| |
| Et program forsøger at udføre en handling der |
| kræver privilegier. Autorisering er påkrævet. |
| |
| Kodeord: [___________________________________] |
| |
| [V] Detaljer: |
| Bruger: Super User (root) |
| Program: /usr/bin/pk-example-frobnicate |
| Handling: org.fd.pk.example.pkexec.run-frobnicate |
| Vendor: Examples for the PolicyKit Project |
| |
| [Annullér] [Autorisering] |
+----------------------------------------------------------+
]]></programlisting>
</textobject>
</mediaobject>
<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), such as
with <filename>pk-example-frobnicate</filename> above, this
could be a security hole. Therefore, as a rule of thumb,
programs for which the default required authorization is
changed, should never implicitly trust user input (e.g. like any
other well-written <emphasis>suid</emphasis> program).
</para>
</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 the link <ulink url="http://lists.freedesktop.org/mailman/listinfo/polkit-devel"/>
on how to subscribe.
</para>
</refsect1>
<refsect1 id="pkexec-see-also">
<title>SEE ALSO</title>
<para>
<citerefentry>
<refentrytitle>polkit</refentrytitle><manvolnum>8</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>pkaction</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>,
<citerefentry>
<refentrytitle>pkcheck</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>
</para>
</refsect1>
</refentry>
|
