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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="uid0"
          xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>uid0</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>uid0</refentrytitle>
    <manvolnum>1</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>uid0</refname>
    <refpurpose>Elevate privileges</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <cmdsynopsis>
      <command>uid0</command>
      <arg choice="opt" rep="repeat">OPTIONS</arg>
      <arg choice="opt" rep="repeat">COMMAND</arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>uid0</command> may be used to temporarily and interactively acquire elavated or different
    privileges. It serves a similar purpose as <citerefentry
    project='man-pages'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry>, but
    operates differently in a couple of key areas:</para>

    <itemizedlist>
      <listitem><para>No execution or security context credentials are inherited from the caller into the
      invoked commands, as they are invoked from a fresh, isolated service forked off the service
      manager.</para></listitem>

      <listitem><para>Authentication takes place via <ulink
      url="https://www.freedesktop.org/wiki/Software/polkit">polkit</ulink>, thus isolating the
      authentication prompt from the terminal (if possible).</para></listitem>

      <listitem><para>An independent pseudo-tty is allocated for the invoked command, detaching its lifecycle and
      isolating it for security.</para></listitem>

      <listitem><para>No SetUID/SetGID file access bit functionality is used for the implementation.</para></listitem>
    </itemizedlist>

    <para>Altogether this should provide a safer and more robust alternative to the <command>sudo</command>
    mechanism, in particular in OS environments where SetUID/SetGID support is not available (for example by
    setting the <varname>NoNewPrivileges=</varname> variable in
    <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).</para>

    <para>Any session invoked via <command>uid0</command> will run through the
    <literal>systemd-uid0</literal> PAM stack.</para>

    <para>Note that <command>uid0</command> is implemented as an alternative multi-call invocation of
    <citerefentry><refentrytitle>systemd-run</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

    <para>The following options are understood:</para>

    <variablelist>
      <varlistentry>
        <term><option>--no-ask-password</option></term>

        <listitem><para>Do not query the user for authentication for privileged operations.</para>

        <xi:include href="version-info.xml" xpointer="v256"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--unit=</option></term>

        <listitem><para>Use this unit name instead of an automatically generated one.</para>

        <xi:include href="version-info.xml" xpointer="v256"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--property=</option></term>

        <listitem><para>Sets a property on the service unit that is created. This option takes an assignment
        in the same format as
        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
        <command>set-property</command> command.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--description=</option></term>

        <listitem><para>Provide a description for the service unit that is invoked. If not specified,
        the command itself will be used as a description. See <varname>Description=</varname> in
        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
        </para>

        <xi:include href="version-info.xml" xpointer="v256"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--slice=</option></term>

        <listitem><para>Make the new <filename>.service</filename> unit part of the specified slice, instead
        of <filename>user.slice</filename>.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--slice-inherit</option></term>

        <listitem><para>Make the new <filename>.service</filename> unit part of the slice the
        <command>uid0</command> itself has been invoked in. This option may be combined with
        <option>--slice=</option>, in which case the slice specified via <option>--slice=</option> is placed
        within the slice the <command>uid0</command> command is invoked in.</para>

        <para>Example: consider <command>uid0</command> being invoked in the slice
        <filename>foo.slice</filename>, and the <option>--slice=</option> argument is
        <filename>bar</filename>. The unit will then be placed under
        <filename>foo-bar.slice</filename>.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>

        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--user=</option></term>
        <term><option>-u</option></term>
        <term><option>--group=</option></term>
        <term><option>-g</option></term>

        <listitem><para>Switches to the specified user/group instead of root.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--nice=</option></term>

        <listitem><para>Runs the invoked session with the specified nice level.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--chdir=</option></term>
        <term><option>-D</option></term>

        <listitem><para>Runs the invoked session with the specified working directory. If not specified
        defaults to the client's current working directory if switching to the root user, or the target
        user's home directory otherwise.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--setenv=<replaceable>NAME</replaceable>[=<replaceable>VALUE</replaceable>]</option></term>

        <listitem><para>Runs the invoked session with the specified environment variable set. This parameter
        may be used more than once to set multiple variables. When <literal>=</literal> and
        <replaceable>VALUE</replaceable> are omitted, the value of the variable with the same name in the
        invoking environment will be used.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><option>--background=<replaceable>COLOR</replaceable></option></term>

        <listitem><para>Change the terminal background color to the specified ANSI color as long as the
        session lasts. If not specified, the background will be tinted in a reddish tone when operating as
        root, and in a yellowish tone when operating under another UID, as reminder of the changed
        privileges. The color specified should be an ANSI X3.64 SGR background color, i.e. strings such as
        <literal>40</literal>, <literal>41</literal>, …, <literal>47</literal>, <literal>48;2;…</literal>,
        <literal>48;5;…</literal>. See <ulink
        url="https://en.wikipedia.org/wiki/ANSI_escape_code#SGR_(Select_Graphic_Rendition)_parameters">ANSI
        Escape Code (Wikipedia)</ulink> for details. Set to an empty string to disable.</para>

        <para>Example: <literal>--background=44</literal> for a blue background.</para>

        <xi:include href="version-info.xml" xpointer="v256"/>
        </listitem>
      </varlistentry>

      <xi:include href="user-system-options.xml" xpointer="machine" />
      <xi:include href="standard-options.xml" xpointer="help" />
      <xi:include href="standard-options.xml" xpointer="version" />
    </variablelist>

    <para>All command line arguments after the first non-option argument become part of the command line of
    the launched process. If no command line is specified an interactive shell is invoked. The shell to
    invoke may be controlled via <option>--setenv=SHELL=…</option> and currently defaults to the
    <emphasis>originating user's</emphasis> shell (i.e. not the target user's!) if operating locally, or
    <filename>/bin/sh</filename> when operating with <option>--machine=</option>.</para>
  </refsect1>

  <refsect1>
    <title>Exit status</title>

    <para>On success, 0 is returned. If <command>uid0</command> failed to start the session or the specified command fails, a
    non-zero return value will be returned.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-run</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry project='man-pages'><refentrytitle>sudo</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>machinectl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>

</refentry>
