systemd/man/pam_systemd.xml

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<refentry id="pam_systemd" conditional='HAVE_PAM'>

  <refentryinfo>
    <title>pam_systemd</title>
    <productname>systemd</productname>

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>pam_systemd</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>pam_systemd</refname>
    <refpurpose>Register user sessions in the systemd login manager</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>pam_systemd.so</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>pam_systemd</command> registers user sessions with
    the systemd login manager
    <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
    and hence the systemd control group hierarchy.</para>

    <para>On login, this module — in conjunction with <filename>systemd-logind.service</filename> — ensures the
    following:</para>

    <orderedlist>
      <listitem><para>If it does not exist yet, the user runtime directory <filename>/run/user/$UID</filename> is
      either created or mounted as new <literal>tmpfs</literal> file system with quota applied, and its ownership
      changed to the user that is logging in.</para></listitem>

      <listitem><para>The <varname>$XDG_SESSION_ID</varname> environment variable is initialized. If auditing is
      available and <command>pam_loginuid.so</command> was run before this module (which is highly recommended), the
      variable is initialized from the auditing session id (<filename>/proc/self/sessionid</filename>). Otherwise, an
      independent session counter is used.</para></listitem>

      <listitem><para>A new systemd scope unit is created for the session. If this is the first concurrent session of
      the user, an implicit per-user slice unit below <filename>user.slice</filename> is automatically created and the
      scope placed into it. An instance of the system service <filename>user@.service</filename>, which runs the
      systemd user manager instance, is started.  </para></listitem>
    </orderedlist>

    <para>On logout, this module ensures the following:</para>

    <orderedlist>
      <listitem><para>If enabled in
      <citerefentry><refentrytitle>logind.conf</refentrytitle>
      <manvolnum>5</manvolnum></citerefentry> (<varname>KillUserProcesses=</varname>), all processes of the session are
      terminated. If the last concurrent session of a user ends, the user's systemd instance will be terminated too,
      and so will the user's slice unit.</para></listitem>

      <listitem><para>If the last concurrent session of a user ends,
      the user runtime directory <filename>/run/user/$UID</filename> and all its
      contents are removed, too.</para></listitem>
    </orderedlist>

    <para>If the system was not booted up with systemd as init system,
    this module does nothing and immediately returns
    <constant>PAM_SUCCESS</constant>.</para>

  </refsect1>

  <refsect1>
    <title>Options</title>

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

    <variablelist class='pam-directives'>

      <varlistentry>
        <term><option>class=</option></term>

        <listitem><para>Takes a string argument which sets the session
        class. The XDG_SESSION_CLASS environmental variable takes
        precedence. One of
        <literal>user</literal>,
        <literal>greeter</literal>,
        <literal>lock-screen</literal> or
        <literal>background</literal>. See
        <citerefentry><refentrytitle>sd_session_get_class</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for details about the session class.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>type=</option></term>

        <listitem><para>Takes a string argument which sets the session
        type. The XDG_SESSION_TYPE environmental variable takes
        precedence. One of
        <literal>unspecified</literal>,
        <literal>tty</literal>,
        <literal>x11</literal>,
        <literal>wayland</literal> or
        <literal>mir</literal>. See
        <citerefentry><refentrytitle>sd_session_get_type</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for details about the session type.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>debug<optional>=</optional></option></term>

        <listitem><para>Takes an optional
        boolean argument. If yes or without
        the argument, the module will log
        debugging information as it
        operates.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Module Types Provided</title>

    <para>Only <option>session</option> is provided.</para>
  </refsect1>

  <refsect1>
    <title>Environment</title>

    <para>The following environment variables are set for the
    processes of the user's session:</para>

    <variablelist class='environment-variables'>
      <varlistentry>
        <term><varname>$XDG_SESSION_ID</varname></term>

        <listitem><para>A session identifier, suitable to be used in
        filenames. The string itself should be considered opaque,
        although often it is just the audit session ID as reported by
        <filename>/proc/self/sessionid</filename>. Each ID will be
        assigned only once during machine uptime. It may hence be used
        to uniquely label files or other resources of this
        session.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_RUNTIME_DIR</varname></term>

        <listitem><para>Path to a user-private user-writable directory
        that is bound to the user login time on the machine. It is
        automatically created the first time a user logs in and
        removed on the user's final logout. If a user logs in twice at
        the same time, both sessions will see the same
        <varname>$XDG_RUNTIME_DIR</varname> and the same contents. If
        a user logs in once, then logs out again, and logs in again,
        the directory contents will have been lost in between, but
        applications should not rely on this behavior and must be able
        to deal with stale files. To store session-private data in
        this directory, the user should include the value of
        <varname>$XDG_SESSION_ID</varname> in the filename. This
        directory shall be used for runtime file system objects such
        as <constant>AF_UNIX</constant> sockets, FIFOs, PID files and
        similar. It is guaranteed that this directory is local and
        offers the greatest possible file system feature set the
        operating system provides. For further details, see the <ulink
        url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
        Base Directory Specification</ulink>. <varname>$XDG_RUNTIME_DIR</varname>
        is not set if the current user is not the original user of the session.</para></listitem>
      </varlistentry>

    </variablelist>

    <para>The following environment variables are read by the module
    and may be used by the PAM service to pass metadata to the
    module:</para>

    <variablelist class='environment-variables'>
      <varlistentry>
        <term><varname>$XDG_SESSION_TYPE</varname></term>

        <listitem><para>The session type. This may be used instead of
        <option>session=</option> on the module parameter line, and is
        usually preferred.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_SESSION_CLASS</varname></term>

        <listitem><para>The session class. This may be used instead of
        <option>class=</option> on the module parameter line, and is
        usually preferred.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_SESSION_DESKTOP</varname></term>

        <listitem><para>A single, short identifier string for the
        desktop environment. This may be used to indicate the session
        desktop used, where this applies and if this information is
        available. For example: <literal>GNOME</literal>, or
        <literal>KDE</literal>. It is recommended to use the same
        identifiers and capitalization as for
        <varname>$XDG_CURRENT_DESKTOP</varname>, as defined by the
        <ulink
        url="http://standards.freedesktop.org/desktop-entry-spec/latest/">Desktop
        Entry Specification</ulink>. (However, note that
        <varname>$XDG_SESSION_DESKTOP</varname> only takes a single
        item, and not a colon-separated list like
        <varname>$XDG_CURRENT_DESKTOP</varname>.) See
        <citerefentry><refentrytitle>sd_session_get_desktop</refentrytitle><manvolnum>3</manvolnum></citerefentry>
        for more details.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_SEAT</varname></term>

        <listitem><para>The seat name the session shall be registered
        for, if any.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$XDG_VTNR</varname></term>

        <listitem><para>The VT number the session shall be registered
        for, if any. (Only applies to seats with a VT available, such
        as <literal>seat0</literal>)</para></listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>

    <programlisting>#%PAM-1.0
auth       required     pam_unix.so
auth       required     pam_nologin.so
account    required     pam_unix.so
password   required     pam_unix.so
session    required     pam_unix.so
session    required     pam_loginuid.so
session    required     pam_systemd.so</programlisting>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-logind.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>logind.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>loginctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>pam.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>pam.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>pam</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='man-pages'><refentrytitle>pam_loginuid</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>