systemd/man/pam_systemd.xml

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<refentry id="pam_systemd" conditional='HAVE_PAM' xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>pam_systemd</title>
    <productname>systemd</productname>
  </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>The module also applies various resource management and runtime parameters to the new session, as
    configured in the <ulink url="https://systemd.io/USER_RECORD">JSON User Records</ulink> of the user, when
    one is defined.</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>

      <listitem><para>The <literal>$TZ</literal>, <literal>$EMAIL</literal> and <literal>$LANG</literal>
      environment variables are configured for the user, based on the respective data from the user's JSON
      record (if it is defined). Moreover, any environment variables explicitly configured in the user record
      are imported, and the umask, nice level, and resource limits initialized.</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><varname>class=</varname></term>

        <listitem><para>Takes a string argument which sets the session class. The <varname>XDG_SESSION_CLASS</varname>
        environment variable (see below) 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>

        <xi:include href="version-info.xml" xpointer="v197"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>type=</varname></term>

        <listitem><para>Takes a string argument which sets the session type. The <varname>XDG_SESSION_TYPE</varname>
        environment variable (see below) 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>

        <xi:include href="version-info.xml" xpointer="v209"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>desktop=</varname></term>

        <listitem><para>Takes a single, short identifier string for the desktop environment. The
        <varname>XDG_SESSION_DESKTOP</varname> environment variable (see below) takes precedence. 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>$XDG_CURRENT_DESKTOP</varname>, as defined by the <ulink
        url="https://standards.freedesktop.org/desktop-entry-spec/latest/">Desktop Entry
        Specification</ulink>. (However, note that the option only takes a single item, and not a colon-separated list
        like <varname>$XDG_CURRENT_DESKTOP</varname>.) See
        <citerefentry><refentrytitle>sd_session_get_desktop</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
        further details.</para>

        <xi:include href="version-info.xml" xpointer="v240"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>default-capability-bounding-set=</varname></term>
        <term><varname>default-capability-ambient-set=</varname></term>

        <listitem><para>Takes a comma-separated list of process capabilities
        (e.g. <constant>CAP_WAKE_ALARM</constant>, <constant>CAP_BLOCK_SUSPEND</constant>, …) to set for the
        invoked session's processes, if the user record does not encode appropriate sets of capabilities
        directly. See <citerefentry
        project='man-pages'><refentrytitle>capabilities</refentrytitle><manvolnum>7</manvolnum></citerefentry>
        for details on the capabilities concept. If not specified, the default bounding set is left as is
        (i.e. usually contains the full set of capabilities). The default ambient set is set to
        <constant>CAP_WAKE_ALARM</constant> for regular users if the PAM session is associated with a local
        seat or if it is invoked for the <literal>systemd-user</literal> service. Otherwise defaults to the
        empty set.</para>

        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>debug</varname><optional>=</optional></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 initialized by the module and available to the processes of the
    user's session:</para>

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

        <listitem><para>A short 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. Combine this ID with the boot
        identifier, as returned by
        <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>, for a
        globally unique identifier.</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="https://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>

      <varlistentry>
        <term><varname>$TZ</varname></term>
        <term><varname>$EMAIL</varname></term>
        <term><varname>$LANG</varname></term>

        <listitem><para>If a JSON user record is known for the user logging in these variables are
        initialized from the respective data in the record.</para>

        <xi:include href="version-info.xml" xpointer="v245"/></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. If these variables are not set when the PAM module is invoked but can be determined
    otherwise they are set by the module, so that these variables are initialized for the session and applications if
    known at all.</para>

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

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

        <xi:include href="version-info.xml" xpointer="v209"/></listitem>
      </varlistentry>

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

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

        <xi:include href="version-info.xml" xpointer="v209"/></listitem>
      </varlistentry>

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

        <listitem><para>The desktop identifier. This may be used instead of <varname>desktop=</varname> on the module
        parameter line, and is usually preferred.</para>

        <xi:include href="version-info.xml" xpointer="v209"/></listitem>
      </varlistentry>

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

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

        <xi:include href="version-info.xml" xpointer="v209"/></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>

        <xi:include href="version-info.xml" xpointer="v209"/></listitem>
      </varlistentry>
    </variablelist>

    <para>If not set, <command>pam_systemd</command> will initialize
    <varname>$XDG_SEAT</varname> and <varname>$XDG_VTNR</varname>
    based on the <varname>$DISPLAY</varname> variable (if the latter is set).</para>
  </refsect1>

  <refsect1>
    <title>Session limits</title>

    <para>PAM modules earlier in the stack, that is those that come before <command>pam_systemd.so</command>,
    can set session scope limits using the PAM context objects. The data for these objects is provided as <constant>NUL</constant>-terminated C strings
    and maps directly to the respective unit resource control directives. Note that these limits apply to individual sessions of the user,
    they do not apply to all user processes as a combined whole. In particular, the per-user <command>user@.service</command> unit instance,
    which runs the <command>systemd --user</command> manager process and its children, and is tracked outside of any session, being shared
    by all the user's sessions, is not covered by these limits.
    </para>

    <para> See
    <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more information about the resources.
    Also, see <citerefentry project='man-pages'><refentrytitle>pam_set_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> for additional information about how to set
    the context objects.
    </para>

    <variablelist class='pam-directives'>
      <varlistentry>
        <term><varname>systemd.memory_max=</varname></term>

        <listitem><para>Sets unit <varname>MemoryMax=</varname>.</para>

        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.tasks_max=</varname></term>

        <listitem><para>Sets unit <varname>TasksMax=</varname>.</para>

        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.cpu_weight=</varname></term>

        <listitem><para>Sets unit <varname>CPUWeight=</varname>.</para>

        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.io_weight=</varname></term>

        <listitem><para>Sets unit <varname>IOWeight=</varname>.</para>

        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>systemd.runtime_max_sec=</varname></term>

        <listitem><para>Sets unit <varname>RuntimeMaxSec=</varname>.</para>

        <xi:include href="version-info.xml" xpointer="v244"/></listitem>
      </varlistentry>
    </variablelist>

    <para>Example data as can be provided from an another PAM module:
      <programlisting>
pam_set_data(handle, "systemd.memory_max", (void *)"200M", cleanup);
pam_set_data(handle, "systemd.tasks_max",  (void *)"50",   cleanup);
pam_set_data(handle, "systemd.cpu_weight", (void *)"100",  cleanup);
pam_set_data(handle, "systemd.io_weight",  (void *)"340",  cleanup);
pam_set_data(handle, "systemd.runtime_max_sec", (void *)"3600", cleanup);
      </programlisting>
    </para>

  </refsect1>

  <refsect1>
    <title>Example</title>

    <para>Here's an example PAM configuration fragment that allows users sessions to be managed by
    <filename>systemd-logind.service</filename>:</para>

    <programlisting>#%PAM-1.0
auth      sufficient pam_unix.so
-auth     sufficient pam_systemd_home.so
auth      required   pam_deny.so

account   required   pam_nologin.so
-account  sufficient pam_systemd_home.so
account   sufficient pam_unix.so
account   required   pam_permit.so

-password sufficient pam_systemd_home.so
password  sufficient pam_unix.so sha512 shadow try_first_pass use_authtok

password  required   pam_deny.so

-session  optional   pam_keyinit.so revoke
-session  optional   pam_loginuid.so
-session  optional   pam_systemd_home.so
<command>-session  optional   pam_systemd.so</command>
session   required   pam_unix.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><refentrytitle>pam_systemd_home</refentrytitle><manvolnum>8</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>