systemd/man/pam_systemd_home.xml

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<refentry id="pam_systemd_home" conditional='ENABLE_PAM_HOME'>

  <refentryinfo>
    <title>pam_systemd_home</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>pam_systemd_home</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>pam_systemd_home</refname>
    <refpurpose>Authenticate users and mount home directories via <filename>systemd-homed.service</filename>
    </refpurpose>
  </refnamediv>

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

  <refsect1>
    <title>Description</title>

    <para><command>pam_systemd_home</command> ensures that home directories managed by
    <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    are automatically activated (mounted) on user login, and are deactivated (unmounted) when the last
    session of the user ends. For such users, it also provides authentication (when per-user disk encryption
    is used, the disk encryption key is derived from the authentication credential supplied at login time),
    account management (the <ulink url="https://systemd.io/USER_RECORD/">JSON user record</ulink> embedded in
    the home store contains account details), and implements the updating of the encryption password (which
    is also used for user authentication).</para>
  </refsect1>

  <refsect1>
    <title>Options</title>

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

    <variablelist class='pam-directives'>

      <varlistentry>
        <term><varname>suspend=</varname></term>

        <listitem><para>Takes a boolean argument. If true, the home directory of the user will be suspended
        automatically during system suspend; if false it will remain active. Automatic suspending of the home
        directory improves security substantially as secret key material is automatically removed from memory
        before the system is put to sleep and must be re-acquired (through user re-authentication) when
        coming back from suspend. It is recommended to set this parameter for all PAM applications that have
        support for automatically re-authenticating via PAM on system resume. If multiple sessions of the
        same user are open in parallel the user's home directory will be left unsuspended on system suspend
        as long as at least one of the sessions does not set this parameter to on. Defaults to
        off.</para>

        <para>Note that TTY logins generally do not support re-authentication on system resume.
        Re-authentication on system resume is primarily a concept implementable in graphical environments, in
        the form of lock screens brought up automatically when the system goes to sleep. This means that if a
        user concurrently uses graphical login sessions that implement the required re-authentication
        mechanism and console logins that do not, the home directory is not locked during suspend, due to the
        logic explained above. That said, it is possible to set this field for TTY logins too, ignoring the
        fact that TTY logins actually don't support the re-authentication mechanism. In that case the TTY
        sessions will appear hung until the user logs in on another virtual terminal (regardless if via
        another TTY session or graphically) which will resume the home directory and unblock the original TTY
        session. (Do note that lack of screen locking on TTY sessions means even though the TTY session
        appears hung, keypresses can still be queued into it, and the existing screen contents be read
        without re-authentication; this limitation is unrelated to the home directory management
        <command>pam_systemd_home</command> and <filename>systemd-homed.service</filename> implement.)</para>

        <para>Turning this option on by default is highly recommended for all sessions, but only if the
        service managing these sessions correctly implements the aforementioned re-authentication. Note that
        the re-authentication must take place from a component running outside of the user's context, so that
        it does not require access to the user's home directory for operation. Traditionally, most desktop
        environments do not implement screen locking this way, and need to be updated
        accordingly.</para>

        <para>This setting may also be controlled via the <varname>$SYSTEMD_HOME_SUSPEND</varname>
        environment variable (see below), which <command>pam_systemd_home</command> reads during initialization and sets
        for sessions. If both the environment variable is set and the module parameter specified the latter
        takes precedence.</para></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>The module implements all four PAM operations: <option>auth</option> (to allow authentication using
    the encrypted data), <option>account</option> (because users with
    <filename>systemd-homed.service</filename> user accounts are described in a <ulink
    url="https://systemd.io/USER_RECORD/">JSON user record</ulink> and may be configured in more detail than
    in the traditional Linux user database), <option>session</option> (because user sessions must be tracked
    in order to implement automatic release when the last session of the user is gone),
    <option>password</option> (to change the encryption password — also used for user authentication —
    through PAM).</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>$SYSTEMD_HOME=1</varname></term>

        <listitem><para>Indicates that the user's home directory is managed by <filename>systemd-homed.service</filename>.</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>$SYSTEMD_HOME_SUSPEND=</varname></term>

        <listitem><para>Indicates whether the session has been registered with the suspend mechanism enabled
        or disabled (see above). The variable's value is either <literal>0</literal> or
        <literal>1</literal>. Note that the module both reads the variable when initializing, and sets it for
        sessions.</para></listitem>
      </varlistentry>

    </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>

    <para>Here's an example PAM configuration fragment that permits users managed by
    <filename>systemd-homed.service</filename> to log in:</para>

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

account   required   pam_nologin.so
<command>-account  sufficient pam_systemd_home.so</command>
account   sufficient pam_unix.so
account   required   pam_permit.so

<command>-password sufficient pam_systemd_home.so</command>
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
<command>-session  optional   pam_systemd_home.so</command>
-session  optional   pam_systemd.so
session   required   pam_unix.so</programlisting>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-homed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>homed.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>homectl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>pam_systemd</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>
    </para>
  </refsect1>

</refentry>