systemd/man/pam_systemd_loadkey.xml

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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="pam_systemd_loadkey" conditional='HAVE_PAM' xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>pam_systemd_loadkey</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>pam_systemd_loadkey</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>pam_systemd_loadkey</refname>
    <refpurpose>Read password from kernel keyring and set it as PAM authtok</refpurpose>
  </refnamediv>

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

  <refsect1>
    <title>Description</title>

    <para><command>pam_systemd_loadkey</command> reads a NUL-separated password list from the kernel keyring,
    and sets the last password in the list as the PAM authtok, which can be used by e.g.
    <citerefentry project='man-pages'><refentrytitle>pam_get_authtok</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
    </para>

    <para>The password list is supposed to be stored in the "user" keyring of the root user,
    by an earlier call to
    <citerefentry><refentrytitle>systemd-ask-password</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    with <option>--keyname=</option>.
    You can pass the keyname to <command>pam_systemd_loadkey</command> via the <option>keyname=</option> option.</para>

  </refsect1>

  <refsect1>
    <title>Options</title>

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

    <variablelist class='pam-directives'>

      <varlistentry>
        <term><varname>keyname=</varname></term>

        <listitem><para>Takes a string argument which sets the keyname to read.
        The default is <literal>cryptsetup</literal>.
        During boot,
        <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
        stores a passphrase or PIN in the keyring.
        The LUKS2 volume key can also be used, via the <option>link-volume-key</option> option in
        <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

        <table>
          <title>
            Possible values for <varname>keyname</varname>.
          </title>

          <tgroup cols='2'>
            <colspec colname='value' />
            <colspec colname='description' />
            <thead>
              <row>
                <entry>Value</entry>
                <entry>Description</entry>
              </row>
            </thead>
            <tbody>
              <row>
                <entry>cryptsetup</entry>
                <entry>Passphrase or recovery key</entry>
              </row>
              <row>
                <entry>fido2-pin</entry>
                <entry>Security token PIN</entry>
              </row>
              <row>
                <entry>luks2-pin</entry>
                <entry>LUKS2 token PIN</entry>
              </row>
              <row>
                <entry>tpm2-pin</entry>
                <entry>TPM2 PIN</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

        <xi:include href="version-info.xml" xpointer="v255"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><varname>debug</varname></term>

        <listitem><para>The module will log debugging information as it operates.</para>

        <xi:include href="version-info.xml" xpointer="v255"/></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Example</title>

    <para>This module is intended to be used when you use LUKS with a passphrase, enable autologin in the display
    manager, and want to unlock Gnome Keyring / KDE KWallet automatically. So in total, you only enter one password
    during boot.</para>

    <para>You need to set the password of your Gnome Keyring/KWallet to the same as your LUKS passphrase.
    Then add the following lines to your display manager's PAM config under <filename>/etc/pam.d/</filename> (e.g.
    <filename>sddm-autologin</filename>):</para>

    <programlisting>
-auth       optional    pam_systemd_loadkey.so
-auth       optional    pam_gnome_keyring.so
-session    optional    pam_gnome_keyring.so auto_start
-session    optional    pam_kwallet5.so auto_start
</programlisting>

    <para>And add the following lines to your display manager's systemd service file, so it can access root's keyring:</para>

    <programlisting>
[Service]
KeyringMode=inherit
</programlisting>

    <para>In this setup, early during the boot process,
    <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
    will ask for the passphrase and store it in the kernel keyring with the keyname <literal>cryptsetup</literal>.
    Then when the display manager does the autologin, <command>pam_systemd_loadkey</command> will read the passphrase
    from the kernel keyring, set it as the PAM authtok, and then <command>pam_gnome_keyring</command> and
    <command>pam_kwallet5</command> will unlock with the same passphrase.</para>
  </refsect1>

</refentry>