systemd/man/systemd-cryptsetup@.service.xml

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<refentry id="systemd-cryptsetup@.service" conditional='HAVE_LIBCRYPTSETUP'>

  <refentryinfo>
    <title>systemd-cryptsetup@.service</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-cryptsetup@.service</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-cryptsetup@.service</refname>
    <!-- <refname>system-systemd\x2dcryptsetup.slice</refname> — this causes meson to go haywire because it
         thinks this is a (windows) path. Let's just not create the alias for this name, and only include it
         in the synopsis. -->
    <refname>systemd-cryptsetup</refname>
    <refpurpose>Full disk decryption logic</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>systemd-cryptsetup@.service</filename></para>
    <para><filename>system-systemd\x2dcryptsetup.slice</filename></para>
    <para><filename>systemd-cryptsetup</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><filename>systemd-cryptsetup@.service</filename> is a service responsible for setting up encrypted
    block devices. It is instantiated for each device that requires decryption for access.</para>

    <para><filename>systemd-cryptsetup@.service</filename> instances are part of the
    <filename>system-systemd\x2dcryptsetup.slice</filename> slice, which is destroyed only very late in the
    shutdown procedure. This allows the encrypted devices to remain up until filesystems have been unmounted.
    </para>

    <para><filename>systemd-cryptsetup@.service</filename> will ask
    for hard disk passwords via the <ulink
    url="https://systemd.io/PASSWORD_AGENTS/">password agent logic</ulink>, in
    order to query the user for the password using the right mechanism at boot
    and during runtime.</para>

    <para>At early boot and when the system manager configuration is reloaded, <filename>/etc/crypttab</filename> is
    translated into <filename>systemd-cryptsetup@.service</filename> units by
    <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>

    <para>In order to unlock a volume a password or binary key is
    required. <filename>systemd-cryptsetup@.service</filename> tries to acquire a suitable password or binary
    key via the following mechanisms, tried in order:</para>

    <orderedlist>
      <listitem><para>If a key file is explicitly configured (via the third column in
      <filename>/etc/crypttab</filename>), a key read from it is used. If a PKCS#11 token, FIDO2 token or
      TPM2 device is configured (using the <varname>pkcs11-uri=</varname>, <varname>fido2-device=</varname>,
      <varname>tpm2-device=</varname> options) the key is decrypted before use.</para></listitem>

      <listitem><para>If no key file is configured explicitly this way, a key file is automatically loaded
      from <filename>/etc/cryptsetup-keys.d/<replaceable>volume</replaceable>.key</filename> and
      <filename>/run/cryptsetup-keys.d/<replaceable>volume</replaceable>.key</filename>, if present. Here
      too, if a PKCS#11/FIDO2/TPM2 token/device is configured, any key found this way is decrypted before
      use.</para></listitem>

      <listitem><para>If the <varname>try-empty-password</varname> option is specified it is then attempted
      to unlock the volume with an empty password.</para></listitem>

      <listitem><para>The kernel keyring is then checked for a suitable cached password from previous
      attempts.</para></listitem>

      <listitem><para>Finally, the user is queried for a password, possibly multiple times, unless
      the <varname>headless</varname> option is set.</para></listitem>
    </orderedlist>

    <para>If no suitable key may be acquired via any of the mechanisms describes above, volume activation fails.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>
     </para>
  </refsect1>

</refentry>