systemd/man/integritytab.xml

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

  <refentryinfo>
    <title>integritytab</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>integritytab</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>integritytab</refname>
    <refpurpose>Configuration for integrity block devices</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>/etc/integritytab</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>The <filename>/etc/integritytab</filename> file describes
    integrity protected block devices that are set up during
    system boot.</para>

    <para>Empty lines and lines starting with the <literal>#</literal>
    character are ignored. Each of the remaining lines describes one
    verity integrity protected block device. Fields are delimited by
    white space.</para>

    <para>Each line is in the form<programlisting><replaceable>volume-name</replaceable> <replaceable>block-device</replaceable>
    <replaceable>[keyfile|-]</replaceable> <replaceable>[options|-]</replaceable></programlisting>
    The first two fields are mandatory, the remaining two are optional and only required if user specified non-default options during integrity format.</para>

    <para>The first field contains the name of the resulting integrity volume; its block device is set up
    below <filename>/dev/mapper/</filename>.</para>

    <para>The second field contains a path to the underlying block device, or a specification of a block device via
    <literal>UUID=</literal> followed by the UUID,
    <literal>PARTUUID=</literal> followed by the partition UUID,
    <literal>LABEL=</literal> followed by the label,
    <literal>PARTLABEL=</literal> followed by the partition label.
    </para>

    <para>The third field if present contains an absolute filename path to a key file or a <literal>-</literal>
    to specify none.  When the filename is present, the "integrity-algorithm" defaults to <literal>hmac-sha256</literal>
    with the key length derived from the number of bytes in the key file.  At this time the only supported integrity algorithm
    when using key file is hmac-sha256.  The maximum size of the key file is 4096 bytes.
    </para>

     <para>The fourth field, if present, is a comma-delimited list of options or a <literal>-</literal> to specify none. The following options are
    recognized:</para>
      <variablelist>

      <varlistentry>
        <term><option>allow-discards</option></term>

        <listitem><para>
        Allow the use of discard (TRIM) requests for the device.
        This option is available since the Linux kernel version 5.7.
        </para>

        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>mode=(journal|bitmap|direct)</option></term>

        <listitem><para>
        Enable journaled, bitmapped or direct (passthrough) mode. Journaled mode is the default when this option is not specified.
        It provides safety against crashes, but can be slow because all data has to be written twice.
        Bitmap mode is more efficient since it requires only a single write, but it is less reliable because if data corruption happens when the machine crashes, it may not be detected.
        Direct mode disables the journal and the bitmap. Corresponds to the "direct writes" mode documented in
        <ulink url="https://docs.kernel.org/admin-guide/device-mapper/dm-integrity.html">the dm-integrity documentation</ulink>.
        Note that without a journal, if there is a crash, it is possible that the integrity tags and data will not match. If used, the journal-*
        options below will have no effect if passed.
        </para>

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

      <varlistentry>
        <term><option>journal-watermark=[0..100]%</option></term>

        <listitem><para>
        Journal watermark in percent. When the journal percentage exceeds this watermark, the journal flush will be started.  Setting a value of
        "0%" uses default value.
        </para>

        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>journal-commit-time=[0..N]</option></term>

        <listitem><para>
        Commit time in milliseconds. When this time passes (and no explicit flush operation was issued), the journal is written.  Setting a value of
        zero uses default value.
        </para>

        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>data-device=/dev/disk/by-...</option></term>

        <listitem><para>
        Specify a separate block device that contains existing data. The second field specified in the
        integritytab for block device then will contain calculated integrity tags and journal for data-device,
        but not the end user data.
        </para>

        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
      </varlistentry>

      <varlistentry>
        <term><option>integrity-algorithm=[crc32c|crc32|sha1|sha256|hmac-sha256]</option></term>

        <listitem><para>
        The algorithm used for integrity checking.  The default is crc32c. Must match option used during format.
        </para>

        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
      </varlistentry>
    </variablelist>

    <para>At early boot and when the system manager configuration is
    reloaded, this file is translated into native systemd units by
    <citerefentry><refentrytitle>systemd-integritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>
    <example>
      <title>/etc/integritytab</title>
      <para>Set up two integrity protected block devices. </para>

      <programlisting>home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8 - journal-commit-time=10,allow-discards,journal-watermark=55%
data PARTUUID=5d4b1808-be76-774d-88af-03c4c3a41761 - allow-discards
</programlisting>
    </example>

    <example>
      <title>/etc/integritytab</title>
      <para>Set up 1 integrity protected block device using defaults </para>

      <programlisting>home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8</programlisting>
    </example>

    <example>
      <title>/etc/integritytab</title>
      <para>Set up 1 integrity device using existing data block device which contains user data </para>

      <programlisting>home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8 - data-device=/dev/disk/by-uuid/9276d9c0-d4e3-4297-b4ff-3307cd0d092f</programlisting>
    </example>

    <example>
      <title>/etc/integritytab</title>
      <para>Set up 1 integrity device using a HMAC key file using defaults </para>

      <programlisting>home PARTUUID=4973d0b8-1b15-c449-96ec-94bab7f6a7b8 /etc/hmac.key</programlisting>
    </example>

  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-integritysetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-integritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>integritysetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
    </para>
  </refsect1>

</refentry>