systemd/man/systemd-mountfsd.service.xml

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<refentry id="systemd-mountfsd.service" conditional='ENABLE_MOUNTFSD'>

  <refentryinfo>
    <title>systemd-mountfsd.service</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-mountfsd.service</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-mountfsd.service</refname>
    <refname>systemd-mountfsd</refname>
    <refpurpose>Disk Image File System Mount Service</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>systemd-mountfsd.service</filename></para>
    <para><filename>/usr/lib/systemd/systemd-mountfsd</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><command>systemd-mountfsd</command> is a system service that dissects disk images, and returns mount
    file descriptors for the file systems contained therein to clients, via a Varlink IPC API.</para>

    <para>The disk images provided must contain a raw file system image or must follow the <ulink
    url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification/">Discoverable
    Partitions Specification</ulink>. Before mounting any file systems authenticity of the disk image is
    established in one or a combination of the following ways:</para>

    <orderedlist>
      <listitem><para>If the disk image is located in a regular file in one of the directories
      <filename>/var/lib/machines/</filename>, <filename>/var/lib/portables/</filename>,
      <filename>/var/lib/extensions/</filename>, <filename>/var/lib/confexts/</filename> or their
      counterparts in the <filename>/etc/</filename>, <filename>/run/</filename>,
      <filename>/usr/lib/</filename> it is assumed to be trusted.</para></listitem>

      <listitem><para>If the disk image contains a Verity enabled disk image, along with a signature
      partition with a key in the kernel keyring or in <filename>/etc/verity.d/</filename> (and related
      directories) the disk image is considered trusted.</para></listitem>
    </orderedlist>

    <para>This service provides one <ulink url="https://varlink.org/">Varlink</ulink> service:
    <constant>io.systemd.MountFileSystem</constant> which accepts a file descriptor to a regular file or
    block device, and returns a number of file descriptors referring to an <function>fsmount()</function>
    file descriptor the client may then attach to a path of their choice.</para>

    <para>The returned mounts are automatically allowlisted in the per-user-namespace allowlist maintained by
    <citerefentry><refentrytitle>systemd-nsresourced.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>

    <para>The file systems are automatically
    <citerefentry project='man-pages'><refentrytitle>fsck</refentrytitle><manvolnum>8</manvolnum></citerefentry>'ed
    before mounting.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para><simplelist type="inline">
      <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      <member><citerefentry><refentrytitle>systemd-nsresourced.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
    </simplelist></para>
  </refsect1>
</refentry>