systemd-stable/man/systemd-volatile-root.service.xml

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<refentry id="systemd-volatile-root.service">

  <refentryinfo>
    <title>systemd-volatile-root.service</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd-volatile-root.service</refentrytitle>
    <manvolnum>8</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd-volatile-root.service</refname>
    <refname>systemd-volatile-root</refname>
    <refpurpose>Make the root file system volatile</refpurpose>
  </refnamediv>

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

  <refsect1>
    <title>Description</title>

    <para><filename>systemd-volatile-root.service</filename> is a service that replaces the root directory with a
    volatile memory file system (<literal>tmpfs</literal>), mounting the original (non-volatile)
    <filename>/usr/</filename> inside it read-only. This way, vendor data from <filename>/usr/</filename> is available as
    usual, but all configuration data in <filename>/etc/</filename>, all state data in <filename>/var/</filename> and all
    other resources stored directly under the root directory are reset on boot and lost at shutdown, enabling fully
    stateless systems.</para>

    <para>This service is only enabled if full volatile mode is selected, for example by specifying
    <literal>systemd.volatile=yes</literal> on the kernel command line. This service runs only in the initrd,
    before the system transitions to the host's root directory. Note that this service is not used if
    <literal>systemd.volatile=state</literal> is used, as in that mode the root directory is non-volatile.
    </para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>