enables fully state-less boots were the vendor-supplied OS is used as shipped, with only default
configuration and no stored state in effect, as <filename>/etc</filename> and <filename>/var</filename> (as
well as all other resources shipped in the root file system) are reset at boot and lost on shutdown. If this
- setting is set to <literal>state</literal> the root file system is mounted as usual, however
+ setting is set to <literal>state</literal> the root file system is mounted read-only, however
<filename>/var</filename> is mounted as a volatile memory file system (<literal>tmpfs</literal>), so that the
- system boots up with the normal configuration applied, but all state reset at boot and lost at shutdown. For details,
- see
+ system boots up with the normal configuration applied, but all state reset at boot and lost at shutdown. If
+ this setting is set to <literal>overlay</literal> the root file system is set up as
+ <literal>overlayfs</literal> mount combining the read-only root directory with a writable
+ <literal>tmpfs</literal>, so that no modifications are made to disk, but the file system may be modified
+ nonetheless with all changes being lost at reboot. For details, see
<citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
lost at shutdown, as <filename>/etc</filename> and <filename>/var</filename> will be served from the (initially
unpopulated) volatile memory file system.</para>
- <para>If set to <option>state</option> the generator will leave the root
- directory mount point unaltered, however will mount a <literal>tmpfs</literal> file system to
- <filename>/var</filename>. In this mode the normal system configuration (i.e. the contents of
- <literal>/etc</literal>) is in effect (and may be modified during system runtime), however the system state
- (i.e. the contents of <literal>/var</literal>) is reset at boot and lost at shutdown.</para>
+ <para>If set to <option>state</option> the generator will leave the root directory mount point unaltered,
+ however will mount a <literal>tmpfs</literal> file system to <filename>/var</filename>. In this mode the normal
+ system configuration (i.e. the contents of <literal>/etc</literal>) is in effect (and may be modified during
+ system runtime), however the system state (i.e. the contents of <literal>/var</literal>) is reset at boot and
+ lost at shutdown.</para>
+
+ <para>If this setting is set to <literal>overlay</literal> the root file system is set up as
+ <literal>overlayfs</literal> mount combining the read-only root directory with a writable
+ <literal>tmpfs</literal>, so that no modifications are made to disk, but the file system may be modified
+ nonetheless with all changes being lost at reboot.</para>
<para>Note that in none of these modes the root directory, <filename>/etc</filename>, <filename>/var</filename>
or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.</para>
- <para>Note that enabling this setting will only work correctly on operating systems that can boot up with only
- <filename>/usr</filename> mounted, and are able to automatically populate <filename>/etc</filename>, and also
- <filename>/var</filename> in case of <literal>systemd.volatile=yes</literal>.</para></listitem>
+ <para>Note that with the exception of <literal>overlay</literal> mode, enabling this setting will only work
+ correctly on operating systems that can boot up with only <filename>/usr</filename> mounted, and are able to
+ automatically populate <filename>/etc</filename>, and also <filename>/var</filename> in case of
+ <literal>systemd.volatile=yes</literal>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>