niceSOFT/systemd: The systemd System and Service Manager

man/systemd.mstack.xml
126 строк7 KB
Ulrich Ölmann
man/systemd.mstack: fix typos
17 июн 2026, 09:34
17 июн 2026, 09:346cf4171
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->

<refentry id="systemd.mstack">

  <refentryinfo>
    <title>systemd.mstack</title>
    <productname>systemd</productname>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.mstack</refentrytitle>
    <manvolnum>7</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.mstack</refname>
    <refpurpose>Mount stacks in self descriptive directories</refpurpose>
  </refnamediv>

  <refsect1>
    <title>Description</title>

    <para>Directories with the <literal>.mstack/</literal> suffix may encode 'mount stacks' for assembling OS
    mount hierarchies based on bind and overlay mounts, for use in
    <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
    <option>--mstack=</option> switch or the service manager's <option>RootMStack=</option> setting for
    services. <literal>.mstack/</literal> directories may contain various files and subdirectories, where
    each will effect one layer of an <literal>overlayfs</literal> mount, or a bind mount. The name of the
    file or subdirectory indicates how it shall be used in the mount hierarchy. Specifically, the following
    names are defined:</para>

    <orderedlist>
      <listitem><para>A <filename>layer@<replaceable>id</replaceable>/</filename> directory will be turned into
      a layer of an overlayfs mount. The <literal>id</literal> identifier is used to define the order of the
      layers: a version sort is executed, with the first entry being the bottom layer in the
      <literal>overlayfs</literal> stack, and the last entry becoming the highest layer (precisely:
      highest "lowerdir") in the <literal>overlayfs</literal> stack.</para></listitem>

      <listitem><para>Similar, a <filename>layer@<replaceable>id</replaceable>.raw</filename> regular file
      will be mounted as a DDI, and the resulting mount will be turned into an overlayfs layer, following the
      same sorting rules.</para></listitem>

      <listitem><para>An <filename>rw</filename> directory will be turned into a writable layer at the very top
      of the <literal>overlayfs</literal> stack. A subdirectory <filename>data</filename> of it will become
      the "upperdir", a subdirectory <filename>work</filename> will become the "workdir". Note that these two
      subdirectories do not need to be created explicitly, they are created automatically on first use should
      they be missing.</para></listitem>

      <listitem><para>A <filename>bind@<replaceable>location</replaceable>/</filename> directory will be bind
      mounted to the mount point indicated by the <varname>location</varname> identifier, in read-write
      fashion. The location is encoded via the same escaping logic used for naming <literal>.mount</literal>
      units, i.e. slashes become dashes.</para></listitem>

      <listitem><para>Similar, a
      <filename>bind@<replaceable>location</replaceable>.raw</filename> file will be mounted as a DDI, and the
      resulting mount bind mounted to the specified location.</para></listitem>

      <listitem><para>A <filename>robind@<replaceable>location</replaceable>/</filename> is treated very
      similar to <filename>bind@<replaceable>location</replaceable>/</filename>, but the resulting bind mount
      is read-only.</para></listitem>

      <listitem><para>Similar, <filename>robind@<replaceable>location</replaceable>.raw</filename> creates a
      read-only bind mount from a DDI.</para></listitem>

      <listitem><para>If a <filename>root/</filename> subdirectory exists, it is used as root of the
      resulting mount hierarchy, and only the <filename>usr/</filename> subtree of the overlayfs mount will
      be bound to <filename>usr/</filename> in the hierarchy.</para></listitem>
    </orderedlist>

    <para>Note that each of the entry types above may be a symbolic link pointing to a directory or image
    file, instead a directory or image file itself.</para>

    <para>On each listed file or subdirectory type the
    <citerefentry><refentrytitle>systemd.v</refentrytitle><manvolnum>7</manvolnum></citerefentry>
    functionality may be used, for automatic selection of versioned resources.</para>

    <para>Use the
    <citerefentry><refentrytitle>systemd-mstack</refentrytitle><manvolnum>1</manvolnum></citerefentry> tool
    to process or mount <filename>.mstack/</filename> directories from the command line.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <para>The following <filename>.mstack/</filename> consists of two read-only overlayfs layers as DDI, plus one
    writable directory on top. The read-only layers are symlinked:</para>

    <orderedlist>
      <listitem><para><filename>foobar.mstack/layer@0.raw</filename> → <filename>../base.raw</filename></para></listitem>
      <listitem><para><filename>foobar.mstack/layer@1.raw</filename> → <filename>../app.raw</filename></para></listitem>
      <listitem><para><filename>foobar.mstack/rw/</filename></para></listitem>
    </orderedlist>

    <para>The following <filename>.mstack/</filename> consists of a read-only DDI mounted to <literal>/usr/</literal>
    and writable root:</para>

    <orderedlist>
      <listitem><para><filename>waldo.mstack/layer@0.raw</filename> → <filename>../vendor.raw</filename></para></listitem>
      <listitem><para><filename>waldo.mstack/root/</filename></para></listitem>
    </orderedlist>

    <para>The following <filename>.mstack/</filename> consists of a read-only DDI mounted as root, but a
    writable <filename>/var/</filename> mounted on top:</para>

    <orderedlist>
      <listitem><para><filename>quux.mstack/layer@0.raw</filename> → <filename>../myapp1.raw</filename></para></listitem>
      <listitem><para><filename>quux.mstack/bind:var</filename> → <filename>../myapp1-var/</filename></para></listitem>
    </orderedlist>
  </refsect1>

  <refsect1>
      <title>See Also</title>
      <para><simplelist type="inline">
        <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd-mstack</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd.v</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
        <member><citerefentry><refentrytitle>systemd-vpick</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
      </simplelist></para>
  </refsect1>

</refentry>