systemd-stable/man/systemd.preset.xml

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<refentry id="systemd.preset">

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

    <authorgroup>
      <author>
        <contrib>Developer</contrib>
        <firstname>Lennart</firstname>
        <surname>Poettering</surname>
        <email>lennart@poettering.net</email>
      </author>
    </authorgroup>
  </refentryinfo>

  <refmeta>
    <refentrytitle>systemd.preset</refentrytitle>
    <manvolnum>5</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>systemd.preset</refname>
    <refpurpose>Service enablement presets</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <para><filename>/etc/systemd/system-preset/*.preset</filename></para>
    <para><filename>/run/systemd/system-preset/*.preset</filename></para>
    <para><filename>/usr/lib/systemd/system-preset/*.preset</filename></para>
    <para><filename>/etc/systemd/user-preset/*.preset</filename></para>
    <para><filename>/run/systemd/user-preset/*.preset</filename></para>
    <para><filename>/usr/lib/systemd/user-preset/*.preset</filename></para>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>Preset files may be used to encode policy which units shall
    be enabled by default and which ones shall be disabled. They are
    read by <command>systemctl preset</command> (for more information
    see
    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
    which uses this information to enable or disable a unit according
    to preset policy. <command>systemctl preset</command> is used by
    the post install scriptlets of RPM packages (or other OS package
    formats), to enable/disable specific units by default on package
    installation, enforcing distribution, spin or administrator preset
    policy. This allows choosing a certain set of units to be
    enabled/disabled even before installing the actual package.</para>

    <para>For more information on the preset logic please have a look
    at the <ulink
    url="https://www.freedesktop.org/wiki/Software/systemd/Preset">Presets</ulink>
    document.</para>

    <para>It is not recommended to ship preset files within the
    respective software packages implementing the units, but rather
    centralize them in a distribution or spin default policy, which
    can be amended by administrator policy.</para>

    <para>If no preset files exist, <command>systemctl
    preset</command> will enable all units that are installed by
    default. If this is not desired and all units shall rather be
    disabled, it is necessary to ship a preset file with a single,
    catchall "<filename>disable *</filename>" line. (See example 1,
    below.)</para>
  </refsect1>

  <refsect1>
    <title>Preset File Format</title>

    <para>The preset files contain a list of directives consisting of
    either the word <literal>enable</literal> or
    <literal>disable</literal> followed by a space and a unit name
    (possibly with shell style wildcards), separated by newlines.
    Empty lines and lines whose first non-whitespace character is # or
    ; are ignored.</para>

    <para>Presets must refer to the "real" unit file, and not to any aliases. See
    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
    for a description of unit aliasing.</para>

    <para>Two different directives are understood:
    <literal>enable</literal> may be used to enable units by default,
    <literal>disable</literal> to disable units by default.</para>

    <para>If multiple lines apply to a unit name, the first matching
    one takes precedence over all others.</para>

    <para>Each preset file shall be named in the style of
    <filename>&lt;priority&gt;-&lt;policy-name&gt;.preset</filename>. Files
    in <filename>/etc/</filename> override files with the same name in
    <filename>/usr/lib/</filename> and <filename>/run/</filename>.
    Files in <filename>/run/</filename> override files with the same
    name in <filename>/usr/lib/</filename>. Packages should install
    their preset files in <filename>/usr/lib/</filename>. Files in
    <filename>/etc/</filename> are reserved for the local
    administrator, who may use this logic to override the preset files
    installed by vendor packages. All preset files are sorted by their
    filename in lexicographic order, regardless of which of the
    directories they reside in. If multiple files specify the same
    unit name, the entry in the file with the lexicographically
    earliest name will be applied. It is recommended to prefix all
    filenames with a two-digit number and a dash, to simplify the
    ordering of the files.</para>

    <para>If the administrator wants to disable a preset file supplied
    by the vendor, the recommended way is to place a symlink to
    <filename>/dev/null</filename> in
    <filename>/etc/systemd/system-preset/</filename> bearing the same
    filename.</para>
  </refsect1>

  <refsect1>
    <title>Examples</title>

    <example>
      <title>Default to off</title>

      <programlisting># /usr/lib/systemd/system-preset/99-default.preset

disable *</programlisting>
    </example>

    <para>This disables all units. Due to the filename prefix
    <literal>99-</literal>, it will be read last and hence can easily
    be overridden by spin or administrator preset policy.</para>

    <example>
      <title>A GNOME spin</title>

      <programlisting># /usr/lib/systemd/system-preset/50-gnome.preset

enable gdm.service
enable colord.service
enable accounts-daemon.service
enable avahi-daemon.*</programlisting>

    </example>

    <para>This enables the three mentioned units, plus all
    <filename>avahi-daemon</filename> regardless of which unit type. A
    file like this could be useful for inclusion in a GNOME spin of a
    distribution. It will ensure that the units necessary for GNOME
    are properly enabled as they are installed. It leaves all other
    units untouched, and subject to other (later) preset files, for
    example like the one from the first example above.</para>

    <example>
      <title>Administrator policy</title>

      <programlisting># /etc/systemd/system-preset/00-lennart.preset

enable httpd.service
enable sshd.service
enable postfix.service
disable *</programlisting>
    </example>

    <para>This enables three specific services and disables all
    others. This is useful for administrators to specifically select
    the units to enable, and disable all others. Due to the filename
    prefix <literal>00-</literal> it will be read early and
    override all other preset policy files.</para>
  </refsect1>

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>