systemd/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="http://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>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;program&gt;.conf</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 alphabetical
                order, regardless in which of the directories they
                reside, to guarantee that a specific preset file takes
                precedence over another file with an alphabetically
                earlier name, if both files contain lines that apply
                to the same unit names. It is recommended to prefix
                all file names with two-digit number, to simplify
                ordering.</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 file name.</para>
        </refsect1>

        <refsect1>
                <title>Example</title>

                <example>
                        <title>Default off example <filename>/usr/lib/systemd/system-preset/99-default.preset</filename>:</title>

                        <programlisting>disable *</programlisting>
                </example>

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

                <example>
                        <title>A GNOME spin example <filename>/usr/lib/systemd/system-preset/50-gnome.preset</filename>:</title>

                        <programlisting>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 <filename>/etc/systemd/system-preset/00-lennart.preset</filename>:</title>

                        <programlisting>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 file name prefix
                <literal>00-</literal> it will be read early and hence
                overrides 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>