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<?xml version="1.0"?>
<!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
This file is part of systemd.
Copyright 2011 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<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><priority>-<policy-name>.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>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 filename 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 filename
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>
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