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d923e42eed
The man pages didn't ever mention that symlinks to units can be created, and what exactly this means. Fix that omission, and disallow presets on alias names.
194 lines
7.8 KiB
XML
194 lines
7.8 KiB
XML
<?xml version="1.0"?>
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<!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2011 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd.preset">
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<refentryinfo>
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<title>systemd.preset</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.preset</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.preset</refname>
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<refpurpose>Service enablement presets</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>/etc/systemd/system-preset/*.preset</filename></para>
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<para><filename>/run/systemd/system-preset/*.preset</filename></para>
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<para><filename>/usr/lib/systemd/system-preset/*.preset</filename></para>
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<para><filename>/etc/systemd/user-preset/*.preset</filename></para>
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<para><filename>/run/systemd/user-preset/*.preset</filename></para>
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<para><filename>/usr/lib/systemd/user-preset/*.preset</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>Preset files may be used to encode policy which units shall
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be enabled by default and which ones shall be disabled. They are
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read by <command>systemctl preset</command> (for more information
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see
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>)
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which uses this information to enable or disable a unit according
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to preset policy. <command>systemctl preset</command> is used by
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the post install scriptlets of RPM packages (or other OS package
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formats), to enable/disable specific units by default on package
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installation, enforcing distribution, spin or administrator preset
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policy. This allows choosing a certain set of units to be
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enabled/disabled even before installing the actual package.</para>
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<para>For more information on the preset logic please have a look
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at the <ulink
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url="http://freedesktop.org/wiki/Software/systemd/Preset">Presets</ulink>
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document.</para>
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<para>It is not recommended to ship preset files within the
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respective software packages implementing the units, but rather
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centralize them in a distribution or spin default policy, which
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can be amended by administrator policy.</para>
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<para>If no preset files exist, <command>systemctl
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preset</command> will enable all units that are installed by
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default. If this is not desired and all units shall rather be
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disabled, it is necessary to ship a preset file with a single,
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catchall "<filename>disable *</filename>" line. (See example 1,
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below.)</para>
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</refsect1>
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<refsect1>
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<title>Preset File Format</title>
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<para>The preset files contain a list of directives consisting of
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either the word <literal>enable</literal> or
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<literal>disable</literal> followed by a space and a unit name
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(possibly with shell style wildcards), separated by newlines.
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Empty lines and lines whose first non-whitespace character is # or
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; are ignored.</para>
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<para>Presets must refer to the "real" unit file, and not to any aliases. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for a description of unit aliasing.</para>
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<para>Two different directives are understood:
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<literal>enable</literal> may be used to enable units by default,
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<literal>disable</literal> to disable units by default.</para>
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<para>If multiple lines apply to a unit name, the first matching
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one takes precedence over all others.</para>
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<para>Each preset file shall be named in the style of
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<filename><priority>-<policy-name>.preset</filename>. Files
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in <filename>/etc/</filename> override files with the same name in
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<filename>/usr/lib/</filename> and <filename>/run/</filename>.
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Files in <filename>/run/</filename> override files with the same
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name in <filename>/usr/lib/</filename>. Packages should install
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their preset files in <filename>/usr/lib/</filename>. Files in
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<filename>/etc/</filename> are reserved for the local
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administrator, who may use this logic to override the preset files
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installed by vendor packages. All preset files are sorted by their
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filename in lexicographic order, regardless of which of the
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directories they reside in. If multiple files specify the same
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unit name, the entry in the file with the lexicographically
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earliest name will be applied. It is recommended to prefix all
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filenames with a two-digit number and a dash, to simplify the
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ordering of the files.</para>
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<para>If the administrator wants to disable a preset file supplied
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by the vendor, the recommended way is to place a symlink to
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<filename>/dev/null</filename> in
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<filename>/etc/systemd/system-preset/</filename> bearing the same
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filename.</para>
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</refsect1>
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<refsect1>
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<title>Example</title>
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<example>
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<title>Default off example <filename>/usr/lib/systemd/system-preset/99-default.preset</filename>:</title>
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<programlisting>disable *</programlisting>
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</example>
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<para>This disables all units. Due to the filename prefix
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<literal>99-</literal>, it will be read last and hence can easily
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be overridden by spin or administrator preset policy or
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suchlike.</para>
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<example>
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<title>A GNOME spin example <filename>/usr/lib/systemd/system-preset/50-gnome.preset</filename>:</title>
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<programlisting>enable gdm.service
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enable colord.service
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enable accounts-daemon.service
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enable avahi-daemon.*</programlisting>
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</example>
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<para>This enables the three mentioned units, plus all
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<filename>avahi-daemon</filename> regardless of which unit type. A
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file like this could be useful for inclusion in a GNOME spin of a
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distribution. It will ensure that the units necessary for GNOME
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are properly enabled as they are installed. It leaves all other
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units untouched, and subject to other (later) preset files, for
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example like the one from the first example above.</para>
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<example>
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<title>Administrator policy <filename>/etc/systemd/system-preset/00-lennart.preset</filename>:</title>
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<programlisting>enable httpd.service
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enable sshd.service
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enable postfix.service
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disable *</programlisting>
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</example>
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<para>This enables three specific services and disables all
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others. This is useful for administrators to specifically select
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the units to enable, and disable all others. Due to the filename
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prefix <literal>00-</literal> it will be read early and hence
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overrides all other preset policy files.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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