mirror of
https://github.com/systemd/systemd.git
synced 2024-12-23 21:35:11 +03:00
229 lines
11 KiB
XML
229 lines
11 KiB
XML
<?xml version="1.0"?>
|
|
<!--*-nxml-*-->
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
<refentry id="systemd.preset">
|
|
|
|
<refentryinfo>
|
|
<title>systemd.preset</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>systemd.preset</refentrytitle>
|
|
<manvolnum>5</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>systemd.preset</refname>
|
|
<refpurpose>Service enablement presets</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<para><simplelist>
|
|
<member><filename>/etc/systemd/system-preset/*.preset</filename></member>
|
|
<member><filename>/run/systemd/system-preset/*.preset</filename></member>
|
|
<member><filename>/usr/local/lib/systemd/system-preset/*.preset</filename></member>
|
|
<member><filename>/usr/lib/systemd/system-preset/*.preset</filename></member>
|
|
<member><filename>/etc/systemd/user-preset/*.preset</filename></member>
|
|
<member><filename>/run/systemd/user-preset/*.preset</filename></member>
|
|
<member><filename>/usr/local/lib/systemd/user-preset/*.preset</filename></member>
|
|
<member><filename>/usr/lib/systemd/user-preset/*.preset</filename></member>
|
|
</simplelist></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> which uses this information to
|
|
enable or disable a unit. Depending on that policy, <command>systemctl preset</command> is identical to
|
|
<command>systemctl enable</command> or <command>systemctl disable</command>.
|
|
|
|
<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. For more information, see
|
|
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</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, see below.</para>
|
|
|
|
<para>If no preset files exist, preset operations 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>
|
|
|
|
<para>When the machine is booted for the first time,
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> will
|
|
enable/disable all units according to preset policy, similarly to <command>systemctl
|
|
preset-all</command>. Also see <varname>ConditionFirstBoot=</varname> in
|
|
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> and
|
|
"First Boot Semantics" in
|
|
<citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
|
|
</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Preset File Format</title>
|
|
|
|
<para>The preset files contain a list of directives, one per line. Empty lines and lines whose first
|
|
non-whitespace character is <literal>#</literal> or <literal>;</literal> are ignored. Each directive
|
|
consists of one of the words <literal>enable</literal>, <literal>disable</literal>, or
|
|
<literal>ignore</literal>, followed by whitespace and a unit name. The unit name may contain shell-style
|
|
wildcards.</para>
|
|
|
|
<para>For the enable directive for template units, one or more instance names may be specified as a
|
|
space-separated list after the unit name. In this case, those instances will be enabled instead of the
|
|
instance specified via DefaultInstance= in the unit.</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>Three different directives are understood: <literal>enable</literal> may be used to enable units by
|
|
default, <literal>disable</literal> to disable units by default, and <literal>ignore</literal> to ignore
|
|
units and leave existing configuration intact.</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>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>Enable multiple template instances</title>
|
|
|
|
<programlisting># /usr/lib/systemd/system-preset/80-dirsrv.preset
|
|
|
|
enable dirsrv@.service foo bar baz</programlisting>
|
|
</example>
|
|
|
|
<para>This enables all three of <filename>dirsrv@foo.service</filename>,
|
|
<filename>dirsrv@bar.service</filename> and <filename>dirsrv@baz.service</filename>.</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>Motivation for the preset logic</title>
|
|
|
|
<para>Different distributions have different policies on which services shall be enabled by default when
|
|
the package they are shipped in is installed. On Fedora all services stay off by default, so that
|
|
installing a package will not cause a service to be enabled (with some exceptions). On Debian all
|
|
services are immediately enabled by default, so that installing a package will cause its services to be
|
|
enabled right-away.</para>
|
|
|
|
<para>Even within a single distribution, different spins (flavours, remixes, whatever you might want to
|
|
call them) of a distribution also have different policies on what services to enable, and what services
|
|
to leave off. For example, Fedora Workstation will enable <command>gdm</command> as display manager by
|
|
default, while the Fedora KDE spin will enable <command>sddm</command> instead.</para>
|
|
|
|
<para>Different sites might also have different policies what to turn on by default and what to turn
|
|
off. For example, one administrator would prefer to enforce the policy of "<command>sshd</command> should
|
|
be always on, but everything else off", while another one might say "<command>snmpd</command> always on,
|
|
and for everything else use the distribution policy defaults".</para>
|
|
|
|
<para>Traditionally, policy about which services shall be enabled were implemented in each package
|
|
individually. This made it cumbersome to implement different policies per spin or per site, or to create
|
|
software packages that do the right thing on more than one distribution. The enablement mechanism was
|
|
also encoding the enablement policy.</para>
|
|
|
|
<para>The preset mechanism allows clean separation of the enablement mechanism (inside the package
|
|
scriptlets, by invoking <command>systemctl preset</command>) and enablement policy (centralized in the
|
|
preset files), and lifts the configuration out of individual packages. Preset files may be written for
|
|
specific distributions, for specific spins or for specific sites, in order to enforce different policies
|
|
as needed. It is recommended to apply the policy encoded in preset files in package installation
|
|
scriptlets.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para><simplelist type="inline">
|
|
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd-delta</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
</simplelist></para>
|
|
|
|
<para><citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
has a discussion of packaging scriptlets.</para>
|
|
|
|
<para>Fedora page introducing the use of presets:
|
|
<ulink url="https://fedoraproject.org/wiki/Features/PackagePresets">Features/PackagePresets</ulink>.
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|