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systemd/man/systemd.preset.xml
Tom Gundersen 12b42c7667 man: revert dynamic paths for split-usr setups
This did not really work out as we had hoped. Trying to do this upstream
introduced several problems that probably makes it better suited as a
downstream patch after all. At any rate, it is not releaseable in the
current state, so we at least need to revert this before the release.

 * by adjusting the path to binaries, but not do the same thing to the
   search path we end up with inconsistent man-pages. Adjusting the search
   path too would be quite messy, and it is not at all obvious that this is
   worth the effort, but at any rate it would have to be done before we
   could ship this.

 * this means that distributed man-pages does not make sense as they depend
   on config options, and for better or worse we are still distributing
   man pages, so that is something that definitely needs sorting out before
   we could ship with this patch.

 * we have long held that split-usr is only minimally supported in order
   to boot, and something we hope will eventually go away. So before we start
   adding even more magic/effort in order to make this work nicely, we should
   probably question if it makes sense at all.
2015-06-18 19:47:44 +02:00

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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">
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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 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>