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590 lines
33 KiB
XML
590 lines
33 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"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 2010 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 General Public License as published by
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the Free Software Foundation; either version 2 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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General Public License for more details.
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You should have received a copy of the GNU 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.unit">
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<refentryinfo>
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<title>systemd.unit</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.unit</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.unit</refname>
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<refpurpose>systemd unit configuration files</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd.service</filename>,
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<filename>systemd.socket</filename>,
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<filename>systemd.device</filename>,
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<filename>systemd.mount</filename>,
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<filename>systemd.automount</filename>,
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<filename>systemd.swap</filename>,
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<filename>systemd.target</filename>,
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<filename>systemd.path</filename>,
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<filename>systemd.timer</filename>,
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<filename>systemd.snapshot</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>A unit configuration file encodes information
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about a service, a socket, a device, a mount point, an
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automount point, a swap file or partition, a start-up
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target, a file system path or a timer controlled and
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supervised by
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. The
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syntax is inspired by <ulink
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url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
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Desktop Entry Specification</ulink> <filename>.desktop</filename> files, which are in turn
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inspired by Microsoft Windows
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<filename>.ini</filename> files.</para>
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<para>This man pages lists the common configuration
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options of the all unit types. These options need to
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be configured in the [Unit] resp. [Install]
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section of the unit files.</para>
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<para>In addition to the generic [Unit] and [Install]
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sections described here each unit should have a
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type-specific section, e.g. [Service] for a service
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unit. See the respective man pages for more
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information.</para>
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<para>Unit files may contain additional options on top
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of those listed here. If systemd encounters an unknown
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option it will write a warning log message but
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continue loading the unit. If an option is prefixed
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with <option>X-</option> it is ignored completely by
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systemd. Applications may use this to include
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additional information in the unit files.</para>
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<para>Boolean arguments used in unit files can be
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written in various formats. For positive settings the
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strings <option>1</option>, <option>yes</option>,
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<option>true</option> and <option>on</option> are
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equivalent. For negative settings the strings
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<option>0</option>, <option>no</option>,
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<option>false</option> and <option>off</option> are
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equivalent.</para>
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<para>Time span values encoded in unit files can be
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written in various formats. A stand-alone number
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specifies a time in seconds. If suffixed with a time
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unit, the unit is honored. A concatenation of
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multiple value with units is supported, in which case
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the values are added up. Example: "50" refers to 50
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seconds; "2min 200ms" refers to 2 minutes plus 200
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milliseconds, i.e. 120200ms. The following time units
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are understood: s, min, h, d, w, ms, us.</para>
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<para>Empty lines and lines starting with # or ; are
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ignored. This may be used for commenting. Lines ending
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in a backslash are concatenated with the following
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line while reading and the backslash is replaced by a
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space character. This may be used to wrap long lines.</para>
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<para>If a line starts with <option>.include</option>
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followed by a file name the specified file will be
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read as if its contents where listed in place of the
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<option>.include</option> directive.</para>
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<para>Along with a unit file
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<filename>foo.service</filename> a directory
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<filename>foo.service.wants/</filename> may exist. All
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units symlinked from such a directory are implicitly
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added as dependencies of type
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<varname>Wanted=</varname> to the unit. This is useful
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to hook units into the start-up of other units,
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without having to modify their unit configuration
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files. For details about the semantics of
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<varname>Wanted=</varname> see below. The preferred
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way to create symlinks in the
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<filename>.wants/</filename> directory of a service is
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with the
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<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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tool which reads information from the [Install]
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section of unit files. (See below.)</para>
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<para>Note that while systemd offers a flexible
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dependency system between units it is recommended to
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use this functionality only sparsely and instead rely
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on techniques such as bus-based or socket-based
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activation which makes dependencies implicit, which
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both results in a simpler and more flexible
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system.</para>
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<para>Some unit names reflect paths existing in the
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file system name space. Example: a device unit
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<filename>dev-sda.device</filename> refers to a device
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with the device node <filename>/dev/sda</filename> in
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the file system namespace. If this applies a special
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way to escape the path name is used, so that it is
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usable as part of a file name. Basically, given a
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path, "/" is replaced by "-", and all unprintable
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characters and the "-" are replaced by C-style "\x20"
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escapes. The root directory "/" is encoded as single
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dash, while otherwise the initial and ending "/" is
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removed from all paths during transformation. This
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escaping is reversible.</para>
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<para>Optionally, units may be instantiated from a
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template file at runtime. This allows creation of
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multiple units from a single configuration file. If
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systemd looks for a unit configuration file it will
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first search for the literal unit name in the
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filesystem. If that yields no success and the unit
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name contains an @ character, systemd will look for a
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unit template that shares the same name but with the
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instance string (i.e. the part between the @ character
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and the suffix) removed. Example: if a service
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<filename>getty@tty3.service</filename> is requested
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and no file by that name is found, systemd will look
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for <filename>getty@.service</filename> and
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instantiate a service from that configuration file if
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it is found. To refer to the instance string from
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within the configuration file you may use the special
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<literal>%i</literal> specifier in many of the
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configuration options. Other specifiers that may be
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used are <literal>%n</literal>, <literal>%N</literal>,
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<literal>%p</literal>, <literal>%P</literal> and
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<literal>%I</literal>, for the full unit name, the
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unescaped unit name, the prefix name, the unescaped
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prefix name and the unescaped instance name,
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respectively. The prefix name here refers to the
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string before the @, i.e. "getty" in the example
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above, where "tty3" is the instance name.</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>Unit file may include a [Unit] section, which
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carries generic information about the unit that is not
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dependent on the type of unit:</para>
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<variablelist>
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<varlistentry>
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<term><varname>Names=</varname></term>
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<listitem><para>Additional names for
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this unit. The names listed here must
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have the same suffix (i.e. type) as
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the unit file name. This option may be
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specified more than once, in which
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case all listed names are used. Note
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that this option is different from the
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<varname>Alias=</varname> option from
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the [Install] section mentioned
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below. See below for details.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Description=</varname></term>
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<listitem><para>A free-form string
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describing the unit. This is intended
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for use in UIs to show descriptive
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information along with the unit
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name.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Requires=</varname></term>
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<listitem><para>Configures requirement
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dependencies on other units. If this
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units get activated the units listed
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here will be activated as well. If one
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of the other units gets deactivated or
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its activation fails, this unit will
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be deactivated. This option may be
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specified more than once, in which
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case requirement dependencies for all
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listed names are created. Note that
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requirement dependencies do not
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influence the order in which services
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are started or stopped. This has to be
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configured independently with the
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<varname>After=</varname> or
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<varname>Before=</varname> options. If
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a unit
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<filename>foo.service</filename>
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requires a unit
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<filename>bar.service</filename> as
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configured with
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<varname>Requires=</varname> and no
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ordering is configured with
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<varname>After=</varname> or
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<varname>Before=</varname>, then both
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units will be started simultaneously
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and without any delay between them if
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<filename>foo.service</filename> is
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activated. Often it is a better choice
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to use <varname>Wants=</varname>
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instead of
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<varname>Requires=</varname> in order
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to achieve a system that is more
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robust when dealing with failing
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services.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>RequiresOverridable=</varname></term>
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<listitem><para>Similar to
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<varname>Requires=</varname>.
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Dependencies listed in
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<varname>RequiresOverridable=</varname>
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which cannot be fulfilled or fail to
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start are ignored iff the startup was
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explicitly requested by the user. If
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the start-up was pulled in indirectly
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by some dependency or automatic
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start-up of units that is not
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requested by the user this dependency
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must be fulfilled and otherwise the
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transaction fails. Hence, this option
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may be used to configure dependencies
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that are normally honored unless the
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user explicitly starts up the unit, in
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which case whether they failed or not
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is irrelevant.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Requisite=</varname></term>
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<term><varname>RequisiteOverridable=</varname></term>
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<listitem><para>Similar to
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<varname>Requires=</varname>
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resp. <varname>RequiresOverridable=</varname>. However,
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if a unit listed here is not started
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already it will not be started and the
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transaction fails
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immediately.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Wants=</varname></term>
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<listitem><para>A weaker version of
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<varname>Requires=</varname>. A unit
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listed in this option will be started
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if the configuring unit is. However,
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it the listed unit fails to start up
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or cannot be added to the transaction
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this has no impact on the validity of
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the transaction as a whole. This is
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the recommended way to hook start-up
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of one unit to the start-up of another
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unit. Note that dependencies of this
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type may also be configured outside of
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the unit configuration file by
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adding a symlink to a
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<filename>.wants/</filename> directory
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accompanying the unit file. For
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details see above.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Conflicts=</varname></term>
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<listitem><para>Configures negative
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requirement dependencies. If a unit
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that has a
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<varname>Conflicts=</varname> setting
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on another unit starting the former
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will stop the latter and vice
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versa. Note that this setting is
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independent of and orthogonal to the
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<varname>After=</varname> and
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<varname>Before=</varname> ordering
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dependencies.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Before=</varname></term>
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<term><varname>After=</varname></term>
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<listitem><para>Configures ordering
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dependencies between units. If a unit
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<filename>foo.service</filename>
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contains a setting
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<option>Before=bar.service</option>
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and both units are being started
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<filename>bar.service</filename>'s
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start-up is delayed until
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<filename>foo.service</filename> is
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started up. Note that this setting is
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independent of and orthogonal to the
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requirement dependencies as configured
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by <varname>Requires=</varname>. It is
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a common pattern to include a unit
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name in both the
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<varname>After=</varname> and
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<varname>Requires=</varname> option in
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which case the unit listed will be
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started before the unit that is
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configured with these options. This
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option may be specified more than
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once, in which case ordering
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dependencies for all listed names are
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created. <varname>After=</varname> is
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the inverse of
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<varname>Before=</varname>, i.e. while
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<varname>After=</varname> ensures that
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the configured unit is started after
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the listed unit finished starting up,
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<varname>Before=</varname> ensures the
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opposite, i.e. that the configured
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unit is fully started up before the
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listed unit is started. Note that when
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two units with an ordering dependency
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between them are shut down, the
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inverse of of the start-up order is
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applied. i.e. if a unit is configured
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with <varname>After=</varname> on
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another unit, the former is stopped
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before the latter if both are shut
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down. If one unit with an ordering
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dependency on another unit is shut
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down while the latter is started up,
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the shut down is ordered before the
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start-up regardless whether the
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ordering dependency is actually of
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type <varname>After=</varname> or
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<varname>Before=</varname>. If two
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units have no ordering dependencies
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between them they are shut down
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resp. started up simultaneously, and
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no ordering takes
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place. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>RecursiveStop=</varname></term>
|
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<listitem><para>Takes a boolean
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argument. If <option>true</option> and
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the unit stops without this being
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requested by the user all units
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depending on it will be stopped as
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well. (e.g. if a service exits or
|
|
crashes on its own behalf, units using
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it will be stopped) Note that normally
|
|
if a unit stops without user request
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|
units depending on it will not be
|
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terminated. Only if the user requested
|
|
shutdown of a unit all units depending
|
|
on the unit will be shut down as well
|
|
and at the same time. Defaults to
|
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<option>false</option>.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>StopWhenUnneeded=</varname></term>
|
|
|
|
<listitem><para>Takes a boolean
|
|
argument. If <option>true</option>
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|
this unit will be stopped when it is
|
|
no longer used. Note that in order to
|
|
minimize the work to be executed
|
|
systemd will by default not stop units
|
|
unless they are conflicting with other
|
|
units, or the user explicitly
|
|
requested their shut down. If this
|
|
option is set a unit will be
|
|
automatically cleaned up if no other
|
|
active unit requires it. Defaults to
|
|
<option>false</option>.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>OnlyByDependency=</varname></term>
|
|
|
|
<listitem><para>Takes a boolean
|
|
argument. If <option>true</option>
|
|
this unit may only be activated
|
|
indirectly. In this case explicit
|
|
start-up requested by the user is
|
|
denied, however if it is started as
|
|
dependency of another unit start-up
|
|
will succeed. This is mostly a safety
|
|
feature to ensure that the user does
|
|
not accidentally activate units that are
|
|
not intended to be activated
|
|
explicitly. This option defaults to
|
|
<option>false</option>.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>DefaultDependencies=</varname></term>
|
|
|
|
<listitem><para>Takes a boolean
|
|
argument. If <option>true</option>
|
|
(the default), a few default
|
|
dependencies will implicitly be
|
|
created for the unit. The actual
|
|
dependencies created depend on the
|
|
unit type. For example, for service
|
|
units, these dependencies ensure that
|
|
the service is started only after
|
|
basic system initialization is
|
|
complete and is properly terminated on
|
|
system shutdown. See the respective
|
|
man pages for details. Generally, only
|
|
services involved with early boot or
|
|
late shutdown should set this option
|
|
to <option>false</option>. It is
|
|
highly recommended to leave this
|
|
option enabled for the majority of
|
|
common units. If set to
|
|
<option>false</option> this option
|
|
does not disable all implicit
|
|
dependencies, just non-essential
|
|
ones.</para></listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
|
|
<para>Unit file may include a [Install] section, which
|
|
carries installation information for the unit. This
|
|
section is not interpreted by
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
during runtime. It is used exclusively by the
|
|
<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
|
tool during installation of a unit:</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><varname>Alias=</varname></term>
|
|
|
|
<listitem><para>Additional names this
|
|
unit shall be installed under. The
|
|
names listed here must have the same
|
|
suffix (i.e. type) as the unit file
|
|
name. This option may be specified
|
|
more than once, in which case all
|
|
listed names are used. At installation
|
|
time,
|
|
<command>systemd-install</command>
|
|
will create symlinks from these names
|
|
to the unit file name. Note that this
|
|
is different from the
|
|
<varname>Names=</varname> option from
|
|
the [Unit] section mentioned above:
|
|
The names from
|
|
<varname>Names=</varname> apply
|
|
unconditionally if the unit is
|
|
loaded. The names from
|
|
<varname>Alias=</varname> apply only
|
|
if the unit has actually been
|
|
installed with the
|
|
<command>systemd-install</command>
|
|
tool. Also, if systemd searches for a
|
|
unit, it will discover symlinked alias
|
|
names as configured with
|
|
<varname>Alias=</varname>, but not
|
|
names configured with
|
|
<varname>Names=</varname> only. It is
|
|
a common pattern to list a name in
|
|
both options. In this case, a unit
|
|
will be active under all names if
|
|
installed, but also if not installed
|
|
but requested explicitly under its
|
|
main name.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>WantedBy=</varname></term>
|
|
|
|
<listitem><para>Installs a symlink in
|
|
the <filename>.wants/</filename>
|
|
subdirectory for a unit. This has the
|
|
effect that when the listed unit name
|
|
is activated the unit listing it is
|
|
activated
|
|
too. <command>WantedBy=foo.service</command>
|
|
in a service
|
|
<filename>bar.service</filename> is
|
|
mostly equivalent to
|
|
<command>Alias=foo.service.wants/bar.service</command>
|
|
in the same file.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>Also=</varname></term>
|
|
|
|
<listitem><para>Additional units to
|
|
install when this unit is
|
|
installed. If the user requests
|
|
installation of a unit with this
|
|
option configured
|
|
<command>systemd-install</command>
|
|
will automatically install units
|
|
listed in this option as
|
|
well.</para></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para>
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|