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da49e9ab | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
da49e9ab | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
9 | <refentry id="systemd.target"> | |
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10 | <refentryinfo> |
11 | <title>systemd.target</title> | |
12 | <productname>systemd</productname> | |
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13 | </refentryinfo> |
14 | ||
15 | <refmeta> | |
16 | <refentrytitle>systemd.target</refentrytitle> | |
17 | <manvolnum>5</manvolnum> | |
18 | </refmeta> | |
19 | ||
20 | <refnamediv> | |
21 | <refname>systemd.target</refname> | |
22 | <refpurpose>Target unit configuration</refpurpose> | |
23 | </refnamediv> | |
24 | ||
25 | <refsynopsisdiv> | |
26 | <para><filename><replaceable>target</replaceable>.target</filename></para> | |
27 | </refsynopsisdiv> | |
28 | ||
29 | <refsect1> | |
30 | <title>Description</title> | |
31 | ||
32 | <para>A unit configuration file whose name ends in | |
33 | <literal>.target</literal> encodes information about a target unit | |
34 | of systemd, which is used for grouping units and as well-known | |
35 | synchronization points during start-up.</para> | |
36 | ||
37 | <para>This unit type has no specific options. See | |
38 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
39 | for the common options of all unit configuration files. The common | |
40 | configuration items are configured in the generic [Unit] and | |
41 | [Install] sections. A separate [Target] section does not exist, | |
42 | since no target-specific options may be configured.</para> | |
43 | ||
44 | <para>Target units do not offer any additional functionality on | |
45 | top of the generic functionality provided by units. They exist | |
46 | merely to group units via dependencies (useful as boot targets), | |
47 | and to establish standardized names for synchronization points | |
48 | used in dependencies between units. Among other things, target | |
49 | units are a more flexible replacement for SysV runlevels in the | |
50 | classic SysV init system. (And for compatibility reasons special | |
51 | target units such as <filename>runlevel3.target</filename> exist | |
52 | which are used by the SysV runlevel compatibility code in systemd. | |
53 | See | |
54 | <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
55 | for details).</para> | |
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56 | </refsect1> |
57 | ||
58 | <refsect1> | |
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59 | <title>Automatic Dependencies</title> |
60 | ||
61 | <refsect2> | |
62 | <title>Implicit Dependencies</title> | |
63 | ||
64 | <para>There are no implicit dependencies for target units.</para> | |
65 | </refsect2> | |
66 | ||
67 | <refsect2> | |
68 | <title>Default Dependencies</title> | |
69 | ||
70 | <para>The following dependencies are added unless | |
71 | <varname>DefaultDependencies=no</varname> is set:</para> | |
72 | ||
73 | <itemizedlist> | |
74 | <listitem><para>Target units will automatically complement all | |
75 | configured dependencies of type <varname>Wants=</varname> or | |
76 | <varname>Requires=</varname> with dependencies of type | |
77 | <varname>After=</varname> unless <varname>DefaultDependencies=no</varname> | |
78 | is set in the specified units. Note that <varname>Wants=</varname> or | |
79 | <varname>Requires=</varname> must be defined in the target unit itself — if | |
80 | you for example define <varname>Wants=</varname>some.target in | |
81 | some.service, the automatic ordering will not be added.</para></listitem> | |
82 | ||
83 | <listitem><para>Target units automatically gain <varname>Conflicts=</varname> | |
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84 | and <varname>Before=</varname> dependencies against |
85 | <filename>shutdown.target</filename>.</para></listitem> | |
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86 | </itemizedlist> |
87 | </refsect2> | |
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88 | </refsect1> |
89 | ||
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90 | <refsect1> |
91 | <title>Example</title> | |
92 | ||
93 | <example> | |
94 | <title>Simple standalone target</title> | |
95 | ||
96 | <programlisting># emergency-net.target | |
97 | ||
98 | [Unit] | |
99 | Description=Emergency Mode with Networking | |
100 | Requires=emergency.target systemd-networkd.service | |
101 | After=emergency.target systemd-networkd.service | |
102 | AllowIsolate=yes</programlisting> | |
103 | ||
104 | <para>When adding dependencies to other units, it's important to check if they set | |
105 | <varname>DefaultDependencies=</varname>. Service units, unless they set | |
106 | <varname>DefaultDependencies=no</varname>, automatically get a dependency on | |
107 | <filename>sysinit.target</filename>. In this case, both | |
108 | <filename>emergency.target</filename> and <filename>systemd-networkd.service</filename> | |
109 | have <varname>DefaultDependencies=no</varname>, so they are suitable for use | |
110 | in this target, and do not pull in <filename>sysinit.target</filename>.</para> | |
111 | ||
112 | <para>You can now switch into this emergency mode by running <varname>systemctl | |
113 | isolate emergency-net.target</varname> or by passing the option | |
114 | <varname>systemd.unit=emergency-net.target</varname> on the kernel command | |
115 | line.</para> | |
116 | ||
117 | <para>Other units can have <varname>WantedBy=emergency-net.target</varname> in the | |
118 | <varname>[Install]</varname> section. After they are enabled using | |
119 | <command>systemctl enable</command>, they will be started before | |
120 | <varname>emergency-net.target</varname> is started. It is also possible to add | |
121 | arbitrary units as dependencies of <filename>emergency.target</filename> without | |
122 | modifying them by using <command>systemctl add-wants</command>. | |
123 | </para> | |
124 | </example> | |
125 | </refsect1> | |
126 | ||
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127 | <refsect1> |
128 | <title>See Also</title> | |
129 | <para> | |
130 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
131 | <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
132 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
133 | <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
134 | <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
135 | </para> | |
136 | </refsect1> | |
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137 | |
138 | </refentry> |