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eec575d8 | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
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5 | |
6 | <refentry id="systemd.device"> | |
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7 | <refentryinfo> |
8 | <title>systemd.device</title> | |
9 | <productname>systemd</productname> | |
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10 | </refentryinfo> |
11 | ||
12 | <refmeta> | |
13 | <refentrytitle>systemd.device</refentrytitle> | |
14 | <manvolnum>5</manvolnum> | |
15 | </refmeta> | |
16 | ||
17 | <refnamediv> | |
18 | <refname>systemd.device</refname> | |
19 | <refpurpose>Device unit configuration</refpurpose> | |
20 | </refnamediv> | |
21 | ||
22 | <refsynopsisdiv> | |
23 | <para><filename><replaceable>device</replaceable>.device</filename></para> | |
24 | </refsynopsisdiv> | |
25 | ||
26 | <refsect1> | |
27 | <title>Description</title> | |
28 | ||
29 | <para>A unit configuration file whose name ends in | |
30 | <literal>.device</literal> encodes information about a device unit | |
31 | as exposed in the | |
32 | sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
33 | device tree.</para> | |
34 | ||
35 | <para>This unit type has no specific options. See | |
36 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
37 | for the common options of all unit configuration files. The common | |
38 | configuration items are configured in the generic | |
39 | <literal>[Unit]</literal> and <literal>[Install]</literal> | |
40 | sections. A separate <literal>[Device]</literal> section does not | |
41 | exist, since no device-specific options may be configured.</para> | |
42 | ||
43 | <para>systemd will dynamically create device units for all kernel | |
44 | devices that are marked with the "systemd" udev tag (by default | |
45 | all block and network devices, and a few others). This may be used | |
46 | to define dependencies between devices and other units. To tag a | |
47 | udev device, use <literal>TAG+="systemd"</literal> in the udev | |
48 | rules file, see | |
49 | <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
50 | for details.</para> | |
51 | ||
52 | <para>Device units are named after the <filename>/sys</filename> | |
53 | and <filename>/dev</filename> paths they control. Example: the | |
54 | device <filename noindex='true'>/dev/sda5</filename> is exposed in | |
55 | systemd as <filename>dev-sda5.device</filename>. For details about | |
56 | the escaping logic used to convert a file system path to a unit | |
57 | name see | |
58 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> | |
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59 | |
60 | <para>Device units will be reloaded by systemd whenever the | |
61 | corresponding device generates a <literal>changed</literal> event. | |
62 | Other units can use <varname>ReloadPropagatedFrom=</varname> to react | |
63 | to that event</para> | |
c129bd5d | 64 | </refsect1> |
798d3a52 | 65 | |
c129bd5d | 66 | <refsect1> |
aed5cb03 | 67 | <title>Automatic Dependencies</title> |
798d3a52 | 68 | |
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69 | <refsect2> |
70 | <title>Implicit Dependencies</title> | |
71 | ||
72 | <para>Many unit types automatically acquire dependencies on device | |
73 | units of devices they require. For example, | |
74 | <filename>.socket</filename> unit acquire dependencies on the | |
75 | device units of the network interface specified in | |
76 | <varname>BindToDevice=</varname>. Similar, swap and mount units | |
77 | acquire dependencies on the units encapsulating their backing | |
78 | block devices.</para> | |
79 | </refsect2> | |
80 | ||
81 | <refsect2> | |
82 | <title>Default Dependencies</title> | |
45f09f93 | 83 | |
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84 | <para>There are no default dependencies for device units.</para> |
85 | </refsect2> | |
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86 | </refsect1> |
87 | ||
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88 | <refsect1> |
89 | <title>The udev Database</title> | |
90 | ||
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91 | <para>Unit settings of device units may either be configured via unit files, or directly from the udev |
92 | database. The following udev device properties are understood by the service manager:</para> | |
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93 | |
94 | <variablelist class='udev-directives'> | |
95 | <varlistentry> | |
96 | <term><varname>SYSTEMD_WANTS=</varname></term> | |
97 | <term><varname>SYSTEMD_USER_WANTS=</varname></term> | |
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98 | <listitem><para>Adds dependencies of type <varname>Wants=</varname> from the device unit to the specified |
99 | units. <varname>SYSTEMD_WANTS=</varname> is read by the system service manager, | |
100 | <varname>SYSTEMD_USER_WANTS=</varname> by user service manager instances. These properties may be used to | |
101 | activate arbitrary units when a specific device becomes available.</para> | |
102 | ||
103 | <para>Note that this and the other udev device properties are not taken into account unless the device is | |
104 | tagged with the <literal>systemd</literal> tag in the udev database, because otherwise the device is not | |
105 | exposed as a systemd unit (see above).</para> | |
106 | ||
107 | <para>Note that systemd will only act on <varname>Wants=</varname> dependencies when a device first becomes | |
108 | active. It will not act on them if they are added to devices that are already active. Use | |
109 | <varname>SYSTEMD_READY=</varname> (see below) to configure when a udev device shall be considered active, and | |
110 | thus when to trigger the dependencies.</para> | |
111 | ||
112 | <!-- Note that we don't document here that we actually apply unit_name_mangle() to all specified names, since | |
113 | that's kinda ugly, and people should instead specify correctly escaped names --> | |
114 | ||
115 | <para>The specified property value should be a space-separated list of valid unit names. If a unit template | |
116 | name is specified (that is, a unit name containing an <literal>@</literal> character indicating a unit name to | |
117 | use for multiple instantiation, but with an empty instance name following the <literal>@</literal>), it will be | |
118 | automatically instantiated by the device's <literal>sysfs</literal> path (that is: the path is escaped and | |
119 | inserted as instance name into the template unit name). This is useful in order to instantiate a specific | |
120 | template unit once for each device that appears and matches specific properties.</para></listitem> | |
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121 | </varlistentry> |
122 | ||
123 | <varlistentry> | |
124 | <term><varname>SYSTEMD_ALIAS=</varname></term> | |
125 | <listitem><para>Adds an additional alias name to the device | |
126 | unit. This must be an absolute path that is automatically | |
127 | transformed into a unit name. (See above.)</para></listitem> | |
128 | </varlistentry> | |
129 | ||
130 | <varlistentry> | |
131 | <term><varname>SYSTEMD_READY=</varname></term> | |
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132 | <listitem><para>If set to 0, systemd will consider this device unplugged even if it shows up in the udev |
133 | tree. If this property is unset or set to 1, the device will be considered plugged if it is visible in the udev | |
134 | tree.</para> | |
135 | ||
136 | <para>This option is useful for devices that initially show up in an uninitialized state in the tree, and for | |
137 | which a <literal>changed</literal> event is generated the moment they are fully set up. Note that | |
138 | <varname>SYSTEMD_WANTS=</varname> (see above) is not acted on as long as <varname>SYSTEMD_READY=0</varname> is | |
139 | set for a device.</para></listitem> | |
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140 | </varlistentry> |
141 | ||
142 | <varlistentry> | |
143 | <term><varname>ID_MODEL_FROM_DATABASE=</varname></term> | |
144 | <term><varname>ID_MODEL=</varname></term> | |
145 | ||
146 | <listitem><para>If set, this property is used as description | |
147 | string for the device unit.</para></listitem> | |
148 | </varlistentry> | |
149 | ||
150 | </variablelist> | |
151 | ||
152 | </refsect1> | |
153 | ||
154 | <refsect1> | |
155 | <title>See Also</title> | |
156 | <para> | |
157 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
158 | <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
159 | <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>, | |
160 | <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>, | |
161 | <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
162 | </para> | |
163 | </refsect1> | |
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164 | |
165 | </refentry> |