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7 This file is part of systemd.
9 Copyright 2010 Lennart Poettering
11 systemd is free software; you can redistribute it and/or modify it
12 under the terms of the GNU Lesser General Public License as published by
13 the Free Software Foundation; either version 2.1 of the License, or
14 (at your option) any later version.
16 systemd is distributed in the hope that it will be useful, but
17 WITHOUT ANY WARRANTY; without even the implied warranty of
18 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 Lesser General Public License for more details.
21 You should have received a copy of the GNU Lesser General Public License
22 along with systemd; If not, see <http://www.gnu.org/licenses/>.
25 <refentry id="systemd.device">
27 <title>systemd.device</title>
28 <productname>systemd</productname>
32 <contrib>Developer</contrib>
33 <firstname>Lennart</firstname>
34 <surname>Poettering</surname>
35 <email>lennart@poettering.net</email>
41 <refentrytitle>systemd.device</refentrytitle>
42 <manvolnum>5</manvolnum>
46 <refname>systemd.device</refname>
47 <refpurpose>Device unit configuration</refpurpose>
51 <para><filename><replaceable>device</replaceable>.device</filename></para>
55 <title>Description</title>
57 <para>A unit configuration file whose name ends in
58 <literal>.device</literal> encodes information about
59 a device unit as exposed in the
60 sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
63 <para>This unit type has no specific options. See
64 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
65 for the common options of all unit configuration
66 files. The common configuration items are configured
67 in the generic <literal>[Unit]</literal> and
68 <literal>[Install]</literal> sections. A separate
69 <literal>[Device]</literal> section does not exist,
70 since no device-specific options may be
73 <para>systemd will dynamically create device units for
74 all kernel devices that are marked with the "systemd"
75 udev tag (by default all block and network devices,
76 and a few others). This may be used to define
77 dependencies between devices and other units. To tag a
78 udev device, use <literal>TAG+="systemd"</literal> in
79 the udev rules file, see
80 <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
83 <para>Device units are named after the
84 <filename>/sys</filename> and
85 <filename>/dev</filename> paths they control. Example:
86 the device <filename noindex='true'>/dev/sda5</filename> is exposed
87 in systemd as <filename>dev-sda5.device</filename>. For
88 details about the escaping logic used to convert a
89 file system path to a unit name see
90 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
95 <title>The udev Database</title>
97 <para>The settings of device units may either be
98 configured via unit files, or directly from the udev
99 database (which is recommended). The following udev device
100 properties are understood by systemd:</para>
102 <variablelist class='udev-directives'>
104 <term><varname>SYSTEMD_WANTS=</varname></term>
105 <term><varname>SYSTEMD_USER_WANTS=</varname></term>
106 <listitem><para>Adds dependencies of
107 type <varname>Wants</varname> from the
108 device unit to all listed units. The
109 first form is used by the system
110 systemd instance, the second by user
111 systemd instances. Those settings may
112 be used to activate arbitrary units
113 when a specific device becomes
116 <para>Note that this and the
117 other tags are not taken into account
118 unless the device is tagged with the
119 <literal>systemd</literal> string in
120 the udev database, because otherwise
121 the device is not exposed as a systemd
122 unit (see above).</para>
124 <para>Note that systemd will only act
125 on <varname>Wants</varname>
126 dependencies when a device first
127 becomes active. It will not act on
128 them if they are added to devices that
129 are already active. Use
130 <varname>SYSTEMD_READY=</varname> (see
131 below) to influence on which udev
132 event to trigger the dependencies.
137 <term><varname>SYSTEMD_ALIAS=</varname></term>
138 <listitem><para>Adds an additional
139 alias name to the device unit. This
140 must be an absolute path that is
141 automatically transformed into a unit
142 name. (See above.)</para></listitem>
146 <term><varname>SYSTEMD_READY=</varname></term>
147 <listitem><para>If set to 0, systemd
148 will consider this device unplugged
149 even if it shows up in the udev
150 tree. If this property is unset or set
151 to 1, the device will be considered
152 plugged if it is visible in the
153 udev tree. This property has no
154 influence on the behavior when a
155 device disappears from the udev
158 <para>This option is useful to support
159 devices that initially show up in an
160 uninitialized state in the tree, and
161 for which a <literal>changed</literal>
162 event is generated the moment they are
163 fully set up. Note that
164 <varname>SYSTEMD_WANTS=</varname> (see
165 above) is not acted on as long as
166 <varname>SYSTEMD_READY=0</varname> is
167 set for a device.</para></listitem>
171 <term><varname>ID_MODEL_FROM_DATABASE=</varname></term>
172 <term><varname>ID_MODEL=</varname></term>
174 <listitem><para>If set, this property is
175 used as description string for the
176 device unit.</para></listitem>
185 <title>See Also</title>
187 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
188 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
189 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
190 <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
191 <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>