mirror of
https://github.com/systemd/systemd-stable.git
synced 2024-12-23 17:34:00 +03:00
ccd593a61c
This was implied by the need to tag them with "systemd", but let's make this obvious, since it's rather easy to trip over this as a user. Inspired by https://bugzilla.redhat.com/show_bug.cgi?id=1941458.
165 lines
7.8 KiB
XML
165 lines
7.8 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
|
|
<refentry id="systemd.device">
|
|
<refentryinfo>
|
|
<title>systemd.device</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>systemd.device</refentrytitle>
|
|
<manvolnum>5</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>systemd.device</refname>
|
|
<refpurpose>Device unit configuration</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<para><filename><replaceable>device</replaceable>.device</filename></para>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para>A unit configuration file whose name ends in <literal>.device</literal> encodes information about a
|
|
device unit as exposed in the
|
|
sysfs/<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> device
|
|
tree. This may be used to define dependencies between devices and other units.</para>
|
|
|
|
<para>This unit type has no specific options. See
|
|
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
|
|
for the common options of all unit configuration files. The common
|
|
configuration items are configured in the generic
|
|
[Unit] and [Install]
|
|
sections. A separate [Device] section does not
|
|
exist, since no device-specific options may be configured.</para>
|
|
|
|
<para>systemd will dynamically create device units for all kernel devices that are marked with the
|
|
<literal>systemd</literal> udev tag (by default all block and network devices, and a few others). Note
|
|
that <emphasis>if <filename>systemd-udev.service</filename> is not running, no device units will be
|
|
available (for example in a typical container)</emphasis>.</para>
|
|
|
|
<para>Device units are named after the <filename>/sys/</filename>
|
|
and <filename>/dev/</filename> paths they control. Example: the
|
|
device <filename index="false">/dev/sda5</filename> is exposed in
|
|
systemd as <filename>dev-sda5.device</filename>. For details about
|
|
the escaping logic used to convert a file system path to a unit
|
|
name see
|
|
<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
|
|
|
|
<para>To tag a udev device, use <literal>TAG+="systemd"</literal> in the udev rules file, see
|
|
<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry> for details.
|
|
</para>
|
|
|
|
<para>Device units will be reloaded by systemd whenever the
|
|
corresponding device generates a <literal>changed</literal> event.
|
|
Other units can use <varname>ReloadPropagatedFrom=</varname> to react
|
|
to that event.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Automatic Dependencies</title>
|
|
|
|
<refsect2>
|
|
<title>Implicit Dependencies</title>
|
|
|
|
<para>Many unit types automatically acquire dependencies on device
|
|
units of devices they require. For example,
|
|
<filename>.socket</filename> unit acquire dependencies on the
|
|
device units of the network interface specified in
|
|
<varname>BindToDevice=</varname>. Similar, swap and mount units
|
|
acquire dependencies on the units encapsulating their backing
|
|
block devices.</para>
|
|
</refsect2>
|
|
|
|
<refsect2>
|
|
<title>Default Dependencies</title>
|
|
|
|
<para>There are no default dependencies for device units.</para>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>The udev Database</title>
|
|
|
|
<para>Unit settings of device units may either be configured via unit files, or directly from the udev
|
|
database. The following udev device properties are understood by the service manager:</para>
|
|
|
|
<variablelist class='udev-directives'>
|
|
<varlistentry>
|
|
<term><varname>SYSTEMD_WANTS=</varname></term>
|
|
<term><varname>SYSTEMD_USER_WANTS=</varname></term>
|
|
<listitem><para>Adds dependencies of type <varname>Wants=</varname> from the device unit to the specified
|
|
units. <varname>SYSTEMD_WANTS=</varname> is read by the system service manager,
|
|
<varname>SYSTEMD_USER_WANTS=</varname> by user service manager instances. These properties may be used to
|
|
activate arbitrary units when a specific device becomes available.</para>
|
|
|
|
<para>Note that this and the other udev device properties are not taken into account unless the device is
|
|
tagged with the <literal>systemd</literal> tag in the udev database, because otherwise the device is not
|
|
exposed as a systemd unit (see above).</para>
|
|
|
|
<para>Note that systemd will only act on <varname>Wants=</varname> dependencies when a device first becomes
|
|
active. It will not act on them if they are added to devices that are already active. Use
|
|
<varname>SYSTEMD_READY=</varname> (see below) to configure when a udev device shall be considered active, and
|
|
thus when to trigger the dependencies.</para>
|
|
|
|
<!-- Note that we don't document here that we actually apply unit_name_mangle() to all specified names, since
|
|
that's kinda ugly, and people should instead specify correctly escaped names -->
|
|
|
|
<para>The specified property value should be a space-separated list of valid unit names. If a unit template
|
|
name is specified (that is, a unit name containing an <literal>@</literal> character indicating a unit name to
|
|
use for multiple instantiation, but with an empty instance name following the <literal>@</literal>), it will be
|
|
automatically instantiated by the device's <literal>sysfs</literal> path (that is: the path is escaped and
|
|
inserted as instance name into the template unit name). This is useful in order to instantiate a specific
|
|
template unit once for each device that appears and matches specific properties.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SYSTEMD_ALIAS=</varname></term>
|
|
<listitem><para>Adds an additional alias name to the device
|
|
unit. This must be an absolute path that is automatically
|
|
transformed into a unit name. (See above.)</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>SYSTEMD_READY=</varname></term>
|
|
<listitem><para>If set to 0, systemd will consider this device unplugged even if it shows up in the udev
|
|
tree. If this property is unset or set to 1, the device will be considered plugged if it is visible in the udev
|
|
tree.</para>
|
|
|
|
<para>This option is useful for devices that initially show up in an uninitialized state in the tree, and for
|
|
which a <literal>changed</literal> event is generated the moment they are fully set up. Note that
|
|
<varname>SYSTEMD_WANTS=</varname> (see above) is not acted on as long as <varname>SYSTEMD_READY=0</varname> is
|
|
set for a device.</para></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term><varname>ID_MODEL_FROM_DATABASE=</varname></term>
|
|
<term><varname>ID_MODEL=</varname></term>
|
|
|
|
<listitem><para>If set, this property is used as description
|
|
string for the device unit.</para></listitem>
|
|
</varlistentry>
|
|
|
|
</variablelist>
|
|
|
|
</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.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
|
|
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
</para>
|
|
</refsect1>
|
|
|
|
</refentry>
|