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<?xml version='1.0'?> <!--*-nxml-*-->
<?xml-stylesheet type="text/xsl" href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="systemd.device">
<refentryinfo>
<title>systemd.device</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</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.</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 <literal>[Unit]</literal> and
<literal>[Install]</literal> sections. A separate
<literal>[Device]</literal> 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 "systemd"
udev tag (by default all block and network devices,
and a few others). This may be used to define
dependencies between devices and other units. 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 are named after the
<filename>/sys</filename> and
<filename>/dev</filename> paths they control. Example:
the device <filename noindex='true'>/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>
</refsect1>
<refsect1>
<title>The udev Database</title>
<para>The settings of device units may either be
configured via unit files, or directly from the udev
database (which is recommended). The following udev device
properties are understood by systemd:</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 all listed units. The
first form is used by the system
systemd instance, the second by user
systemd instances. Those settings may
be used to activate arbitrary units
when a specific device becomes
available.</para>
<para>Note that this and the
other tags are not taken into account
unless the device is tagged with the
<literal>systemd</literal> string 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 influence on which udev
event to trigger the dependencies.
</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 visible in the
udev tree. This property has no
influence on the behavior when a
device disappears from the udev
tree.</para>
<para>This option is useful to support
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>8</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>
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