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<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 is 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>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>