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b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik<refentry id="systemd.device">

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refentryinfo>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <title>systemd.device</title>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <productname>systemd</productname>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <authorgroup>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <author>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <contrib>Developer</contrib>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <firstname>Lennart</firstname>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <surname>Poettering</surname>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <email>lennart@poettering.net</email>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik </author>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik </authorgroup>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik </refentryinfo>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refmeta>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refentrytitle>systemd.device</refentrytitle>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <manvolnum>5</manvolnum>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik </refmeta>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refnamediv>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refname>systemd.device</refname>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refpurpose>Device unit configuration</refpurpose>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik </refnamediv>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refsynopsisdiv>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <para><filename><replaceable>device</replaceable>.device</filename></para>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik </refsynopsisdiv>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <refsect1>

b24e4bec819b29f1ec8e77083d4e7610c5dd9c77Lukas Slebodnik <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>