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NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | THE UDEV DATABASE | SEE ALSO | COLOPHON |
SYSTEMD.DEVICE(5) systemd.device SYSTEMD.DEVICE(5)
systemd.device - Device unit configuration
device.device
A unit configuration file whose name ends in ".device" encodes
information about a device unit as exposed in the sysfs/udev(7)
device tree.
This unit type has no specific options. See systemd.unit(5) 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.
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 "TAG+="systemd"" in the udev rules file, see udev(7) for details.
Device units are named after the /sys and /dev paths they control.
Example: the device /dev/sda5 is exposed in systemd as
dev-sda5.device. For details about the escaping logic used to convert
a file system path to a unit name see systemd.unit(5).
Device units will be reloaded by systemd whenever the corresponding
device generates a "changed" event. Other units can use
ReloadPropagatedFrom= to react to that event.
Implicit Dependencies
Many unit types automatically acquire dependencies on device units of
devices they require. For example, .socket unit acquire dependencies
on the device units of the network interface specified in
BindToDevice=. Similar, swap and mount units acquire dependencies on
the units encapsulating their backing block devices.
Default Dependencies
There are no default dependencies for device units.
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:
SYSTEMD_WANTS=, SYSTEMD_USER_WANTS=
Adds dependencies of type Wants= from the device unit to the
specified units. SYSTEMD_WANTS= is read by the system service
manager, SYSTEMD_USER_WANTS= by user service manager instances.
These properties may be used to activate arbitrary units when a
specific device becomes available.
Note that this and the other udev device properties are not taken
into account unless the device is tagged with the "systemd" tag
in the udev database, because otherwise the device is not exposed
as a systemd unit (see above).
Note that systemd will only act on Wants= dependencies when a
device first becomes active. It will not act on them if they are
added to devices that are already active. Use SYSTEMD_READY= (see
below) to configure when a udev device shall be considered
active, and thus when to trigger the dependencies.
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 "@" character indicating a unit name to
use for multiple instantiation, but with an empty instance name
following the "@"), it will be automatically instantiated by the
device's "sysfs" 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.
SYSTEMD_ALIAS=
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.)
SYSTEMD_READY=
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 option is useful for devices that initially show up in an
uninitialized state in the tree, and for which a "changed" event
is generated the moment they are fully set up. Note that
SYSTEMD_WANTS= (see above) is not acted on as long as
SYSTEMD_READY=0 is set for a device.
ID_MODEL_FROM_DATABASE=, ID_MODEL=
If set, this property is used as description string for the
device unit.
systemd(1), systemctl(1), systemd.unit(5), udev(7),
systemd.directives(7)
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 246 SYSTEMD.DEVICE(5)
Pages that refer to this page: init(1) , systemd(1) , systemd.mount(5) , systemd.socket(5) , systemd.swap(5) , systemd.unit(5) , 30-systemd-environment-d-generator(7) , daemon(7) , systemd.directives(7) , systemd.index(7) , systemd.syntax(7) , udev(7) , udevadm(8)