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NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | THE UDEV DATABASE | OPTIONS | SEE ALSO | COLOPHON |
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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 may be used to define dependencies between
devices and other units.
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). Note that if
systemd-udevd.service is not running, no device units will be
available (for example in a typical container).
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).
To tag a udev device, use "TAG+="systemd"" in the udev rules
file, see udev(7) for details.
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.
Device unit files may include [Unit] and [Install] sections,
which are described in systemd.unit(5). No options specific to
this file type are supported.
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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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
[email protected]
systemd 257~devel SYSTEMD.DEVICE(5)
Pages that refer to this page: systemd(1), systemd.mount(5), systemd.socket(5), systemd.swap(5), systemd.unit(5), daemon(7), systemd.directives(7), systemd.index(7), systemd.syntax(7), udev(7), udevadm(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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