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).
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:
SYSTEMD_WANTS=, SYSTEMD_USER_WANTS=¶Adds dependencies of type
Wants 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.
Note that this and the other tags are not taken into
account unless the device is tagged with the
"systemd" string 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 influence on
which udev event to trigger the dependencies.
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 property has no influence on the behavior when a device disappears from the udev tree.
This option is useful to support 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.