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.