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 automatically create dynamic 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.
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 properties are understood by systemd:
SYSTEMD_WANTS=¶Adds dependencies of
                                type Wants from
                                this unit to all listed units. This
                                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 systemd
                                unit.
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 the moment it shows up 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.
ID_MODEL_FROM_DATABASE=, ID_MODEL=¶If set, this property is used as description string for the device unit.