NAME

       systemd.device - Device unit configuration

SYNOPSIS

       device.device

DESCRIPTION

       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.

AUTOMATIC DEPENDENCIES

   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.

THE UDEV DATABASE

       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.

OPTIONS

       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.

SEE ALSO

       systemd(1), systemctl(1), systemd.unit(5), udev(7), systemd.directives(7)