SYSTEMD.DEVICE(5)                               SYSTEMD.DEVICE(5)

          systemd.device - Device unit configuration


          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

          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

          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

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     SYSTEMD.DEVICE(5)                               SYSTEMD.DEVICE(5)

          following udev device properties are understood by the
          service manager:

              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.

              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.)

              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.

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     SYSTEMD.DEVICE(5)                               SYSTEMD.DEVICE(5)

              If set, this property is used as description string for
              the device unit.

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

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