systemd.device

SYSTEMD.DEVICE(5)                systemd.device                SYSTEMD.DEVICE(5)



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 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).

       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.

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



systemd 246                                                    SYSTEMD.DEVICE(5)