# systemd.device

## 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.
    


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