systemd.device(5) — Linux manual page


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

NAME         top

       systemd.device - Device unit configuration

SYNOPSIS         top


DESCRIPTION         top

       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.


   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 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.

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

SEE ALSO         top

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

COLOPHON         top

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       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
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systemd 247                                                SYSTEMD.DEVICE(5)

Pages that refer to this page: init(1)systemd(1)systemd.mount(5)systemd.socket(5)systemd.swap(5)systemd.unit(5)30-systemd-environment-d-generator(7)daemon(7)systemd.directives(7)systemd.index(7)systemd.syntax(7)udev(7)udevadm(8)