systemd.device(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | AUTOMATIC DEPENDENCIES | THE UDEV DATABASE | SEE ALSO | COLOPHON

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

NAME         top

       systemd.device - Device unit configuration

SYNOPSIS         top

       device.device

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 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-udev.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         top

   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         top

       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         top

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

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-27.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 249                                            SYSTEMD.DEVICE(5)

Pages that refer to this page: systemd(1)systemd.mount(5)systemd.socket(5)systemd.swap(5)systemd.unit(5)daemon(7)systemd.syntax(7)udev(7)udevadm(8)