udevsystemds

udevsystemds is a term used to describe the integrated device-management stack that combines the Linux udev device manager with the systemd init and service manager. In this model, udev handles runtime device discovery, event generation, and device node management, while systemd coordinates service activation and related workloads based on those events.

Operation proceeds as follows: when the kernel generates a hardware event, the udev daemon receives it, applies configured rules, creates or renames device nodes under /dev, and may invoke external programs. systemd uses these events to manage device units (.device) and to trigger services through udev rules. This integration enables automatic actions such as starting a daemon when a USB device is connected or mounting a filesystem when a block device becomes available.

Rules and naming are central to udevsystemds. Udev rules define how to match devices and what actions to take, including creating symlinks and setting permissions. Systemd provides a tight integration through systemd-udev, with the udev daemon exposed as systemd-udevd and the udevadm tool available for inspection and control. Device units in systemd model hardware devices in the dependency graph, permitting unit activation based on device availability and facilitating dynamic service orchestration.

History and usage notes: the integration evolved as udev became part of the broader systemd ecosystem in many Linux distributions, yielding a unified approach to hardware initialization and hotplug management. Some distributions still maintain alternative device-management stacks, but the prevailing model emphasizes the udev-systemd integration for dynamic device handling and service activation.

See also: udev, systemd, systemd-udev, libudev.