udev (user space /dev) is a user space system that enables the operating system administrator to register user space handlers for events. The events received by udev's daemon are mainly generated by the Linux kernel in response to physical events relating to peripheral devices. As such, udev's main purpose is to act upon peripheral detection and hot-plugging, including actions that return control to the kernel, e.g. loading kernel modules or device firmware. Another component of this detection is adjusting the permissions of the device to be accessible to non-root users and groups.

As the successor of devfsd and hotplug, udev also manages device nodes in the /dev directory by adding, symlinking and renaming them. udev replaces the functionality of both hotplug and hwdetect.

udev handles separate events concurrently (in parallel), leading to a potential performance improvement over older systems.