In the Linux 2.6 and later kernel, udev provides a userspace solution for the dynamic /dev directory, with persistent device naming. As part of the hotplug system, udev is executed if a device is added or removed from the system.

A list of rules is used to match against specific device attributes. The udev rules infrastructure (defined in the /etc/udev/rules.d directory) provides stable names for all disk devices, regardless of their order of recognition or the connection used for the device. The udev tools examine every appropriate block device that the kernel creates to apply naming rules based on certain buses, drive types, or file systems. For information about how to define your own rules for udev, see Writing udev Rules.

Along with the dynamic kernel-provided device node name, udev maintains classes of persistent symbolic links pointing to the device in the /dev/disk directory, which is further categorized by the by-id, by-label, by-path, and by-uuid subdirectories.

	Note
Other programs besides udev, such as LVM or md, might also generate UUIDs, but they are not listed in /dev/disk.