The udev device manager runs as a systemd service to help provide software with predictable and managed access to system devices exposed by the kernel. Typically. udev manages the permissions of device nodes, creates symbolic links in the /dev/ directory to make device names more predictable and easier to identify, or renames network interfaces.

The udev device manager dynamically creates or removes device node files at boot time. When creating a device node, udev reads the device's /sys directory for attributes such as the label, serial number, and bus device number.

udev can use persistent device names to guarantee consistent naming of devices across reboots, regardless of their order of discovery. Persistent device names are especially important when using external storage devices.

udev also handles device driver events that are triggered by the kernel and uses the rules defined in its configuration to trigger particular actions. For example, if a USB storage device is connected to the system, the kernel notifies udev and udev notifies the appropriate handler so that the device can be mounted. Also, if a network cable is connected to a network interface card, the kernel notifies udev of the state change and udev notifies NetworkManager so that the appropriate action can take place to connect to the network.

The configuration file for udev is /etc/udev/udev.conf, in which you can define the udev_log logging priority, which can be set to err, info and debug. Note that the default value is err. Further configuration of rules used by udev are handled in individual rules files in /etc/udev/rules.d/.

For more information, see the udev(7) manual page.

udev is a component of systemd, also see Oracle Linux 8: Managing the System With systemd.

For more information about the kernel virtual file systems and device driver modules, see Oracle Linux 8: Managing Kernels and System Boot,