The command devlabel restart is called from the /etc/rc.sysinit script when the system is booted as well as by the appropriate scripts in the /etc/hotplug/ directory.
The restart option to devlabel reads the list of devices in the configuration file (/etc/sysconfig/devlabel) and follows the symbolic links to determine if the device still exists in its former location, such as /dev/hdb1. If the symbolic link is invalid, an attempt is made to find the new location of the disk based on the disk's UUID. If a disk with the same UUID is found, the symbolic link is updated to point to the new location of the drive, the configuration file is updated with the new location, and a message similar to the following is displayed:
Device name incorrectly detected for symlink /dev/work! The device /dev/hdb1 is now /dev/hdd1. The symlink /dev/work will now point to the new device name.
If a disk with the UUID is not found (for example, the disk was removed), the following is displayed:
The device /dev/hdb1 no longer seems to exist. Because of this, the symlink /dev/work -> /dev/hdb1 will not be available. The reference to this symlink in /etc/sysconfig/devlabel will be ignored.
The entry for the device is not removed from the configuration file; it is just ignored for this instance.