Using UUID to Deal With Disks

UUID (Universal Unique Identifier) notation is another way provided by Linux to access your disks. Unlike the standard /dev/hda1, /dev/sda2 notation, it is linked specifically to a particular piece of hardware (whereas /dev/ notation can shift between disks depending on how they're plugged in). This means you don't have the risk of a system reconfiguration causing disks to be renamed, and thus causing knock-on breakage of things that reference that disk.

OK, so, first, how do you find out the UUID of your disk? The command blkid can be used — here's its output for one of my disks:

# blkid /dev/hda1 /dev/hda1: UUID="0ef96300-36c0-4575-8a1d-2d36ff4cd585" SEC_TYPE="ext2" TYPE="ext3"

Alternatively, you can look at the /dev/disk/by_uuid/ directory to see which UUID is associated with which disk. (Use df to find out what device names you currently have mounted.)

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You can also do this the other way around, starting from the UUID: findfs UUID=uuid will tell you which disk is associated with that UUID.

Once you have the UUID of a device, you can use it with mount by using the -U switch:

mount -U 0ef96300-36c0-4575-8a1d-2d36ff4cd585 /mnt/disk1

or, you can use it in your /etc/fstab by putting UUID=uuid at the start of the relevant line, instead of /dev/hdaX.

To assign a UUID to a disk, use tunefs. You can generate your own UUID with the command uuidgen. Then type:

tune2fs -U uuid /dev/sda2

This might come in handy if, say, you've cloned your disk (e.g., by using dd) and must be able to mount both the original and the clone. Assign it a new UUID and you're away!