USB disk's UUID changing?!

I'm trying to add an entry to /etc/fstab so that a USB hard disk is mounted each boot.

The problem is that when I use

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sudo blkid

to get the UUID, and add it to

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fstab

in the standard way (i.e.

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UUID=xx

), the next time I boot I get a message saying the UUID wasn't recognised and the disk can't be mounted.

When I use blkid to check, I find the UUID of the disk is completely different. I haven't done anything to the disk in-between times — not even unplugged it!

Am I missing something important? I thought UUIDs were supposed to be, well, unique identifiers.

Hi rspi, I've never used the "blkid" command to get a disk's UUID - my approach is outlined within my webpages at http://www.cpmspectrepi.webspace.virgin ... ticks.html . The only times I've known a UUID to change is when a (flash)disk is re-formatted and/or partioned (sometimes the UUID is that of the partition) or (under Windows XP) when the partition has been "repaired" by checkdisk (this "screwed-up" dual-booting of my netbook when I'd resized some partitions to make more room for, what was then, Ubuntu Netbook edition.
Hope that's of some help).
Trev.

Hi Trevor, thanks for the link!

I just tried it again with a fresh install and both blkid and your method of viewing /dev/disk/by-uuid reported the same values.

When I edited fstab and rebooted, everything worked fine.

This time around, however, I rebooted after formatting the new USB disk. I think this helped because I suspect I was seeing an older cached value for the disk that related to the old partition on the disk.

The moral of the story: If adding a new disk to the system and reformatting it, reboot before attempting to find out the UUID to add to /etc/fstab.