USB disk's UUID changing?!

3 posts
by rspi » Thu Mar 14, 2013 3:15 pm
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
Code: Select all
sudo blkid
to get the UUID, and add it to
Code: Select all
in the standard way (i.e.
Code: Select all
), 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.
Posts: 8
Joined: Thu Mar 14, 2013 3:08 pm
by FTrevorGowen » Thu Mar 14, 2013 5:46 pm
Hi rspi, I've never used the "blkid" command to get a disk's UUID - my approach is outlined within my webpages at ... 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).
Usually running Raspbian* on 11 Pi's (an A, B1, 2xB2, 2xB+, A+, P2B, 3xP0, P3B). See:
* Still "Wheezy" on some, but "Jessie" now on the newer Pi's.
User avatar
Forum Moderator
Forum Moderator
Posts: 3639
Joined: Mon Mar 04, 2013 6:12 pm
Location: Bristol, U.K.
by rspi » Fri Mar 15, 2013 2:06 pm
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.
Posts: 8
Joined: Thu Mar 14, 2013 3:08 pm