On Thu, Mar 06, 2025 at 12:46:23AM +0100, Kjetil Torgrim Homme wrote: > hey people, thank you for XFS! > > tl;dr: consider changing the kernel message "Filesystem has duplicate > UUID - can't mount" to include a hint about the existence of the nouuid > mount option. perhaps append " (use -o nouuid?)" to message? This looks good at first, but adding a message like this has a big down side IMHO. This leads users to simply attempt to do that even in cases when they shouldn't. As an example, in a common multipath environment with dm-multipath, an user might accidentally attempt to mount both individual paths to the same device, and this uuid duplicate check protects against such cases, which might end in disaster. On a mid term here, I think we could improve xfs(5) to include a bit more information about duplicated uuids. Carlos > > sad backstory: > > today I tried to use LVM snapshots to make consistent backups of XFS, > but I was stumped by: > > mount: /mnt/snap: wrong fs type, bad option, bad superblock on /dev/mapper/vg0-test--snap, missing codepage or helper program, or other error. > dmesg(1) may have more information after failed mount system call. > > and dmesg said: > > XFS (dm-7): Filesystem has duplicate UUID d806fb70-8d81-4e57-a7e3-c2ed0a14af59 - can't mount > > so - I thought the solution was to change the UUID of my snapshot using > `xfs_admin -U generate`. this is the response (when the snapshot is of > an active filesystem): > > ERROR: The filesystem has valuable metadata changes in a log which needs to > be replayed. Mount the filesystem to replay the log, and unmount it before > re-running xfs_admin. If you are unable to mount the filesystem, then use > the xfs_repair -L option to destroy the log and attempt a repair. > Note that destroying the log may cause corruption -- please attempt a mount > of the filesystem before doing this. > > so since I was unable to mount the filesystem, I tried xfs_repair -L -- > which took a very long time and in the end gave me a corrupt filesystem. > > ... and then I found out about -o nouuid, so there was a happy ending :) > but I think it's a reasonably simple fix to give a hint to the user in > the kernel error message. > > thank you! > -- > venleg helsing, > Kjetil T. >
