to. den 06. 03. 2025 klokka 11.00 (+0100) skreiv Carlos Maiolino:
> 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.
makes sense.
> On a mid term here, I think we could improve xfs(5) to include a bit more
> information about duplicated uuids.
>
current text:
Each XFS filesystem is labeled with a Universal Unique Identifier
(UUID). The UUID is stored in every allocation group header and is used
to help distinguish one XFS filesystem from another, therefore you
should avoid using dd(1) or other block-by-block copying programs to
copy XFS filesystems. If two XFS filesystems on the same machine
have the same UUID, xfsdump(8) may become confused when doing
incremental and resumed dumps. xfsdump(8) and xfsrestore(8) are
recommended for making copies of XFS filesystems.
perhaps add a sentence at the end of that, "To mount a snapshot of an
already mounted filesystem, use mount option \fBnouuid\fR."
possibly also something about this in xfs_admin(8)?
current text:
-U uuid
Set the UUID of the filesystem to uuid. A sample UUID
looks like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16".
The uuid may also be nil, which will set the filesystem
UUID to the null UUID. The uuid may also be generate,
which will generate a new UUID for the filesystem. Note
that on CRC-enabled filesystems, this will set an
incompatible flag such that older kernels will not be
able to mount the filesystem. To remove this
incompatible flag, use restore, which will restore the
original UUID and remove the incompatible feature flag
as needed.
suggested addition: "A transient snapshot which conflicts with a mounted
filesystem can alternatively be mounted with the option \bBnouuid\fR."
what do you think?
--
venleg helsing,
Kjetil T.
