RE: install linux on an external drive

On 2016-10-24 08:58, Carruth, Rusty wrote:
> NOTE! WARNING! BEWARE!!! DD will almost certainly copy the UUID from
> the source partition to the destination partition! I do NOT know what
> havoc will result when linux looks for that UUID and finds 2…. (I’d
> guess it takes the first one it finds

Yes, mount goes through all the block devices probably starting with
the first SCSI disk. If it's looking for a UUID and finds it on
/dev/sda3, that's the one it'll use, even if the same UUID is on
/dev/sdb1 . I think. IIRC, the label detection code in mount did that
the last time I looked at it.

> (I know about the UUID copy because I do that here at work all the
> time. In my case, it’s a feature. In your case, it’s a bug)

If you know you want to have the same UUID on 2 filesystems, you can
use "dumpe2fs -h /dev/sdNN | grep UUID" , then pass the big hex string
to the -U option of mkfs when you're making the new filesystem. Or the
-U option of tune2fs if you've already done mkfs and copied stuff.

IMHO, using filesystem labels is preferable to using UUIDs in
/etc/fstab . Labels can be made short and meaningful to humans, while
UUIDs really can't. (OK, -U feedface-dead-beef-0000-123456789abc works,
but is silly.) Distros probably go the UUID route because it's
generally easy to assume that UUIDs are unique, while filesystem labels
may not be.

--
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