[dm-crypt] UUID question

Arno Wagner arno at wagner.name
Tue Dec 18 09:57:44 CET 2012

On Tue, Dec 18, 2012 at 09:12:01AM +0100, Marc Ballarin wrote:
> Am 18.12.2012 01:36, schrieb Arno Wagner:
> >On Mon, Dec 17, 2012 at 04:10:50PM -0800, David Li wrote:
> >>Hi, I wonder if the dm-crypt partition UUID (shown in blkid -p <dev>) can
> >>be used to uniquely associate it with the set of keys the partition will
> >>need. Are there any cases that the UUID would change during the partition's
> >>lifetime?
> >
> >The UUID is actually a filesystem attribute, not a partition
> >attribute...
> This depends on the partition format in use. For example GPT, and
> maybe others, provide an additional UUID for partititons (actually
> GPT even supports Labels):
> $ sudo blkid -p /dev/sda1
> /dev/sda1: LABEL="data_usb"
> UUID="9b70c4bf-6b40-4be3-9cb7-030db682ad35" VERSION="1.0"
> TYPE="ext4" USAGE="filesystem" PART_ENTRY_SCHEME="gpt"
> PART_ENTRY_UUID="3d18a590-d329-4a82-be02-c3588098d625"
> PART_ENTRY_TYPE="0fc63daf-8483-4772-8e79-3d69d8477de4"
> PART_ENTRY_SIZE="3907027087" PART_ENTRY_DISK="8:0"
> Whereas dos/mbr does not:
> $sudo blkid -p /dev/sda1
> /dev/sda1: UUID="b786a3a4-26e7-4765-aed1-9bc472522c06" VERSION="1.0"
> TYPE="ext4" USAGE="filesystem" PART_ENTRY_SCHEME="dos"
> While the GPT UUID should never change, it might happen if some
> bogus resizing tool is used.
> So, if a LUKS-UUID is available I would always prefer it and only
> fall back to partition UUIDs when not using LUKS.
> Regards,
> Marc

Interesting. Seems (again), my view of things is too simplistic ;-)

Anyways, the gist is that change of UUIDs is not something that 
should ordionarily happen during the lifetime of whatever
carries it.

Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
GnuPG: ID: CB5D9718  FP: 12D6 C03B 1B30 33BB 13CF  B774 E35C 5FA1 CB5D 9718
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision. -- Bertrand Russell

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