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_NUMBER="1" PART_ENTRY_OFFSET="2048"
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"
PART_ENTRY_TYPE="0x83" PART_ENTRY_FLAGS="0x80" PART_ENTRY_NUMBER="1"
PART_ENTRY_OFFSET="2048" PART_ENTRY_SIZE="63997952" PART_ENTRY_DISK="8:0"
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
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