From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <ballarin.marc@gmx.de>
Received: from mail.saout.de ([127.0.0.1])
 by localhost (mail.saout.de [127.0.0.1]) (amavisd-new, port 10024)
 with ESMTP id zW1KZqCfjylI for <dm-crypt@saout.de>;
 Tue, 18 Dec 2012 09:24:30 +0100 (CET)
Received: from mout.gmx.net (mout.gmx.net [212.227.15.19])
 by mail.saout.de (Postfix) with ESMTP
 for <dm-crypt@saout.de>; Tue, 18 Dec 2012 09:24:29 +0100 (CET)
Received: from mailout-de.gmx.net ([10.1.76.16]) by mrigmx.server.lan
 (mrigmx001) with ESMTP (Nemesis) id 0MKffd-1TmnQ90TEl-0022T0 for
 <dm-crypt@saout.de>; Tue, 18 Dec 2012 09:11:58 +0100
Message-ID: <50D02551.9050009@gmx.de>
Date: Tue, 18 Dec 2012 09:12:01 +0100
From: Marc Ballarin <Ballarin.Marc@gmx.de>
MIME-Version: 1.0
References: <CAADET=cgxphPsmRCR3SQTU_cXefhW1Zk86ut_vUpVoKW_3d-bw@mail.gmail.com>
 <20121218003612.GA14871@tansi.org>
In-Reply-To: <20121218003612.GA14871@tansi.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [dm-crypt] UUID question
List-Id: <dm-crypt.saout.de>
List-Unsubscribe: <http://www.saout.de/mailman/options/dm-crypt>,
 <mailto:dm-crypt-request@saout.de?subject=unsubscribe>
List-Archive: <http://www.saout.de/pipermail/dm-crypt/>
List-Post: <mailto:dm-crypt@saout.de>
List-Help: <mailto:dm-crypt-request@saout.de?subject=help>
List-Subscribe: <http://www.saout.de/mailman/listinfo/dm-crypt>,
 <mailto:dm-crypt-request@saout.de?subject=subscribe>
To: dm-crypt@saout.de

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