[dm-crypt] LUKS GPT GUID

Pali Rohár pali.rohar at gmail.com
Sun Jan 26 11:17:11 CET 2014

2014-01-26 Milan Broz <gmazyland at gmail.com>:
> On 01/26/2014 02:40 AM, Pali Rohár wrote:
>> Hello,
>> according to wikipedia [1] and other sites (e.g. [2]) MBR partition ID
>> for LUKS is E8. I tried to find GPT partition GUID for LUKS, but there
>> is nothing on wikipedia [3] nor google... So has LUKS already
>> preferred/assigned GUID for GPT partition table? There is already GPT
>> GUID for linux data, raid, swap, lvm and home partitions (see [3]), so
>> I think that LUKS should have GUID too.
> Hi,
> this is wonderful... who assigned E8 type? I thought LUKS has no assigned
> partition type and also I doubt LVM2 type is properly assigned too
> (it is probably form the LVM1 age when it was implemented in-kernel directly
> and partition type was important to detect it.) But not sure about this.
> Anyway, today partition type is ignored (both in LVM and LUKS), so it is really
> just for convenience for other applications.
> (Anyway, code should always use (lib)blkid to detect what's really on the device,
> not trust partition id.)
> For GPT GUID, I would like to know how these GUID codes appeared in libfdisk
> and how this was standardized for LVM. LUKS should have GUID too then...
> (cc to Karel as util-linux/libfdisk maintainer ;-)
> If this is really used, both should be documented in LUKS specification.
> Thanks,
> Milan
>> [1] - http://en.wikipedia.org/wiki/Partition_type
>> [2] - http://www.win.tue.nl/~aeb/partitions/partition_types-1.html
>> [3] - http://en.wikipedia.org/wiki/GUID_Partition_Table

I know that linux ignoring MBR partition ID and also GPT GUID.
Filesystems are detected by magic headers... But other systems (like
windows) are still using MBR partition ID and also GPT partition GUID.
So it is still good to store these information. Also if you want, you
can create udev rule to map some MBR ID/GPT GUID partition to some
name (maybe together with other information).

And who assigned E8 for LUKS? I really do not know. I thought that if
wikipedia and also other sources on internet specifing it is standard
and it is using by some applications...

Also I do not know who assigning GPT GUID for partitions. For me it
looks like application developer is choosing one GUID randomly...

CCing Roderick W. Smith, who maintaing gdisk utility. Roderick, who
and how assinged GPT GUIDs which you added to gdisk program? What do
you know about GPT GUID for LUKS?

Pali Rohár
pali.rohar at gmail.com

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