[CentOS] Two partitions with samd UUID??

[Robert Nichols]

On 06/16/2015 06:43 AM, James Hogarth wrote:
> On 16 Jun 2015 12:12, "Always Learning" <centos at u64.u22.net> wrote:
>>
>>
>> On Tue, 2015-06-16 at 11:30 +0100, John Hodrien wrote:
>>> On Tue, 16 Jun 2015, Always Learning wrote:
>>>
>>>> ON Centos 5, using GPARTED I created partitions for filing systems
> ext3
>>>> and ext4. 4 primary and unlimited (except by space) extended
> partitions.
>>>> That suggests those partitions are not GPT but old fashioned M$DOS
>>>
>>> If it is old fashioned MSDOS, you can have four total primary and
> extended,
>>> not four primary plus extended.  An extended partition then provides a
>>> container for further logical partitions.
>>
>> Yes you are correct. Maximum 4 primary or maximum 3 primary and 1
>> extended which is then sub-divided into more partitions.
>>
>>> LUKS provides a UUID, so being encrypted isn't a barrier to having a
> UUID.
>>
>> But my point was M$ DOS partitions, not being GPT partitions, can have
>> UUIDs. The original poster appeared to suggest that was not possible. He
>> wrote
>>
>
> Those were filesystem UUIDs not partition UUIDs ...

LUKS physical volume UUIDs, actually. When you create a LUKS logical 
volume within that PV, it also has a UUID, and a filesystem within that 
LUKS LV will have its own UUID. These are all part of the partition's 
_content_. A GPT partition has its own UUID, independent of the 
partition's content. An MSDOS partition does not.

> LUKS has its own header similar to ext4, lvm, etc headers which has a UUID
> in it.
>
> This UUID being associated with the LUKS header indicates it is not a
> partition UUID.
>
> A dd of this (or lvm snapshot) to another partition will keep the same UUID.

Indeed. If your version of cryptsetup is new enough (supports the 
"--header" option), try doing the luksFormat operation with a detached 
header. Now you will find that your LUKS partition no longer has a UUID.

> A partition UUID within a GPT table would not be persisted in this manner,
> and msdos labeled disks have no concept of this to begin with.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.