[CentOS] Two partitions with samd UUID??

[jd1008]

On 06/15/2015 07:56 AM, Robert Nichols wrote:
> On 06/14/2015 10:08 PM, jd1008 wrote:
>>
>>
>> On 06/14/2015 08:58 PM, John R Pierce wrote:
>>> On 6/14/2015 6:55 PM, Timothy Murphy wrote:
>>>> Maybe I used dd at some point.
>>>> Would this keep the same UUID?
>>>
>>> DD just does a blind block by block copy between two devices or files.
>>>
>>>
>>>
>> I thought that uuid had nothing to do with drive content,
>> so dd would have (should have had) nothing to do with it.
>
> You thought wrong. The UUID for a GPT partition is a number that is
> recorded in the GPT. The UUID for a filesystem is a number that is
> recorded in the filesystem super block. The UUIDs for LVM physical
> or logical volumes are numbers recorded in the LVM header. Etc.,
> etc., etc. When you use dd to copy them, the UUIDs get copied
> too, and significant confusion can result.
>
> Now, the drive itself does have a UUID derived from information
> that includes the serial number. But, unless you are referencing
> the drive by /dev/disk/by-uuid/*, you are not making use of it.
> I've occasionally used /dev/disk/by-id/xxx to select a particular
> drive partition that could not be reliably identified in any other
> way (encrypted swap partition on a non-GPT drive), but I don't
> recall ever using /dev/disk/by-uuid/.
>
Thanx for the update
but what about non-gpt and non lvm partitions?
What is used as inp
nut to create a universally unique id?

(Actually, for an id to be universally unique, one would almost
nee knowledge of all existing id's.
So, I do not have much credence in this universal uniqueness.