[CentOS] Two partitions with samd UUID??

jd1008
Mon, 15 Jun 2015 03:08:36 -0000

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.
I thought it had to do with information when the device
is queried (manufacturer's name (id), device model, date
of manufacturer, serial number ....etc).
But ....
https://liquidat.wordpress.com/2013/03/13/uuids-and-linux-everything-you-ever-need-to-know/
says:
After generating 1 billion UUIDs every second for the next
100 years, the probability of creating just one duplicate
would be about 50%. The probability of one duplicate would
be about 50% if every person on earth owns 600 million UUIDs.
Linux generates uuids   in the file listed at
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?id=refs/tags/v3.8

and you can generate new ones via proc:


$ cat /proc/sys/kernel/random/uuid eaf3a162-d770-4ec9-a819-ec96d429ea9f

There is also the library libuuid
<http://linux.die.net/man/3/libuuid>which is used by |uuidgen|and
especially
by the ext2/3/4 tools E2fsprogs to generate UUIDs:

$ uuidgen f81cc383-aa75-4714-aa8a-3ce39e8ad33c