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Old 08-12-2018, 09:27 AM   #1
l0f4r0
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Are GUIDs really unique?


From the internet, it seems that GUIDs are kinds of 16 bytes hashes and so are meant to be pretty unique and are generated when partitions are created.
However, sites like Wikipedia (see https://en.wikipedia.org/wiki/GUID_Partition_Table, chapter "Partition type GUIDs") reference some partition type GUIDs. Indeed, my SWAP partition GUID (which I can obtain via "lsblk -o parttype') is the same than the one on Wikipedia.
So, are GUIDs really unique please?
 
Old 08-12-2018, 10:34 AM   #2
bodqhrohro
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You muddle up GUIDs used for identificating the partition itself and the type of partition. GUIDs of partitions itself, of course, have to be unique. But GUIDs used for types are not generated by partition managing software every time: they were generated once when the standards were developed, and are just shipped with such software.

In MBR era, a list of one-byte numbers was used to represent partition types. But the growing number of different filesystems and their purposes exposed the outrageous non-scalability of such a solution. So GPT developers decided to abandon the problem for near and far future, and replaced them not with two-bytes or even four-bytes codes, but with GUIDs right away. They still are a fixed list, but they are much more sparse and not ordered.
 
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Old 08-12-2018, 04:36 PM   #3
l0f4r0
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So it seems that I mixed up unique partitions GUIDs with partition types GUIDs. Right?
 
Old 08-12-2018, 04:49 PM   #4
JeremyBoden
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Universally Unique identifiers are usually called UUID's.
At least the blkid command lists the UUID's of my disk partitions.

GUID's sounds very similar to GID's.
 
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Old 08-12-2018, 06:23 PM   #5
l0f4r0
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Quote:
Originally Posted by JeremyBoden View Post
At least the blkid command lists the UUID's of my disk partitions.
Thanks for the "blkid" command hint. It looks similar to "lsblk".
However, following bodqhrohro's remark, I don't understand now the difference between "lsblk -o parttype" and the PARTUUID info from "blkid -o full". The sequences are not the same so there must be a difference somewhere...

PS: the difference betwwen GUID and UUID seems very tenuous. Some sources indicate that GUID would be more Windows specific.
 
Old Yesterday, 01:15 PM   #6
jefro
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Not really unique in theory. In practice yes.


https://www.quora.com/What-is-the-di...-UUID-and-GUID seems to be a rather good explanation.


How to use them. https://betterexplained.com/articles...uide-to-guids/

Last edited by jefro; Yesterday at 01:17 PM.
 
Old Yesterday, 01:43 PM   #7
bodqhrohro
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Quote:
Originally Posted by l0f4r0 View Post
So it seems that I mixed up unique partitions GUIDs with partition types GUIDs. Right?
Yes.

Quote:
Originally Posted by l0f4r0 View Post
Some sources indicate that GUID would be more Windows specific.
Technically they are almost the same. You won't see any difference if not checking them with a very strict pattern. And even the name of GPT stands for "GUID Partition Table", so I don't see any reasons for doubt.
 
  


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