PARTUUID and UUID

PARTUUID is a UUID identifier of partition stored within GPT partition table. This UUID is available to Linux kernel during boot and so it can be specified as rootfs=PARTUUID=<UUID>.

On the other hand, UUID is identifier stored within file system itself, and it’s not available during boot.
But it is available after the initramfs is booted (from within fstab file).

To list all UUID’s and PARTUUIDs, do this:

lsblk -o NAME,UUID,PARTUUID

Other available disk identifiers

root@device:~# tree -L 1 /dev/disk/                                                                                                                                                                                                   
/dev/disk/
|-- by-diskseq
|-- by-id
|-- by-label
|-- by-partuuid
|-- by-path
`-- by-uuid

Short UUIDS ???

Short UUID such as 076c4a2a-03 are caused by partition table being DOS partition table, not GPT.
In such case, the UUID is taken from the MBR ID value, with appended partition index.
So if MBR ID is 076c4a2a, and partition number is 3, PARTUUID would be 076c4a2a-03.