The UUID of a Linux partition is the Universally Unique IDentifier of that partition. I would say with a fair bit of confidence that in this and most scenarios, the Linux partition UUID has more of a local machine scope.
This ID is used in a few places to identify the partition. The most notable being your /etc/fstab file, which manages the mounting of partitions at boot time. Here is a little snippet from mine…
# <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc nodev,noexec,nosuid 0 0 # / was on /dev/sdc3 during installation UUID=9467f4de-4231-401f-bcaa-fee718d49e85 / ext4 errors=remount-ro 0 1 # swap was on /dev/sdb1 during installation UUID=aabe7e48-2d11-421f-8609-7ea9d75e7f9b none swap sw 0 0
Why would you need to change a partition UUID?
The main reason being a clash of ID’s. Technically the likelihood of creating 2 identical UUID’s is very rare (read more on the Random UUID probability of duplicates). But there may be cases where you clone a partition using DD or Clonezilla and the clone resides on the same machine – different physical hard drive or partition.
Cloning using both the tools mentioned above will create an exact copy of the partition all the way down to the UUID – and now you have 2 partitions with the same UUID. From the example of my /etc/fstab above, the UUID is no longer unique and it will mount the first partition it finds with that UUID.
How do I change the UUID?
This isn’t hard at all.
First find the device path
You can find the device path using the following command:
Your output will look something like this:
sudo blkid /dev/sdb1: UUID="aabe7e48-2d11-421f-8609-7ea9d75e7f9b" TYPE="swap" /dev/sdc1: UUID="9467f4de-4231-401f-bcaa-fee718d49e85" TYPE="ext4" /dev/sdc3: UUID="93a54a4a-e0f5-4152-ae59-2245e8d16ee4" TYPE="ext4" /dev/sde5: UUID="9467f4de-4231-401f-bcaa-fee718d49e85" TYPE="ext4" /dev/sde6: LABEL="var" UUID="30433f28-1b79-4b4d-9985-fef5b1c886b5" TYPE="ext4"
Here you can see that /dev/sdc1 and /dev/sde5 have the same UUID. The path of the partition I want to change is /dev/sde5
Secondly, generate a UUID
This is simple, the following command will output a UUID like below:
Finally apply the new UUID to the partition
This is also another command, tune2fs, which will apply our new UUID to our device path:
sudo tune2fs /dev/sde5 -U f0acce91-a416-474c-8a8c-43f3ed3768f9
Done, now you can update your grub to include the correct UUID’s to reduce any risk of your system confusing the partitions.