Ubuntu - Grub - Grub not using UUID for the root device instead it uses /dev/sda1 or other device name

How does Grub determine the root device name?

By default, grub will WANT or TRY to use the UUID as the root device, UNLESS in /etc/default/grub you enable the feature of GRUB_DISABLE_LINUX_UUID=true.

Usually this is not there at all or it is just commented out.

Grub uses scripts in is /etc/grub.d which are called when you run update grub.

The one we really care about is the 10_linux file.

NOTE: It does not matter if your fstab is updated to use UUID, this script does not care about fstab or the current root filesystem.

What it does is look for entries in /dev/disk/by-uuid and if it finds a UUID for the root device it will assign it like normal.
- Example: root=UUID=theUUIDhere

NOTE: /dev/disk/by-uuid is really just a series of UUIDs in that directory that are symlinked to their actual device name.

This is how the grub 10_linux script associates the UUID to the root device and sets up the root=UUID.

However, if it does not find a UUID entry in /dev/disk/by-uuid then it falls back to using the actual raw device name whether it be /dev/md2 or /dev/sda1 or /dev/vda1 etc…

NOTE: Do not modify grub.cfg manually, as the next kernel update will cause grub to revert back to the device name.