set root= set root device for grub (and uses grub’s device designation). As far as I can understand it can be used multiple times throughout grub.cfg
Simplest way to test it or feel it, so to say, is to drop into grub interactive mode, set root and then try
cat some file or open another grub config with
is equivalent to
– i.e. you can set root once so that you don’t have to enter in on every other line.
Also note that tab completion works in grub’s cli interface, it helps greatly with finding files you need.
Here’s it explained a bit in grub’s manual:
Root in the line
linux... is setting root partition (not grub’s root device!) for linux kernel. grub itself doesn’t need it or use it – it’s just passes it as is to Linux kernel. If you don’t set root here or set it incorrectly – Linux won’t be able to boot.
From grub’s manual:
Command: linux file …
Load a Linux kernel image from file. The rest of the line is passed verbatim as the kernel command-line .
You’re right, as far as I know, here you can use the same notations an in /etc/fstab.
Does this answer you question?