How does the grub efi know where to look for the grub.cfg?

[Arjun Krishnan]

I installed grub-efi using

    grub-install --efi-directory=/mnt/efi --boot-directory=/boot
--target=x86_64-efi

I did not specify a root partition anywhere (like you used to have to,
when installing it to the mbr), so how does grub set its $root and
$prefix?

So I looked at a dual booting system that has two efi grub
installations, ubuntu and arch. It has a /efi/ubuntu directory that
has a grubx64.efi file and a grub.cfg. This grub.cfg simply sets the
correct prefix and root. I suppose the --efi-directory is used as a
system root partition. However, inside /efi/arch I simply have a
grubx64.efi. The root and prefix are nowhere to be found. I even when
I tried to read the efi file in hex.

How does the grubx64.efi on the arch side figure out the correct
system root partition?


Arjun