Permanently fix absolute location of the GRUB folder

[Luí­s Moreira de Sousa]

Dear all,

I recently hit a relatively common problem whit the Ubuntu 16.04 installer, 
that misconfigures the location of the GRUB folder [0]. In such cases the 
system boots into a rescue shell with the following messages:

error: file '/grub/i386-pc/normal.mod' not found.

Entering rescue mode...

grub rescue>

This means GRUB was able to boot, but it is looking for its modules in the 
wrong place. The well known solution is to instruct GRUB on the fly on the 
location of its modules [1]. In my case this is:

grub rescue> set prefix=(hd1,msdos2)/boot/grub

grub rescue> insmod normal

grub rescue> normal

This resumes the boot process successfully. However, the next time the system 
is booted GRUB falls back again to the rescue console, and it must be 
instructed again on the location of its modules. I have reinstalled GRUB but it 
did not fix the issue.

I then tried the Boot-Repair tool, starting by confirming the GRUB location, it 
is apparently correct: /boot/grub on sdg2. I then ran the Recommended Repair 
diagnosis, the full output is on Pastebin [2]. The diagnosis output also 
reported the correct location for GRUB:

sdg2: __________________________________________________________________________

    File system:       ext4

    Boot sector type:  -

    Boot sector info:

    Operating System:  Ubuntu 16.04.3 LTS

    Boot files:        /boot/grub/grub.cfg /etc/fstab

                       /boot/grub/i386-pc/core.img

However, there is an error at the very end of the report, that points to an 
issue with device.map:

grub-probe: error: cannot find a GRUB drive for /dev/sdi1.  Check your 
device.map.

Unhide GRUB boot menu in sdg2/boot/grub/grub.cfg

An error occurred during the repair.

Any suggestion on what can be made about this?

Thank you.

[0] https://askubuntu.com/q/266429/177437
[1] https://askubuntu.com/a/462995/177437
[2] http://paste.ubuntu.com/25915919/

--
Luís de Sousa