Recently when trying Kubuntu 19.04 as dual boot with Ubuntu I got a error “Error: unknown filesystem. grub rescue>”, I can’t boot my system and also not able to boot any live USB as my system gone to GRUB2 Rescue Mode.
then I tried the code below
grub rescue>ls (hd0) (hd0,1) (hd0,2) (hd0,3) (hd0,4)
then I tried
grub rescue> set root=(hd0,2)
grub rescue> set prefix=(hd0,2)/boot/grub
grub rescue> insmod normal
grub rescue> normal
Note : (hd0,2) is working for me.
Now once you boot into Ubuntu, run the following two commands as well:
sudo grub-install /dev/sda
Now my system works boot normally .