Repairing grub boot in EFI system running Ubuntu

sudo fdisk -l
#now identify EFI and linux partitions and set them here
#e.g.:
EFI=/dev/nvme0n1p1
LIN=/dev/nvme0n1p6

sudo apt -y install grub-efi
sudo mkdir /media/root && sudo mount $LIN /media/root
sudo mkdir /media/efi && sudo mount $EFI /media/efi
sudo grub-install --target=x86_64-efi $EFI --efi-directory=/media/efi --boot-directory=/media/root/boot

# see https://askubuntu.com/questions/831216/how-can-i-reinstall-grub-to-the-e...