how to install grub in ubuntu code example
Example 1: install grub manually
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB
Example 2: install grub manually
# grub-mkconfig -o /boot/grub/grub.cfg
# grub-install --target=x86_64-efi --efi-directory=esp --bootloader-id=GRUB
# grub-mkconfig -o /boot/grub/grub.cfg