rescue grub uefi boot from live cd

grub.sh

sudo mount /dev/sda2 /mnt
sudo mkdir /mnt/boot/efi
sudo mount /dev/sda1 /mnt/boot/efi
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo cp /etc/resolv.conf /mnt/etc/resolv.conf
#### after reboot, ubuntu 18.04, sudo ln -s ../run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
sudo chroot /mnt
apt install -y grub-efi-amd64-bin
grub-install /dev/sda

#### update /etc/fstab