1. Boot from a Live-USB
2. List the partitions
fdisk -l
3. Mount Linux including /boot, EFI and special Live-USB (/dev /dev/pts /proc /sys) partitions under /mnt
mount /dev/sda7 /mnt mount /dev/sda6 /mnt/boot mount /dev/sda2 /mnt/boot/efi mount --bind /dev /mnt/dev mount --bind /dev/pts /mnt/dev/pts mount --bind /proc /mnt/proc mount --bind /sys /mnt/sys
4. Change root to /mnt
chroot /mnt
5. Configure and install grub
update-grub grub-install exit reboot