sudo su
mkdir /mnt/sda1
mount /dev/sda1 /mnt/sda1 
mount -t proc proc /mnt/sda1/proc
mount -o bind /sys /mnt/sda1/sys 
mount --bind /dev /mnt/sda1/dev

chroot /mnt/sda1 /bin/bash 

grub-install /dev/sda
grub-mkconfig -o /boot/grub/grub.cfg