Recuperar Grub Linux

sudo fdisk -l
sudo mount /dev/sda2 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev/pts /mnt/dev/pts

sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt
grub-install --recheck /dev/sda

Reiniciar arrancando del grub del disco

sudo update-grub2

Si falla instalar grub2

sudo apt-get install grub2