ubuntu grub restore or rescue after windows install ,the simple way

Total 8 lines:

sudo mount /dev/sdXX /mnt

sudo mount /dev/sdY /mnt/boot/efi   (sdY is of EFI partition)

for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt$i; done   (single for loop for all dev mount)

sudo chroot /mnt

sudo update-grub

sudo grub-install /dev/sdX   (eg: sda or sdb)

exit  (to exit chroot)

umount -a   (umount all dev that have been mounted)

reboot

another simple technique is to use --root-directory option in grub-install command after mounting the linux partition and finally do update-grub



Source: http://askubuntu.com/questions/83771/recovering-grub-after-installing-windows-7