lubuntu@lubuntu:~$ sudo mount /dev/sda2 /mnt
mount: /dev/sda2 is already mounted or /mnt busy
       /dev/sda2 is already mounted on /mnt
       /dev/sda2 is already mounted on /mnt/boot
lubuntu@lubuntu:~$ sudo mount --bind /dev /mnt/dev
lubuntu@lubuntu:~$ sudo mount --bind /proc /mnt/proc
lubuntu@lubuntu:~$ sudo mount --bind /sys /mnt/sys
lubuntu@lubuntu:~$ sudo chroot /mnt
root@lubuntu:/# grub-install /dev/sda
Installing for i386-pc platform.
Installation finished. No error reported.
root@lubuntu:/# update-grub2
Generating grub configuration file ...
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
Found Windows 7 (loader) on /dev/sda1
done
root@lubuntu:/# exit
exit
lubuntu@lubuntu:~$ cd ~
lubuntu@lubuntu:~$ sudo umount /mnt/dev
lubuntu@lubuntu:~$ sudo umount /mnt/proc
lubuntu@lubuntu:~$ sudo umount /mnt/sys
lubuntu@lubuntu:~$ sudo umount /mnt/
umount: /mnt/: target is busy
        (In some cases useful info about processes that
         use the device is found by lsof(8) or fuser(1).)
lubuntu@lubuntu:~$