root@lubuntu:/# dpkg-reconfigure grub-efi-amd64
Generating grub configuration file ...
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
Found linux image: /boot/vmlinuz-4.8.0-28-generic
Found initrd image: /boot/initrd.img-4.8.0-28-generic
grub-probe: error: cannot find a GRUB drive for /dev/sdc1.  Check your device.map.
done
root@lubuntu:/#