for n in /proc /sys /dev /dev/pts /run; do mount --bind $n /target/$n; done
chroot /target
echo "GRUB_ENABLE_CRYPTODISK=y" >> /etc/default/grub
mount /dev/mapper/LUKS_boot /boot
mount /dev/vda1 /boot/efi
grub-install /dev/vda1
update-grub
exit