Regenerate GRUB boot in dual-boot EFI environment
# fdisk -l /dev/sda
/dev/sda1 2048 206847 204800 100M EFI System
/dev/sda7 702326784 849127423 146800640 70G Linux filesystem
# ls /mnt/p1
EFI 'System Volume Information'
# grub-install -v -d /mnt/p7/usr/lib/grub/x86_64_efi --boot-directory=/mnt/p7/boot --efi-directory=/mnt/p1
Regenerate device.map (optional)
# grub-mkdevicemap -m /mnt/sda7/boot/grub/device.map