GRUB Reinstall

EFI

TBD

BIOS

Based on https://wiki.archlinux.org/index.php/GRUB#Installation and https://unix.stackexchange.com/a/346206

target_device=/dev/sda
grub-install --target=i386-pc  --boot-directory=/mnt/arch/boot --root-directory=/mnt/arch  "$target_device"