How to add Windows 10 to GRUB on Arch install With EFI?

Question

I just installed Arch Linux and with GRUB and want to add my windows 10 with EFI partition to grub.

Now I have Arch installed on the hard drive /dev/sdc/ with a EFI system on /dev/sdc1. On an other hard drive I have Windows 10 installed where the efi drive is /dev/sda1 .

I tried to follow the arch wiki but could not find out were to get the EFI system partition for the command esp/EFI/Microsoft/Boot/bootmgfw.efi. Do I have to mount the windows 10 drive if yes where should I mount it to?

Answer 1

Get the UUID with: sudo grub-probe -t fs_uuid -d /dev/sda1

and then add an entry for Windows at the end of your grub.cfg:

menuentry "Windows 10" {
insmod part_gpt
insmod fat
insmod search_fs_uuid
insmod chain
search --fs-uuid --no-floppy --set=root XXXXXXXXX
chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi
}

Answer 2

Normally grub-mkconfig should auto-detect dual booted operating systems (via the os-prober utility). This, however, requires you to have the Windows drive mounted. For example, try this:

$ mkdir -p /mnt/windows
$ mount /dev/sda1 /mnt/windows
$ grub-mkconfig -o /boot/grub/grub.cfg

It should now automatically detect your Windows installation and you should be able to boot into Windows.

Another important thing to note regarding the previous answer to this question: you should never manually edit /boot/grub/grub.cfg, since it can easily be overwritten by tools like grub-mkconfig (and the syntax isn't really all that intuitive either way).