How to Add Windows 10 to Grub

Problem

Recently I installed Arch Linux on my laptop and forgot to set up a dual boot with my Windows 10 partition. I ended up with a Grub OS list containing only the Arch Linux option and no way of accessing my Windows 10 partition.

WARNING: My Windows 10 partition uses UEFI boot. If you have anything different, like a different version of Windows or a Legacy boot type this process might not work for you.

Here is how I solved it.

Solution

The following lines need to be added to /etc/grub.d/40_custom:

# Windows 10 EFI entry
if [ "${grub_platform}" == "efi" ]; then
  menuentry "Microsoft Windows 10 UEFI" {
    insmod part_gpt
    insmod fat
    insmod search_fs_uuid
    insmod chain
    search --fs-uuid --set=root $hings_string $fs_uuid
    chainloader /EFI/Microsoft/Boot/bootmgfw.efi
  }
fi

$esp = Where your windows partition is mounted. In my case, Windows is installed on /dev/sda and it created three partitions out of it: /dev/sda1, /dev/sda2 and /dev/sda3. In this case, \$esp was /dev/sda1.

How to obtain the value of $fs_uuid?

grub-probe --target=fs_uuid $esp/EFI/Microsoft/Boot/bootmgfw.efi

How to obtain the value of $hings_string?

grub-probe --target=hints_string $esp/EFI/Microsoft/Boot/bootmgfw.efi

You should end up with a block similar to this:

# Windows 10 EFI entry
if [ "${grub_platform}" == "efi" ]; then
  menuentry "Microsoft Windows 10 UEFI" {
    insmod part_gpt
    insmod fat
    insmod search_fs_uuid
    insmod chain
    search --fs-uuid --set=root --hint-bios=hd0,gpt1 --hint-efi=hd0,gpt1 --hint-baremetal=ahci0,gpt1 1234-AB1c
    chainloader /EFI/Microsoft/Boot/bootmgfw.efi
  }
fi

After adding this section to your /etc/grub.d/40_custom file, you need to regenerate the grub.cfg file:

grub-mkconfig -o /boot/grub/grub.cfg

Wrapping up

Beware of the Windows version and which type of boot you have. If you have any questions, please, don’t hesitate to contact me.

I hope it helps!