My system has the following drives: a 500GB SSD, a 2TB HDD, and a 32GB Optane card. I'm running Debian 10 from a partition on the SSD (sda), and Windows 10 from the HDD+Optane Intel RST RAID drive (sdb).

Currently I switch between Debian and Win10 by pressing F8 on startup or changing the BIOS setup. I know that grub should be able to show me all the bootup options though. I have looked into grub-customizer but couldn't figure it out. How can I add the Win10 boot option from the different drive into the grub options?

  • If both operating systems use the same boot style (either UEFI or legacy), then using GRUB to present them both in the boot menu should be possible, and if the os-prober package is installed, update-grub should be detecting Windows 10 automatically. However, if one OS uses native UEFI and the other uses legacy boot methods, pressing F8/using BIOS settings might be the only way.
    – telcoM
    Apr 7, 2020 at 13:24

1 Answer 1


Solved it. The os-prober never returned anything from the terminal running from root (sudo -i). However, what worked:

I added this entry to the Grub list (using grub-customizer or editing the file /etc/grub/40_custom directly)

menuentry "Windows 10 (UEFI)" {
search --set=root --file /EFI/Microsoft/Boot/bootmgfw.efi
chainloader /EFI/Microsoft/Boot/bootmgfw.efi

Help from here: https://askubuntu.com/questions/211339/invalid-efi-file-path-while-booting-windows

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