os-prober doesn't see Windows installations in an EFI system

[DiegoRivera]

On a multiboot installation of Ubuntu Yakkety and Windows using UEFI, everything was working properly. Upon update to Zesty, os-prober was unable to locate the Windows partition and thus Grub (2.02~beta3-4ubuntu2 and previous Zesty versions) wasn't generating the correct bootable entries for it.

I edited /usr/lib/os-probes/mounted/efi/20microsoft to fix the issue by updating it to the latest GRUB's expectations. The original script only output 3 columns: the device name, the label, and "Windows". GRUB was expecting 4 columns: the device name + EFI path (separated with @), the label, "Windows", and "efi".

The script needed to be modified to properly handle these changes. I'm attaching the updated script, which works with both giving the device name and the EFI mount path, producing what I believe to be the correct output for both.

This updated prober script fixes the issue by correctly chaining to the Windows boot manager.

OS-prober also has an issue where the scripts in the "efi" directory (/usr/lib/os-probes/mounted/efi) aren't called, but instead need to be "moved" (copied) into the parent directory. This is a gap that needs bridging (i.e. make os-prober also run those scripts automatically).

The expectation is that running "update-grub" would result in all available boot options being detected and accounted for as per what grub supports. Clearly that wasn't happening until the aforementioned script was fixed and placed in the right location.

Cheers!

[Dimitri John Ledkov (xnox)]

windows bootloader detection has improved in recent releases. thus I am expecting for this to be fixed in focal.