[Solved] Grub Lost Windows Option in Dual Boot Setup

[DocTomJP]

After many years, suddenly the grub menu has lost the option to boot windows in a dual boot system. I rarely use Windows, but I do need it on infrequent occasions.
I suspect that this has occurred due to a recent Debian upgrade because it has occurred on two laptop computers in our house, both of which were upgraded at about the same time. The same disappearance of a grub windows option at boot occurred on both machines, one of which has a legacy bios with Debian 12/Win 7, and the other is an UEFI Debian 12/Win 10 system.
I may be entirely wrong about the cause (Debian 12 upgrade), but I post here because of my suspicion.

In any case, I will be very grateful for any advice, as so far my attempts to overcome the problem have failed completely, and I am nervous that I may do something such that I will lose the Debian system as well as the Windows.
Tom.

[kalle123]

Have a look here ...

viewtopic.php?p=784661&hilit=GRUB_DISAB ... ER#p784661

KH

[DocTomJP]

KH, many thanks indeed for your quick and effective response. I have just implemented the solution on the Deb/Win7 laptop (legacy boot) and everything works perfectly. Tomorrow I will check the UEFI machine, fully expecting the same good result.
I will confirm the result in another post.
Thanks again, Tom.

[kalle123]

Glad I could give a hand.

Regards KH

[DocTomJP]

I just tried the solution on the UEFI Debian 12/Win 10 laptop. Unfortunately it did not work.
The solution worked without any issues on the older legacy bios Debian 12/ Win 7 system, the boot into Windows option appearing at first reboot. But I could not get any progress on the UEFI system.
Any further help please?
Tom.

[pbear]

I've given up on os-prober. Instead, I use a custom.cfg file. 40_custom in /etc/grub.d does the same thing, but I think custom.cfg is easier.

Several ways to do this. Here's one. Run these three commands:

Code: Select all

lsblk -f
sudo touch /boot/grub/custom.cfg
EDITOR='gedit -w' sudoedit /boot/grub/custom.cfg

Copy this into the file, then save and close:

Code: Select all

menuentry "Windows 10" {
     insmod part_gpt
     insmod fat
     insmod chain
     search --no-floppy --fs-uuid --set=root <UUID-of-EFI-Partition>
     chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}

Note: The UUID will be eight characters, in the form 38EC-CDB2. FYI, the same file can be used to put Linux OSs on the boot list, but the form of entry is different.
FWIW, I always disable os-prober when using a custom.cfg file. The command is sudo chmod -x /etc/grub.d/30_os-prober.

[DocTomJP]

pbear, many thanks for your help with my problem.

I have not attempted your proposed solution, as I did not see your post until I opened this thread just now, after I had attempted further myself to solve the issue.

In fact I did succeed. I am not sure how. I booted to the bios, and did nothing significant other than perhaps elevating the Windows boot item above a USB boot item so that the order is Debian then windows.
Then I tried os-prober again, and for the first time (after several attempts over the previous days) it found the Windows EFI System Partition.
I thought that this seemed encouraging, so I rebooted, and hey presto. the Windows option in Grub was restored, and I am able to boot into Debian or Windows from the Grub menu.

So very many thanks. I shall save the details of your post for future reference,and use if the problem reappears.

Both yourself and and Kallie123 before have been very helpful, and I am grateful for your time and kindness.
Tom.

[pbear]

Glad to hear the problem has been solved.

... did nothing significant other than perhaps elevating the Windows boot item above a USB boot item so that the order is Debian then windows.

Well, no, that wouldn't be the explanation. Grub update doesn't consult NVRAM, which is where that list is stored.

[DocTomJP]

Pbear, thanks. So I am at a loss to know what caused the windows option to appear after the last attempt with os-prober, having failed on several previous attempts.
No matter, it is solved now, and I have marked it as such.
Once again many thanks, Tom.

[layna64]

pbear, many thanks for your help with my problem.

I have not attempted your proposed solution, as I did not see your post until I opened this thread just now, after I had attempted further myself to solve the issue.

In fact I did succeed. I am not sure how. I booted to the bios, and did nothing significant other than perhaps elevating the Windows boot item above a USB boot item so that the order is Debian then windows.
Then I tried os-prober again, and for the first time (after several attempts over the previous days) it found the Windows EFI System Partition.
I thought that this seemed encouraging, so I rebooted, and hey presto. the Windows option in Grub was restored, and I am able to boot into Debian or Windows from the Grub menu.

So very many thanks. I shall save the details of your post for future reference,and use if the problem reappears.

Both yourself and and Kallie123 before have been very helpful, and I am grateful for your time and kindness.
Tom.

Thanks for good informetion.