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I had a smoothly running dual boot system with Ubuntu and Windows 10. After installing Ubuntu 22.04 I first didn’t see any boot loader at all. After fixing this with this help (https://www.computerbase.de/forum/threads/dual-boot-linux-windows-10-grub-nicht-sichtbar.2037349/) I see the boot loader but Windows is not included. I have the same error message as reported here: Installed Ubuntu alongside Windows 10 and now Windows doesn't boot but wondered if that will really help and is really the best solution.

I found this (Ubuntu 20.04 Windows 10 not detected in dual boot) but is it really necessary to install again?

It seems that proposed solution refer to different installation modes. I think it’s UEFI for both of them though. I found this article: https://wiki.ubuntuusers.de/GRUB_2/Grundlagen/ which recommends a setting up an ESP with Gparted but I hesitate moving things around with not enough knowledge and I already see a FAT32 EFI System partition in Gparted

Alex
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  • If you installed Ubuntu in legacy mode and Windows is UEFI, then yes, you need to reinstall Ubuntu UEFI. You have to boot the installation USB as UEFI. – Nmath Aug 11 '22 at 23:22
  • You should turn off the Windows "Fast Boot" option. "Fast Boot" leaves Windows' partitions unreadable by Linux. – waltinator Aug 12 '22 at 01:13
  • Does this answer your question? In a dual boot system, how does the BIOS choose which bootloader to run? – karel Aug 12 '22 at 09:24
  • I think both are installed in the correct way. How do I check it, to be sure? How should I turn off Windows boot option, when there is no Windows accessible? I’m not sure about the solution in the link, since it is also about converting. I’m not sure that this is the problem actually – Alex Aug 12 '22 at 12:32
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    I understand that os-prober has been removed from 22.04 – C.S.Cameron Aug 12 '22 at 15:06
  • When using update-grub, os-prober seems to be used: “Warning: os-prober will be executed to detect other bootable partitions.” Still, Windows is not listed in the grub menu. – Alex Aug 12 '22 at 22:42
  • Yea, just tried 22.04.1 and os-prober is working okay. – C.S.Cameron Aug 12 '22 at 23:40
  • I wanted to follow this advice: https://askubuntu.com/questions/1260263/installed-ubuntu-alongside-windows-10-and-now-windows-doesnt-boot and created a Windows Boot Stick with WoeUSB. I selected to boot from USB first but it’s not happening: Grub shows up, offering only Windows. Not sure whether this is the next problem or part of the solution – Alex Aug 13 '22 at 09:56
  • Finally was able to boot Windows, followed the advice mentioned above in Windows. Had and error when entering c:\windows /s c: (error copying boot files) which I ignored. After that, Windows booted but GRUB doesn’t show up. I can access it via UEFI boot options though – Alex Aug 13 '22 at 10:57
  • I used boot-repair in a live ubuntu session. Now it worked without errors. Changed boot preferences in the submenu of OS bootloader. Grub shows up and has a “Windows Boot loader” as one of the boot options. I guess that’s it – Alex Aug 13 '22 at 14:57

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