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I have a dual-boot setup, with Linux Mint 19.3 and Windows 10 each installed on a separate disk. Windows says that it is installed in a "Legacy/BIOS mode", and so I used this mode to install Linux as well. The installer detected the Win bootloader correctly, but after the installation there was no Windows entry in GRUB and no method of fixing this I found online has worked for me. I can boot into Win by using the BIOS menu, Win works fine, and so does Linux.

Here's my boot repair summary: http://paste.ubuntu.com/p/PV79583Jtc . And either I am not using boot-repair correctly or it doesn't help in my case, I've tried numerous combinations of settings and none worked.

I assume that there is something that I'm missing/have configured wrong, but I'd like to find out what that is, instead of just bruteforcing a system-reinstall...

Thank you for your answers

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  • Linux Mint is installed in UEFI mode (GPT partitioned disk with an ESP) and not in BIOS/legacy mode. Your boot mode in the BIOS is set to UEFI/CSM (both) and not to legacy only.
    – Freddy
    May 17 '20 at 19:33
  • Ok, reviewed my BIOS settings, and all options that have a "Legacy only" mode were already set to that (CSM support: on; LAN PXE Boot Option ROM: off; Storage Boot Option Control: Legacy; Other PCI Device ROM priority: Legacy), using Gigabyte Auros B450. Is there another setting that I am missing or did I misunderstand you?
    – nisnan
    May 17 '20 at 19:45
  • "CSM (Compatibility Support Module) on" means that UEFI is enabled with legacy support and you booted the installer in UEFI mode. Maybe there is an option to turn UEFI off (in my BIOS there are three options "UEFI Only/Both/Legacy Only"). Another option is to build an USB installer that doesn't support UEFI, so you can only boot and install in legacy mode.
    – Freddy
    May 17 '20 at 20:01
  • Ok, theoretically then I could also try to convert my Win installation into UEFI mode? Because it's either this which would leave both if my OSs (supposedly) intact or a full reinstall of Linux...
    – nisnan
    May 17 '20 at 21:42
  • Yes, either change Linux to legacy or Windows to UEFI or live with it as it currently is. Converting Windows to UEFI is probably the best choice.
    – Freddy
    May 17 '20 at 21:47
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So the solution was to convert my Windows installation to UEFI (using mbr2gpt within Windows), after that I had to set grub back as the default and all works fine.

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