Fresh install of Win10, then fresh install of Xubuntu 20.04.3: Both installed, but no boot manager/option shows up to select Ubuntu - Windows just boots as if noone else was there.
![Confused :?](./images/smilies/icon_confused.gif)
I've searched the web and it seems to be a common problem, but possibly due to different reasons.
Therefore, everything I've tried didn't work:
- Disabled non-UEFI (legacy) boot options in BIOS. Then reinstall Xubuntu. Just to make sure that the first installation wasn't a legacy-MBR one by accident. Same result.
- boot-repair: bailed out with a strange error message, saying Windows was not shutdown but merely hybernating (*).
- bcdedit: copy Windows entry and modify it to point to \EFI\ubuntu\shimx64.efi (or grubx64.efi). Both didn't work (Error code 0xc000007b).
- etc etc... aarrrgh!
So I knew the installation basically works.
[SOLUTION]
My BIOS (MSI Mortar Max B450M Mainboard) had "BIOS CSM/UEFI Mode" selected, instead of just "UEFI".
CSM stands for "Compatibility Support Module". Wikipedia says:
Long story short: 3 things to do.The Compatibility Support Module (CSM) is a component of the UEFI firmware that provides legacy BIOS compatibility by emulating a BIOS environment, allowing legacy operating systems and some option ROMs that do not support UEFI to still be used.
- Disable "fast startup" in Windows10.
- Set BIOS mode to UEFI (disable CSM).[/b]
- Set the default UEFI boot order in the BIOS to default to "ubuntu".
![Shocked :shock:](./images/smilies/icon_eek.gif)
2. Makes thing do "clean UEFI". No legacy fallback hacks coming in the way.
3. This loads GRUB by default, which should have "Windows 10" as option in its menu
![Smile :)](./images/smilies/icon_smile.gif)
Windows' boot loader seems to have issues loading non-Microsoft kernels. Surprise?