I can't find a way to have a dual boot Ubuntu/Windows 10 in GRUB

Michael-A-D

3/7/24, 11:33 AM

I had an old computer with ubuntu 22.04 and I'm acquired a new one with windows 10 on its own. Both work as expected. I decided to plug my old SSD into the new computer, configure its BIOS so that it boots with GRUB, and hoped to configure GRUB to get a dual boot option.

Unfortunately I can't find a way to boot on windows from GRUB (I get a black screen when I try). I can still pick my OS by changing the boot order of both drives in the BIOS but it's quite uncomfortable.

I ran boot-info and boot-repair, here is the pastebin from boot-info: https://paste.ubuntu.com/p/vTMBVj8DKf/

This might be the solution (note that I tried several workarounds like copying my windows boot partition to the same SSD as the GRUB partition, so boot-info now might show weird UUIDs or whatever):

WindowsEFI detected. Please disable BIOS-compatibility/CSM/Legacy mode in your UEFI firmware, and use this software from a live-CD (or live-USB) that is compatible with UEFI booting mode. For example, use a live-USB of Boot-Repair-Disk-64bit (www.sourceforge.net/p/boot-repair-cd), after making sure your BIOS is set up to boot USB in EFI mode.

But I'm not aware of the difference between UEFI/EFI and can't find the adequate option in BIOS.

Any guess on what I should do next?

Thanks for reading!

0 + 4

dual-boot

windows

oldfred

3/7/24, 2:51 PM

Difficult to mix UEFI & BIOS boot. You cannot on same drive, and can with difficulty on separate drives, but not recommended. You may have to change UEFI settings to CSM/Legacy/BIOS boot mode to boot sda and change back to UEFI boot mode to boot NVMe drive. UEFI & BIOS are not compatible, so once you start to boot in one mode, you cannot switch, or grub can then only boot other installs in same boot mode. Some new systems now only have UEFI mode as Microsoft has required vendors to install Windows in UEFI mode since 2012. Systems that old will not support Windows 11.

Michael-A-D

3/7/24, 5:28 PM

Not sure if I'm understanding right, is this correct? Right now I'm in BIOS mode, so GRUB can boot on ubuntu but not windows, since my ubuntu install is the only one in BIOS mode. If I were in UEFI mode, GRUB could boot on windows but not ubuntu, since my windows install if the only one in UEFI mode. It seems to me that I need to reinstall either ubuntu is UEFI mode, or windows in BIOS mode if I want GRUB to be able to boot both. I'd rather reinstall windows since I've only started using it and there is not so much to re-do. Would that work and is that a decent solution? Thanks anyway!

Michael-A-D

3/7/24, 5:34 PM

There is something I don't get tho, why is the windows boot manager able to boot in windows anyway? Would it work to add ubuntu to the windows boot manager (I've seen people doing that, but I'm like Jon Snow when it comes to windows boot manager: I know nothing).

oldfred

3/7/24, 6:26 PM

While UEFI installs should use gpt partitioning, Ubuntu lets installs use a MBR(msdos) partitioned drive. You can add an ESP (FAT32 with boot flag) and use Boot-Repair booted in UEFI mode & maybe advanced mode to uninstall the BIOS version of grub and convert to UEFI version of grub. Best long term to convert to gpt, but that may erase drive, so good backups required. Possible conversion without erase, but grub & fstab will need updates. http://www.rodsbooks.com/gdisk/mbr2gpt.html

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