Force to install Ubuntu only in Legacy

Solution 1:

I have the same issue on a pre-uefi GA-EX58-UD4P mb with award bios. I get the fatal error installing ubuntu 20.04 on a new SSD. A live boot-repair usb also fails to install boot loader due to the session having booted in "compatibility" mode. I did find a work around by shutting down after a "fatal error" install, then plugging in and booted an old ubuntu hdd. Then did "sudo update-grub". Shut down + unplugged the old hdd. Booted the new install and the link to it appeared in the grub bootloader screen. I suspect using a live usb session to mount the disk the failed install is located on then using "sudo update-grub" might have worked too.