Comment 17 for bug 1284085

So that's definitely a legacy bios installation, which really isn't recommended anymore for most systems because EFI boot usually works fine and exposes more functionality.

I'd at least like to confirm that booting in native EFI works without nr_cpus=1. You should be able to just run 'sudo apt-get install grub-efi', then when you reboot rEFInd will have an option that's labeled something like "Boot EFI\ubuntu\grub64.efi". Use that one, remove nr_cpus=1, and let us know what happens. Note that this will remove grub-pc, but it doesn't actually erase grub so you should still be able to boot back to the legacy mode if something goes wrong.

I'm also curious whether you're intentionally doing the legacy bios install. If not, how exactly are you flashing the iso and starting the installer? The only way I can get that is to select the "Boot Legacy OS from HD" option to start the installer.