[tde-users] Re: [OT] Need help installing Ubuntu on an EFI (not UEFI) machine

J Leslie Turriff composed on 2022-05-31 15:23 (UTC-0500): It's possible to have a UEFI on one disk and MBR/Legacy on another, but you'd have to manually construct required stanzas to enable booting one type from the other type. That's no problem at if you don't mind booting from the PC's BBS menu whenever you wish to boot from the other disk. Also, other can be added to current and vice versa manually by constructing /boot/grub2/custom.cfg and/or editing one of nn_CUSTOM in /etc/grub.d/. I've never actually tried booting UEFI Linux from Legacy Grub, but I have booted Legacy Linux from UEFI Grub. I never spent much time marrying Legacy with UEFI, because it's so much simpler just to get used to using the BBS hotkey when needed. What could possibly be different about the basics between EFI and UEFI I've never pondered, other than without U it would be older and thus less well developed than newer versions.

I have 8 UEFI PCs including 1 Mac. All but the first are booting UEFI. UEFI is more sophisticated and IMO a vast improvement. Its different, but in this case different is better. My first that isn't using UEFI was my first exposure to UEFI, and an upgrade that included moving 3 disks with RAID1 on 2 of them, so I was only interested in quick success, not learning RAID in a UEFI context at the same time as learning UEFI.

IIRC, I have only one out of 30+ working multi- multiboot PCs on which Ubuntu is installed other than on an only disk. One OS installation per disk I never do.

IMO, your best way forward, subject to any EFI limitations imposed by your PC, is to install Ubuntu in EFI mode, then at some point in time convert the openSUSE installation to EFI mode.