Still not using UEFI. Should I?

[Virginio Miranda]

Not necessarily:
https://superuser.com/questions/1165...rtitioned-disk

Your setup is the second one: "In this variant, the first stage of GRUB still resides in the MBR"

" BIOS-mode GRUB on MBR -- This is the traditional PC configuration. In it, GRUB is split into multiple stages. The first stage resides in the first 440 bytes of the Master Boot Record (MBR). This first stage then loads and executes a second stage of GRUB, which typically resides in the sectors immediately following the MBR. This space is officially unallocated on most MBR disks, so putting GRUB code there is a bit risky; but it usually works OK. Additional code resides in files, typically in the /boot/grub directory of the OS used to install GRUB. There are numerous variants on this configuration possible. For instance, putting the GRUB first stage in a Partition Boot Record (PBR; the first sector of a partition) was once popular, but is pretty uncommon today, and in fact I'm not 100% sure that modern GRUB 2 still supports this option. "

Only for clarification:

This method still works on modern GRUB2. I still use this ancient method.

[oshunluvr]

Kind of necro-posting here, but I have discovered a fairly simple and reasonable way to dual boot two or more Kubuntu installs while using EFI.

The first install "owns" grub and boots to the grub menu. Then when doing subsequent installs, simply use "manual partitioning" and do not select and "use" the /boot/efi partition. This will generate warnings from the installer about not being able to boot. Once installation of the additional Kubuntu is complete, boot back into the first install, enable and edit /etc/grub.d/40_custom and add the needed boot entry to boot the second install, and update grub.

On the next reboot, both Kubuntu installs are selectable and bootable. Since Kubuntu creates and updates the links "vmlinuz" and "initrd.img" and their ".old" versions, using those links instead of the specific kernel versions in 40_custom allows you to boot either the current or most previous kernel by simply adding two stanzas in 40_custom or building a nested menu similar to the default grub menu.

One thing to note is the first Kubuntu install holds the needed GRUB and EFI files. If you want to remove it, you must first re-install and update GRUB from a different install before removing the first install.