How to add EFI but keep existing legacy boot capability (hybrid boot)

[ed-agoff]

I have created a bootable USB installation of 12.04.5 using an MBR-formatted stick and legacy grub installed to the MBR. I've got as far as understanding I need a FAT32 partition for /boot/efi, and found various instructions on how to enable/repair legacy or EFI boot, but performing one always seems to corrupt the other (https://help.ubuntu.com/community/UEFI, https://help.ubuntu.com/community/Grub2/Installing, et al).

Given my existing legacy bootable stick, two partitions, sda1 = 200MB FAT32, sda2 = ext4,

How to I add EFI and retain legacy boot capability?

[oldfred]

Better to use gpt partitioning. UEFI has to boot from a FAT32 partition and UEFI normally is gpt. Ubuntu installer often is MBR(msdos) with just one FAT32 partition and that will work for many systems. We see a few that UEFI only boots from gpt.

Flash drive to boot in UEFI or BIOS - sudodus
https://help.ubuntu.com/community/Installation/UEFI-and-BIOS
https://help.ubuntu.com/community/Installation/FromUSBStick#Ubuntu_single_boot_in_UEFI_mode
A new and so far successful attempt to create a stable portable system, that works in UEFI and BIOS mode
http://ubuntuforums.org/showthread.php?t=2213631&p=13262506#post13262506
http://spblinux.de/blog/2013/06/uefi-and-bios-bootable-usb-stick-with-grub2/
http://askubuntu.com/questions/559007/is-it-still-possible-to-install-ubuntu-to-an-external-harddrive-with-uefi

[sudodus]

Welcome to the Ubuntu Forums :-)

Are you talking about an installed system or a persistent live system? (See the following link for details about these different kinds of systems)

Try Ubuntu (Kubuntu, Lubuntu, Xubuntu, ...) before installing it (http://ubuntuforums.org/showthread.php?t=2230389)

How do you intend to use your system?

[ed-agoff]

sudodus, I'm talking about an installed system.

Thanks, oldfred! Your response was very informative. And the last link was excellent:
http://askubuntu.com/questions/559007/is-it-still-possible-to-install-ubuntu-to-an-external-harddrive-with-uefi

I had to move to 14.04, since the 12.04 grub-install didn't include the efi options, and the steps in link above ("Add an ESP to an existing installation with MBR") worked like a charm!