Booting Ubuntu on a UEFI computer

[Rashkae]

EFI partition and bios-grub are mutually exclusive.  This does not mean
that both can't exist on the same drive, but only one will be used
during the boot process.


bios-grub paritition is used with legacy, pre-EFI boot BIOS.  In theory,
the CSM should also be able to load boot code from bios-grub.  In
practice, the one time I tried this it would not work.  I didn't really
trouble shoot it, as it was more or less irrelevant.

bios-grub exists because of the new hard drive partition scheme, GPT.
When a large capacity hard drive is formatted GPT, or if you just want
the greater flexibility of GPT partitioning, GRUB can no longer embed
boot code in unused space the way it used to.  In short, if your hard
drive is partitioned with GPT partitions, you will need a bios-grub
partition to boot with a legacy, pre-efi BIOS.


Here is where I think you are getting into trouble.  For Ubuntu
installer to properly configure EFI boot, you have to boot the install
CD with EFI.  With CSM enabled, your motherboard will allow you to boot
the CDROM in legacy mode, in which case, the installer will not load the
kernel modules needed to install EFI boot environment.  I have even seen
many motherboards that boot CDROM in legacy mode by default.

When your system is booting, there should be a way to choose a one time
boot media.  In your choices, you should see for an option that
explicitly offers UEFI on the CDROM.  If it's too obscure, you can try
just disabling the CSM, (and therefore, no legacy boot whatsoever.)