I have been trying to install 16.04 to a friend's Macbook Pro (7,1) with the intention of dual booting.
I was following these instructions (https://help.ubuntu.com/community/MactelSupportTeam/AppleIntelInstallation). I installed ReFIT, made a live USB and partitioned successfully using Disk Utility. However I made an error (under 'Start Installing'): I installed the systems side by side instead of manually allocating the partitions so that grub would be installed to my root partition.
Now when i open Gparted in the live CD i get a Libparted error: "The primary GPT table is corrupt, but the backup appears OK, so that will be used"
If i click OK, i see that i have a 200MiB EFI system partition at the start of the drive.
Based on responses to this question, i will open up a new question trying to solve this problem.
Regarding the Ubuntu installation, i worked out that rEFIt was no longer supported, to i uninstalled that and installed rEFInd.
Now when i boot the machine I get to the rEFInd screen, I see 3 large logos, above 5 smaller logos.
The First large logo: Ubuntu logo, on the hard disk, described as: “Boot EFI\ubuntu\grub64.efi from EFI”
The Second large logo: OSX logo, on the hard disk, described as: “Boot Mac OSX from Macintosh HD”
The Third large logo: Ubuntu logo, on the hard disk, described: “Boot boot\vmlinnuz-184.108.40.206-generic.efi.signed from 10GiB ext4 volume”
First small logo: a key, described as: “Start MOK utility at EFI\ubuntu\MokManager.efi on EFI
Second small logo: About rEFInd
Third small logo: Shutdown computer
Fourth small logo: Reboot computer
Fifth small logo: Start firmware update utility at EFI\ubuntu\fwupx64.efi on EFI
Clicking the first large logo boots the GRUB menu. The screen then takes on the purple hue of an Ubuntu launch before the screen blinks ad goes black. I have to hard reset to get the machine back
Clicking the second large logo successfully boots OSX
Clicking the third large logo posts a whole lot of text to the screen, before the screen blinks and goes black. I have to hard reset to get the machine back
If I hold down ‘alt’ key at start up I only get the option to boot to the Mac partition, clicking this launches OXS.
I have tried running the boot info script mentioned in the answer below, but in mac when i try to launch the unzipped tarball 'bootinfoscript' (using sudo) i get: 'sudo: command not found'. Am I meant to be running this script from the live instance of ubuntu?
Thanks for the help on this, sorry if i am not keeping up with something straighforward.