I read quite a lot of wrong and contradictory information when I searched for feasibility of installing Ubuntu on my 2006 MacBook Pro. Part of the problem is that users don’t all understand the pieces of the puzzle involved to boot a Mac into Ubuntu, but the multitude of variants of MacBook Pro, with varying technology in them, causes confusion and contribute to user’s ignorance.
First, Mac doesn’t implement the traditional BIOS used to boot nowadays PCs. They rather implement an Extensible Firmware Interface (EFI), a more modern way of booting computers than the BIOS, dating from the 80s. Newer PCs start to replace the obsolete BIOS with such an EFI, called Unified EFI or more commonly UEFI. No problem, I thought at first, Ubuntu now supports UEFI booting. I UEFI boot onto Ubuntu several times a week. However, Apple introduced several tweaks to the EFI, making it almost unusable for other purposes than booting Mac OS X.
In my particular case, the Mac’s EFI was 32 bits, which means I could EFI boot only 32 bits operating systems. However, although Ubuntu supports UEFI booting, it doesn’t on my Mac, maybe because the Mac’s EFI is too different from a UEFI. Apparently some people successively UEFI booted their Ubuntu installation, either by using unofficial Mac variants of old Ubuntu versions or a kind of patchy program EFI booting and offering the Ubuntu’s ISO as a kind of virtual device. The later requires a version of Ubuntu supporting loopback booting, and that’s again only old versions. Quite annoying, isn’t it? I don’t want to install a 12.04 then dist-upgrade to 14.04, then 14.10!
Note that newer Mac computers have a 64-bit EFI, and it is well possible that it is able to boot Ubuntu and maybe even Windows, in a native way. That means no need for BootCamp anymore to hack the GPT to fake a MBR; both Ubuntu and Windows supports booting from UEFI and GPT!
While I thought Mac’s EFI only supports native EFI booting, I discovered that it has the necessary compatibility module to boot into BIOS-based environment. Maybe I got this CSM added by a firmware upgrade I obtained when installing all available updates. That means a Mac can boot a Ubuntu live DVD in BIOS-based mode. In theory, that would mean it can boot a 64-bit DVD even though it is 32-bit EFI. In practice, no, reason still to be determined. I thus can only boot 32 bit OS.
Moreover, no matter how hard I tried, I wasn’t able to boot Ubuntu off a USB key. I tried installing rEFInd to avoid having to press the infamous defective Option key at boot to get Apple’s boot menu (using an external keyboard), but rEFInd can only boot from the hard drive, ignoring the USB key or telling Apple’s firmware doesn’t support well booting from an external device.
At least, Ubuntu boots from the DVD. In theory, I should be able to install it on a partition on my hard drive and boot from there, but I didn’t do it for the moment.