Ubuntu on Mac Mini questions: manually booting without grub, and preserving GPT partition

[Jason Heeris]

About a year ago I decided to try for a sole-Ubuntu installation on my Mac
Mini 6,1. I got it to work, but I never followed through on my promise to
write it up[1]. This time, I'm installing 14.04, and I am determined to
record the details! Really.

The only complication is that I want to have an EFI-booted system, and the
usual installation uses BIOS emulation. Note that this is mostly for
science — I want to see if it's (a) possible and (b) repeatable.

I already have a very good starting point in the form of Mike Homney's
instructions[2]. The basic process is this:

1. Do normal installation up until partitioning
2. Leave a 100MB empty partition at the start of the drive, but partition
the rest as normal
3. Continue with installation to /dev/sda2
4. Don't install grub
5. Reboot into the new system
6. Manually set up the EFI partition so the Mac Mini recognises it (this
requires an extra PPA and some apt-installed packages) and install grub to
that

I'm trying to figure out what to do about step 5. The reason I don't
install grub during the installation itself is because I think,
theoretically, step 6 should take care of it after that point. Because I'm
trying to record the minimal required steps here, if I don't *need* to do
something, I would prefer not to do it. But of course, without grub in the
MBR, the system won't boot.

Question 1: Is it possible to get the USB installer to somehow boot into
/dev/sda2 manually? I tried using the rescue mode shell, with /dev/sda2 as
the root, but I didn't have access to the distribution's whole set of
tools, nor could I resolve server names (I had a network connection... just
no resolution for some reason).

Question 2: Let's say I start with a GPT-partitioned disk (ie. a fresh
install of OS X), and run the Ubuntu installer. I get to the partitioning
stage and set up my partitions manually. Will the installer retain the GPT,
or will it replace it with an MBR partition table?

Cheers,
— Jason Heeris

[1] https://lists.ubuntu.com/archives/ubuntu-users/2013-August/271091.html
[2] http://glandium.org/blog/?p=2830
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