Pretty close.
Back up your external sd card. It may get temporarily or completely hosed.
Must be on a stock-based rom, or however rumrunner says.
Make a live whatever of ubuntu, all directions here -
https://help.ubuntu.com/community/LiveCD
You want rev 12.04 LTS, also linked above.
You want the 32-bit version, it will download as an iso file, and then go to:
Finder -> Applications -> Utilities -> Disk Utility => use that to make a bootable cd from the image.
Booting is not fast. Even when it looks up, give a few minutes.
The only snag people seem to hit sometimes is getting networking up so give it a test run, and if it causes trouble, it's still fixable. Reasonable to expect that you'll get a driver pop-up and then a lan card icon in your upper right. Tap that to config your wifi drivers if it comes up. At that point, I prefer to tap the empty wifi icon and uncheck wifi, give it half a minute and then repeat to check it back on. That seems to scan more quickly for networks in my case.
If network problems persist, see -
http://androidforums.com/computers/646562-ethernet-problems-in-ubuntu-12-04-a.html
Now - you've done a test run, you're happy.
Easiest way to get to your files - either surf to here and follow links - or just email yourself the links to your gmail account, and access gmail via Firefox, you'll see an icon for it.
To get a Linux terminal window, that's control-alt-T and alt=option on a Mac keyboard.
You want to boot right into Linux, and get the mini-sdk there if you need to check connectivity with your phone - but rumrunner doesn't seem to require it.
You're going to download it with Firefox, that will put into your download directory.
Rumrunner says to do:
tar -zxf rumrunner<
device>_<
version>.tgz
sudo ./sujo
But - first you have to get there, that's done with (open a terminal window, control-alt-T) and then issue:
cd Downloads
To change to that directory.
Tip: since you're going to be running a live CD, you won't have anything in your way in your Downloads folder and can probably get away with just saying:
tar -zxf *.tgz
And save some typing.
Remember to avoid any USB 3 ports, use USB 2 only.
7. Profit.