Booting Linux Live USB on a MacBook Air

I have a MacBook Air with an Intel i7 core running OS X Lion 10.7.5. Booting linux from a flash drive was not straightforward, to the point that when I finally got it working I laughed with surprise. Evidently doing such things is not part of the one true Apple way. The instructions were cobbled together from from here and here with a fair bit of trial and error. Needless to say, the procedures documented on the Ubuntu website did not work for me.

1. Download rEFIt-0.14.dmg from SourceForge, install, and reboot. 


2. Download the linux image, in my case Ubuntu 12.04.03 for 64-bit Mac (AMD64) desktop CD.


3. Open a terminal window and convert the linux image by typing
   hdiutil convert -format UDRW -o converted.img.dmg [original].iso. (In my case this step seemed to be completely unnecessary because the converted file was identical to the original when I checked its MD5 hash.) Check the size of the disk image using: du -h converted.img.dmg


4. Insert a flash drive 1 GB or larger into a USB port on the Mac. Open Disk Utility from /Applications/Utilities and select the flash disk. Make absolutely sure that you have selected the flash disk and not your hard drive! Erase the disk specifying Mac OS Extended (Journaled) format.






5. Select the Partition tab, hit the Options button, and choose GUID Partition Table. Create a partition large enough for the Ubuntu disk image using Mac OS Extended (Journaled) format.






6. From the command line, find which disk is your flash drive by typing: diskutil list


7. Unmount the disk using: diskutil unmountDisk /dev/diskN
   where N is the disk number you found in the previous step.


8. Copy the image over to the flash drive:
   sudo dd if=converted.img.dmg of=/dev/diskN bs=1m


9. Restart the Mac with the flash drive still inserted and select the external drive icon ("Boot Legacy OS from HD") from the rEFIt menu.


10. While Ubuntu is starting to boot press Escape then F6 and select the noapic and nomodeset menu options.