Installing Linux on 64-bit Mac that has the old 32-bit EFI firmware

If you have and older Mac that has a 64-bit processor but the 32-bit 1,1 or 2,1 EFI firmware (eg. a 2009 Mac Mini Core 2 Duo) and you want to install a recent 64-bit version of Linux on it, the 32-bit EFI firmware will leave you stuck at a prompt like this:

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1.

2.

3.

Select CD-ROM Boot Type :
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with an unresponsive keyboard and no way to proceed.

There are instuctions out there for mashing the keyboard like a two-year-old with a xylophone before the prompt comes up and hoping the keyboard buffer will make it through, but I could never get that to work.

There are also instructions out there for people installing recent versions of Windows having the same problem to create an install DVD that only has one boot option so the prompt doesn't happen. 

My solution for Linux, Fedora 24 specifically, used the same general idea (a boot disc that only has the legacy BIOS boot option), and could be adapted to other distros easily enough. To do this you need the following:

1. A Linux box with mkisofs installed
2. Enough free space to hold two copies of the install CD/DVD you are working with.

Step 1.

Make a directory in your home directory to hold the install files called "CD_root" (or whatever, just use the same directory name in place of "CD_root" in step 7.) You can do this from the command line or the file manager of your choice.

Step 2.

Copy the content of your install CD/DVD (or mounted ISO image) into this directory with the folder structure intact. Again, you can do this from the command line or the file manager of your choice.

Step 3.

Inside the directory you created in step 1, delete the "EFI" subdirectory and all its contents.

Step 4.

Inside the directory you created in step 1, go into the "images" subdirectory and delete "efiboot.img" and "macboot.img".

Step 5.

In the same directory ("images") edit TRANS.TBL to remove the references to the files you just deleted in step 4 and save the file. The total contents of the file when you are done should be:

F PRODUCT.IMG;1
     product.img

Step 6.

Inside the directory you created in step 1, go into the "isolinux" subdirectory any open "isolinux.cfg". Look for a section like this:

label linux
  menu label ^Start Fedora-Workstation-Live 24
  kernel vmlinuz
  append initrd=initrd.img root=live:CDLABEL=Fedora-WS-Live-24-1-2 rd.live.image quiet

It's the CDLABEL you need to know for the next step, in this case it is Fedora-WS-Live-24-1-2

Step 7.

From the command line issue this command, varied as necessary in the notes below:

mkisofs -V Fedora-WS-Live-24-1-2 -o fedora24-64w32boot.iso -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table CD_root

Where you would replace "Fedora-WS-Live-24-1-2" with whatever CDLABEL you found in step 6. "fedora24-64w32boot.iso" can be whatever you want to call the resulting ISO file. "CD_root" should be replace with whatever folder name you used in step 1.

You can now burn the resulting ISO file to disc and use it to boot the Mac without the impassable prompt. I'm assuming you know to press "C" while booting to boot to CD/DVD or you wouldn't have gotten to the impassable prompt in the first place.