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SDB Talk:Installation on a Mac
The first rEFInd paragraph is very wrong, but I don't want to simply delete it without writing more in its place. I just don't know what to replace it with. Forum thread Installation-on-a-Mac details my iMac experience last summer and last month. I used rEFInd with Snow Leopard, but never got rEFInd to work again after upgrading to El Capitan. UEFI Grub is loading MacOS.
Highlights of my configuration include renaming /etc/grub.d/40_custom to 06_custom, but not changing its content; and booting from /boot/grub2/custom.cfg that I created entirely from scratch, little different than how I multiboot on generic UEFI PCs. This produces an identical Grub menu head regardless whether 15.0 or 15.1 has last wrested ostensible boot control from the other.
My directories in /boot/efi/EFI/ are named APPLE, opensuse150 and opensuse151, the latter two via customization of /etc/default/grubs' GRUB_DISTRIBUTOR= lines. They are the names shown by efibootmgr. My /etc/default/grub files also contain GRUB_DISABLE_OS_PROBER=true, since the most used Grub menu entries at runtime are those at the top, leaving whatever follows to be ignored unless a prior kernel or rescue boot are wanted or needed.
This was most important to me: Booting From Install CD / DVD
To make your Mac boot from a Linux or Windows CD or DVD, you need to hold down the 'Alt' key as the Mac starts up (EFI-Boot), keep holding it down until it is obvious the CD is booting (pre 2012).
On a MacBook Air (booting from a pen drive) the alt/option key needs to be pressed. Boot to the installation via the EFI method (you should see a selection after pressing the alt/option key).
=> There is an alternative way to boot from DVD which does not work.
Installing newer versions of oS on older Macs (2009-ish) can't be done.
The .iso for recent versions of openSUSE uses a 16 bit FAT EFI partition. This will not boot from USB on older Mac machines (mine is a 2009 so I can only speak for machines from that year). The EFI partition must be 12 bit FAT. Leap 15.0 is the last version that uses a 12 bit FAT partition. It might be worth noting this in the documentation. You'll have to upgrade all the way up from 15.0 to whatever version of oS is available.
12 bit FAT supports a maximum of 32MB partition size. Microsoft-created ESP partitions, which are usually 100MB, create 32 bit ESP. My 2007 Mac has no problem booting 15.2's USB.