Various forum comments I found googling imply that the problem is that grub doesn't understand the partitioning format that the Mac uses (though, annoyingly enough, the partition editor seems just fine with it and there's now warning until the entire operating system has been installed).
I've worked around it by wiping the partition table with Linux fdisk and installing the machine Linux-only for the time being. -- Installer crashes on GRUB on iMac 17" Core 2 Duo https://launchpad.net/bugs/89937 -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
