Comment 9 for bug 1547599

after some more digging the problems might be related to the fact that the disk partition table was left in the hybrid GPT/MBR format and thus the mac is booting in the efi mode. according to http://www.rodsbooks.com/ubuntu-efi/ this might cause limited support for nvidia graphics card and related bios rom problems. in other words, the mac is not booting in the bios compatibility mode.

since ubuntu is the only operating system on the machine, i will reinstall it by wiping the disk and using a dos partition table. this should force the mac to boot into the bios mode. unfortunately, since ubuntu 16.04 desktop dvd does not boot via the optical drive, i have to use ubuntu 15.10 server cd and then do-release-upgrade since 16.04 desktop does not fit into a standard cd.