Re: Ubuntu 13.10 installation on iMac 21,5 inch radeon 4670 black screen
I seem to have the same type of system as you (iMac mid-2010, modelID 11,2, with radeon 4670) and I've also tried to install linux, in my case alongside OSX.
I agree that, to install linux, you need an external monitor.
I believe this is because the linux kernel radeon module has its video output connections reversed for this system.
The internal monitor connection is called 'eDP' and the external connection is called 'DisplayPort0'. The radeon kernel module seems to default to 'DisplayPort0' at startup, or resume after sleep. If that connection is not terminated (cable plugged in to monitor) X doesn't run. Even virtual terminals are missing.
If you plug external cable to a monitor (switched on or not) then you will get virtual terminals, but not X, unless you start kdm manually. X then shows on 'eDP'.
I have set this up only for Fedora 20 so far, booting from refind, installed in OSX.
Ubuntu disks and USB sticks seem to be unbootable despite trying several different methods of preparing them. My OSX disk is gpt with protective MBR.
Sorry I haven't got an answer but I may have explained why it happens.
I have reported the radeon module problem to fedora and ubuntu; I believe it has been passed on to kernel developers.
I really would like to switch to linux, but this video problem is too severe to cope with, so I have installed linux in virtualbox on OSX for now.
Windows is cheap, but linux is free