I have a 27" iMac that the screen goes black on when trying to boot off of install media. I've tried multiple flavors of Ubuntu, Makulu, Fedora, etc.. and they all do the same thing. I've tried DVD and USB drives, and encounter the same thing. The computer is still running when this happens. Slackware will go through the install, but then doesn't boot. I've installed various versions of Linux on my MacBook Pro 17" laptop without problem, and have installed a lot of distros throughout the years. Not sure where to go from here though. This 27" iMac was given to me to use at work, and would make a perfect linux box for me, so I'm hoping I can get some good advice.

Model: - iMac (27-inch Late 2009) (CTO)Graphics
Display Size: - 27-inch
Graphics Card: - ATI Radeon HD 4850
Card Memory: - 512 MB
Max. Resolution: - 2560 x 1440
BLU / Coating: - LED backlit TFT, Glossy
Networking
AirPort: - Built-in AirPort Extreme (802.11a/b/g/n)
Ethernet: - 10/100/1000BASE-T (RJ-45)
Bluetooth: - Built-in Bluetooth 2.1 + EDR
Infrared: - For use with Apple Remote only.
Modem: - Optional Apple USB Modem.
Ports and Expansion
USB: - 4 ports (USB 2.0)
FireWire: - 1 port (FW800)
Display port: - Mini DisplayPort
Card Slot: - SD
Thunderbolt: - No

I had a similar problem with a Lenovo laptop. I eventually traced it to the brightness controls working the wrong way round. Try pressing the reduce brightness key, if there is one on the keyboard. It only happens with Linux - the keys work normally on Windows.

This is a very old bug that no one seems interested in fixing. I posted the same question back in 2010. The problem is that the open source driver switches the primary display to the external displayPort, and will only show up on an external monitor.

Up until last year there was the flgrx driver that solved the problem But AMD discontinued it. The newer AMD-GPU driver doesn't support the older graphics cards like the Radeon HD4850.

You can run the machine crippled, by adding "nomodeset" to the grub boot parameters, but forget about doing things like watching videos, playing games or using any graphic editing software.


If anyone has a solution for running an up to date version of ubuntu (or any other distro) on a late 2009 iMac, without crippling it, please let us know.

Bit slow but I was able to boot Ubuntu via a ext usb hard-drive. I did this

Step 1: Turn on your Mac by pressing the power button by choosing Restart in the Apple menu, or restart it if it's already on. Step 2: Press and hold the Option (⌥) key immediately upon hearing the startup chime. Release the key after Startup Manager appears. Select your external drive and hope for the best You of course have to have installed the Ubuntu distro onto the hard drive initially.

Whoa!! Thanks for the tip! I've been trying for a while. When I saw your comment about the external display, I gave it a go. The installer booted up on both displays, something it hasn't done before. Always had that black screen. I wanted to use this machine with two displays anyway, so this is a win!

I'm installing the 2021-04 Kubuntu right now, no special bootup options :-)

Thanks!