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I have two video cards, one running each of two identical monitors. My main card is an Nvidia GeForce 750 Ti, and the secondary is a Radeon HD5500. When I boot from live USB, the monitor attached to the HD5500 displays the desktop, and the other displays a gray screen with a flashing cursor (but doesn't do anything else). After installing, the desktop shows up on the GeForce, and the Radeon monitor is blank.

I followed this guide to attempt to install proprietary Nvidia drivers, but it didn't work. So I tried downloading the package straight from Nvidia. I think that worked, but I'm not sure (I'm completely new to this). I then tried to select a different driver for the Radeon from the list on the Additional Drivers settings tab. Now when I boot Ubuntu, the Radeon monitor gets no signal, and the GeForce monitor displays black.

What did I do wrong, and how do I fix it?

Ubuntu 14.04 dual boot with Windows 8.1 U1

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    I think Xorg is incapable to span a desktop across multiple graphics adapters. – David Foerster Mar 9 '15 at 15:35
  • Is there any way around it using 3rd party software, proprietary drivers, etc? Seems like a strange limitation of something as open as Linux. – Ryan Riegner Mar 13 '15 at 0:20
  • As far as I know, there's no software that can do this on Linux at the moment. “Open” means, that a solution is possible, not that a solution exists. It looks like you'll have to write drivers and modify the other involved subsystems yourself (or find somebody who does it for you). – David Foerster Mar 13 '15 at 15:22
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You didn't do anything wrong. What you're trying to do is "impossible". Both graphics cards have their own discrete memory and you need a shared frame buffer between the two to make this work...

The BumbleBee project is doing this for Intel and NVidia cards, but they don't support AMD/ATI cards, so unless you start programming this yourself for AMD, it's "impossible"... (for a certain definition of impossible. Look up Charles De Gaulle)

Sorry to be the harbinger of bad news...

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  • That's unfortunate. So it's impossible to spread a desktop across multiple video cards, unless they are both Nvidia? But I can still do multiple monitors on a single card, right? – Ryan Riegner Mar 13 '15 at 0:17
  • I know that with NVidia, it is possible, and with Bumblebee it is possible to combine Intel and NVidia. I also know that with NVidia and ATI it's not possible... – Fabby Mar 13 '15 at 8:55

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