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I see that this is possible on a T520 apparently (Triple-head on a Lenovo T520), but I can't see anyone claiming it's possible on a T420.

I'm running 12.04 and have Bumbleebee installed and working fine but I can't get the display port monitor to display anything. The power light flicks on, but things only render on my VGA output monitor, and Ubuntu's display settings don't detect the third monitor.

I'm not concerned with power management, ie, am happy to leave set on discrete graphics in the BIOS if that helps.

Is this possible? Thanks.

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The most likely situation is that the display output that is not working is directly wired to the discrete graphics card. The solution to this hasn't been fully implemented in Linux at the time of this writing (2013-03-19), but it is underway: it's called reverse-PRIME.

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The answer of @213441265152351 is right but it's not only most likely ;-) The DVI and Display Port are wired to the NVidia graphics while the VGA is wired to the Intel chip.

I'm facing the same problem with the DVI ports on my docking station. I didn't even get it to work by switching to discrete graphics in the BIOS.

I'm hoping for the properitary driver Nvidia is finally working on but it has been a long time since the last news on that.

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