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This question already has an answer here:

I'm using:

  • Alienware M14xR2 laptop running Ubuntu 14.10
  • 2 * DELL U2412M monitors attached via HDMI and VGA
  • Optimus graphics (Intel + nVidia GeForce GT 650M) running with nvidea-346 and nvidia-prime, with Prime setup in nvidia-settings GUI to use the NVidia GPU
  • built-in laptop monitor disabled

Problems

  • Ubuntu Display GUI correctly detects the two monitors, but Nvidia cannot see any displays (although it does see one X "screen" of size 3840x1200 pixels i.e. the resolution of each monitor combined)
  • System behaves as though the two monitors are just one screen. If I maximise a window, it is maximised over both monitors and the file menu appears only at the top of the second screen which is very annoying
  • Nvidia 346 Settings Manager crashes if I click 'Detect Displays'

Note, this follows on from a related problem I reported here: Dual monitor setup, why does NVidia 340 Prime only detect one monitor?

Here you can see Nvidia does not recognize any displays:

$ lspci | grep VGA

00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
01:00.0 VGA compatible controller: NVIDIA Corporation GK107M [GeForce GT 650M] (rev a1)

$ /usr/lib/nvidia-346/bin/nvidia-xconfig --query-gpu-info

Number of GPUs: 1

GPU #0:

Name : GeForce GT 650M

UUID : GPU-8d5fcaf0-264e-39ec-f176-17a1ceb538fa

PCI BusID : PCI:1:0:0

Number of Display Devices: 0

$ xrandr --query

Screen 0: minimum 8 x 8, current 3840 x 1200, maximum 16384 x 16384
DP-0 disconnected primary (normal left inverted right x axis y axis)
DP-1 disconnected (normal left inverted right x axis y axis)
LVDS1 connected
   1600x900       60.0 +   40.0  
DP1 disconnected
DP2 disconnected
HDMI1 connected 1920x1200+0+0 518mm x 324mm
   1920x1200      60.0*+
HDMI2 disconnected
VGA1 connected 1920x1200+1920+0 518mm x 324mm
   1920x1200      60.0*+  
VIRTUAL1 disconnected

marked as duplicate by Zanna, user364819, Anwar, Charles Green, user117103 May 26 '17 at 15:38

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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I forget the exact name of setting its on now (haven't used Nvidia in a while) but it spans across all displays

What you need to do is go to open the NVIDIA Control Panel and select "Set up Multiple Displays"

From the left pane, choose X Server Display Configuration. Now click each screen you want setup (one at a time) in the dialog window and click Configure. Then enableTwinView, or separate X display (requires restart)

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    Unfortunately the problem is that Nvidia does not even detect the displays (only the Ubuntu Screen Settings GUI can detect them both). I have updated the question with the nvidia-xconfig cmd output to clarify the issue. – neutreno Jan 27 '15 at 18:21
  • Is this of any help? – geoffmcc Jan 27 '15 at 18:29
  • Thanks @geoffmcc , but it didn't really help. I discovered that it seems to be a bug in the Nvidia drivers (refer to my answer). – neutreno Jan 28 '15 at 2:19
  • Did you install using ppa:xorg-edgers or some other way? – geoffmcc Jan 28 '15 at 2:31
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I purged all the Nvidia drivers and resorted to using the OS Nouveau drivers as a temporary fix. The previous releases of the Nvidia drivers did not help. Thus it appears to be a bug in the official Nvidia drivers as the Nouveau drivers resolve the above issues.

However, Nouveau also introduces other problems since they are just a reverse engineer of the official drivers and do not support the latest features and fixes required by power users or for work purposes.

It would appear that Nvidia still have very little interest in properly supporting Ubuntu. I have had never ending problems over the last few years on numerous different systems with their Ubuntu drivers :(

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