Ubuntu 14.04 Unknown Display

I recently had trouble with my Nvidia GTX760 recognizing one of two identical monitors, both of which worked fine with a Macbook Air and DisplayLink USB adapter.  The Ubuntu default Nouveau driver wouldn’t find the monitor at all, while the Nvidia 331 driver would only allow 640×480 or 800×600 resolution.  Eventually I found the display log was reporting an issue obtaining the EDID, a small packet of data reported by monitors describing their capabilities (make, model, resolution, etc).

/var/log/Xorg.0.log
...
[ 11972.301] (**) NVIDIA(0): Unable to read EDID for display device DFP-3
...

Since I had an identical monitor I was able to force the system to use that EDID. Save the good EDID. Create the xorg.conf file. With /etc/X11/xorg.conf saved to the disk, a CustomEDID option can be added.

/etc/X11/xorg.conf
...
Section "Monitor"
    ...
    Option	   "CustomEDID" "DFP-3:/home/matt/hardware/acer-v226hql-edid.bin"
EndSection
...
Section "Screen"
    ...
    SubSection     "Display"
        Depth       24
    	Option	   "CustomEDID" "DFP-3:/home/matt/hardware/acer-v226hql-edid.bin"
    EndSubSection
EndSection

If it’s not fixed upon reboot, check if the xorg.conf file was renamed.  There’s currently a bug, and a workaround, but hopefully that’s resolved soon.

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