Dual GPU, Dual monitor: second monitor black with a shadow of the mouse

Question

I have a monitor connected to each of my GTX 980 Ti, on Ubuntu 16.04. The NVIDIA X Server setting is successfully detecting two monitors and two screens with the absolute position of screen1 set to +1920+0.

Here is my xorg.conf file:

# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 375.20  (buildd@lcy01-26)  Sat Nov 19 12:38:43 UTC 2016

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    Screen      1  "Screen1" RightOf "Screen0"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
EndSection

Section "Files"
EndSection

Section "InputDevice"
    # generated from default
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol" "auto"
    Option         "Device" "/dev/psaux"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"
    # generated from default
    Identifier     "Keyboard0"
    Driver         "kbd"
EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "ViewSonic VX2433wm"
    HorizSync       24.0 - 82.0
    VertRefresh     50.0 - 75.0
    Option         "DPMS"
EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "ViewSonic VP2365WB"
    HorizSync       24.0 - 82.0
    VertRefresh     50.0 - 75.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 980 Ti"
    BusID          "PCI:1:0:0"
EndSection

Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 980 Ti"
    BusID          "PCI:2:0:0"
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "DFP-0"
    Option         "metamodes" "nvidia-auto-select +0+0"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen1"
    Device         "Device1"
    Monitor        "Monitor1"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "DFP-0"
    Option         "metamodes" "nvidia-auto-select +0+0"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

However, my second monitor (Monitor1, Screen1) is blank (black). But the weird part is: I can move my mouse over to the second screen and I will see a black cross with white boundaries where my mouse is supposed to be. I see nothing else on this second screen (all black) and I cannot dray a window over to it.

Here is the output of running: sudo lshw -c video

*-display               
       description: VGA compatible controller
       product: GM200 [GeForce GTX 980 Ti]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:135 memory:de000000-deffffff memory:c0000000-cfffffff memory:d0000000-d1ffffff ioport:e000(size=128) memory:df000000-df07ffff
  *-display
       description: VGA compatible controller
       product: GM200 [GeForce GTX 980 Ti]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:02:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:136 memory:dc000000-dcffffff memory:a0000000-afffffff memory:b0000000-b1ffffff ioport:d000(size=128) memory:dd000000-dd07ffff

I have tried playing with the xorg.conf as well as the NVIDIA X Server Settings, but nothing has worked so far and my second monitor is still blank. This issue was raised when I upgraded from 14.04 to 16.04. I have a dual OS installation with windows, and the second monitor is OK on my other OS.

Solution

After days of trouble, I finally found the solution, or maybe just a workaround: The multiple monitor setup would not work unless you enable Xinerama in the nvidia-settings.

To do so:

• open a terminal, write sudo nvidia-settings

• In the X Server Display Configurations, enable Xinerama

• Save to X Configuration File (you may want to create a backup of your xorf.conf file prior to this step). Close the settings window.

• In terminal, run sudo service lightdm restart

Comments

[Miladiouss]

Thank you, that fixed my problem on Ubuntu 16. Very helpful.

[Xiuchao Wu]

I follow your steps, however, my Ubuntu can not detect the second GPU now, how can I fix this problem?

[Andor Kiss]

Okay, this works in that it stretches the screen over two monitors, but its not a true dual head configuration.