I am using Google Translate because English is not very good.
I am sorry if there is content difficult to understand.

```
$ uname -srvpio
Linux 4.15.0-23-generic #25-Ubuntu SMP Wed May 23 18:02:16 UTC 2018 x86_64 x86_64 GNU/Linux

$ nvidia-smi 
Fri Jul 13 14:12:01 2018       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 390.67                 Driver Version: 390.67                    |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  GeForce 940MX       Off  | 00000000:01:00.0 Off |                  N/A |
| N/A   47C    P0    N/A /  N/A |    726MiB /  2004MiB |      4%      Default |
+-------------------------------+----------------------+----------------------+

```

If you are using a NVIDIA GPU built-in laptop please try the following method.



Execute `prime-select query`.
If the output is not `nvidia`, execute `prime-select nvidia` and restart it.



Please execute `lshw -C display`.

■ *-display UNCLAIMED If is a device of `vendor: Intel Corporation`
If `nomodeset` or `i915.modeset=0` is included in GRUB_CMDLINE_LINUX_DEFAULT or GRUB_CMDLINE_LINUX in `/etc/default/grub`, delete it, run update-grub and restart it.

■ *-display UNCLAIMED If is a device of `vendor: NVIDIA Corporation`
If `nomodeset` or `nvidia-drm.modeset=0` is included in GRUB_CMDLINE_LINUX_DEFAULT or GRUB_CMDLINE_LINUX in `/etc/default/grub`, delete it, run update-grub and restart it.



If `inxi` is not installed, please run `apt-get install -y inxi`.

Please execute `inxi -G`.

If `drivers: nvidia` is displayed, you need to add the following to `/etc/X11/xorg.conf`.
```
Section "Device"
    Identifier "intel"
    Driver "modesetting"
    Option "AccelMethod" "None"
EndSection
```

If `drivers: modesetting,nvidia` is displayed, please delete or comment out `Monitor "Monitor 0"` from `Section "Screen"` including `Device "nvidia"`.
```
Section "Screen"
    Identifier "intel"
    Device "intel"
    Monitor "Monitor 0"
EndSection

Section "Screen"
    Identifier "nvidia"
    Device "nvidia"
# Monitor "Monitor 0"
    DefaultDepth 24
    Option "AllowEmptyInitialConfiguration" "on"
    Option "IgnoreDisplayDevices" "CRT"
    Option "ConstrainCursor" "off"
    SubSection "Display"
        Depth 24
        Modes "nvidia-auto-select"
    EndSubSection
EndSection
```
Then restart it or execute `service gdm3 restart`.
that's all.

This problem is caused by the fact that nvidia-xconfig generated /etc/X11/xorg.conf does not include the loading of the modesetting driver, and the monitor output is connected to the nvidia device.
(I am not familiar with X11 so I do not know if that is correct)



Perhaps the smallest /etc/X11/xorg.conf that solves this problem is:
(BusID varies depending on the environment)
```
Section "ServerLayout"
    Identifier "layout"
    Screen 0 "nvidia"
    Inactive "intel"
EndSection

Section "Device"
    Identifier "intel"
    Driver "modesetting"
    BusID "PCI: 0 @ 0: 2: 0"
    Option "AccelMethod" "None"
EndSection

Section "Screen"
    Identifier "intel"
    Device "intel"
EndSection

Section "Device"
    Identifier "nvidia"
    Driver "nvidia"
    BusID "PCI: 1 @ 0: 0: 0"
    Option "ConstrainCursor" "off"
EndSection

Section "Screen"
    Identifier "nvidia"
    Device "nvidia"
    Option "AllowEmptyInitialConfiguration" "on"
    Option "IgnoreDisplayDevices" "CRT"
EndSection
```


The contents of my /etc/X11/xorg.conf are as follows.
```
# nvidia-xconfig: X configuration file generated by nvidia-xconfig
# nvidia-xconfig:  version 390.67  (buildmeister@swio-display-x64-rhel04-18)  Fri Jun  1 04:26:22 PDT 2018

Section "ServerLayout"
    Identifier     "layout"
    Screen      0  "nvidia" 0 0
    Inactive       "intel"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
EndSection

Section "InputDevice"
    # generated from default
    Identifier     "Keyboard0"
    Driver         "keyboard"
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 "Monitor"
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "Unknown"
    HorizSync       28.0 - 33.0
    VertRefresh     43.0 - 72.0
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "intel"
    Driver         "modesetting"
    Option         "AccelMethod" "None"
    BusID          "PCI:0@0:2:0"
EndSection

Section "Device"
    Identifier     "nvidia"
    Driver         "nvidia"
    BusID          "PCI:1@0:0:0"
EndSection

Section "Screen"
    Identifier     "intel"
    Device         "intel"
    Monitor        "Monitor0"
EndSection

Section "Screen"
    Identifier     "nvidia"
    Device         "nvidia"
#    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "AllowEmptyInitialConfiguration" "on"
    Option         "IgnoreDisplayDevices" "CRT"
    Option         "ConstrainCursor" "off"
    SubSection     "Display"
        Depth       24
        Modes      "nvidia-auto-select"
    EndSubSection
EndSection

```