integrated graphic card as primary monitor + nvidia gtx 1080ti for gpu computing

hi folks, im having some trouble on configuring nvidia-settings in xorg. i have i7 8700k and 2x gtx 1080tis.
i would like to use integrated graphic card of i7 8700k as primary monitor where i can read and do my research stuff, 2 1080ti should only do gpu computing. Ubuntu 16.04 is the os, nvidia 390 driver is insalled. in bios integrated graphic card is enabled (igpu) , everything works fine. i have primary monitor and 2x 1080ti do gpu computing on 100%, accept i cant set --cool-bits=28 in nvidia-settings which lets me overclocking and fan speed regulation of both cards. my xorg.conf gets overwritten to this:

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

Section “Device”
Identifier “nvidia”
Driver “nvidia”
BusID “PCI:2@0:0:0”
Option “ConstrainCursor” “off”
EndSection

Section “Screen”
Identifier “nvidia”
Device “nvidia”
Option “AllowEmptyInitialConfiguration” “on”
Option “IgnoreDisplayDevices” “CRT”

nvidia-settings -a “[gpu:0]/GPUFanControlState=1” -a “[fan:0]/GPUTargetFanSpeed=50” gives me:
ERROR: Error assigning value 50 to attribute ‘GPUTargetFanSpeed’ (men:0[fan:0]) as specified in assignment ‘[fan:0]/GPUTargetFanSpeed=50’ (Unknown Error).

So i cant regulate fan speed of both 1080tis or overclock them. Any help?

thanks
sb

In fact, you’re using one 1080 for graphics currently, the intel is just a slave output using PRIME. The xorg.conf gets created on every DE start by Ubuntu’s gpumanager. You can prevent that by using the kernel parameter
nogpumanager
If you really want to use just the intel for graphics, that’s not easy to achieve with 16.04 due to the way the drivers are packaged there. You would have to upgrade to 18.04 and then carefully crate an xorg.conf.