How to setup a dummy display in ubuntu?

ref: https://techoverflow.net/2019/02/23/how-to-run-x-server-using-xserver-xorg-video-dummy-driver-on-ubuntu/

https://tecadmin.net/how-to-install-xrdp-on-ubuntu-20-04/

http://cosmolinux.no-ip.org/raconetlinux2/vnc.html

https://support.anydesk.com/zh-cn/knowledge/command-line-interface-for-linux

to setup the dummy display:-

sudo apt install xserver-xorg-video-dummy

save the following lines as dummy-1080.conf

 Section "Monitor"

  Identifier "Monitor0"

  HorizSync 28.0-80.0

  VertRefresh 48.0-75.0

  # https://arachnoid.com/modelines/

  # 1920x1080 @ 60.00 Hz (GTF) hsync: 67.08 kHz; pclk: 172.80 MHz

  Modeline "1920x1080_60.00" 172.80 1920 2040 2248 2576 1080 1081 1084 1118 -HSync +Vsync

EndSection

Section "Device"

  Identifier "Card0"

  Driver "dummy"

  VideoRam 256000

EndSection

Section "Screen"

  DefaultDepth 24

  Identifier "Screen0"

  Device "Card0"

  Monitor "Monitor0"

  SubSection "Display"

    Depth 24

    Modes "1920x1080_60.00"

  EndSubSection

EndSection

to run the dummy display:-

sudo X -config dummy-1920x1080.conf

to start a program in a display:-

DISPLAY=:0 firefox

to start a program in a specific display:-

sudo X :7 -config dummy-1920x1080.conf

DISPLAY=:7 firefox

(you will see error if other display already used that number)

to stop the current display service:-

sudo service gdm stop

sudo service lightdm stop

to get the list of current display:-

ps aux | grep Xorg