Fix for DWService Headless

If HDMI is plugged in at boot, the monitor works, and you can remote in.
If HDMI is unplugged at boot, the dummy display driver takes over, and you can remote in.

If the monitor is plugged in or unplugged after boot, you can use the shell connection to run vnc-display.sh to re-check for HDMI and configure the X-server accordingly.

• Step 1

apt install xserver-xorg-video-dummy
nano /etc/X11/xorg.conf.d/10-headless.conf

10-headless.conf's content:

Section "Monitor"
    Identifier  "VirtualMonitor"
    HorizSync   30.0-62.0
    VertRefresh 50.0-70.0
    Modeline "1920x1080" 172.80 1920 2040 2248 2576 1080 1081 1084 1118
EndSection

Section "Device"
    Identifier  "VirtualCard"
    Driver      "dummy"
    VideoRam    256000
EndSection

Section "Screen"
    Identifier  "VirtualScreen"
    Device      "VirtualCard"
    Monitor     "VirtualMonitor"
    DefaultDepth 24
    SubSection "Display"
        Depth   24
        Modes   "1920x1080"
    EndSubSection
EndSection

• Step 2:

nano /etc/systemd/system/vnc-display.service

vnc-display.service's content:

[Unit]
Description=Configure VNC dummy screen
After=systemd-user-sessions.service

[Service]
ExecStart=/usr/local/bin/vnc-display.sh

[Install]
WantedBy=multi-user.target

nano /usr/local/bin/vnc-display.sh

vnc-display.sh's content:

#!/bin/bash
# Check connected displays
HDMI_STATUS=`cat /sys/class/drm/card1-HDMI-A-1/status`
if [ $HDMI_STATUS = "connected" ]
then
  # If yes, disable the dummy driver configuration by renaming the file
  sudo mv /etc/X11/xorg.conf.d/10-headless.conf /etc/X11/xorg.conf.d/10-headless.conf.bak
else
  # If no, enable the dummy driver configuration by restoring the file
  sudo mv /etc/X11/xorg.conf.d/10-headless.conf.bak /etc/X11/xorg.conf.d/10-headless.conf
  sudo X :0 -config /etc/X11/xorg.conf.d/10-headless.conf &
fi
systemctl restart gdm3
systemctl daemon-reload

sudo chmod +x /usr/local/bin/vnc-display.sh
systemctl enable vnc-display.service