Add dummy screen on startup if no monitor is plugged in

Dockerfile

@@ -179,6 +179,7 @@ RUN \
             xserver-xorg-input-libinput \
             xserver-xorg-legacy \
             xserver-xorg-video-all \
+            xserver-xorg-video-dummy \
             xvfb \
     && \
     echo "**** Section cleanup ****" \

overlay/etc/cont-init.d/70-configure_xorg.sh

@@ -85,6 +85,13 @@ function configure_x_server {
     else
         echo "Leaving evdev inputs disabled"
     fi
+
+    monitor_connected=$(cat /sys/class/drm/card*/status | awk '/^connected/ { print $1; }' | head -n1)
+    if [[ "X${monitor_connected}" == "X" ]]; then
+        echo "No monitors connected. Installing dummy xorg.conf"
+        # Use a dummy display input
+        cp -fv /templates/xorg/xorg.dummy.conf /etc/X11/xorg.conf
+    fi
 }
 
 if ([ "${MODE}" != "s" ] && [ "${MODE}" != "secondary" ]); then

overlay/templates/xorg/xorg.dummy.conf

@@ -0,0 +1,21 @@
+Section "Device"
+    Identifier      "Configured Video Device"
+    Driver          "dummy"
+EndSection
+
+Section "Monitor"
+    Identifier      "Configured Monitor"
+    HorizSync       31.5-48.5
+    VertRefresh     50-70
+EndSection
+
+Section "Screen"
+    Identifier      "Default Screen"
+    Monitor         "Configured Monitor"
+    Device          "Configured Video Device"
+    DefaultDepth    24
+    SubSection      "Display"
+    Depth           24
+    Modes           "1600x900"
+    EndSubSection
+EndSection