mjhjmtu

I've read the answers to this question but I don't have ACPI, the /sys/class/drm/card0-socket/status method does not work and the xrandr method chokes my CPU. udevadm monitor shows nothing when (un)plugging the monitor.

I've got a circa 2013 Lenovo ThinkPad w530 with nVidia quadro something. I'm running Lubuntu 18.04 with the nouveau driver. The monitor is a 27" Philips 271S. I'm using a VGA cable.

How do I do detect monitor (un)plugging?

I resorted to polling for the external screen EDID.
I installed the read-edid package, added a line in visudo

%sudo ALL=(ALL:ALL) NOPASSWD:/usr/bin/get-edid

to allow passwordless get-edid and used the following loop:

#!/bin/bash
# edid_based_automatic_display_loop.sh
export NEW_CONNECTION=1
export NEW_DISCONNECTION=1

while :
do
 sleep 1
 sudo get-edid 2>/dev/null|parse-edid 2>/dev/null|grep "PHL 271S7Q">/dev/null
 _DISCONNECTED=`echo $?`
 # echo "DISCONNECTED $_DISCONNECTED"
 if [ $_DISCONNECTED = "0" -a $NEW_CONNECTION = "1" ] ; then
 export NEW_DISCONNECTION=1;
 export NEW_CONNECTION=0;
 bash /home/bruno/.screenlayout/only_external.sh
 elif [ $_DISCONNECTED = "1" -a $NEW_DISCONNECTION = "1" ] ; then
 export NEW_DISCONNECTION=0;
 export NEW_CONNECTION=1;
 bash /home/bruno/.screenlayout/only_laptop.sh
 fi
done