Handle several monitor hotplug efficiently

0_monitor_hotplug.md

Description

Scripts to configure monitor hotplug. It is useful on a laptop that can be connected to some external screens.

Issues

In some cases, when monitor configuration changes plank position is not updated accordingly. A workaround consist in restarting plank. It is killed from monnitor_hotplug.sh script and automatically restarted using plank_forever.sh script that is started from xfce startup application menu.

References

• Systemd units & background processes

95-monitor-hotplug.rules

#/etc/udev/rules.d/95-monitor-hotplug.rules
ACTION=="change", KERNEL=="card[0-9]", SUBSYSTEM=="drm", RUN+="/usr/bin/systemctl start monitor_hot_plug.service"

monitor_hot_plug.service

#/etc/systemd/system/monitor_hot_plug.service
[Unit]
Description=Monitor hotplug

[Service]
Type=simple
RemainAfterExit=no
User=remi
ExecStart=/usr/local/bin/monitor_hotplug.sh

[Install]
WantedBy=multi-user.target

monitor_hotplug.sh

#!/bin/bash

######################################
## /usr/local/bin/hotplug_monitor.sh
######################################
X_USER=remi
MONITOR_0='eDP-1'
MONITOR_2='VGA'
XFCE_PANEL_NAME='panel-1'

export DISPLAY=:0
export XAUTHORITY=/home/$X_USER/.Xauthority
export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus

function add_monitor()
{   
  echo "connect monitor $1" 
  #dual monitor - $1 on right - xfce panel on left of MONITOR_0
  xrandr --output $1 --right-of $MONITOR_0 --preferred  --output $1 --primary >> /tmp/screen

  #Set xfce panel on primary monitor
  # Either use soft solutions but sometimes it does not work
  #xfconf-query -v -c xfce4-panel -p /panels/${XFCE_PANEL_NAME}/output-name -s $1 
  # Or restart panel 
  xfce4-panel -r
  
  #reload conky
  killall -s SIGUSR1 conky    

  # kill plank - it will be automatically restarted by plank_forever.sh script
  killall -s SIGHUP plank
}

function use_laptop_monitor(){
  xrandr --output $MONITOR_0
  #Set xfce panel on MONITOR_0
  # Either use soft solutions but sometimes it does not work
  #xfconf-query -c xfce4-panel -p /panels/${XFCE_PANEL_NAME}/output-name -s $MONITOR_0
  # Or restart panel 
  xfce4-panel -r

  #reload conky
  killall -s SIGUSR1 conky

  # kill plank - it will be automatically restarted by plank_forever.sh script
  killall -s SIGHUP plank
}

# card name can change : https://unix.stackexchange.com/questions/364246/nondeterministic-graphic-cards-device-names
# do not use /sys/class/drm/.../status to get connected devices, they have a different name in xrandr and sys (but we can identify it using edid)

nb_connected_screens_sys_cmd="find /sys/class/drm/*/status -type f -exec grep  -ERi "^connected$" {} \; | grep -c "connected""
nb_connected_screens_sys=$(eval $nb_connected_screens_sys_cmd)
nb_connected_screens_cmd="xrandr |grep -E ' connected ' | grep -c "^.*$""
nb_connected_screens=$(eval $nb_connected_screens_cmd)

while [ "$nb_connected_screens_sys" -ne "$nb_connected_screens" ]
do
  echo "Number of connected screen at sys level : $nb_connected_screens_sys - at xrandr level : $nb_connected_screens"
  nb_connected_screens_sys=$(eval $nb_connected_screens_sys_cmd)
  nb_connected_screens=$(eval $nb_connected_screens_cmd)
  sleep 0.2
done

echo "number of connected screens = $nb_connected_screens"

# a screen has been removed
if [ $nb_connected_screens -eq 1 ]
then
  use_laptop_monitor
  # a screen has been added
elif [ $nb_connected_screens -eq 2 ]
then
  add_monitor $(xrandr |grep -v 'eDP-1' | grep -E ' connected ' | awk -F ' ' '{print $1}') 
else
  echo "Cannot handle $nb_connected_screens"
fi
exit 0

plank_forever.sh

#!/bin/sh
while true
do 
  if ! pgrep plank
  then
    echo 'start plank'
    plank > /dev/null
  fi
  sleep 1
done