Linux - Screen Control

Proven on:

12 (bookworm)

This little setup allows for remote control (via MQTT) of the screen(s) of Linux-based computers.

Specifically set up for all-in-one machines & laptops since these are a little difficult to shut off the screen without shutting down the machine itself.

The Script

• sudo apt install vbetool

The following script needs to run as root...

• sudo vi /usr/local/bin/screenremote.py

#!/usr/bin/env python

import paho.mqtt.client as mqttClient
import time
import os
import subprocess
import socket

###################################################################################################

hostname = socket.gethostname()
broker_address = "skynet"
port = 1883
topic = hostname + "/#"
user = "user"
password = "password"
client = mqttClient.Client(hostname + "control")
client.username_pw_set(user, password=password)

###################################################################################################
##    Broker Connection    ##
###################################################################################################

Connected = False

def on_connect(client, userdata, flags, rc):
    global Connected
    if rc == 0:
        print("           HostName: ", hostname)
        print("Connected to broker: ", broker_address)
        print("      Subscribed to: ", topic)
        print()
        Connected =True
    else:
        print("Connection failed")
        Connected =False

###################################################################################################
##    Message Handling    ##
###################################################################################################

def on_message(client, userdata, message):
    print( " Received message: " + str(message.payload.decode("utf-8")))
    print( "         on topic: " + message.topic)
    #print( "         with QoS: " + str(message.qos))

    time.sleep(1)

### Display control (turn the screen on or off...)
    if message.topic == hostname + "/display":
        command = "/usr/sbin/vbetool dpms " + str(message.payload.decode("utf-8"))
        print( command )
        os.system(command)
### Audio control (something for th future...)
    elif message.topic == hostname + "/audio":
        print("audio stuff")
### Not any sort of valid topic...
    else:
        print("Not Important to us...")

    print()

###################################################################################################

client.on_connect = on_connect
client.on_message = on_message

client.connect(broker_address, port=port)
client.loop_start()

while Connected != True:
    time.sleep(0.1)

client.subscribe(topic)

try:
    while True:
        time.sleep(1)

except KeyboardInterrupt:
    print( "exiting" )
    client.disconnect()
    client.loop_stop()

• sudo chmod +x /usr/local/bin/screenremote.py

This will respond to MQTT messages:

• HOSTNAME/display on
• HOSTNAME/display off

The Service

It works as a systemd service

• sudo vi /etc/systemd/system/remote-screen-control.service

[Unit]
Description=Watch for MQTT messages to turn screen on/off
Documentation=https://wiki.nerdmage.ca/index.php/Linux_-_Screen_Control
After=multi-user.target network.target

[Service]
ExecStart=<code>/usr/local/bin/screenremote.py</code>
Type=simple
Restart=on-failure

[Install]
WantedBy=multi-user.target

• sudo systemctl daemon-reload

• sudo systemctl enable remote-screen-control.service
• sudo systemctl start remote-screen-control.service
• sudo systemctl status remote-screen-control.service

Notes

non vbetool capable systems

For some systems, vbetool fails.

In this case, if the system has X installed (i.e.: it has a GUI), xset might do the job in its place.

• xset -display :0.0 dpms force off
• xset -display :0.0 dpms force on

As of yet... No solution for systems without X.

Python Weirdness

Sometimes, Python & it's tools & modules are a little problematic.

Installing Python3 & paho-mqtt directly will force this to work. (&, of course, you should force it to be Python3...)

• sudo apt install python-is-python3 python3-paho-mqtt

Broker temporarily offline causes failure

If this service loses contact with the broker, it does not try to find it again. Must find a solution to this...

Meanwhile:

• sudo systemctl restart remote-screen-control.service

gets it back online.