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MQTT Setup with Mosquitto

1. Install Mosquitto

sudo apt update
sudo apt install mosquitto mosquitto-clients

2. Start Broker

mosquitto        # Run in foreground  
mosquitto -d     # Run in background

Check status:

sudo systemctl status mosquitto

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3. Subscribe to Topic

In Terminal 1:

mosquitto_sub -h localhost -t "test/topic"

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4. Publish Message

In Terminal 2:

mosquitto_pub -h localhost -t "test/topic" -m "Hello MQTT!"

Message will appear in Terminal 1.

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5. Python (paho-mqtt)

Install:

pip install paho-mqtt

Publisher (publisher.py):

import paho.mqtt.publish as publish
publish.single("test/topic", "Hello from Python!", hostname="localhost")

Subscriber (subscriber.py):

import paho.mqtt.client as mqtt

def on_message(client, userdata, msg):
    print(f"{msg.topic}: {msg.payload.decode()}")

client = mqtt.Client()
client.connect("localhost", 1883, 60)
client.subscribe("test/topic")
client.on_message = on_message
client.loop_forever()