MQTT connection refused when trying to connect from remote machine - mqtt

Question

I am trying to connect to a mosquitto broker, across linux clients. I can get everything working from the local machine, but when trying to connect from another machine I get the error ConnectionRefusedError: [Error 111] Connection refused.
Here is the process:
On the local machine, I install mostquitto, stop the service and start a live instance:
#Terminal 1
sudo service mosquitto stop
mosquitto
I then try and pub and sub, from distinct terminals on that machine:
#Terminal 2
mosquitto_sub -t 'test'
#Terminal 1 shows new connection
#Terminal 3
mosquitto_pub -t 'test' -m 'Hello, world!'
#Terminal 1 shows new connection, and then disconnect.
#Terminal 2 shows 'Hello, world!'
I now try to connect from a remote machine. First I edit the mosquitto config file to allow unauthorized connections:
sudo nano /etc/mosquitto/mosquitto.conf
#Add the following:
listener 1883
allow_anonymous true
protocol mqtt
I note that the mosquitto logs previously showed only local connections allowed, after editing the config file and restarting, the logs no longer show that message.
Then I install paho-mqtt on another machine. I run the following python script:
import paho.mqtt.client as mqtt
client = mqtt.Client('131')
client.connect('192.168.0.146') #The IP of machine 1, running the broker where the code above ran correctly across the terminals
I get the error mentioned above:ConnectionRefusedError: [Error 111] Connection refused. The mosquitto instance on machine 1 shows nothing. Logs show nothing.
I can't work out what is going on. I have read every question on SO that I can find. Nothing goes beyond changing the config file. I have tried running the broker on two machines (laptop and pi). I have tried connecting from multiple different sources: esp32 board, different laptop and pi. Nothing works. I can only assume there is some network-wide problem, but my network isn't isolating devices as I ssh into my pi all the time and have wifi lights and switches running on the LAN.
If anyone can help me troubleshoot I would be very grateful.

Answer 1

Mosquitto will not pick up a default configuration file, you must always pass the configuration file with the -c command line argument or it will fall back to the baked in config (that will only listen on localhost)
The service includes -c /etc/mosquitto/mosquitto.conf to force it to use the config file.