RabbitMQ with MQTT sends message on connect - rabbitmq

Question

I'm using mqtt-launcher (https://github.com/jpmens/mqtt-launcher) to execute commands when a certain MQTT message with the payload "0" was received.
Here is the config
logfile = '/home/user/mqtt-launcher/logfile'
mqtt_broker = 'broker' # default: 'localhost'. If using TLS, this must be set to the domain name signed by$
mqtt_port = 1883 # default: 1883
mqtt_clientid = 'mqtt-launcher-1'
mqtt_username = ''
mqtt_password = ''
mqtt_tls = None # default: No TLS
topiclist = {
# topic payload value program & arguments
"channel/dostuff" : {
'0' : [
'/usr/bin/ssh',
'-i',
'/home/user/.ssh/privatekey',
'user#host',
'script.sh'
]
}
}
Everytime, I start the python script, the shell script is executed twice.
But I want it to execute only once if the MQTT message with the payload "0" is sent.
I made sure the queue which is implicitly created when subscribing was empty before by purging it, then starting mqtt-launcher but still the script is execute twice after the program connected.
When I run user#localhost:~$ mosquitto_sub -h broker -p 1883 -t 'channel/dostuff' -v -u 'user' -P 'mysecurepassword' I get channel/dostuff 0
I'm not familiar with mosquitto but I think that this means I receive a message, right?
I turned of the retain option, restarted openHAB and RabbitMQ, but still the message is sent. Here is the openHAB mqtt.cfg:
broker.url=tcp://broker:1883
broker.user=openhab
broker.pwd=mysecurepassword
broker.qos=1
broker.retain=false
broker.async=false

Answer 1

You have published a message with the payload 0 and the retained bit set.
This means that when ever a client subscribes to that topic the last message with the retained bit set will be delivered to that client.
You can clear the retained message by publishing a message with the retained bit set and a null payload to the same topic. You can do this with the mosquitto_pub command as follows:
mosquitto_pub -t "channel/dostuff" -u 'user' -P 'password' -r -n
You should make sure what ever you are using to publish the message normally is not setting the retained bit.