MQTT retaining unwanted messages

General
1

I have a simple flow, Ubuntu server, 2 Pi-4 Clients. Communication via MQTT between clients and server.
On the server I set the MQTT out node to "Retain Message", so when the client would start it would get the last message. It worked. I no longer need this, but even though I unclicked "Retain Messages", then clients are always pulling a message.

Is there some cache I need clear or what have I missed!!!

Thanks in advance.

2

To clear a retained message on a topic, you need to publish an empty payload with the retain flag set.

1 Like
3

Install the mosquitto-clients package. Then you can send the empty message to your server with the retain bit set from the command line:

mosquitto_pub -h your_server -t "yourTopic" -m "" -r

I find this easier and quicker than doing something with a flow.

4

Using MQTT explorer, you can select the retained item from the tree & simply click the delete button.

1 Like
5

Is MQTT explorer in Node-Red or is it an external app?

6

External application for browsing / viewing your MQTT broker (very professional & user friendly)

7

Wow, Very good program, handy to have, serious information in it. Thank you.

8

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