There was this recent question in which the OP used iot.eclipse.org as an MQTT broker. This server actually runs the latest released version of Mosquitto broker.

I have advised to check the connection on the broker side and I have checked what are the possibilities. I could not find a way to access the logs provided by iot.eclipse.org's Mosquitto broker.

Anyway does someone know a way to get information about my client from a public broker?

1 Answer 1


Subscribing to $SYS/# topic will provide some information about the broker and maybe about the clients. Detailed description of these items can be found here.

There are three main categories to highlight:

  • Static Topics: Messages on a static $SYS topic are not required to be sent on every $SYS topic update interval. These messages are sent once the broker subscribes to the $SYS topic
  • Required Topics: Every broker which claims to support the $SYS topics should support these topics.
  • Optional Topics: A broker implementation may decide if it implements an optional topic.

The one needed to for client status check falls into the "Optional Topics" category.

  • $SYS/clients/[client-id]/ip

  • $SYS/clients/[client-id]/connectedtime

Also, based on this description about Mosquitto's logging, the console log can be logged into a topic ($SYS/broker/log/#) as well.

Two common question are:

  • Can I see all connected clients?
  • Can I list all topics?

The broker doesn’t let you do this directly but by enabling logging to a a topic and monitoring the topic with an MQTT client you can get a good idea.

Probably for privacy and/or security reasons iot.eclipse.org does not have topics for these log entries.

  • No topics for $SYS/clients/

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  • No topics for $SYS/broker/log/#

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For other public brokers these optional topics may exist, you can check them easily with mqtt-spy for example.

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