Logging and debugging#

MQTT.fx writes a log you can read inside the app (the Log tab) and to a log file on disk. The log is the first place to look when a connection, subscription, or script does not behave as expected.

The Log tab#

The Log tab shows MQTT.fx's live log output in a console. Use Clear Console to empty it. The number of characters the console keeps is bounded by the Output Console Max. Characters setting (see Settings) so the console cannot grow without limit.

The log file on disk#

MQTT.fx also writes a log file named mqttfx.log in the MQTT.fx working directory (logging uses Log4j 2):

The log file is the best artifact to attach when reporting a problem to support — it contains more detail than fits on the status line, including the connection options used and the underlying error for failed connections or TLS handshakes.

Using the log to debug#

• Connection problems — the log shows why a connect failed (unreachable host, TLS error, authentication rejected). See Troubleshooting.
• TLS problems — certificate/trust errors appear here in full; the status line only summarizes them. See TLS and security.
• Scripts — logger.* calls from a script are written to the log, and output.print(...) goes to the Scripts console.

Related#

• Settings
• Troubleshooting
• Scripting
• Appendix: file locations