Troubleshoot Modbus RTU device connection

What logs should I be looking at to troubleshoot Modbus RTU device connection issues?

I am running Ignition 8.0.5 on Ubuntu 18.04 and attempting to connect to a Modbus RTU device however connection status just flips between connecting and disconnected.

I have the Serial Support Gateway module installed and have created a device of type “Modbus RTU” (was surprised that there is no field to enter a Modbus address).

I looked at the wrapper.log file but there doesn’t appear to be any mention of the device name in question.

I have confirmed that the computer itself is able to reach the modbus RTU device (outside Ignition) using modpoll (a handy command line modbus scanner).

“Not Connected” with the RTU driver just means it’s failing to open whatever serial port you configured.

You’re running on Linux, so there’s probably some group whatever user you run the Ignition gateway needs to be a part of to have access to the serial ports. I think it’s usually the “dialout” group.

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Thank you, yes the membership in the “dialout” group did resolve the issue.
However I am still interested on where I would look to find some log message that indicated the serial port could not be opened or whatever the issue happens to be on a given day. As helpful as this forum is I would like to get better at diagnosing my own issues.

What logs (etc.) should I be looking at to find detail on device connection issues in general?

You’d have to change the log level for Modbus driver to DEBUG to see the messages. Searching for “drivers.Modbus” on the log levels page in the gateway should show the loggers for any Modbus variant drivers you have.