Unable to get Modbus plugin working

Telegraf
1

I’m using Telegraf 1.17.2 in combination with Influx 1.8.4 and Grafana v7.4.0 on a Raspberry Pi 3 (Raspberry Pi OS Full 32-bit).

If I’m only including inputs.cpu , inputs.mem , … and similar, the entire setup works fine: I can show data from the inputs on the Grafana dashboards.

However, as a next step I wanted to include a Modbus TCP/IP communication to an energy meter. I can poll the energy meter with my computer and with my home automation system, so I’m sure this communication is working.

As soon as I modify the telegraf.conf to include the section below, I can’t restart the telegraf service anymore.

Here is the modification to the telegraf.conf file:

[[inputs.modbus]]
name = "device"
slave_id = 0
timeout = "1s"
controller = "tcp://192.168.17.219:502"
discrete_inputs = [{ name = "start",          address = [0]},]

When I check the status after restarting, it says the Telegraf service failed to start (code = exited, status = 1/failure).

These are only my first steps using Influx and Telegraf, so I might be overlooking something very obvious for all of you…

Thanks for your advice!

2

Start Telegraf manually from the command line and look at the logs, the command should look something like this:

telegraf -config telegraf.conf -test -debug
3

This is what the output looks like:

2021-02-09T12:35:56Z I! Starting Telegraf 1.17.2
2021-02-09T12:35:56Z I! Using config file: /etc/telegraf/telegraf.conf
2021-02-09T12:35:56Z E! [telegraf] Error running agent: Error loading config file 
/etc/telegraf/telegraf.conf: Error parsing data: line 315: invalid TOML syntax

Here is an extract from my config file, starting at line 312 :

discrete_inputs = [
     { name = "start",          address = [0]},
#     { name = "stop",           address = [1]},
#     { name = "reset",          address = [2]},
#     { name = "emergency_stop", address = [3]},
   ]

I’m running a Modbus TCP server simulator on my laptop, so I can manipulate all registers and I am sure they are available to read data from.

4

There is the answer, the config file (which is in TOML format) has an invalid syntax - probably in or around line 315

So I suspect a very simple error, e.g. a missing parenthesis, comma, or something like that.

Maybe leave out the last comma in the array?

5

I removed the three lines starting with the # and now it works…
Looks like you can’t keep commented lines inside the square brackets.

Thanks a lot for sharing your advice!

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