How to measure a Raspberry Pi's temperature and CPU frequency with Telegraf

After 3 years of service, my Raspberry Pi’s filesystem finally got corrupted. I expected it to crash earlier, but it lasted for quite a while!

Even if I had backups, I did have to reinstall it from scratch. I was using Munin to monitor my Raspberry Pi, and I think it’s a good solution for this kind of device because it’s lightweight and performs very little I/O.

Anyway I decided to upgrade my monitoring stack, as on the rest of my infrastructure, with the Telegraf - InfluxDB - Grafana (TIG) stack. I used an USB key (🤷🏻‍♂️) as the storage for InfluxDB. We’ll see how it runs in the long term!

I used the munin-rpi-temp plugin to monitor my RPi’s CPU temperature and frequency. I wanted to have that on the new stack too, so let’s see how I proceeded.

The probes #

The 2 scripts are very simple.

pi@raspberrypi ~> cat /usr/local/bin/rpi-temp
#!/bin/bash

awk '{print $1/1000}' /sys/class/thermal/thermal_zone0/temp

pi@raspberrypi ~> cat /usr/local/bin/rpi-freq
#!/bin/bash

echo "$(( $(cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq)*1000 ))"

Make sure the 2 scripts are executable.

In rpi-temp we divide the output by 1000 to get a result in °C. We use awk in order to have a float.

In rpi-freq with multiply the output by 1000 to get Hertz. It’s an integer so no need for awk.

The Telegraf inputs #

Next, we need Telegraf to execute the scripts and get the output.

[[inputs.exec]]
  commands = ["/usr/local/bin/rpi-temp"]
  name_override = "rpi_temp"
  data_format = "value"
  data_type = "float"

[[inputs.exec]]
  commands = ["/usr/local/bin/rpi-freq"]
  name_override = "rpi_freq"
  data_format = "value"
  data_type = "integer"

Since the output is a simple number, we can use a value as data_format. See the exec plugin documentation for more information.

Grafana visualisation #

I made 2 simple panes:

Here is the JSON for the frequency panel and for the temperature panel.

Enjoy!