Paraphraser/Logging CPU Temperatures.md

## Logging CPU Temperatures.md

      
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              Logging CPU Temperatures.md
            
          
    IOTstack Tutorial: Logging CPU Temperatures

introduction

This gist answers a Discord question. It explains my approach to collecting CPU temperatures by sending the data as an MQTT payload.

I like to think of this approach as working with the MING (Mosquitto, InfluxDB, Node-RED, Grafana) paradigm rather than fighting against it (eg using approaches like SSH calling out of the Node-RED container).

The approach is not tied to the Raspberry Pi that is running IOTstack. If you have several Raspberry Pis, they can all log their temperatures to the Raspberry Pi running IOTstack using exactly the same mechanism.

The concept can also be extended to other types of computer. I'm using it to collect CPU temperatures for macOS systems too.

if you are a Windows user…

Be very careful about copying and pasting text from this gist. Unless you take precautions, Windows will add its CR+LF line-endings and those will cause problems.
collection script


Assumed path name: ~/.local/bin/publish_rpi_temperature


Script content:
 #!/usr/bin/env bash
 
 mkdir -p ~/Logs
 
 mosquitto_pub -h mosquitto.mydomain.com -t "/mytopic/computer/pi" -m "{\
 \"host\": \"$HOSTNAME\", \
 \"temp\": $(vcgencmd measure_temp | cut -c 6-9)\
 }"
The script assumes the Mosquitto clients are installed:
 $ sudo apt install mosquitto-clients
You will need to customise:

The target host "mosquitto.mydomain.com" using the fully-qualified domain name, or host name, or multicast DNS name, or IP address of the Raspberry Pi running IOTstack.
The topic "/mytopic/computer/pi". Although I did not need to use it, I originally added the "/pi" suffix to the topic string in case I needed to know the type of computer that had generated the payload. My Raspberry Pi's use "/pi"; my macOS machines "/mac".

This script is specific to the Raspberry Pi. To port the script to a different type of host you will need to:

find an alternative for vcgencmd; and
make sure that the HOSTNAME environment variable contains a sensible value (eg on macOS, it contains the fully-qualified domain name rather than the host name).


The MQTT messages sent by this script look like this:
/mytopic/computer/mac {"host": "bauxite", "temp": 46.5}
/mytopic/computer/mac {"host": "magnetite", "temp": 28.8}
/mytopic/computer/mac {"host": "gravel", "temp": 35.2}
/mytopic/computer/mac {"host": "marble", "temp": 34.2}
/mytopic/computer/pi {"host": "octopi", "temp": 41.3}
/mytopic/computer/pi {"host": "new-dev", "temp": 43.3}
/mytopic/computer/pi {"host": "iot-hub", "temp": 46.2}
/mytopic/computer/pi {"host": "sec-dev", "temp": 45.2}

scaffolding

$ mkdir -p ~/Logs
The collection script does not normally produce output unless there is an error condition. If the script does not appear to be working, the place to start looking is:
$ tail ~/Logs/publish_rpi_temperature.log

cron job


Preamble (should be common to all crontab files):
 SHELL=/bin/bash
 HOME=/home/pi
 PATH=/home/pi/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin


Event trigger:
 # report system temperature every 5 minutes 
 */5	*	*	*	*	publish_rpi_temperature >>./Logs/publish_rpi_temperature.log 2>&1


influx database

The InfluxDB database needs to be initialised before you can write to it. In this example, the database name is "computer".
$ docker exec -it influxdb influx
> create database computer
> exit
$
Within the "computer" database, each host computer logging temperatures generates its own series:
temperature,system=«hostname»

where "«hostname»" corresponds with the "host" key in the MQTT payload.
three-node flow


A Node-RED three-node flow handles the messages:


an MQTT-in node subscribing to the appropriate topic. In this example the topic is "/mytopic/computer/+" where "+" is a single-level wildcard.


a Change node to prepare the payload for insertion into InfluxDB:
 [
     {
         "temp": payload.temp
     },{
         "system": payload.host
     }
 ]
In words:

temperature is added as a field (data);
the name of the host reporting the temperature is added as a tag (metadata)


an InfluxDB-out node inserts the prepared payload into the database named "computer".


Given the incoming MQTT message:
/mytopic/computer/pi {"host": "iot-hub", "temp": 46.2}

The overall effect of the flow is:
> USE computer
> INSERT temperature,system='iot-hub' temp=46.2
> exit

You should be able to copy the JSON content below and use the "Import" command in the main menu (three horizontal bars "≡" at the top, right of the Node-Red window) to create a new flow containing the three nodes.

Depending on how your system is set up, the flow may need some tinkering before it works.

[
    {
        "id": "cc5ffba5.fdc7c8",
        "type": "tab",
        "label": "CPU Temperatures",
        "disabled": false,
        "info": ""
    },
    {
        "id": "796d8452.225294",
        "type": "change",
        "z": "cc5ffba5.fdc7c8",
        "name": "prepare fields",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "[\t    {\t        \"temp\": payload.temp\t    },{\t        \"system\": payload.host\t    }\t]\t",
                "tot": "jsonata"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 340,
        "y": 100,
        "wires": [
            [
                "d27128f3.4050c8"
            ]
        ]
    },
    {
        "id": "d27128f3.4050c8",
        "type": "influxdb out",
        "z": "cc5ffba5.fdc7c8",
        "influxdb": "626e8bc5.4c702c",
        "name": "write to InfluxDB",
        "measurement": "temperature",
        "precision": "",
        "retentionPolicy": "",
        "database": "",
        "retentionPolicyV18Flux": "",
        "org": "",
        "bucket": "",
        "x": 570,
        "y": 100,
        "wires": []
    },
    {
        "id": "39543010.e0258",
        "type": "mqtt in",
        "z": "cc5ffba5.fdc7c8",
        "name": "/mytopic/computer/+",
        "topic": "/mytopic/computer/+",
        "qos": "2",
        "datatype": "json",
        "broker": "c5d29fb5.89907",
        "x": 130,
        "y": 100,
        "wires": [
            [
                "796d8452.225294"
            ]
        ]
    },
    {
        "id": "626e8bc5.4c702c",
        "type": "influxdb",
        "hostname": "influxdb",
        "port": "8086",
        "protocol": "http",
        "database": "computer",
        "name": "",
        "usetls": false,
        "tls": "",
        "influxdbVersion": "1.x"
    },
    {
        "id": "c5d29fb5.89907",
        "type": "mqtt-broker",
        "name": "Docker MQTT",
        "broker": "mosquitto",
        "port": "1883",
        "clientid": "",
        "usetls": false,
        "compatmode": false,
        "protocolVersion": 4,
        "keepalive": "60",
        "cleansession": true,
        "birthTopic": "",
        "birthQos": "0",
        "birthRetain": "false",
        "birthPayload": "",
        "closeTopic": "",
        "closeQos": "0",
        "closeRetain": "false",
        "closePayload": "",
        "willTopic": "",
        "willQos": "0",
        "willRetain": "false",
        "willPayload": ""
    }
]
example data

$ docker exec -it influxdb influx -precision=rfc3339
Connected to http://localhost:8086 version 1.8.9
InfluxDB shell version: 1.8.9

> use computer
Using database computer

> show series
key
---
temperature,system=bauxite
temperature,system=gravel
temperature,system=iot-hub
temperature,system=magnetite
temperature,system=marble
temperature,system=new-dev
temperature,system=octopi
temperature,system=sec-dev
temperature,system=sjgair

> select * from temperature where time > now() - 10m tz('Australia/Sydney')
name: temperature
time                                system    temp
----                                ------    ----
2021-08-22T23:40:00.271972208+10:00 marble    35.2
2021-08-22T23:40:00.674021388+10:00 magnetite 29.6
2021-08-22T23:40:00.937395236+10:00 gravel    36.6
2021-08-22T23:40:01.065496792+10:00 bauxite   46
2021-08-22T23:40:01.220100822+10:00 sec-dev   46.7
2021-08-22T23:40:01.87568606+10:00  iot-hub   47.7
2021-08-22T23:40:01.892511832+10:00 octopi    40.8
2021-08-22T23:40:02.021640681+10:00 new-dev   42.8
2021-08-22T23:45:00.210631999+10:00 magnetite 28.9
2021-08-22T23:45:00.453033759+10:00 gravel    35.6
2021-08-22T23:45:00.545580449+10:00 bauxite   46.4
2021-08-22T23:45:00.840558319+10:00 marble    35.6
2021-08-22T23:45:01.133290607+10:00 new-dev   43.3
2021-08-22T23:45:01.319572925+10:00 sec-dev   46.2
2021-08-22T23:45:01.977801647+10:00 iot-hub   46.7
2021-08-22T23:45:01.99638355+10:00  octopi    41.3

> exit
$
grafana visualisation

Shows a mixture of Raspberry Pi and macOS CPU temperatures.