Python Script that should feed node-red via MQTT does not start as a service

General
1

Hi all,

I have one raspberry pi running with node-red installed on - everthing is fine.
In parallel there is a mosquitto mqtt broker running - minor issues, but basically fine

Next I would like to automatically run a Python Script that reads data from Powermeter via serial bus, converting the data into MQTT packages, forwarding them to NodeRed.

Whenever I start the script manually, it works fine
When I start the script as a service - following this how-to,

Now that we have our service we need to activate it:

sudo chmod 644 /lib/systemd/system/hello.service
chmod +x /home/pi/hello_world.py
sudo systemctl daemon-reload
sudo systemctl enable hello.service
sudo systemctl start hello.service

it does not start and a status query gives the following error message

image
image963Ă—483 95.6 KB

If I manually start the service with

sudo systemctl start stromzaehler.service

it again works fine.

image
image773Ă—225 31.4 KB

Does it make sense to wait for a certain time after a raspi restart to run this script ?
Or is there another error ?

2

It isn't very clear exactly what problem you are having. Do you mean that the service starts ok when started manually with systemctl, but not when starting automatically on boot?

3

Yes, it does not start during/shortly after bootup (what I expect it to do with these commands):
Now that we have our service we need to activate it:

sudo chmod 644 /lib/systemd/system/stromzaehler.service
chmod +x /home/pi/stromzaehler.py
sudo systemctl daemon-reload
sudo systemctl enable stromzaehler.service
sudo systemctl start stromzaehler.service

But when I start it manually as soon as the raspi is up and running, it starts fine without any issues.

4

Is the python posting to the local mosquitto on that machine?

If you stop mosquitto and then manually start your script does it fail?

5

Yes it does

The script exits with a "broker not found" error when I turn off mosquitto

6

what is the exact code of your service file?

7

Are you waiting for the network to be up in the service script?

8

I use a quick'n'dirty approach to start the Python code that runs my security DVR AI system. I simply use an inject node set to "once on startup" to trigger ab exec node that launches my Python code with node-red running as a service on boot.

1 Like
9

If the python code does not need to be running when node-red is not running, and it can be run as the node-red user, then indeed, starting it from an exec node is a perfectly good way to go.

10

that sounds like a really good idea - this gives me full control on the script-schedule

is it difficult to start a Python Script from within Node-Red ?

11

No it is quite easy, I usually make a shell script and put in it the commands I need to set things up,like changing to a certain directory, initializing the OpenVINO support, etc. Gives me tremendous flexibility.

Here is a sample script I use to start my AI code:

#!/bin/bash
# edit for directory of AI code and model directories,
# Making one symlink beats changing every script and/or multiple node-red nodes
# make symlink to A directory, for example:
# sudo ln -s /home/wally /home/AI
cd /home/AI/AI

export DISPLAY=:0
export XAUTHORITY=/home/AI/.Xauthority

# should be clean shutdown
/usr/bin/pkill -2 -f "AI.py" > /dev/null 2>&1
sleep 5

# but, make sure it goes away before retrying
/usr/bin/pkill -9 -f "AI.py" > /dev/null 2>&1
sleep 1

export PYTHONUNBUFFERED=1
# necessary only if using OpenVINO cv2
##source /opt/intel/openvino/bin/setupvars.sh
##python3 AI_dev.py -nNCS 1 -nTPU 1 -nt 1 -d 1 -cam onvif.txt  >> ../detect/`/bin/date +%F`_AI.log 2>&1 &
python3 AI.py -d 0 -nTPU 1 -y4v -cam 6onvif.txt  2>/dev/null >> ../detect/`/bin/date +%F`_AI.log &

Here is the exec node for it:

[
    {
        "id": "be9701c3.1cb4b",
        "type": "inject",
        "z": "619024c0.35593c",
        "name": "Launch AI",
        "topic": "",
        "payload": "",
        "payloadType": "date",
        "repeat": "",
        "crontab": "",
        "once": true,
        "onceDelay": "2",
        "x": 120,
        "y": 1146,
        "wires": [
            [
                "9497f40a.2d2718"
            ]
        ]
    },
    {
        "id": "9497f40a.2d2718",
        "type": "exec",
        "z": "619024c0.35593c",
        "command": "/home/AI/AI/StartAI.sh",
        "addpay": false,
        "append": "",
        "useSpawn": "false",
        "timer": "",
        "oldrc": false,
        "name": "Autostart",
        "x": 460,
        "y": 1146,
        "wires": [
            [
                "9ae30d45.83d05"
            ],
            [
                "9ae30d45.83d05"
            ],
            []
        ]
    }
]
1 Like
12

You may not need the sophistication of @wb666greene's script. You may well find that it is enough just to run the command in the exec node directly
/usr/bin/python /full/path/to/script.py

13

thats works exactly as expected ! perfect !

But I had to raise the wait time up to 20 seconds .... otherwise the Node-Red + Mosquitto service is not available on my Raspi :slight_smile:

14

This worked fine for me ... for some days.
Then the script failed and it is in an error mode now.
I would like to stop and restart the Python script from within Node-Red ?

Is this possible as well ?

15

You can send a kill command to the exec node. Read the node's help text. Then you can run it again.

16

Yes, this works perfectly fine now :grinning: :+1: :+1:

17

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