Raspberry Pi startup/shutdown signals

This is a simple Python script combined with two systemd services to signal when a Raspberry Pi has started up, shut down, halted, or rebooted. It is composed of four files: configuration file, Python script, and two systemd service definition files.

Install dependencies:

pip3 install paho.mqtt pendulum
Quick note on pendulum: it can be particular about which version is required due to some stagnation in the library maintenance. For the Raspberry Pi 3B+ running Python 3.7.3, I had to install pendulum==2.1.0.

Configuration file:

{
 "mqtt": {
   "address": "localhost",
   "port": 1883,
   "topic_prefix": "RPiDeviceInfo"
 }
}
Quick note on configuration file: The Python script expects the configuration file to be in the same folder as the script and titled config.json.

Python file:

from paho.mqtt import publish
from pendulum import now
from socket import gethostname

import argparse
import json


def mqtt_publish_single(topic, message):

   try:
       publish.single(
           topic=topic,
           payload=json.dumps(message),
           hostname=config['mqtt']['address'],
           port=config['mqtt']['port']
       )
   except ConnectionError as e:
       print(e)
   except OSError as oe:
       print(oe)


def signal(direction):

   # current timestamp in milliseconds
   now_ts = now(tz='UTC').int_timestamp * 1000

   hostname = gethostname()
   hostname = hostname.split('.')[0]

   topic = '{0}/{1}/status'.format(config['mqtt']['topic_prefix'], hostname)

   message = {
       'timestamp': now_ts,
       'signal': direction
   }

   mqtt_publish_single(topic, message)


if __name__ == '__main__':
   # load configuration
   with open('config.json', 'r') as config_file:
       config = json.load(config_file)
   # load command line switches
   parser = argparse.ArgumentParser()
   parser.add_argument('--direction')
   args = parser.parse_args()
   direction = args.direction

   signal(direction)

Startup service:

[Unit]
Description=Sends MQTT message when host has started.
After=network.target

[Service]
Type=simple
User=pi
Group=pi
WorkingDirectory=/var/pyapps/RPiDeviceInfo
StandardOutput=append:/var/log/messages
StandardError=append:/var/log/errors
ExecStart=/bin/true
ExecStop=python3 /var/pyapps/RPiDeviceInfo/piupdownsignal.py --direction up
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
Shutdown service:

[Unit]
Description=Sends MQTT message when host halts, shutdowns, or reboots.
Before=shutdown.target

[Service]
Type=simple
User=pi
Group=pi
WorkingDirectory=/var/pyapps/RPiDeviceInfo
StandardOutput=append:/var/log/messages
StandardError=append:/var/log/errors
ExecStart=/bin/true
ExecStop=python3 /var/pyapps/RPiDeviceInfo/piupdownsignal.py --direction down
RemainAfterExit=yes
You can see the folder structure. In order to link to systemd, I perform the following based on my folder structure:

sudo ln -sf /var/pyapps/RPiDeviceInfo/startup.service /etc/systemd/system/startup.service
sudo ln -sf /var/pyapps/RPiDeviceInfo/shutdown.service /etc/systemd/system/shutdown.service
sudo systemctl daemon-reload
sudo systemctl enable startup
sudo systemctl enable shutdown
sudo systemctl start startup
sudo systemctl start shutdown
If you ever want to remove the services, execute the following statements:

sudo systemctl disable startup
sudo systemctl disable shutdown
I'm using this in Node-RED to send me notifications through IFTTT when my SkyWeather2 Raspberry Pi 3B+ host system powers down or powers up due to power loss through my SolarMAX2 system. I can do a video on how I accomplish that if folks are interested.

Holler if you have any questions.

Thanks,

Jason