Run a python script when start up and SSH not log in

Question

I am new to programming and doing a simple academic project with Raspberry Pi, I have a script which will monitor the changes of database and output the change with 2 different color LED.

I want it to be executed everytime raspberry pi reboot and SSH is not logged in. Currently I have added the task in crontab but it's not executed when reboot. When I run in SSH command line, it works and when i logout PuTTY, it stop.

I have another script in crontab which working well when Pi reboot

My python script

#!/usr/bin/python
import MySQLdb
import RPi.GPIO as GPIO
import time
GPIO.setmode(GPIO.BOARD)
GPIO.setwarnings(False)
GPIO.setup(38,GPIO.OUT) #red(away)
GPIO.setup(40,GPIO.OUT) #green(home)
while True:
 db = MySQLdb.connect(host="localhost", user="ssss", passwd="sssss"$
 #cursor for select
 cur = db.cursor()
 cur.execute("SELECT status FROM home_mode ORDER BY id DESC LIMIT 1")
 last_status = str(cur.fetchone())
 if last_status == "('HOME',)":
 GPIO.output(40, GPIO.HIGH)
 GPIO.output(38, GPIO.LOW)
 elif last_status == "('AWAY',)":
 GPIO.output(40, GPIO.LOW)
 GPIO.output(38, GPIO.HIGH)
 else:
 print "WRONG"
cur.close()
db.close()

The coding maybe very poor because I am really new in python even programming. Hope anyone could give solution/advise, thank you.

Answer 1

A better choice would be to use systemd and its associated systemctl command.

Answer 2

You should use a systemd unit file to start the python script on boot up and run it as service. Just create a new service with:

rpi ~$ sudo systemctl --force --full edit monitor-db.service

In the empty editor insert these statements, save them and quit the editor:

[Unit]
Description=Monitor Database changes
After=multi-user.target
[Service]
ExecStart=/full/path/to/script.py
[Install]
WantedBy=multi-user.target

Enable and check the new service with:

rpi ~$ sudo systemctl enable monitor-db.service
rpi ~$ systemctl status monitor-db.service

Reboot.