Use Monit monitor a python program

Question

I'm using Monit to monitor a system. I have a python file I wish to also monitor, I understand that I need to create a wrapper script as python does not generate pid files. I followed the instructions on this site, however I have been unable to get the script to start. I've never created a wrapper script before, so I think I have an error in my script. The log from monit says "Failed to start"

Monit rule

check process scraper with pidfile /var/run/scraper.pid
   start = "/bin/scraper start"
   stop = "/bin/scraper stop"

wrapper script

#!/bin/bash

PIDFILE=/var/run/scraper.pid

case $1 in
   start)
      echo $$ > ${PIDFILE};
      source /home
      exec python /home/scraper.py 2>/dev/null
   ;;
   stop)
      kill `cat ${PIDFILE}` ;;
   *)
      echo "usage: scraper {start|stop}" ;;
esac
exit 0

Answer 1

Using exec will replace the shell by the exec'd program, this is not what you want to get here, you want your wrapper script to launch the program and detach it before returning, writing its PID to a file so it can be stopped later.

Here's a fixed version:

#!/bin/bash

PIDFILE=/var/run/scraper.pid

case $1 in
   start)
       source /home
       # Launch your program as a detached process
       python /home/scraper.py 2>/dev/null &
       # Get its PID and store it
       echo $! > ${PIDFILE} 
   ;;
   stop)
      kill `cat ${PIDFILE}`
      # Now that it's killed, don't forget to remove the PID file
      rm ${PIDFILE}
   ;;
   *)
      echo "usage: scraper {start|stop}" ;;
esac
exit 0