kill -s SIGINT does not work as expected when launched from init.d script

Question

I want to start some python script (with venv) at startup and monitor the status, for auto restart it if something goes wrong.

I've made: - a simple python example prg.py that sleep forever and exit if it receive a sigint signal.

• a bash script prg.sh that monitor the execution of prg.py. If the process stop, the script restart the program. If the script receive the sigint, it will send a sigint to the prg.py program and exit.

• A init.d script (prg) for start the bash script (prg.sh). The code of prg is not mine, I've found it on GitHub and modified it. I'm searching the link, When I will found it I will edit the post.

prg.py:

import signal
import time

def signal_handler(sig, frame):
  print('sigint')
  quit(0)

signal.signal(signal.SIGINT, signal_handler)
print ('aaa')
while (1):
  time.sleep(1.5)

prg.sh:

#!/bin/bash

#set -x

DIR="/home/pi"
PRESCRIPT="source venv/bin/activate;python --version"
SCRIPT="python prg.py"

EXITDO=0
PID=-1
trap ctrl_c INT
function ctrl_c() {
  echo 'SIGINT intercepted.'
  EXITDO=1
}

#Main loop
while [ $EXITDO -eq 0 ]; do
  echo 'Starting process…'
  cd "$DIR"
  eval $PRESCRIPT
  $SCRIPT &
  PID=$(echo $!)
  echo "Process started with PID: $PID"
  while $(kill -0 $PID) && [ $EXITDO -eq 0 ]; do
    sleep 1
  done
  if [ $EXITDO -eq 0 ]; then
    echo 'Process terminated. Restart.'
  else
    echo 'Kill service.'
    kill -2 $PID
  fi
done

prg:

#!/bin/sh
### BEGIN INIT INFO
# Provides:          prg
# Required-Start:    $local_fs $network $named $time $syslog
# Required-Stop:     $local_fs $network $named $time $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Description:       <DESCRIPTION>
### END INIT INFO
NAME=prg
SCRIPT="/home/pi/prg.sh"

PIDFILE=/var/run/$NAME.pid

start() {
  if [ -f $PIDFILE ] && [ -s $PIDFILE ] && kill -0 $(cat $PIDFILE); then
    echo 'Service already running' >&2
    return 1
  fi
  echo 'Starting service…' >&2
  #local CMD="$SCRIPT &> \"$LOGFILE\" & echo \$!"
  #su -c "$CMD" $RUNAS > "$PIDFILE"
  # Try with this command line instead of above if not workable
  # su -s /bin/sh $RUNAS -c "$CMD" > "$PIDFILE"
  $SCRIPT &
  echo $! > "$PIDFILE"
  PID=$(cat $PIDFILE)
  if kill -0 $(cat $PIDFILE) > /dev/null
  then
    echo "$NAME is now running, the PID is $PID"
  else
    echo ''
    echo "Error! Could not start $NAME!"
  fi
}

stop() {
  if [ ! -f "$PIDFILE" ] || ! kill -0 $(cat "$PIDFILE"); then
    echo 'Service not running' >&2
    return 1
  fi
  echo 'Stopping service…' >&2
  #Kill by pid
  kill -2 $(cat "$PIDFILE")
  #remove .pid file
  sleep 3
  if ! kill -0 $(cat "$PIDFILE"); then
    rm -f "$PIDFILE"
    echo 'Service stopped' >&2
  fi
}

uninstall() {
  echo -n "Are you really sure you want to uninstall this service? That cannot be undone. [yes|No] "
  local SURE
  read SURE
  if [ "$SURE" = "yes" ]; then
    stop
    rm -f "$PIDFILE"
    echo "Notice: log file was not removed: $LOGFILE" >&2
    update-rc.d -f $NAME remove
    rm -fv "$0"
  else
    echo "Abort!"
  fi
}

status() {
    printf "%-50s" "Checking $NAME..."
    if [ -f $PIDFILE ] && [ -s $PIDFILE ]; then
        PID=$(cat $PIDFILE)
            if [ -z "$(ps axf | grep ${PID} | grep -v grep)" ]; then
                printf "%s\n" "The process appears to be dead but pidfile still exists"
            else
                echo "Running, the PID is $PID"
            fi
    else
        printf "%s\n" "Service not running"
    fi
}


case "$1" in
  start)
    start
    ;;
  stop)
    stop
    ;;
  status)
    status
    ;;
  uninstall)
    uninstall
    ;;
  restart)
    stop
    start
    ;;
  *)
    echo "Usage: $0 {start|stop|status|restart|uninstall}"
esac

• If I start prg.sh the program run as expected.

• I can kill prg.py and the prg.sh auto restart the prg.py.

• I can send a sigint to prg.sh and the prg.sh stop the prg.py and close itself.

• I can start the prg with sudo service prg start command and all works fine.

BUT

• in this situation the, if I send a sigint to prg.sh, nothing happen.

• In simple words, service prg stop does not work and I don't understand why.

Thanks in advance.