Bash shell script which let run PROCESS_COMMAND forever until daemon is called with kill parameter.

daemon.sh

#!/usr/bin/env bash
SCRIPT_PATH=$(readlink -f $0)
DIR=$(dirname $SCRIPT_PATH)

PID_DIR="${DIR}/pid"
LOG_DIR="${DIR}/log"

DAEMON_PID_FILE="${PID_DIR}/daemon.pid"
DAEMON_LOG_FILE="${LOG_DIR}/daemon.log"
PROCESS_PID_FILE="${PID_DIR}/process.pid"
PROCESS_LOG_FILE="${LOG_DIR}/process.log"

# Set here whatever you want to run forever!
PROCESS_COMMAND="${DIR}/index.js"

log() {
	DATE=`date +"%Y-%m-%d %H:%M:%S"`
	echo "${DATE} $1" >> $DAEMON_LOG_FILE
}

start() {
	touch $PROCESS_PID_FILE
	nohup $PROCESS_COMMAND &>>$PROCESS_LOG_FILE &
	echo $! > $PROCESS_PID_FILE
	PID=$(cat $PROCESS_PID_FILE)
	log "Process started with $PID"
}

keep_alive() {
	if [ -f $PROCESS_PID_FILE ]
	then
		PID=$(cat $PROCESS_PID_FILE)
		if [ $(ps -Ao pid | grep $PID) ]
		then
			return
		else
			start
		fi
	else
		start
	fi
}

stop() {
	if [ -f $PROCESS_PID_FILE ]
	then
		PID=$(cat $PROCESS_PID_FILE)
		if [ $(ps -Ao pid | grep $PID) ]
		then
			kill -TERM $PID
		fi
		rm $PROCESS_PID_FILE
	fi
}

start_daemon() {
	log "Starting daemon"
	touch $DAEMON_PID_FILE
	echo $$ > $DAEMON_PID_FILE
	trap stop_daemon INT SIGINT TERM SIGTERM
	keep_alive

	while true
	do
		keep_alive
		wait
		sleep 1
	done
}

stop_daemon() {
	log "Stopping daemon"
	stop
	rm $DAEMON_PID_FILE
	log "Daemon stopped"
	exit 0
}

if [ ! -d $PID_DIR ]
then
	mkdir $PID_DIR
fi

if [ ! -d $LOG_DIR ]
then
	mkdir $LOG_DIR
fi

if [ -f $DAEMON_PID_FILE ]
then
	PID=$(cat $DAEMON_PID_FILE)
	if [ $(ps -Ao pid | grep $PID) ]
	then
		if [ "$1" = "kill" ]
		then
			kill -TERM $PID
			echo "Daemon is killed"
		else
			echo "Daemon is running with PID $PID"
		fi

		exit 0
	fi
fi

if [ "$1" = "daemon" ]
then
	start_daemon
fi

if [ "$1" != "kill" ]
then
	nohup "$0" daemon &> /dev/null &
fi

exit 0