How to manage custom Linux daemon

Prelude

Have you ever written Linux daemons? If you don't but you want then you should know that daemons are simple programs. You can just "daemonize" them by default tools.

This tool is called the start-stop-daemon. Of course, you can find some examples of using this tool. Or even go to the official docs, but, unfortunately, this is not so easy as you think. Well, as for me - it was a long way to success. Therefore I'm going to simplify your research process and show ready-to-use code.

Preparing config files

Our daemon based on this project called Chatter. So you can see full code in the GitHub

Running ahead, I can tell you that we'll need only two config-files. These files should be named the same as your service (or project). First one /etc/init.d/chatter

#!/bin/sh
### BEGIN INIT INFO
# Provides:          chatter chatter2
# Required-Start:    $remote_fs $network
# Required-Stop:     $remote_fs $network
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: starts chatter
# Description:       Starts The Chatter Daemon
### END INIT INFO

# Author: Oleksii Svyrydenko <alexslipknot@europe.com>

PATH=/bin:/usr/bin:/sbin:/usr/sbin
NAME=chatter
DESC="Chatter daemon"
DAEMON_PATH=/usr/sbin
PIDFILE=/var/run/$NAME.pid
LOGFILE=/var/log/$NAME.1.log
TIMEOUT=30
SCRIPTNAME=/etc/init.d/$NAME

case "$1" in
  start)
	echo "Starting $NAME"
	start-stop-daemon --start  --pidfile $PIDFILE --make-pidfile  --background --no-close --chdir $DAEMON_PATH --exec $NAME -- -r > $LOGFILE 2>&1
	;;
  stop)
	echo "Stoping $NAME"
	start-stop-daemon --stop --quiet --pidfile $PIDFILE
	start-stop-daemon --stop --quiet --oknodo --retry=0/30/TERM/5/KILL/5 --exec $DAEMON_PATH/$NAME
	rm $PIDFILE
	;;
  restart)
	echo "Restarting $NAME: "
	sh $0 stop
	sleep 20
	sh $0 start
	;;
esac
:

The second one /etc/init/chatter.conf. To be honest, I took it from httpd server or nginx. Just because it works :) And modified them with my requirements

# Author: Oleksii Svyrydenko <alexslipknot@europe.com>

PATH=/sbin:/usr/sbin:/bin:/usr/bin
DESC="Chatter"
NAME=chatter
DAEMON=/usr/sbin/$NAME
DAEMON_ARGS="-r"
PIDFILE=/var/run/$NAME.pid
TIMEOUT=30
SCRIPTNAME=/etc/init.d/$NAME

# Exit if the package is not installed
[ -x "$DAEMON" ] || exit 0

# Load the VERBOSE setting and other rcS variables
. /lib/init/vars.sh

# Define LSB log_* functions.
# Depend on lsb-base (>= 3.0-6) to ensure that this file is present.
. /lib/lsb/init-functions

# Don't run if we are running upstart
if init_is_upstart; then
    exit 1
fi

#
# Function that starts the daemon/service
#
do_start()
{
	# Return
	#   0 if daemon has been started
	#   1 if daemon was already running
	#   2 if daemon could not be started
	start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test > /dev/null \
		|| return 1
	start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON -- \
		$DAEMON_ARGS 2>/dev/null \
		|| return 2
	# Add code here, if necessary, that waits for the process to be ready
	# to handle requests from services started subsequently which depend
	# on this one.  As a last resort, sleep for some time.
}

#
# Function that stops the daemon/service
#
do_stop()
{
	# Return
	#   0 if daemon has been stopped
	#   1 if daemon was already stopped
	#   2 if daemon could not be stopped
	#   other if a failure occurred
	start-stop-daemon --stop --quiet --retry=QUIT/$TIMEOUT/TERM/5/KILL/5 --pidfile $PIDFILE --name $NAME
	RETVAL="$?"
	[ "$RETVAL" = 2 ] && return 2
	# Wait for children to finish too if this is a daemon that forks
	# and if the daemon is only ever run from this initscript.
	# If the above conditions are not satisfied then add some other code
	# that waits for the process to drop all resources that could be
	# needed by services started subsequently.  A last resort is to
	# sleep for some time.
	start-stop-daemon --stop --quiet --oknodo --retry=0/30/TERM/5/KILL/5 --exec $DAEMON
	[ "$?" = 2 ] && return 2
	# Many daemons don't delete their pidfiles when they exit.
	rm -f $PIDFILE
	return "$RETVAL"
}

#
# Function that sends a SIGHUP to the daemon/service
#
do_reload() {
	#
	# If the daemon can reload its configuration without
	# restarting (for example, when it is sent a SIGHUP),
	# then implement that here.
	#
	start-stop-daemon --stop --signal USR2 --quiet --pidfile $PIDFILE --name $NAME
	return 0
}

case "$1" in
    start)
	[ "$VERBOSE" != no ] && log_daemon_msg "Starting $DESC" "$NAME"
	case "$?" in
	    0)
		do_start
		case "$?" in
		    0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
		    2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
		esac
		;;
	    1) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
	esac
	;;
    stop)
	[ "$VERBOSE" != no ] && log_daemon_msg "Stopping $DESC" "$NAME"
	do_stop
	case "$?" in
		0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
		2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
	esac
	;;
    status)
        status_of_proc "$DAEMON" "$NAME" && exit 0 || exit $?
        ;;
    check)
        do_check yes
	;;
    reload|force-reload)
	log_daemon_msg "Reloading $DESC" "$NAME"
	do_reload
	log_end_msg $?
	;;
    reopen-logs)
	log_daemon_msg "Reopening $DESC logs" $NAME
	if start-stop-daemon --stop --signal USR1 --oknodo --quiet \
	    --pidfile $PIDFILE --exec $DAEMON
	then
	    log_end_msg 0
	else
	    log_end_msg 1
	fi
	;;
    restart)
	log_daemon_msg "Restarting $DESC" "$NAME"
	do_stop
	case "$?" in
	  0|1)
		do_start
		case "$?" in
			0) log_end_msg 0 ;;
			1) log_end_msg 1 ;; # Old process is still running
			*) log_end_msg 1 ;; # Failed to start
		esac
		;;
	  *)
	  	# Failed to stop
		log_end_msg 1
		;;
	esac
	;;
    *)
	echo "Usage: $SCRIPTNAME {start|stop|status|restart|reload|force-reload}" >&2
	exit 1
    ;;
esac

Preparing files

Put your executable daemon (in my case it is chatter) into the /usr/sbin/ directory
Set permissions for the files /etc/init.d/chatter and /usr/sbin/chatter to 755. It will allow to execute the files

Enabling daemon

The last one thing you have to do is enabling your daemon by executing a command in the terminal: systemctl enable chatter.service

Make sure that you have permissions for all operations above. Sometimes people make only one mistake with permissions and then looking for issues for weeks!

That's all. If you did all operations then you'll be able to manage your daemon with usual commands: service chatter start, service chatter stop, etc.