On this tutorial I will explain how to create a quick init like script to be run in the background. We will not be adding this script to /etc/init or look into how to run it at startup. Instead we will run it manually. If you are looking for a Systemd version of this tutorial, check out my previous post Creating a Simple Systemd User Service.
First let’s create our service script. This is the daemon that will be running in the background. For this example we will create a script that monitors a log file:
tail -fn0 logfile | \
while read line ; do
echo "$line" | grep "pattern"
if [ $? = 0 ]
then
... do something ...
fi
done
Now let’s create a control script. This script is what we will use to start/stop our daemon.
#!/bin/bash
daemon="[path_to_my_daemon_script]"
name="Name for the service/daemon"
desc="Description for the script"
pid_file="/var/run/[daemon_name].pid"
# Check whether the binary is still present:
test -x "$daemon" || exit 0
case "$1" in
start)
[ -f "$pid_file" ] && { echo "Already running" ; exit 0 ; }
echo "Starting $name"
"$daemon" &
echo $! > "$pid_file"
;;
stop)
[ ! -f "$pid_file" ] && { echo "Not running" ; exit 0 ; }
echo "Stopping $name"
kill "$(cat $pid_file)"
rm "$pid_file"
;;
restart)
$0 stop
$0 start
;;
status)
if [ -e "$pid_file" ]; then
echo "$name is running, pid=$(cat $pid_file)"
else
echo "$name is not running"
exit 1
fi
;;
*)
echo "Usage: $0 {start|stop|status|restart}"
esac
exit 0
Make sure both files are executable and you are ready to start your daemon.
[controlscript] start
You can check the status, stop, etc…
[controlscript] status
