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Monocaffe
Java Daemon
Abril 13th, 2011 - [Enlace local]
Here's a little Bash script to run any Java application as a daemon. The only change you'll have to implement in your Java application is a handler for UNIX kill signals. Something like this:
Signal.handle(new Signal("INT"), new SignalHandler () {That's an example, handle exceptions and other signals properly.
public void handle(Signal sig) {
System.exit(10);
}
});
Now that your application is ready to handle a signal, be sure to be very special with the signal 10 and exit with code 10. Why 10? Read the kill manual page and you'll see there are no standard signals with this value.
Here's the Bash code:
#!/bin/bash
#
# Startup Script
JAVA_HOME="/opt/jre1.6.0_18/"
runnable="com.test.TestApplication"
pid=""
do_start () {
if [ ! -d "${JAVA_HOME}" ] ; then
echo "${JAVA_HOME} Directory doesn't exist."
exit 1
else
if [ ! -x "${JAVA_HOME}/bin/java" ] ; then
echo "Java binary error: not found or not executable"
exit 1
fi
fi
local path="lib/*"
local opts="-Ddebug.level=INFO"
# Launch the process
local exit_code=10
while [ $exit_code -eq 10 ]; do
"${JAVA_HOME}/bin/java" ${opts} -cp "${path}" ${runnable}
exit_code=$?
done
}
do_stop () {
getPID
kill ${pid} > /dev/null 2>&1 && echo "Stoping process ${pid}"
}
do_status () {
getPID
kill -0 ${pid} > /dev/null 2>&1 && echo "Process is running"
}
do_restart () {
getPID
kill -10 ${pid} > /dev/null 2>&1 && echo "Restarting"
}
getPID () {
# not the best, but works on most linux
pid=$( ps -ef | grep ${runnable} | grep -v grep | awk '{ print $2 }' )
}
case ${1} in
start)
do_start
;;
stop)
do_stop
;;
status)
do_status
;;
nohup)
# I really like this hack
nohup $0 start > /dev/null 2>&1 &
;;
restart)
do_restart
;;
*)
echo "Usage: $0 start|nohup|restart|stop|status"
exit 1
;;
esac
exit 0
I believe the script is pretty straight forward. Cool thing is that if you use start, you will run your application normally, but using the nohup option, it will call nohup on the script and run itself in daemon mode. Now, the only way to stop this process is to call the stop option or directly kill it. Also, if your process somehow listens for any event, you can implement a special one which allows the process to restart itself. For example, if your application is a web service, you can call curl http://localhost/restart
