Running java application as linux daemon

Running java application as linux daemon

  March 14, 2013    Suraj Chhetry

---

Linux daemon is a application which runs as a background process,rather than being under the direct control of an interactive user.We can create a java application that can run as daemon process. Here is few step which will help to create a linux daemon process.

1. Create a bash script in /etc/init.d/logging as below

#!/bin/bash
#
# chkconfig: 345 99 05
# description: Java deamon script

# service name with the first letter in lowercase 
serviceNameLo="logger"
# service name   
serviceName="logger"
# OS user name for the service  ,we need to create user, by useradd command    
serviceUser="logger"
# OS group name for the service, we can use usermod -a -G groupName userName
serviceGroup="logger"
# home directory of the service application    
applDir="/opt/logger"   
# home directory of the service user
serviceUserHome="/home/$serviceUser"
# log file for StdOut/StdErr
serviceLogFile="/opt/logger/log/$serviceNameLo.log"
# max number of seconds to wait for the daemon to terminate normally 
maxShutdownTime=15
# name of PID file (PID = process ID number)
pidFile="/opt/logger/temp/$serviceNameLo.pid"
# name of the Java launcher without the path
javaCommand="java"
# arguments for Java launcher     
javaArgs="-jar $applDir/logger.jar"
# command line to start the Java service application
javaCommandLine="java $javaArgs"
# a keyword that occurs on the commandline, used to detect an already running service process and to distinguish it from others
javaCommandLineKeyword="logger.jar"
 
# Makes the file $1 writable by the group $serviceGroup.
function makeFileWritable {
   local filename="$1"
   touch $filename || return 1
   chgrp $serviceGroup $filename || return 1
   chmod g+w $filename || return 1
   return 0; }
 
# Returns 0 if the process with PID $1 is running.
function checkProcessIsRunning {
   local pid="$1"
   if [ -z "$pid" -o "$pid" == " " ]; then return 1; fi
   if [ ! -e /proc/$pid ]; then return 1; fi
   return 0; }
 
# Returns 0 if the process with PID $1 is our Java service process.
function checkProcessIsOurService {
   local pid="$1"
   if [ "$(ps -p $pid --no-headers -o comm)" != "$javaCommand" ]; then return 1; fi
   grep -q --binary -F "$javaCommandLineKeyword" /proc/$pid/cmdline
   if [ $? -ne 0 ]; then return 1; fi
   return 0; }
 
# Returns 0 when the service is running and sets the variable $pid to the PID.
function getServicePID {
   if [ ! -f $pidFile ]; then return 1; fi
   pid="$(<$pidFile)"
   checkProcessIsRunning $pid || return 1
   checkProcessIsOurService $pid || return 1
   return 0; }
 
function startServiceProcess {
   cd $applDir || return 1
   rm -f $pidFile
   makeFileWritable $pidFile || return 1
   makeFileWritable $serviceLogFile || return 1
   cmd="nohup $javaCommandLine >>$serviceLogFile 2>&1 & echo \$! >$pidFile"
   su -m $serviceUser -s $SHELL -c "$cmd" || return 1
   sleep 0.1
   pid="$(<$pidFile)"
   if checkProcessIsRunning $pid; then :; else
      echo -ne "\n$serviceName start failed, see logfile."
      return 1
   fi
   return 0; }
 
function stopServiceProcess {
   kill $pid || return 1
   for ((i=0; i<maxShutdownTime*10; i++)); do
      checkProcessIsRunning $pid
      if [ $? -ne 0 ]; then
         rm -f $pidFile
         return 0
         fi
      sleep 0.1
      done
   echo -e "\n$serviceName did not terminate within $maxShutdownTime seconds, sending SIGKILL..."
   kill -s KILL $pid || return 1
   local killWaitTime=15
   for ((i=0; i<killWaitTime*10; i++)); do
      checkProcessIsRunning $pid
      if [ $? -ne 0 ]; then
         rm -f $pidFile
         return 0
         fi
      sleep 0.1
      done
   echo "Error: $serviceName could not be stopped within $maxShutdownTime+$killWaitTime seconds!"
   return 1; }
 
function startService {
   getServicePID
   if [ $? -eq 0 ]; then echo -n "$serviceName is already running"; RETVAL=0; return 0; fi
   echo -n "Starting $serviceName   "
   startServiceProcess
   if [ $? -ne 0 ]; then RETVAL=1; echo "failed"; return 1; fi
   echo "started PID=$pid"
   RETVAL=0
   return 0; }
 
function stopService {
   getServicePID
   if [ $? -ne 0 ]; then echo -n "$serviceName is not running"; RETVAL=0; echo ""; return 0; fi
   echo -n "Stopping $serviceName   "
   stopServiceProcess
   if [ $? -ne 0 ]; then RETVAL=1; echo "failed"; return 1; fi
   echo "stopped PID=$pid"
   RETVAL=0
   return 0; }
 
function checkServiceStatus {
   echo -n "Checking for $serviceName:   "
   if getServicePID; then
    echo "running PID=$pid"
    RETVAL=0
   else
    echo "stopped"
    RETVAL=3
   fi
   return 0; }
 
function main {
   RETVAL=0
   case "$1" in
      start)                                               # starts the Java program as a Linux service
         startService
         ;;
      stop)                                                # stops the Java program service
         stopService
         ;;
      restart)                                             # stops and restarts the service
         stopService && startService
         ;;
      status)                                              # displays the service status
         checkServiceStatus
         ;;
      *)
         echo "Usage: $0 {start|stop|restart|status}"
         exit 1
         ;;
      esac
   exit $RETVAL
}
 
main $1

2.  sudo chmod a+x /etc/init.d/logging

3.  chkconfig --add logging 

4.  chkconfig --level 2345 logging on

5.  update-rc.d logging defaults

Now , we can start ,stop service using below command

• sudo service logging start
• sudo service logging stop
• sudo service logging restart
• sudo service logging status