How to make a jar file run on startup & and when you log out?

Here's a easy way to do that using SysVInit. Instructions:

1. Create the start and the stop script of your application. Put it on some directory, in our example is:

   • Start Script: /usr/local/bin/myapp-start.sh
   • Stop Script: /usr/local/bin/myapp-stop.sh

   Each one will provide the instructions to run/stop the app. For instance the myapp-start.sh content can be as simple as the following:

   #!/bin/bash
   
   java -jar myapp.jar 
   

   For the stop script it can be something like this:

   #!/bin/bash
   # Grabs and kill a process from the pidlist that has the word myapp
   
   pid=`ps aux | grep myapp | awk '{print $2}'`
   kill -9 $pid
   

2. Create the following script (myscript) and put it on /etc/init.d.

   /etc/init.d/myscript content:

   #!/bin/bash
   # MyApp
   #
   # description: bla bla
   
   case $1 in
       start)
           /bin/bash /usr/local/bin/myapp-start.sh
       ;;
       stop)
           /bin/bash /usr/local/bin/myapp-stop.sh
       ;;
       restart)
           /bin/bash /usr/local/bin/myapp-stop.sh
           /bin/bash /usr/local/bin/myapp-start.sh
       ;;
   esac
   exit 0
   

3. Put the script to start with the system (using SysV). Just run the following command (as root):

   update-rc.d myscript defaults 
   

PS: I know that Upstart is great and bla bla, but I preffer the old SysV init system.

Yes! It is possible. :) Upstart is the way to go to make sure the service stays running. It has five packages, all installed by default:

• Upstart init daemon and initctl utility
• upstart-logd provides the logd daemon and job definition file for logd service
• upstart-compat-sysv provides job definition files for the rc tasks and the reboot, runlevel, shutdown, and telinit tools that provide compatibility with SysVinit
• startup-tasks provides job definition files for system startup tasks
• system-services provides job definition files for tty services

The learning is very enjoyable and well worth it. Upstart has a website: http://upstart.ubuntu.com/

3 quick suggestions...

1. Create a Start script in /etc/rc3.d (multiuser console mode) with corresponding Kill scripts in /etc/rc.0 and /etc/rc6.d to kill your Java program in a controlled way when the system powers down (runevel 0) or reboots (runlevel 6) See An introduction to Runlevels.

   You might be able to start your Java app in runlevel 2 (rc2.d) but, as a crawler, it will need TCP/IP. So make sure your networking service is available/started in your runlevel 2 beforehand. Networking is definitely up in runlevel 3.

   /etc/init.d contains all the actual start/kill scripts. /etc/rcN.d directories just contain links to them, prefixed with S or K to start or kill them respectively, per runlevel N.

2. A process run by crond should persist between logouts. Maybe add it to your crontab.

3. A process run with nohup should also persist. See nohup: run a command even after you logout.

   $ nohup java -jar myapp.jar &
   

   By default, myapp.jar's standard output will go to a file named ./nohup.out, or $HOME/nohup.out if the former isn't writeable.