/etc/init.d/ start up scripts

1. Put your script in the /etc/init.d/ directory. Don't give any extention to your script.
2. Add +x permission (executable) to your script file. For example your script file is nn_script, type in your console

   sudo chmod +x nn_script

3. Add your startup script to system by this command

    sudo update-rc.d nn_script defaults
 Source:
http://embraceubuntu.com/2005/09/07/adding-a-startup-script-to-be-run-at-bootup/