How to write a System V init script to start, sto

Linux: How to write a System V init script to start, stop, and restart my own application or service
Posted by nixcraft in Linux, RedHat/Fedora Linux, Shell scripting, Tips

System V (abbreviated as SysV) is most widely used across most Linux distributions. But what is System V?

Init is the program on Unix and Linux systems which spawns all other processes. It runs as a daemon and typically has PID 1. It is the parent of all processes. Its primary role is to create processes from a script stored in the file /etc/inittab file. The main advantages is flexibility and scalability provided by SysV.

The Runlevels in System V describe certain states. For example:

    * Runlevel 0: Halt
    * Runlevel 1: Single user mode
    * Runlevel 6: Reboot

All System V init scripts are stored in /etc/rc.d/init.d/ or /etc/init.d directory. These scripts are used to control system startup and shutdown. Usually you will find scripts to start a web server or networking. For example you type the command:


# /etc/init.d/httpd start
OR
# /etc/init.d/network restart


In above example httpd or network are System V scripts written in bash or sh shell. Here is a sample shell script:

#!/bin/bash
#
# chkconfig: 35 90 12
# description: Foo server
#

# Get function from functions library
. /etc/init.d/functions

# Start the service FOO
start() {
        initlog -c "echo -n Starting FOO server: "
        /path/to/FOO &
        ### Create the lock file ###
        touch /var/lock/subsys/FOO
        success $”FOO server startup”
        echo
}

# Restart the service FOO
stop() {
        initlog -c “echo -n Stopping FOO server: ”
        killproc FOO
        ### Now, delete the lock file ###
        rm -f /var/lock/subsys/FOO
        echo
}

### main logic ###
case “$1″ in
  start)
        start
        ;;
  stop)
        stop
        ;;
  status)
        status FOO
        ;;
  restart|reload|condrestart)
        stop
        start
        ;;
  *)
        echo $”Usage: $0 {start|stop|restart|reload|status}”
        exit 1
esac

exit 0

Above script is specific to Cent OS or Fedora Core/Red Hat Linux. But it should work on all other Linux distro as well. Make sure you replace the FOO name (word/path start with FOO) with actual application name.