A template for a shutdown init.d script (tested on RHEL)

shutdownscript

#!/bin/bash
# shutdownscript - a template for a script that will run on shutdown
# chkconfig 2345 99 01

# write the name of the file (which will be the daemon here)
scriptname="shutdownscript"

# installation instructions:
#   - save this script in /etc/init.d/[yourscriptname]
#   - chown root:root [yourscriptname]
#   - chmod 755 [yourscriptname]
# register it with chkconfig:
# - chkconfig --add /etc/init.d/[yourscriptname]
# - chkconifg [yourscriptname] on
# start the new daemon
# service [yourscriptname] start

case "$1" in

start)
# need to write a lock file in /var/lock/subsys in order for the shutdown script
# to be registered on shutdown
echo "Registering shutdown script $scriptname"
touch "/var/lock/subsys/$scriptname"
;;

stop)
# first remove lock file
rm -f "/var/lock/subsys/$scriptname"
# now write your bash logic here.....
echo "this is my logic ...."
;;
esac

exit 0