Check out example codes for "rc.local not running centos 6". It will help you in understanding the concepts better.

Code Example 1

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

/sbin/start-stop-daemon -b -c www-data:www-data -S -x /usr/bin/php /var/www/ttrss/update_daemon2.php -- -quiet

exit 0

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