[CentOS] Inquiry:How to make crontab job permanent even after server reboot?

Dear All Please be informed that I have an CentOS 5 server and I need it to be automatically rebooted at pre-specified times . To this end , I tried to set it as its crontab job as the followings : #crontab -e 30 15 * * * reboot It got through but after the server first reboot the crontab job disappeared . So I tried to set it in another way , as the followings : set the cron list in /tmp/temp add the following lines to /etc/rc.local : crontab /tmp/temp But still the crontab job will disappear after the server first reboot . Can you please do me favor and let me know how can I make the crontab job permanent on my CentOS server even after server reboot ? Let me thank you in advance