log in as root
crontab -e # uses vi
At the end of the file just add in your cron job, using the following format:
min hr day month weekday COMMAND
To restart everyday at midnight:
0 0 * * * /sbin/service/ httpd graceful
Back up the wiki at 4:00 AM on Sunday morning
0 4 * * Sun /var/www/html/aw/backup.sh