cron—the clock daemon

cron executes commands at specified dates and times. Regularly scheduled jobs can be specified in the /etc/crontab file. In order to use cron, one of the following must be true: (1) you are superuser; (2) you are regular user, but your user ID is listed in the /etc/cron.allow file; (3) you are regular user, but your system contains a file /etc/cron.deny, which is empty.