Cron is the name of a program that enables the system to execute certain commands or scripts automatically a predetermined specified time/date.
In UNIX, Linux, FreeBSD, and other similar operating systems a crontab file contains instructions to the cron daemon of the general form: ``run this command at this time on this date''. Each user has their own crontab, and commands in any given crontab will be executed as the user who owns the crontab.
In FreeBSD the cron utility searches /var/cron/tabs for crontab files which are named after accounts in /etc/passwd; crontabs found are loaded into memory. The cron utility also searches for /etc/crontab which is in a different format. The cron utility then wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When executing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab, if such exists).