Cron

References:http://www.cyberciti.biz/faq/how-do-i-add-jobs-to-cron-under-linux-or-unix-oses/

Cron is one of the most useful tool in Linux or UNIX like operating systems. The cron service (daemon) runs in the background and constantly checks:

• /etc/crontab (file)
• /etc/cron.*/ (directories)
• /var/spool/cron/ (directory)

There are two different types of configuration files:

1. Linux system crontab
2. The user crontabs