There are times when there’s a need for running a group of tasks automatically at certain times in the future. These tasks are usually administrative, but could be anything - from making database backups to downloading emails when everyone is asleep.
Cron is a time-based job scheduler in Unix-like operating systems, which triggers certain tasks at a point in the future. The name originates from the Greek word χρόνος (chronos), which means time.
The most commonly used version of Cron is known as Vixie Cron, originally developed by Paul Vixie in 1987.
This piece is an in-depth walkthrough of this program, and a reboot of this ancient, but still surprisingly relevant post.