8.1. cron: schedule commands
Under Linux, periodic execution is normally handled by the cron daemon. cron starts when the system boots and remains running as long as the system is up. cron reads one or more configuration files containing lists of command lines and times at which they are to be invoked. The command lines are executed by sh, so almost anything you can do by hand from the shell can also be done with cron.
cron originally appeared in the UNIX family tree in the 1970s. Linux distributions include a version known as ISC cron or “Vixie-cron,” named after its author, Paul Vixie. It’s is a modern rewrite that provides added functionality with less mess.
A cron configuration file is called a “crontab,” short for “cron table.” ...