The system scheduler on UNIX and Linux systems is called
cron. Its purpose is to run commands, series of commands, or scripts on a predetermined schedule. Normally these tasks are performed on systems that run 24 hours a day, 7 days a week. Writing
cron scripts to perform system maintenance, backups, monitors, or any other job that you would want to run on a schedule is a very common task. There are a few subtleties with
cron however, that many users and administrators may be unaware of.
On a UNIX or Linux system, the
cron daemon process runs all the time. A daemon is generally a program that runs as a background task and provides some type of service, in this case a scheduler. A run control (
rc) script starts ...