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What is a 'cron job'?

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March 22, 2009 4:08PM

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A 'cron job' is a recurring, scheduled job entry on Unix/Linux systems. Consequently, this question should likely be re-categorized to fall under the Linux OS category.

For example, say we have written a nifty little shell script or 'C' program that starts ntpd (Network Time Protocol Daemon) to set the system time accurately and then shuts down the ntp daemon. If we wanted to run our little program twice a day, for instance, at a specific time, we would likely use cron to handle it for us.

Our cron tab entry might look something like the following...

01 06,18 * * * /usr/local/bin/ntpstart.sh

The above entry will run the /usr/local/bin/ntpstart.sh shell script at 1 minute after 06:00 and 1 minute after 18:00 hours, every day of the week, every week of the year. See the man page for 'cron' on your system for more details. [JMH]