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12.19.06
Cron Isn't Working?
 By A.P. Lawrence
Let's just get this out of the way first: when someone says cron is not working, it almost always is, and they have just misunderstood something basic.
Usually that's not understanding the environment that cron scripts run under or that the machine was physically shut off at the time cron was supposed to do something.
However, for the sake of completeness, we'll run through everything you might check, including the rare case of cron itself not running at all.
You'll find a "cron" script in /etc/init.d on most systems. I say "most" not because I've ever seen it anywhere else, but because it could be started elsewhere. For example, Mac OS X cron is handled by "launchd" (and is not used for anything by default). Ubuntu is going to be changing init soon (see Replacing init with Upstart), and Upstart will eventually replace cron entirely. I expect that soon enough "cron" will be replaced everywhere, if not by Upstart then by something very like it. But that's still the future as I write this, so I'll assume your cron starts from /etc/init.d. Therefore, the very first question is "Did that script run?":
The "ls -lut" shows the time the file was last "used" - executed or read. This system was booted just prior to that time, so this makes sense. Is cron still running?
OK so far. Next we'll see if it has looked at its files:
Cron should read /etc/crontab when it starts up, so this matches. What /etc/crontab actually does depends on your system. For example, this is from an older RedHat system:
Continue reading this article.
About the Author:
A.P. Lawrence provides SCO Unix and Linux consulting services http://www.pcunix.com
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