[Gllug] Advanced versions of cron for scheduling

[Richard Jones]

We are currently using cron to schedule batch jobs which must be run
at certain times of the day, but we're starting to hit limits with
this approach.  So as a result we're casting around looking for a
"better cron".

Some of the things we'd like to do, but cron makes unnecessarily
difficult:

(1) Run one job straight after another/some others have finished.

This can be done using script1 && script2, but what if we want a job
to run after several other jobs have finished, provided they all
finish successfully.  And in a maintainable fashion.

(2) Run a job continually - after it finishes, schedule it to run
again.

A shell script, while true; do ... done, solves this, but there are
maintainability concerns (eg for one, how to start the script when the
machine boots, from a non-root user account, without requiring root
access?).

(3) Set a time limit on a job.

If it exceeds the time limit, either send mail warning about this, or
kill it -- we'd want to control which, because sometimes killing a job
can result in loss of data, for reasons outside of our control.

(4) Running jobs regularly, but at odd intervals.

For example, one request I've had was to run a job every 45 minutes.
This isn't easy to express in a crontab.

(5) Keep the crontab file under CVS control.

(6) Ensure only one job is running at once.

At the moment we're using lock files stored in $HOME.

I've looked at launchd (ugly, undocumented XML syntax, and doesn't do
half the stuff we want anyway), and at this slashdot article
[http://ask.slashdot.org/article.pl?sid=05/05/13/0225245] but we
haven't really found anything suitable yet.

Rich.

-- 
Richard Jones, CTO Merjis Ltd.
Merjis - web marketing and technology - http://merjis.com
Team Notepad - intranets and extranets for business - http://team-notepad.com
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