Overview

cronwrap is a wrapper script for cron jobs, written to mitigate some common pitfalls of cron jobs on systems I admin, where I tend to not write the jobs themselves but have to pick up the pieces when things explode.

See [http://www.zomo.co.uk/2010/02/cron/] for more about the motivation. The key aims are

• prevent multiple runs of the same job piling up by using a lock
• store output in a timestamped directory
• make it easy for external monitoring to determine health of cron jobs

Absent from this incarnation are the SNMP and email hooks that other variants enjoy.

Comments and criticism welcome.

Two variants are here: cronwrap.lockf which uses FreeBSD's lockf binary, and cronwrap.lockrun which uses a more cross-platform locker, lockrun

Requirements

• lockrun for cronwrap.lockrun
• for the additional scripts, working fuser, pgrep/pkill and /proc
• jobs to exit non-zero on error

External bits

• A (heh) cron job to age out old cronwrap logs
• A monitoring system to care about the OK, FAIL, LOCK markers

Usage

See comments within cronwrap for details, but here's an example cron.d snippet

*/5 * * * * nobody cronwrap update-local-cache 300 /usr/local/bin/cache-update -v local

Here 300 is an interval specification. cronwrap itslef doesn't use it but writes it to the job's status directory as interval, so that a monitor can compare it to the adjacent last_ran value.

Contents

cronwrap.lockf - wrapper itself cronwrap.lockrun - wrapper itself

check_cronwrap - a Nagios test to guage the health of cronwrapped jobs

show-cronwap-log - since the output of a running is in a temporary file, it can be hard to find. this script finds it, useful to work out what a long-running job is up to.

kill-cronwrap-job - kills the the job that cronwrap (and thus lockrun) is managing useful to nuke a wedged job that is holding up

cronweb.rb - diddy Sinarta web app to provide a web view on cronwrap status and logs

The last three are decidedly less portable than the main cronwrap script.

Thanks

Steve Friedl's nifty lockrun tool provides an elegant way to lock jobs from overlapping. It's way better than any homegrown effort of mine. http://unixwiz.net/tools/lockrun.html

This version of cronwrap was written mostly on Deluxe Online's dime, so thanks to them for letting me share it. http://deluxeonline.co.uk/

License

Relesed under a BSD license, see LICENSE. Non-warranty in there too.

Author

Jon Stuart, jon@zomo.co.uk, Zomo Technology Ltd, 2010.