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busybox crond / crontab fields
I could not find easily what expressions are valid in crontab files for the busybox crond daemon. The man pages I found are minimalists – as busybox is itself – and only list the options that the crond
commands accepts. No doc lists what you may write in the crontab file itself. I had to “use the source, Luke !”.
Here is the relevant part of ''crond.c'' file for busybox 1.13.2
What does it tells us ? well, you can use things like this :
- example-cron
MAILTO=me@somewhere.com * * * * * touch /tmp/everyminute.$$ 0-55/5 * * * * touch /tmp/every-5-minutes.$$ MAILTO= 5,11,19,37,59 1,3,5,7,11,13,17,19,23 * * * touch /tmp/prime.$$ 11,17,30-50/3 5,7,11-22/5,23 * jan-oct/3,12 sun-3/2 touch /tmp/guess-when.$$
MAILTO=
may be obeyed or not, depending on the fact that your busybox crond was compiled with option for sending mail or not. How you can check that ? Don't know.
Errors
What if you enter something invalid ? In my case, there wass just a warning in the log. If you use this
11,17,30-50/3 5,7,11-22/5,23 * jan-oct-nob/3,12 sun-3/2 touch /tmp/guess-when.$$
here is what you get in the logs
Jan 3 06:51:24 (none) cron.err crond[14635]: crond (busybox 1.13.2) started, log level 8 Jan 3 06:51:24 (none) cron.err crond[14635]: user root: parse error at jan-oct-nob/3,12