Contributed by rueda on from the not-a-random-walk dept.
Thanks to the following
commit
by Todd Miller (millert@),
cron(8)
now supports random values in a range
with a step value
(i.e.
"<lo>~<hi>/<step>"
in
crontab(5) entries):
CVSROOT: /cvs Module name: src Changes by: millert@cvs.openbsd.org 2023/05/06 17:06:27 Modified files: usr.sbin/cron : crontab.5 entry.c macros.h Log message: Support random offsets when using ranges with a step value in cron. This extends the random range syntax to support step values. Instead of choosing a random number between the high and low values, the field is treated as a range with a random offset less than the step value. This can be used to avoid thundering herd problems where multiple machines contact a server all at the same time via cron jobs. The syntax is similar to the existing range/step syntax but uses a random range. For example, instead of "0-59/10" in the minutes field, "0~59/10" can be used to run a command every 10 minutes where the first command starts at a random offset in the range [0,9]. The high and low numbers are optional, "~/10" can be used instead. Requested by job@, OK phessler@
(Comments are closed)
By John McCue (jmcunx) jmcq66@comcast.net on
Nice, I really like all the changes happening with cron
If I understand the usage, if I specify "~/20" in the minutes field, will the job start somewhere between minutes 0-19 ?
Comments
By grey (grey) on http://www.artkiver.com
That would be my guess? I'm not sure and haven't tested personally yet so others please feel free to correct me. This seems similar to -j (jitter) in FreeBSD's cron (which some have referred to as "Vixie cron" but I think Paul Vixie (cited in the manpage of OpenBSD as well) would probably need to shed more light on the branching of that feature without referring to older source code changes in another project, which I guess I'll leave as "an exercise for the reader" (though honestly now I am curious where/when such feature was introduced).
By Ampie Niemand (Ampie) ampien@gmail.com on
Hi, I believe ~/20 means every 20 minutes randomly within the hour.
Comments
By John McCue (jmcunx) jmcq66@comcast.net on
That makes sense
so if I have ~/20, it could execute as:
r1: 17 mins (random time picked)
r2: Then between 37 -- 57 or probably between 20 -- 40 minutes
r3: r2 +20 before the end of the hour or somewhere between 40 -- 59
I will play with it once it hits cron to be sure