illumos gate

Is there another popular cron implementation that already provides a syntax for this? If so, it seems like it'd be good to avoid inventing another.

Here is what I found just now:

• isc/vixie cron - could not find something like this
• dcron - could not find something like this
• anacron - has a RANDOM_DELAY option, only one minute resolution (https://www.man7.org/linux/man-pages/man5/anacrontab.5.html)
• cronie - has a has RANDOM_DELAY option, only one minute resolution. Also supports a "~" syntax to pick a random value between two numbers at startup. (https://github.com/cronie-crond/cronie/blob/master/man/crontab.5#L153)
• fcron - has a "jitter" option that accepts 0-255 seconds of random delay (http://fcron.free.fr/doc/en/fcrontab.5.html)

I have a draft up on gerrit that uses RANDOMIZED_DELAY in seconds. Happy to either change it to RANDOM_DELAY in minutes or to something like JITTER if we want to keep a way to specify seconds. Any preferences?

I've updated the CR to use RANDOM_DELAY in minutes to match the cronie syntax.

Testing:

I copied the cron + crontab binaries into place, restarted cron and added the following crontab entries:

* * * * * python -c 'from datetime import datetime; print(datetime.now())' >> /tmp/cron-none.log
RANDOM_DELAY=0
* * * * * python -c 'from datetime import datetime; print(datetime.now())' >> /tmp/cron-0.log
RANDOM_DELAY=1
* * * * * python -c 'from datetime import datetime; print(datetime.now())' >> /tmp/cron-1.log
RANDOM_DELAY=2
* * * * * python -c 'from datetime import datetime; print(datetime.now())' >> /tmp/cron-2.log

The logfiles confirm that the expected delay is used:

==> /tmp/cron-none.log <==
2022-01-09 15:27:00.371923
2022-01-09 15:28:00.423843
2022-01-09 15:29:00.497000
2022-01-09 15:30:00.549232
2022-01-09 15:31:00.626922
2022-01-09 15:32:00.705032
2022-01-09 15:33:00.757227
2022-01-09 15:34:00.834806
2022-01-09 15:35:00.881519
2022-01-09 15:36:00.960147

==> /tmp/cron-0.log <==
2022-01-09 15:27:00.371923
2022-01-09 15:28:00.423879
2022-01-09 15:29:00.496990
2022-01-09 15:30:00.549232
2022-01-09 15:31:00.626864
2022-01-09 15:32:00.705005
2022-01-09 15:33:00.757234
2022-01-09 15:34:00.834862
2022-01-09 15:35:00.878436
2022-01-09 15:36:00.960147

==> /tmp/cron-1.log <==
2022-01-09 15:26:55.345657
2022-01-09 15:27:55.397663
2022-01-09 15:28:44.470520
2022-01-09 15:29:16.522952
2022-01-09 15:30:44.600610
2022-01-09 15:31:08.653651
2022-01-09 15:32:28.731371
2022-01-09 15:33:12.808530
2022-01-09 15:34:33.854378
2022-01-09 15:35:22.911618

==> /tmp/cron-2.log <==
2022-01-09 15:20:06.903962
2022-01-09 15:22:15.064165
2022-01-09 15:23:16.119293
2022-01-09 15:24:07.196130
2022-01-09 15:26:04.320180
2022-01-09 15:28:24.443297
2022-01-09 15:30:37.575247
2022-01-09 15:31:10.679027
2022-01-09 15:33:02.783068
2022-01-09 15:35:57.929780

Providing invalid parameters for the RANDOMIZED_DELAY option is handled as expected:

Invalid delay: RANDOM_DELAY=-1
crontab: errors detected in input, no crontab file generated.

Invalid delay: RANDOM_DELAY=foo
crontab: errors detected in input, no crontab file generated.

Man page was looked at with

man -M  usr/src/man/ crontab.1

Also more complex crontab entries still work as expected

*/2 * * * * python -c 'from datetime import datetime; print(datetime.now())' >> /tmp/cron-every-two-mins-no-random.log

2022-01-29 17:52:00.439984
2022-01-29 17:54:00.470712
2022-01-29 17:56:00.501591
2022-01-29 17:58:00.531602
2022-01-29 18:00:00.561686
2022-01-29 18:02:00.592390
2022-01-29 18:04:00.623266
2022-01-29 18:06:00.653606
2022-01-29 18:08:00.684327
2022-01-29 18:10:00.717579