That is a lot of words to cover a simple concept: The specific random values are selected when cron(5) loads the crontab file. New numbers are chosen when crontab -e is used.
If you understand that, the conclusions are obvious. Raul Miller <rauldmil...@gmail.com> wrote: > That's a poorly phrased question, to be honest. > > In one sense the point in time where the job is scheduled has to be > different -- it's a point in time in a different 24 hour period. > > But in another sense (a sense closer to what you probably intended) > the point in time can't be guaranteed to be different. There's a > finite number of minutes in a day and picking one pseudo-randomly > would occasionally collide. Consider, as an extreme example, a system > which reboots often and is only up for 1 minute every 24 hour period. > > But, such collisions should be rare, and that specific extreme case > example was ludicrous. > > Anyways, on a normally operating machine, you should expect the same > minute to be used slightly more often than once every four years. And, > a difference less than 2 minutes would happen more often (around once > a year, depending on exactly where you draw the line). > > But, if you don't trust what I have said here (and maybe you should > not) what you really want to understand is the algorithm being used, > and the best way to discover that is to look at the implementation. > https://www.openbsd.org/anoncvs.html -- Specifically, you'll want to > look at the implementation of get_range() in usr.sbin/cron/entry.c > > FYI, > > > -- > Raul > > On Thu, Apr 16, 2020 at 12:41 PM Andreas Kusalananda Kähäri > <andreas.kah...@abc.se> wrote: > > > > Thanks for that! > > > > Also, considering a job scheduled like > > > > ~ ~ * * * somecommand > > > > I'm assuming, provided that the cron daemon is not restarted, this would > > run the job at a single random point in each 24h period, right? A > > *different* point in time, each 24 period? > > > > > > > > On Thu, Apr 16, 2020 at 10:28:34AM -0600, Theo de Raadt wrote: > > > Yes. > > > > > > But that problem already existed with the minutes field being >close to > > > the moment cron was restarted. > > > > > > Only difference is now you don't know the minute. > > > > > > > > > Andreas Kusalananda Kähäri <andreas.kah...@abc.se> wrote: > > > > > > > Thanks for the ~ crontab(5) feature! > > > > > > > > Question: If the cron daemon is restarted (e.g. via reboot) during the > > > > interval during which a cron job may be randomly triggered, is there a > > > > risk (or even guarantee) that the job may run a second time? > > > > > > > > > > > > Regards, > > > > > > > > -- > > > > Andreas (Kusalananda) Kähäri > > > > SciLifeLab, NBIS, ICM > > > > Uppsala University, Sweden > > > > > > > > . > > > > > > > > -- > > Andreas (Kusalananda) Kähäri > > SciLifeLab, NBIS, ICM > > Uppsala University, Sweden > > > > . > > >
