Re: questions about cron.daily

[Dan Ritter <dsr@randomstring.org>]

Tom Furie wrote: 
> On Fri, Apr 07, 2023 at 08:05:18AM +0800, ken@openmbox.net wrote:
> > Are the time format in /etc/crontab just random? why they are 6:25, 6:47
> > etc?
> 
> They aren't *random*, though they are somewhat arbitrary. The daily tasks
> run at 6:25, a time chosen by someone somewhere back in the mists of time as
> a time that the system is likely to be quiet. The daily tasks still run on
> the days the weekly tasks are scheduled, so some time displacement is
> factored in to give the daily job time to finish. Likewise with the monthly
> allowing for both the daily and weekly.

It's also the case that if you have a dozen, hundred or ten
thousand machines, you might not want them all doing the same
thing at precisely the same time -- especially if it's disk,
power or network intensive.

So spreading out jobs is often a good idea. Automated deployment
systems usually come with a way of randomizing the initial
install of a cronjob.


-dsr-