Re: Time-change behavior for cron(8)

[Paul Goyette <paul%vps1.whooppee.com@localhost>]

On Sat, 27 Sep 2014, Christos Zoulas wrote:

> In article <Pine.NEB.4.64.1409280629180.18862%vps1.whooppee.com@localhost>,
> Paul Goyette  <paul%whooppee.com@localhost> wrote:
> > The man page for cron(8) says
> >
> > 	Daylight Saving Time and other time changes
> >
> > 	     ...
> >
> > 	     Time changes of more than 3 hours are considered to be
> > 	     corrections to the clock or timezone, and the new time
> > 	     is used immediately.
> >
> >
> > However this does not seem to be working.  I've recently updated my
> > machine's time-zone from US/Pacific to Asia/Manila.  Yet my daily(5)
> > continues to run based on the original time-zone.  The zone change
> > amounts to a 15-hour difference, certainly enough to trigger the above
> > 3-hour rule.
>
> I don't think that this sentence is worded properly. It means changes
> to system time (the clock), not timezone. In FEATURES:

It's very confusing, especially since the elided text dealing with 
changes to/from "summer time" do not affect "the clock" yet special 
pains are taken to avoid missing or duplicating activities.

> 	 TZ can be set, but cron ignores it other than passing
> 	 it on through to the commands it runs.

Yes setting TZ within the crontab itself has that effect.

But setting CRON_TZ _does_ affect cron(8)'s interpretation of the 
time/date fields in subsequent job lines.  So it would imply that the 
current time-zone (or CRON_TZ if defined) should affect scheduling of 
jobs, and thus changes to time-zone should cause jobs to reschedule.

As written, the man page strongly implies that the jobs are scheduled 
based on local/apparent/displayed time (and NOT based on system clock 
time), and changes to timezone should be observed whther the changes 
are made via CRON_TZ or by changes to /etc/localtime.

> > In order to get the schedule to sync-up with the new zone, I had to
> > kill(1) and then restart cron.
>
> Right...

It might be nice to have a 'kill -HUP' option to effect a restart ore 
easily?


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