[Ilugc] [LIH]Re: [TwinCLinG] [Cross-Post] How does Linux cron deal with DST?

[Suresh Ramasubramanian]

Binand Sethumadhavan wrote:
> Today (or rather, tonight) is when most of North America switches to
> Daylight Saving Time. I am curious how Linux cron deals with this
> change. I'd imagine:

Different distros seem to handle it differently - possibly using patched 
cron versions.

This patch makes cron use UTC http://widell.fulhack.nu/bd/dst/

	srs

ps: cron (1M) on hp/ux - http://docs.hp.com/en/B2355-90129/cron.1M.html

> Spring and Autumn Time Transitions
> 
> On the days of daylight savings (summer) time transition (in time zones and countries where daylight savings time applies), cron schedules commands differently from normal.
> 
> In the following description, an ambiguous time refers to an hour and minute that occurs twice in the same day because of a daylight savings time transition (usually on a day during the Autumn season). A nonexistent time refers to an hour and minute that does not occur because of a daylight savings time transition (usually on a day during the Spring season). DST-shift refers to the offset that is applied to standard time to result in daylight savings time. This is normally one hour, but can be any combination of hours and minutes up to 23 hours and 59 minutes (see tztab(4)).
> 
> When a command is specified to run at an ambiguous time, the command is executed only once at the first occurrence of the ambiguous time.
> 
> When a command is specified to run at a nonexistent time, the command is executed after the specified time by an amount of time equal to the DST-shift. When such an adjustment would conflict with another time specified to run the command, the command is run only once rather than running the command twice at the same time.
> 
> Commands that are scheduled to run during all hours (there is a * is in the hour field of the crontab entry) are scheduled without any adjustment.



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