What exactly is required for a daylight savings change?

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Joined: 2008/10/07 01:05:04

What exactly is required for a daylight savings change?

Postby AlanWalker » 2008/10/07 01:34:26

Hi All,

I am a little confused about exactly what is required for a daylight savings update.

Given that "yum update tzdata" would update all of the timezone files in /usr/share/zoneinfo,
and/or changing the /etc/localtime (whether by copying from a relevant timezone file or creating a symlink) will be enough to make the time change at the appropriate time,

My real questions are:
Is it necessary to restart crond after updating /etc/localtime? (I'm pretty sure that the answer to this is yes)
Can the restart of crond be done before the daylight savings takes effect or does it have to be done after the hour shifts?
More to the point, if Yum updates the time zone data, will an automatic yum update do a restart of the crond service (or others affected)? (I think the answer to this is no)
and would a yum update of tzdata (whether automatic or manual) give any hint that restarts of crond are required? (again, I think that is no).
Does all software strictly use /etc/localtime, or does some use /etc/localtime and others use /usr/share/zoneinfo/?

So what would be an experienced sysadmin's view of "best practice" for updating daylight savings changes? Would I be correct in assuming that a tzdata update or /etc/localtime change is necessary followed by a restart of crond (and whatever else may use Time Zone information), but when should the restart of crond (and other services) be done? Should that be when the /etc/localtime is correct, or after the daylight savings takes effect?

Sorry if this is basic stuff, but I can't seem to find all this information in one place. I just got bitten by a system updating its time correctly but cron jobs didn't change to follow.