[CentOS] UTC vs local time

Ross S. W. Walker rwalker at medallion.com
Thu Aug 23 13:30:58 UTC 2007


> From: centos-bounces at centos.org 
> [mailto:centos-bounces at centos.org] On Behalf Of Alain Spineux
> 
> On 8/23/07, Steve Berg <sberg at mississippi.com> wrote:
> 
> 	Simon Jolle wrote:
> 	> Hi list
> 	>
> 	> I always configure my systems to use our local time 
> (in my case
> 	> /usr/share/zoneinfo/Europe/Zurich) and disable UTC.
> 	>
> 	> What are the differences between UTC and local time? 
> What are their 
> 	> respective advantages and disadvantages?
> 	>
> 	> When to use UTC?
> 	>
> 	> cheers
> 	> Simon
> 	>
> 	>
> 	Not sure if Zurich has any sort of Daylight Savings 
> like we do here in
> 	the US but that is one good reason to use UTC.  Since 
> our clocks shift 
> 	by an hour twice a year it can make log files confusing 
> and have other
> 	side effects.  Using UTC you get a standard time that 
> never shifts.
> 	(Except for the odd leap second every so often.)  
> Personally I use UTC
> 	on my home system and let my shell convert it to my 
> local time zone.
> 	For servers that I manage I always use UTC to avoid the 
> one hour shifts
> 	of DST.
> 
> 
> 
> My understanding of UTC is different :-). 
> For me the only thing changing is the time the hardware/BIOS 
> clock maintains.
> At boot time the kernel read the hwclock apply the local->UTC 
> conversion if required and 
> work only and in any case in UTC. Then application like date, 
> ls, syslog make conversion 
> to localtime when printing time to the user using TZ 
> environement variable or /etc/localtime

I think they were talking about the representation of the UTC
clock under a running Linux environment rather then how it is
saved in the BIOS.

It pretty much is a personal preference, I prefer local time so
I don't have to do math in my head, but for most applications
you can have them write their log entries in local or UTC time.
Sendmail comes to mind here.

DST changes don't bother me, I know when they're going to happen
so it doesn't confuse me when I look at the logs, and most log
analyzers that are worth the money know when to anticipate a
time shift in the logs too.

-Ross

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