From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of Alain Spineux

On 8/23/07, Steve Berg sberg@mississippi.com wrote:

Simon Jolle wrote:

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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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--On Thursday, August 23, 2007 12:53 PM +0200 Mogens Kjaer mk@crc.dk wrote:

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When to use UTC?

Always :-)

Hehe, I'd love to eliminate local time and I particularly hate daylight saving time. I hate all the clock-changing and getting up an hour earlier. If businesses and schools need to change when they open, then they should change their schedules, and not fiddle around with what's supposed to be a standard measurement. Imagine if we had to change the length of our rulers twice a year! Imagine if 10 degrees meant something different in summer than in winter!

I work and play with people from across North America and around the world and it can be troublesome to coordinate schedules when "5 pm" means something different to everybody. At least the advent of the railroads introduced the idea of standard time, even if it was still only good locally, not globally.

/rant

Mogens Kjaer spake the following on 8/23/2007 11:17 PM:

Kenneth Porter wrote:

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--On Thursday, August 23, 2007 12:53 PM +0200 Mogens Kjaer mk@crc.dk wrote:

...

...

When to use UTC?

Always :-)

Hehe, I'd love to eliminate local time and I particularly hate daylight saving time.

This is irrelevant.

If I set my BIOS clock to use UTC the date command will still show me the correct wall-clock time, including DST.

If I dualboot with Windows, Windows will change the clock when DST changes, then time will be wrong in Linux, hence the need for the two possibilities.

Mogens

You can also tell windows to not follow DST updates.