[gentoo-server] UTC vs. localtime

[gentoo-server] UTC vs. localtime

[Robert Larson]

Hello list,

I just recently switched a few of my servers of to UTC from localtime due to 
an new application deployment relying on UTC time.  I am now having problems 
with this as the real time is not reflected.  I also made these changes to 
gentoo running in usermode linux on one of the machines, and it is now doubly 
off.

I have NTP setup and running on all of these machines, and the TZ environment 
variable is not set.  And, the time would be accurate, if I was on the 
equater; I am not.

This is what I changed:
/etc/conf.d/clock: CLOCK="UTC"
/etc/localtime -> /usr/share/zoneinfo/UTC
It was:
/etc/conf.d/clock: CLOCK="local"
/etc/localtime -> /usr/share/zoneinfo/<my timezone>

I have another machine that does reflect the proper time, and it is set as 
follows:
/etc/conf.d/clock: CLOCK="UTC"
/etc/localtime -> /usr/share/zoneinfo/<my timezone>

At this point, I am a little confused.  These are production systems, and I 
wanted to ask before I just go trying things.  Is it possible that I just 
need to set the clock?  If so, does that mean ntpclient and ntpd either 
haven't been doing their job, or their syncing to the wrong timezone?

I appreciate the help.  :)

Robert
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Re: [gentoo-server] UTC vs. localtime

[Jason Harley]

On Tue, 2005-08-09 at 11:58 -0500, Robert Larson wrote:
<snip>
> I have another machine that does reflect the proper time, and it is set as 
> follows:
> /etc/conf.d/clock: CLOCK="UTC"
> /etc/localtime -> /usr/share/zoneinfo/<my timezone>

It's my understanding that this is proper -- you're saying your hardware
clock is set to UTC/Zulu/Prime Meridian and that your local time zone is
the proper timezone for the area your server lives in.

This is the way I've always done it, but I admit that I haven't done a
terrible amount of research on the issue.

Cheers,
./JRH

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Re: [gentoo-server] UTC vs. localtime

[Ron Bickers]

On Tue August 9 2005 12:58 pm, Robert Larson wrote:

> I just recently switched a few of my servers of to UTC from localtime due
> to an new application deployment relying on UTC time.

Your new application should be able to work the way you had it before.  If it 
requires your local timezone to be UTC, it was poorly designed; complain to 
the developers.

> This is what I changed:
> /etc/conf.d/clock: CLOCK="UTC"
> /etc/localtime -> /usr/share/zoneinfo/UTC

This says your hardware clock is set to the UTC time, and your local timezone 
is also UTC.  That's why you're not getting the right local time.

> It was:
> /etc/conf.d/clock: CLOCK="local"
> /etc/localtime -> /usr/share/zoneinfo/<my timezone>

This is the correct way to configure the clock if your hardware clock is set 
to the local time.

> I have another machine that does reflect the proper time, and it is set as
> follows:
> /etc/conf.d/clock: CLOCK="UTC"
> /etc/localtime -> /usr/share/zoneinfo/<my timezone>

This is the correct way to configure the clock if your hardware clock is set 
to UTC time.  The correct adjustment will be made from the hardware clock 
when it needs the local time.

> Is it possible that I
> just need to set the clock?  If so, does that mean ntpclient and ntpd
> either haven't been doing their job, or their syncing to the wrong
> timezone?

If you set CLOCK="UTC", the hardware clock will get set to the same thing no 
matter what your /etc/localtime is.  However, you need to correctly set your 
timezone so you will get the correct local time.

You should check the man pages on this to be sure, but NTP will not adjust 
the clock by more than a certain amount at once, so you may need to set it 
manually with 'date' to something close to the current time.

Hope this helps.

-- 
Ron
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Re: [gentoo-server] UTC vs. localtime

[Ben Munat]

Ron Bickers wrote:
> 
> You should check the man pages on this to be sure, but NTP will not adjust 
> the clock by more than a certain amount at once, so you may need to set it 
> manually with 'date' to something close to the current time.
> 
I just dealt with this on a new gentoo install last night (it's amazing how much one can 
forget between installs!).

The ntp ebuild comes with two rc scripts: ntpd and ntp-client. ntpd you already know 
about, but if you run ntp-client ("/etc/init.d/ntp-client start", that is...), it will 
fetch the correct time and set it for you (using a command called ntpdate... it's 
configured in /etc/conf.d/ntp-client). Then ntpd can keep the time correctly.

b


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Re: [gentoo-server] UTC vs. localtime

[A. Khattri]

On Tue, 9 Aug 2005, Robert Larson wrote:

> At this point, I am a little confused.  These are production systems, and I
> wanted to ask before I just go trying things.  Is it possible that I just
> need to set the clock?  If so, does that mean ntpclient and ntpd either
> haven't been doing their job, or their syncing to the wrong timezone?

Is the BIOS set to UTC?


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Re: [gentoo-server] UTC vs. localtime

[Robert Larson]

On Wednesday 10 August 2005 08:39 am, A. Khattri wrote:
> On Tue, 9 Aug 2005, Robert Larson wrote:
> > At this point, I am a little confused.  These are production systems, and
> > I wanted to ask before I just go trying things.  Is it possible that I
> > just need to set the clock?  If so, does that mean ntpclient and ntpd
> > either haven't been doing their job, or their syncing to the wrong
> > timezone?
>
> Is the BIOS set to UTC?
>
Actually, yes.  And, changing the /etc/localtime to my timezone worked, thank 
you! :)
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Re: [gentoo-server] UTC vs. localtime

[Andrew Cowie]

On Tue, 2005-09-08 at 11:58 -0500, Robert Larson wrote:
> I just recently switched a few of my servers to UTC from localtime 

My sense is that the responses you received in this thread, while
helpful, sorta missed the point.

There's no reason for a server to have any system-wide timezone other
than UTC, so yes,

> /etc/conf.d/clock: CLOCK="UTC"
> /etc/localtime -> /usr/share/zoneinfo/UTC

is correct. In fact, setting the hardware clock to UTC is most correct
for any Linux system - the only tie to mess with it is if the Linux
installation on a machine co-exists with a broken OS, say, Windows
perhaps.

But here's the real trick: *any* individual application can localize the
timezone information it gets by [re]setting the TZ environment variable.
And that should be all you have to worry about.

An example of that in action is slashtime, my timezone tool; see
http://www.operationaldynamics.com/time and the underlying code at
http://research.operationaldynamics.com/projects/scripts/#slashtime
It really isn't much more than resetting the TZ variable for various
timezones I'm interested in, and then calling strftime() a bunch.

AfC
Canberra


[P.S. You may have to recorrect the hardware clock *once*, see `hwclock
--help`. Also, be aware that NTP will only act if the skew is within
certain limits, so if you're way out, it won't do anything]

-- 
Andrew Frederick Cowie
Managing Director
Operational Dynamics Consulting Pty Ltd

http://www.operationaldynamics.com/
Management Consultants specializing in strategy,
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and systems behind the mission critical enterprise.

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Re: [gentoo-server] UTC vs. localtime

[Benjamin Smee]

heya,

On Thu, 2005-08-11 at 12:51 +1000, Andrew Cowie wrote:
> On Tue, 2005-09-08 at 11:58 -0500, Robert Larson wrote:
> > I just recently switched a few of my servers to UTC from localtime 
> 
> My sense is that the responses you received in this thread, while
> helpful, sorta missed the point.

Agreed! You beat me to the post :)

> There's no reason for a server to have any system-wide timezone other
> than UTC, so yes,
> 
> > /etc/conf.d/clock: CLOCK="UTC"
> > /etc/localtime -> /usr/share/zoneinfo/UTC
> 
> is correct. In fact, setting the hardware clock to UTC is most correct
> for any Linux system - the only tie to mess with it is if the Linux
> installation on a machine co-exists with a broken OS, say, Windows
> perhaps.
> 
> But here's the real trick: *any* individual application can localize the
> timezone information it gets by [re]setting the TZ environment variable.
> And that should be all you have to worry about.

Precisely the point. It is worth noting though that the root user should
never set anything in .bash_profile (or equivalent) to change the TZ
var, that should only be done as a user requiring the different time
view. 


On a different note, while someone mentioned the users of ntp-client and
ntpd, it is worth mentioning that openntp doesn't require the same setup
as it IS capable of making large adjustments by itself (ie no annoying
ntpdate -b before starting) and so you can just add the one init script
as supplied. In fact as general I like openntp as a replacement to ntp
BUT AFAIK it doesn't have a ntpq equivalent so its hard to know if its
actually working and how the different peers are functioning.

> [P.S. You may have to recorrect the hardware clock *once*, see `hwclock
> --help`. Also, be aware that NTP will only act if the skew is within
> certain limits, so if you're way out, it won't do anything]

Also worth noting the option:

CLOCK_SYSTOHC="yes"

in /etc/conf.d/clock. This will sync your system time to HW clock on
shutdown and is not a bad idea if you are using a NTPd system.

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