Re: Clock problems

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Date: Mon, 18 Apr 2005 14:55:24 -0400
To: For users of Fedora Core releases <fedora-list@redhat.com>

On 4/18/05, Neal Wilkinson <forums.lists@comcast.net> wrote:
> On Mon, 2005-04-18 at 13:55 -0400, David Cary Hart wrote:
> Just right clicking and choosing "adjust date and time." Has always
> worked in the past. I set it to set itself and the stupid thing is
> reading UCT and so all my time stamps are screwed up. I can "display"
> another time zone (even mine) but it still stamps everything UCT.

First, internally almost all timestamps are stored in UTC anyway.
This includes file dates, kernel clock, and so forth. It is just the user
interface software which translates the UTC times into your local
time. So I doubt that your timestamps are really goofed up.

Now which timezone you see is controled by the /etc/sysconfig/clock
configuration file. This is what the system-config-date GUI tool
modifies for you, but you can just as easily edit it by hand. For
example in a typical Eastern Time in the USA, the file might
look like,

ZONE="America/New_York"
UTC=true
ARC=false

The ZONE variable describes which timezone you're in. Actually
this is just a config setting....see below for how the real timezone
is determined.

The UTC describes whether your hardware clock (the one on the
motherboard with the battery) keeps UTC or local time. If you're
dual booting with Windows you'll want it false since Windows always
assumes local time (hence the daylight savings dialog box that
always pops up twice a year). However, if you aren't sharing with
Windows you should probably keep the hardware clock in UTC all
the time. (This shows up as the "System clock uses UTC" checkbox
in the dialog).

The ARC setting (and optionally a SRM setting) are only used on
old DEC Alpha platforms.

See the man page for hwclock(8) for additional information.

Now, the real timezone used to display times is determined for
each process by this set of steps...

1. If the $TZ environment variable is set, use that.
2. If the /etc/localtime file exists, use that (this is a binary file)
3. Otherwise use UTC.

This also means that if you have a multi-user system, each
use could have their own timezone independent of each other.
(The timezone is an application concept, not a kernel property).

Typically under Fedora, it is #2 above which gets used. The
/etc/localtime file is a copy of the corresponding timezone
information file under the /usr/share/zoneinfo directory. For
example, to force your timezone to Eastern USA, your could do

 cp /usr/share/zoneinfo/America/New_York /etc/localtime

-- 
Deron Meranda
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• Previous message: Shawn Burgwald: "Drive limit for FC3 ???"
• In reply to: Neal Wilkinson: "Re: Clock problems"
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