Hi Mark,
On Wed, 18 Apr 2001, Mark Hannah wrote:
> Can anyone help me with a problem that has been driving me crazy for the last
> few weeks?
>
> Since we switched to BST, my linux time has somehow got an hour ahead.
> I can chage the time by doing :-
>
> date --set='-1 hour'
>
> but, on the next re-boot the time reverts back to being an hour fast.
> Can anyone tell me what is going on?
Is this a dual boot with a windows machine, by an chance ?
Ok, There are two distinct clocks on a PC a `hardware' clock (works when
the power is off, but tends to drift badly) and a `system' clock
(maintained by Linux in software, generally a lot better but not perfect).
On power-up (in /etc/rc.d/rc.sysinit for the curious), Linux reads the
time from the hardware clock. There are two conventions for the hardware
clock: storing UTC or local time. If you store UTC in your hardware clock,
then you don't have to alter the clock when entering BST, if you store
local time then you do.
To alter the hardware clock, use the hwclock command, e.g.:
hwclock (look at current time in hardware clock)
hwclock --systohc (copies system clock to hardware clock, assuming
hardware clock stores local time)
hwclock --systohc --utc (as above but hardware clock stores UTC)
Unfortunately, windows assumes that the hardware clock stores the local
time and will adjust the clock accordingly when entering BST, hence the
problem. You can either reset the clock to UTC and live with windows
having the wrong idea of time, or update Linux to mirror windows'
behaviour. If you have a RedHat machine, look at the /etc/sysconfig/clock
file and change UTC=true to UTC=false.
HTH
Paul.
PS. If you are going to use ntp (which is very good) make sure you've
updated your copy. There's a vulnerability that can lead to a remote root
compromise. Updates are available from RedHat (and I assume SuSE,
mandrake, ...)
------------------------------------------------------------------------------
Paul Millar yo-yo, n. :
Particle Physics Theory Group Something that is occasionally
Department of Physics and Astronomy up but normally down.
University of Glasgow, (see also Computer)
Glasgow G12 8QQ, [EMAIL PROTECTED]
Scotland +44 (0)141 330 4717
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