[Mailman-Users] Re: funkiness after reboot/clock loosing time

David Champion dgc at uchicago.edu
Thu Sep 21 08:22:37 CEST 2000

On 2000.09.20, in <00d501c02385$dff43540$6a365d18 at groovebox>,
	"jordan" <blurr at txraves.org> wrote:
> this may be a dumb question but, whats the diff between the 
> system clock and hardware clock?  and is there any parallel
> in the dos/windows world(having to sync the 2 clocks)?

The system clock is your kernel's sense of time, regulated by some
arbitrary and undefined timing circuitry.  The hardware clock is a
battery-backed oscillator that keeps time even when your system is
down, braindead, or running DOS.

DOS and Windows detect and sync the clock automatically, and have for
the last 7 years or so.  Linux and *BSD do not.  DOS wants to keep the
hardware clock tuned to your local time, but Unixes prefer to keep it
in GMT.  You thus need some way to configure *how* your hardware clock
will be copied into the system clock at boot time.  setclock does
this.  Most stock Linux distributions will run setclock automatically,
but you have to configure it to get the right results.

Early PC's didn't have hardware clocks.  When Linux first rolled
around, hw clocks were a feature you could not depend on.

Nowadays the only reason your PC wouldn't have a hardware clock is that
your clock battery has died.  If you cannot restore time from your hw
clock, your should find the battery and try replacing it.  These are
standard parts, not hard to find if you have the part number.  They
last several years, though, so if your machine is relatively new, this
is almost certainly not your problem.

 -D.	dgc at uchicago.edu	NSIT	University of Chicago

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