In article ,
David Nebenzahl wrote:

On 8/13/2009 4:58 AM root spake thus:

isw wrote:

What the NTP process does is essentially to monitor the local clock
compared to a reference to understand just what its errors are, and
synthesize a "perfect" clock from it. The synthesized clock can remain
within a few microseconds (or better) of a reference timekeeper all the
time.

Maybe that works if you leave the computer on all the time. I started
the ntpd daemon early in the morning and by late afternoon the time
was, once again, way the hell off. Since I only care one time, one
day a week what the time is I have set up crontab entries to do the
job.

I see the problem, that seems to have been missed by those suggesting a
software kluge that periodically stuffs the clock with the right value.

Here's an idea I haven't seen in this thread yet: If you're really
interested in getting to the bottom of this problem, how about trying to
determine whether it's the actual clock (RTCC hardware) that's off, or
whether the OS is missing interrupts or there's some other software problem?

How about booting the computah under some other OS, say Windoze or even
DOS, and running a utility that checks the RTCC for accuracy? (Don't
know of any, but I'm ass-uming that there are lots of such utilities out
there. Maybe there's even one for Linux.) That way you could know
whether the clock needs to be tweaked (new crystal as suggested by
others), or whether it's an OS problem.

Just an idea.

As I said earlier, if the local clock (crystal, whatever) is
free-running (not synced to a standard reference using e.g. ntpd), it
*will not* stay accurate because it *cannot* be running at precisely the
proper rate all the time. No matter how often you set it. No matter how
often you tweak that little capacitor (which is very likely *not there*
to tweak in the first place. You can *never* get it "right on". The
question is not whether it is ever "correct", but only how fast it
diverges from "correct" whenever you stop messing with it. The
brilliance and elegance of NTP is that it can take that crappy,
imprecise, piece of temperature-sensitive quartz, and from it synthesize
an amazingly precise timekeeper.

Isaac