Summary: keeping clients clock in sync with server

From: William LeFebvre (
Date: Fri Apr 27 1990 - 11:20:04 CDT

Well, it looks like I am one of the few people left in the workd that
hasn't heard about NTP. Actually, I did know about it, but it didn't
occur to me that (a) it was being used so widely or (b) that it would
solve this particular problem. But it will.

NTP is the Network Time Protocol. It is still somewhat experimental,
but it comes highly recommended by many people. The NTP daemon can
keep the clock on your machine accurate to within (I think) several
milliseconds. It does this by talking with estabilshed time servers
on the Internet, whcih in turn use radios tuned to the WWV stations to
keep their clocks in sync. There are also provisions for setting up
and using your own WWV radios (like Heathkit's "most accurate clock").
Note, however, if you are not on the Internet, then this package
cannot talk to those servers. You would need to have some reliable
source of true time.

There are two packages: ntpd and xntpd, the latter being a little
harder to install than the former. Both are available via anonymous
FTP from in pub/ntp/ntp3.4 and pub/ntp/xntp. There is
also a mailing list for this protocol and program suite:
"". Subscription request should be sent to
"". I am now looking in to using this for
my machines (an I hope to set up a campus-wide ntp system for

Second: many people say that they have something set up in cron to
periodically do rdates. Some people did these once a day, other did
it more frequently. Everyone who uses this method says that they have
not experienced any ill-effects from it. Quite a few people said that
you should make sure that the clients do their rdates at different
times. Many clients hitting the same server with "rdate" requests at
the same time can cause problems.

Others had home-grown methods that are basically variations on the
rdate idea. Someone wrote their own version of rdate that uses
"adjtime" to get the clock in sync.

I received over 50 message---far too many to list the names of all the
senders. My thanks to all. If you have any questions about this,
just let me know.

                William LeFebvre
                Computing Facilities Manager and Analyst
                Department of Electrical Engineering and Computer Science
                Northwestern University

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