At 03:49 PM 9/21/00 +0800, Gregory Hosler wrote:
>
>Why rdate, instead if ntp, or timed ? (just trying to understand why one
>verses the other...)
rdate has the advantage of being very very easy to use, but it will not
really give you the correct time. A program like ntpdate (or other one-shot
ntp client) will (AFAIK) give you a marginally more exact match to a
particular time server, but your clock will still drift off the correct
time (on PC's a clock drift of 1 to 2 seconds per day is not uncommon). A
more complex system like xntpd will allow you to average time from several
upstream time servers (so your clock won't be wrong just because your 'net
connection is lagged or because the particular time server you pick is
offline) and average the answers over time, meaning that if you have a good
internet connection you can get your clock to within a couple of ms of the
correct time, and since the daemon constantly corrects for drift and chats
with time servers many times a day (as needed) your clock actually stays
right on, rather than drifting off until a sudden jump when you sync it.
IMHO The main reason why a person would want something like xntpd is for
time dependant applications across multiple machines (e.g. if I write my
code from Windows but compile it with a GNU Makefile in Linux I REALLY want
the machine clocks to be in lockstep with each other so that make can
accurately judge modification times), this doesn't actually require the
clocks to be accurate, only consistent, but once you've setup your own ntp
server making it sync to other public NTP servers is so easy that there's
no good reason not to (unless you don't have a full time 'net connection).
--
Someday I'll find that peer and reset his connection!
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