Date: Thu, 6 Apr 2000 10:48:33 -0700 (PDT) From: Dave Runkle <drunkle@home.com> To: Zhihui Zhang <zzhang@cs.binghamton.edu> Cc: Dave Runkle <drunkle@home.com>, Freebsd Questions <freebsd-questions@FreeBSD.ORG> Subject: Re: Best Time Synch Utility Message-ID: <Pine.BSF.4.10.10004061005210.40807-100000@xb.fiddi.com> In-Reply-To: <Pine.GSO.3.96.1000406102647.1032B-100000@sol.cs.binghamton.edu>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, 6 Apr 2000, Zhihui Zhang wrote:
> Can you tell me how precision this command rdate can achieve
> (ms or us)?
> Thanks.
> -Zhihui
Rdate is just a simple little utility that just plucks time from
one server of your choice. It's small and handy, nothing to set up,
just give the command and you're done. There are many time servers
to choose from, and if all you want is to set your time once a day,
then you can use a single-poll utility like rdate. If the server
you're polling gets accurate time (don't they all get their time
from the US Atomic clock in Colorado?), then you'll have a
reasonably correct time.
If you *really* need accuracy, precision in timekeeping, then you
would need to get one of the utilites that poll multiple servers.
Then it really becomes an art - if you're polling multiple time
servers, you've got to take into consideration the distance they are
away, how long it takes the 'time' to get to you, then you've got to
work some sort of average-magic over the data you get from the
various time servers, and you've got your own clock-drift to think
of too. Figure in TTL values, thrown in some Borax and you've got
what... a reasonably correct time. :)
So anyway, to answer your question, no I can't tell you precisely
how many milliseconds rdate would vary from xnptd or another one.
It depends on how accurate you *need* to be.
I'm always late anyway, so what do I care about another 1.5
thousandths of a second?
See the manpage for ntpq, xntpd, xntpdc.
Dennis Ferguson, the writer of xntpd, writes:
BUGS
Xntpd has gotten rather fat. While not huge, it has gotten
larger than might be desireable for an elevated-priority daemon
running on a workstation, particularly since many of the fancy
features which consume the space were designed more with a busy
primary server, rather than a high stratum workstation, in mind.
Whew! I think it's 'time' for a cuppa!
Dave
>
> On Thu, 6 Apr 2000, Dave Runkle wrote:
> > [snip]
> > A really simple one (and it's in the ports) is 'rdate', but
> > size ain't everything. ;) The pkg is only 4k in size. It
> > can be done via cron, once daily, weekly, whatever, stuck in
> > periodic, or even executed from the command line, to set time
> > on your machine or just to check time.
> >
> > # /usr/local/sbin/rdate -s time.u.washington.edu
> >
> > will set your box to the time at your favorite time-server, or just
> >
> > $ /usr/local/sbin/rdate -p time.u.washington.edu
> > Thu Apr 6 09:36:02 2000
> > $
> >
> > to give you the time. User privs to 'print' the time, root to
> > actually set the machine. It has a ' -a ' switch to 'gradually skew
> > the time' to match the server without a sudden hop.
> >
> > Dave
>
>
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.4.10.10004061005210.40807-100000>