NTPD and SecureLevel

[Martin O'Nions]

It's configurable. By default, ntpd will step or 'jump' corrections greater
than 128ms and slew anything smaller. Since it's normally running
continually in the background, I'd consider it unusual for ntpd to need to
make a >128ms correction except perhaps on boot (when any drift in the CMOS
clock will need to be rectified). You can however force it to always correct
time using slewing by specifying the -x option (bearing in mind it takes 33
minutes to slew 1 second). You can also change the step threshold from 128ms
if you really feel the need, using the tinker command in ntp.conf IIRC.

If your machine is going to be regularly powered down for a period, then an
ntpdate at startup seems reasonable. If it'll be running most of the time
though with ntpd active, it shouldn't be making anything more than very
minor slewed corrections, albeit on a frequent basis.

At least, that's how it's always worked for me...

> -----Original Message-----
> From: owner-freebsd-stable at freebsd.org [mailto:owner-freebsd-
> stable at freebsd.org] On Behalf Of David Magda
> Sent: 17 June 2004 01:39
> To: Harlan Stenn
> Cc: freebsd-stable at freebsd.org
> Subject: Re: NTPD and SecureLevel
> 
> 
> On Jun 16, 2004, at 20:03, Harlan Stenn wrote:
> 
> >> ntpd(8) doesn't actually change the time by making it 'jump' to the
> >> correct time; it slows down or speeds up the rate at which the timer
> >> runs at.
> >
> > Sometimes ntpd will step (jump) the time.
> 
> Yes, I've noticed that as well (it appears in my logs). AFAICT there's
> a period of time in which NTPd needs to 'stabilize' and then it slews
> the time after that point. It's been a while since I've looked into the
> NTP algorithm in detail though.
> 
> You may want to ask about it in the Usenet group
> comp.protocols.time.ntp for details.
> 
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