[TriLUG] ntp questions

Ryan Leathers Ryan.Leathers at globalknowledge.com
Wed Oct 13 09:39:13 EDT 2004


Suppose I get the current time like so:
[root at example]# /usr/sbin/ntpdate -u 152.2.21.1
13 Oct 09:09:19 ntpdate[23705]: step time server 152.2.21.1 offset
-269.813884 sec

Now I set the hardware clock like so:
[root at example]# /sbin/hwclock --systohc

When I get the time again using ntpdate there will be some offset like so:
[root at example]# /usr/sbin/ntpdate -u 152.2.21.1
13 Oct 09:10:26 ntpdate[23709]: adjust time server 152.2.21.1 offset
0.000708 sec

So my questions about ntp are these:
Once I have configured ntp.conf, set the hardware clock to ntp time and
started ntpd, I still expect some drift.
I understand that if the drift becomes too great then ntp will "give up" and
I'll be left to my system clock.
How much drift is "too much"?

I also assume that NTP will handle drift just peachy fine in all but the
most bizarre circumstances.  Still, I'm the kind of guy who wears a belt AND
suspenders.  How can I tell if the system clock is being correctly governed
by ntp? 

Given the following command and output:
[root at example]# /usr/sbin/ntpq -c rv 152.2.21.1
status=06f4 leap_none, sync_ntp, 15 events, event_peer/strat_chg,
version="ntpd 4.1.1a at 1.791 Tue May  7 12:32:32 EDT 2002 (3)",
processor="sun4u", system="SunOS5.8", leap=00, stratum=2, precision=-18,
rootdelay=17.917, rootdispersion=23.312, peer=34696, refid=time-a.nist.gov,
reftime=c517ab68.525afc36  Wed, Oct 13 2004  9:26:00.321, poll=10,
clock=c517ac63.fc442048  Wed, Oct 13 2004  9:30:11.985, state=4,
offset=-2.989, frequency=7.621, jitter=4.703, stability=0.010

I am curious about where the values reftime, clock, and offset come from.
I can't find a man entry for ntpq :(





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