[ntp:questions] drift file set to -500

Martin Burnicki martin.burnicki at meinberg.de
Thu Nov 29 14:13:38 UTC 2007


Aggie,

Aggie wrote:
> Harlan,
> 
> I have been usign the -g option everytime i run ntpd.

This is only to allow a large initial time offset to be accepted by ntpd.
Normally ntpd stops itself if the time offset exceeds ~1000 seconds, and
adds a warning to the syslog saying you should first set the system time
manually to approximately the right time.

>> Do I recall you said you were using HZ=60?  If so, I recommend trying
>> HZ=100 instead.
> 
> Ok, I will try that tomorrow. I'm testing how many second I gain
> without runninig ntpd. Btw, what is the HZ for? what does it do?

HZ is a constant value indicating how many timer tick interrupts occur per
second. On a Unix-like system you can modify that value and recompile the
kernel to change the timer tick rate according to your needs.

HZ=60 should yield a timer tick interval of 16.667 ms. Many Linux systems
run with HZ=100, and Windows usually has a timer tick interval of 15.625 ms
which is ~1/64Hz. I'm absolutely not familiar with VxWorks, so I don't know
whether it's more like Windows, more like Unix, or whatever, and whether
the timer tick rate can be changed in VxWorks.
 
>> If you look at your logfile output, are you seeing time steps of
>> approximately the same amount at approximately the same time intervals?
> 
> Where do I check the time step? please give me know instruction for
> this.

If VxWorks provides a logging mechanism like syslog under Unix, or the event
log under Windows, you should see the log messages there. If you have
configured ntpd to write to its own log file (if that's supported under
VxWorks) then you should look at that file. 

Every time ntpd steps the time a "time reset" message is generated, followed
by a "synchronization lost" message because ntpd resets its internal
filters.

Having a look at the loopstats, and how the offset develops, might give us
more clues ...

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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