[Sussex] NTP Server....

[Andy Smith]

On Wed, Apr 04, 2007 at 09:13:21PM +0100, Richie Jarvis wrote:
> Hi All,
> 
> I recently reinstalled my MythTV server on ubuntu 6.10, and have been 
> having real trouble with times.  What seems to be happening is that the 
> clock is running ahead by about 30 minutes.  I've setup NTP (first with 
> the deb pkg defaults, and recently using pool.ntp.org), and made sure 
> that ntp-server is running.  I have verified that its running, and seems 
> to be receiving times using ntp -p:
> 
> root at sam:/var/log/mythtv# ntpq -p
>     remote           refid      st t when poll reach   delay   offset  
> jitter
> ==============================================================================
> pool.ntp.org    83.170.73.8      3 u    7   64    1   24.319  -1090.6   
> 0.001
> LOCAL(0)        73.78.73.84      5 l    6   64    1    0.000    0.000   
> 0.001
> 
> This would seem to imply (to my untrained eyes) that its working - yet I 
> keep having to reset the time, by shutting down the ntp-server, and 
> running ntpdate pool.ntp.org

1090ms is a very big offset.  But you only have one server, so that
one server could be wrong -- servers in pool.ntp.org are only
periodically tested to see if they are sane; I once saw one that was
wrong by ten years!

I suggest using at least:

0.uk.pool.ntp.org
1.uk.pool.ntp.org
2.uk.pool.ntp.org
3.uk.pool.ntp.org
0.pool.ntp.org
1.pool.ntp.org
2.pool.ntp.org

That way at least one or two bad clocks won't affect you and you can
focus on your own problems.

> Has anyone else had similar NTP issues, and knows whats going on?

What is the hardware?  Some of the embedded and low power CPUs have
very poor clock sources and you need to tell Linux to use a
different source.

For example until a patch made it into the kernel to use a different
time source, my soekris router would lose ticks when the CPU was
sleeping, so the clock went slow by around half an hour a day.

Once the offset gets too big, ntp will give up trying to correct it
and you end up having to use ntpdate.  Don't be tempted to just cron
ntpdate; that will skew the clock every so often which can be quite
bad!

Cheers,
Andy

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