[ntp:questions] Severe time drift for Undisciplined Local Clock

deon at nulan.co.za deon at nulan.co.za
Wed Mar 28 15:38:34 UTC 2007


Hi all

We have a setup for a group of Linux machines (2.6.8 kernel,FC3) which  
is NOT connected to any outside network. One of the machines has been  
made the Time Server. It uses as it's reference the on-board hardware  
clock (computer motherboard hardware clock, Real Time Clock (RTC)). In  
NTP terminology this referred to as the Undisciplined local clock.

These machines all perform the same function and has some I/O cards  
that causes a heavy interrupt load. The Linux System Clock is  
synchronised to the hardware clock yet experiences upto 1 hour  
timedrift per month!

I have attempted various solutions to no avail. I have read that a  
very high interrupt load will cause the kernel to miss clock cycles  
but why would that matter if the source is a piece of external  
hardware? Further, it seems that the kernel is adjusting the RTC since  
when you get the time from the RTC, it's the same as the System Clock.  
I have checked that the kernel is not in in "11 minute mode" by using   
adjtimex (as per the man page of hwclock). Perhaps I am reading it  
wrong?

In any case here is my /etc/ntp.conf file:

restrict default nomodify notrap
restrict 127.0.0.1
server 127.127.1.0 prefer
fudge 127.127.1.0 stratum 0
driftfile /var/lib/ntp/drift
broadcastdelay 0.008
restrict <ipaddres.255>

My /etc/adjtime file contains nothing

Any suggestions will be appreciated!

Deon




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