[ale] Issues with NTP - synchronizes, then falls behind...

[Chris Woodfield]

Hi,

Having a major problem with a server that's running Debian 4.0 - can't  
seem to keep the clock in sync.

I believe that the root cause is that my motherboard's hardware clock  
is running slow, but I'm trusting that ntpd should correct for that -  
which it is not.

When I start ntp up, it connects to multiple pool.ntp.org servers, and  
appears to properly synch up the internal clock. However, within a few  
minutes, that clock is several seconds behind - what's more is that  
ntp seems to detect this, as shown in the offset field of ntpq -p, but  
doesn't seem interesting in correcting it.

As the diag shows below, I'm skewing a full 10 seconds within 10  
minutes - is this just too far of a delta for ntp to be able to work  
with? If so, is there a config option to resolve this?

Here's a quick shell script I wrote to demonstrate the problem -  
192.168.0.155 is a Mac that syncs to time.apple.com.

--
echo -n "Initial Localtime: "
date
echo -n "Initial RemoteTime: "
ssh 192.168.0.155 date
sudo /etc/init.d/ntp restart
for VAR in 1 2 3 4 5
do
  sleep 90
  ntpq -p
  echo -n "Localtime: "
  date
  echo -n "Remotetime: "
  ssh 192.168.0.155 date
done
--

And the output - note that on first run, it goes from 6 seconds behind  
before ntp restart to ~2 seconds, but then drifts out to a full 10  
seconds behind at the end of the 450 seconds it takes the script to run.

rekoil at tino:~$ sh ntp_run
Initial Localtime: Sun Jul 26 11:45:34 EDT 2009
Initial RemoteTime: Sun Jul 26 11:45:40 EDT 2009
Stopping NTP server: ntpd.
Starting NTP server: ntpd.
      remote           refid      st t when poll reach   delay    
offset  jitter
= 
= 
= 
= 
= 
= 
========================================================================
  host2.kingrst.c 173.14.47.149    2 u   41   64    1   50.214   
844.062   0.001
  mainframe.cynac 216.218.254.202  2 u   27   64    1   31.627   
1142.33   0.001
Localtime: Sun Jul 26 11:47:13 EDT 2009
Remotetime: Sun Jul 26 11:47:15 EDT 2009
      remote           refid      st t when poll reach   delay    
offset  jitter
= 
= 
= 
= 
= 
= 
========================================================================
  host2.kingrst.c 173.14.47.149    2 u    3   64    7   49.684   
2195.19 1354.11
  mainframe.cynac 216.218.254.202  2 u   51   64    3   31.627   
1142.33 1393.21
Localtime: Sun Jul 26 11:48:43 EDT 2009
Remotetime: Sun Jul 26 11:48:47 EDT 2009
      remote           refid      st t when poll reach   delay    
offset  jitter
= 
= 
= 
= 
= 
= 
========================================================================
  host2.kingrst.c 173.14.47.149    2 u   28   64   17   49.684   
2195.19 1922.28
  mainframe.cynac 216.218.254.202  2 u   14   64   17   31.310   
3886.57 1925.79
Localtime: Sun Jul 26 11:50:13 EDT 2009
Remotetime: Sun Jul 26 11:50:19 EDT 2009
      remote           refid      st t when poll reach   delay    
offset  jitter
= 
= 
= 
= 
= 
= 
========================================================================
  host2.kingrst.c 173.14.47.149    2 u   52   64   37   49.684   
2195.19 2647.40
  mainframe.cynac 216.218.254.202  2 u   38   64   37   31.310   
3886.57 2153.12
Localtime: Sun Jul 26 11:51:43 EDT 2009
Remotetime: Sun Jul 26 11:51:51 EDT 2009
      remote           refid      st t when poll reach   delay    
offset  jitter
= 
= 
= 
= 
= 
= 
========================================================================
  host2.kingrst.c 173.14.47.149    2 u   16   64  177   48.996   
8992.49 5287.44
  mainframe.cynac 216.218.254.202  2 u    2   64  177   31.310   
3886.57 3275.18
Localtime: Sun Jul 26 11:53:14 EDT 2009
Remotetime: Sun Jul 26 11:53:24 EDT 2009

Relevant config stuff:

root     22986  0.0  0.1   5492  1692 ?        Ss   11:45   0:00 /usr/ 
sbin/ntpd -p /var/run/ntpd.pid -u 0:0 -g
By default Debian 5 runs ntp as UID ntp, changed to root to eliminate  
potential permissions issues...

from ntp.conf:
server 0.debian.pool.ntp.org iburst dynamic
server 1.debian.pool.ntp.org iburst dynamic

Thanks,

-Chris