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

Stephen R. Blevins srblevi at worldnet.att.net
Sun Jul 26 15:08:33 EDT 2009


Don't know if they support NTP, but the NIST Time and Frequency Division 
may be of help.  http://tf.nist.gov/

YMMV.

Stephen R. Blevins
srblevi at worldnet.att.net


Chris Woodfield wrote:
> After some more poking around, managed to get this fixed, but figured  
> I'd share the solution...
> 
> The problem wasn't anything in ntp - it was, in fact, a crappy  
> internal clocksource. However, on most systems there are multiple  
> clock sources available, and changing them is only an echo $source > / 
> sysfile away.
> 
> Specifically on my box, the magic command was:
> 
> tino:~# cat /sys/devices/system/clocksource/clocksource0/ 
> available_clocksource
> tsc hpet acpi_pm jiffies
> tino:~# cat /sys/devices/system/clocksource/clocksource0/ 
> current_clocksource
> tsc
> tino:~# echo acpi_pm > /sys/devices/system/clocksource/clocksource0/ 
> current_clocksource
> tino:~# cat /sys/devices/system/clocksource/clocksource0/ 
> current_clocksource
> acpi_pm
> 
> Then, in /boot/grub/menu.lst, add "clocksource=acpi_pm" to your kernel  
> boot command args.
> 
> I picked "acpi_pm" because that seems to be the source most often  
> mentioned in the googled results I found when looking this up.  
> However, I couldn't seem to find anywhere was any sort of  
> documentation on what each of these clocksources actually *are*.  
> Anyone able to explain this further?
> 
> Thanks,
> 
> -Chris
> 
> On Jul 26, 2009, at 11:57 AM, Chris Woodfield wrote:
> 
>> 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
>> _______________________________________________
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>> http://mail.ale.org/mailman/listinfo/ale
>>
> 
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