[ale] Solved - Re: Issues with NTP - synchronizes, then falls behind...
Chris Woodfield
rekoil at semihuman.com
Sun Jul 26 18:07:23 EDT 2009
I think these are internal clocking systems that are available in the
kernel, and if you had an external device such as a GPS receiver,
you'd see that in the available_clocksource readout also. I'd just
like to know what the difference between the multiple "sources"
available in the kernel are.
-C
On Jul 26, 2009, at 3:08 PM, Stephen R. Blevins wrote:
> 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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>>
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