[ntp:questions] how did ntp service set the maxallowphaseoffset

xiaoniao112233 at gmail.com xiaoniao112233 at gmail.com
Tue Nov 26 02:34:09 UTC 2013

在 2013年11月25日星期一UTC+8下午10时36分19秒,Martin Burnicki写道:
> xiaoniao112233 at gmail.com wrote: > hello : > I had recently start a work about ntp service ,my friends and me use > windows and linux to sync time in ntp.we could use w32time service to > sync linux in ntp. I hope the Linux machine is the NTP server, and your Windows machine is the NTP client. Linux and other Unix-like systems are usually much better timekeepers than Windows is. > In windows we could I found that in the registry: > HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config\ > MaxAllowedPhaseOffset may be could set the offset time between the > local time and the server that they will be synchronize. If out of > range of MaxAllowedPhaseOffset in seconds ,they synchronize,otherwise > not. But I have a question that Is there a paremeter in ntp service > that control the offset like in registry above in windows. As has been noted by others here, ntpd tries to slew the system time smoothly if the estimated time difference is below a certain limit, and just steps the system time if if the determined offset exceeds this limit for some time. The limit is usually 128 ms, but can be changed. Unfortunately you don't tell which Windows version and which version of the NTP service you are using. If you are encountering problems getting the Windows time adjusted properly by ntpd then a a Windows bug can be the reason why. Some Windows versions don't apply small time adjustments to the system time at all. For example, if NTP applies an adjustment less than 16 ticks to the Windows time this is simply ignored by Windows. However, NTP expects the adjustment to have some effect, but if there is no effect then the next time comparison yields a much larger difference than expected, and thus causes another adjustment which is probably larger than necessary. As a summary this can cause large swings in the time adjustment values. A developer version of the NTP package contains a workaround for this Windows bug. The report and fix are discussed here: NTP Bug 2328 - Vista/Win7 time keeping inaccurate and erratic https://bugs.ntp.org/show_bug.cgi?id=2328 The bug report contains a link to the Microsoft support web page explaining the bug: SetSystemTimeAdjustment May Lose Adjustments Less than 16 http://support.microsoft.com/kb/2537623 Even though the MS report only mentions Windows 7, the Windows Server 2008 kernel is similar to Windows 7 and has probably the same bug. So if you want to give it a try you can download a developer version of the NTP package which includes a workaround here: http://support.ntp.org/people/burnicki/windows/ You should try the release version first. Just unzip the ZIP archive, stop the NTP service, copy all extracted files over the files in your NTP installation directory (e.g. C:\Program Files (x86)\NTP\bin\), and restart the NTP service. Also all newer development versions of the NTP binaries should include this. We have found that this version has greatly improved the resulting accuracy on Windows 7 and Windows Server 2008 installations. Please note under Windows you should configure all upstream servers with a line reading server aa.bb.cc.dd iburst minpoll 6 maxpoll 6 where aa.bb.cc.dd has to be replaced with the host name or IP address of your NTP server. Please don't use polling intervals below 6 with the developer version since this prevents the workaround from working correctly as discussed in the bug report. Also, if you don't limit the upper bounds of the polling interval by "maxpoll 6" you may run into this bug: NTP Bug 2341 - ntpd fails to keep up with clock drift at poll > 7 http://bugs.ntp.org/show_bug.cgi?id=2341 On the other hand, the developer version above configured with regard to the hints above has fixed the timekeeping and significantly increase the time accuracy in a number of installations of Windows 7 and Windows server 2008. Hope this helps. Martin -- Martin Burnicki Meinberg Funkuhren Bad Pyrmont Germany

Windows system :Windows Server 2008 R2;
Windows Server 2008 R2 ----NTP sync-----Linux Cent OS 6.2-----w32TIME Sync------Windows XP/7

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