Hello everybody, I am trying to have a stable system clock on my Xen based VPS, so I installed ntpd. When I used ntpdate once a day, I noticed that the drift is quite a lot. So after I use ntpd, based on the output on the syslog, it seems that my system clock is drifting for about 2.3 seconds in 16 minutes as below:
Aug 22 19:14:59 myvhost ntpd[3688]: time reset +2.431644 s Aug 22 19:15:28 myvhost ntpd[3688]: synchronized to 213.239.214.170, stratum 2 Aug 22 19:15:54 myvhost ntpd[3688]: synchronized to 213.133.108.253, stratum 2 Aug 22 19:16:42 myvhost ntpd[3688]: synchronized to 213.9.73.106, stratum 2 Aug 22 19:30:45 myvhost ntpd[3688]: time reset +2.314923 s Aug 22 19:31:01 myvhost ntpd[3688]: synchronized to 213.9.73.106, stratum 2 Aug 22 19:31:43 myvhost ntpd[3688]: synchronized to 213.239.195.212, stratum 2 Aug 22 19:32:15 myvhost ntpd[3688]: synchronized to 213.9.73.106, stratum 2 Aug 22 19:46:06 myvhost ntpd[3688]: time reset +2.275680 s Aug 22 19:46:41 myvhost ntpd[3688]: synchronized to 213.9.73.106, stratum 2 Aug 22 19:47:17 myvhost ntpd[3688]: synchronized to 213.133.108.253, stratum 2 Aug 22 19:48:04 myvhost ntpd[3688]: synchronized to 213.239.195.212, stratum 2 Aug 22 19:48:12 myvhost ntpd[3688]: synchronized to 213.9.73.106, stratum 2 From what I understood, ntp is used to compensate the drifting instead of changing the clock as ntpdate does, which makes the system clock jumps. But when I run the following command, I can see that ntp is doing the same as ntpdate: # while true; do date; sleep 1; done . . Sat Aug 22 19:30:41 CEST 2009 Sat Aug 22 19:30:42 CEST 2009 Sat Aug 22 19:30:46 CEST 2009 <-- jumps 4 seconds Sat Aug 22 19:30:47 CEST 2009 Sat Aug 22 19:30:48 CEST 2009 . . Sat Aug 22 19:46:02 CEST 2009 Sat Aug 22 19:46:03 CEST 2009 Sat Aug 22 19:46:06 CEST 2009 <-- jumps 3 seconds Sat Aug 22 19:46:07 CEST 2009 Sat Aug 22 19:46:08 CEST 2009 . . I think the only way to prevent this kind of jumping clock affect, is to adjust the kernel clock tick and frequency. On my server at home, I can do that using the adjtimex. But on my VPS, I can not because I don't have /dev/rtc or any rtc device. Is there any way to compensate the clock tick and frequency without having /dev/rtc? I know that it is problematic to run ntpd on Xen domU, but could anybody give me some suggestion to have a stable system clock? FYI, the only settings that I have tried are the followings: myvhost:~# cat /proc/sys/xen/independent_wallclock 1 myvhost:~# cat /sys/devices/system/clocksource/clocksource0/current_clocksource jiffies Thanks a lot in advance for your help. Kind regards, Anto _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
