[Dovecot] "Time just moved backwards" in Dovecot in a Xen DomU

[Patrick Domack]

If you notice in your ntpq dumps you did, you have >400ms of jitter.
That is a hell of alot.

I dunno if it makes a difference but you used 3 servers from the same  
edu, and they have 90ms on them, shouldn't matter, if they where the  
only ones with jitter I would replace them, but all 4 of your entries  
have high jitter.

Jitter stops ntp from doing it's job properly. I'm not sure what is  
causing you jitter to be so bad, but it's caused by the delay amount  
changing from packet to packet. The delay should stay consistant (like  
a ping time). If it keeps bouncing all over the place, ntp can't  
figure out what time it really is, cause it doesn't know how long that  
packet was on the network. You can safely ignore offset, it is just  
how much different your clock is from what the other computer is.

Try adding some of the pool servers in there, like:
server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org

I assume your in the us atleast, if not you could change to eu or  
something (check www.pool.ntp.org)

A few samples from my dom0's (and noticing lots of people changed from  
st 2/3 up to 1 lately it seems)

      remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*18.26.4.105     .PPS.            1 u  813 1024  377    7.939   -2.960   0.937
+64.90.182.55    .ACTS.           1 u  487 1024  377    9.375    4.435   0.670
+204.152.184.72  .GPS.            1 u  339 1024  377   82.343   -6.345   0.956
-10.1.11.62      206.246.118.250  2 u    3   16  377    0.191    0.965   0.085
  10.1.11.69      10.1.11.61       3 u   15   16  376    0.146    0.448   0.036

      remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*206.246.118.250 .ACTS.           1 u  642 1024  377   11.615    1.992   0.934
+209.51.161.238  .CDMA.           1 u  955 1024  377    9.701   -0.562   0.200
-128.105.39.11   128.105.201.11   2 u  665 1024  377   37.122   -2.228   0.634
-10.1.11.61      18.26.4.105      2 u   10   16  376    0.184   -0.916   0.247
+10.1.11.69      10.1.11.61       3 u   11   16  376    0.215   -0.542   0.023

      remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+128.59.16.20    204.123.2.5      2 u   40   64  377    1.873   -0.291   0.092
-198.82.1.203    198.82.247.164   2 u   32   64  357   16.517   -3.454   0.300
-128.2.129.21    69.10.36.2       3 u   41   64  377   28.699    4.447   0.094
-132.236.56.250  129.6.15.29      2 u    2   64  377    9.290   -2.892   0.295
*10.1.11.61      18.26.4.105      2 u    1   16  377    0.161   -0.455   0.051
+10.1.11.62      206.246.118.250  2 u    5   16  377    0.206    0.546   0.020



Quoting PGNet Dev <pgnet.dev+dovecot at gmail.com>:

> just fwiw,  as of 10/06/09 19:03:27 still no errors.  apparently,
> time's moving forward again ...
>
> so, it seems the config above works.  why some others have NOT seen
> the same problems, remains for me a bit of a mystery.
>