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I have many linux Virtual machine on ESXI, I have configured one linux machine as NTP server and that server is updating its time from NTP server over internet, this server is working properly and updating its time from NTP servers over internet and I can see that from command ntpq -p. Now other virtual machines are taking it as NTP server for some reason it is not updating its time, the result of ntpq -p is as follows

     remote           refid      st t when poll reach   delay   offset  jitter
 X.Y.177.90.75   .INIT.          16 u    - 1024    0    0.000    0.000   0.000
 X.Y.90.1    .INIT.          16 u    - 1024    0    0.000    0.000   0.000

I have been waiting for more than 10 hours but the result never changed !!! :( no firewall issues, configurations on both client and servers are same a part from server IPs and clients are pointing towards local server and local server is pointing towards internet server !!! BTW, I have debian as linux !!! :(

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A reachability of zero suggests that the VMs cannot communicate with one another - either because of basic network issues or due to firewall settings.

I would carry out a range of tests using

  • ping from NTP client to NTP server (but Ping is sometimes blocked by FW)
  • ssh from NTP client to NTP server (arguably less often blocked)
  • ntpdate -d

I have assumed that both and are local addresses of local VMs running NTP as a service. If this isn't the case, please update your question to clarify this point.

P.S. As a sidenote, in the past, my experience has been that you need at least three local NTP servers in a network to provide reliable service to other computers in the network (otherwise clocks sometimes don't converge).

P.P.S I have a feeling VMs may be better off using the host clock than NTP. Using NTP on VMs used to be problematic

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@AAB: You can update your question with new information. This is especially useful if you need to format it or if it is too long for a comment. So long as it clarifies the question, editing your question is an appropriate way to use superuser. – RedGrittyBrick Nov 7 '12 at 9:49

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