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Accepted
Martin
Asked: 2010-07-16 05:48:18 +0800 CST

what is the easiest way to test the impact of NTP step changes on other software?

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During testing of our configuration of Red Hat Cluster System, NTP stepped the time by 16 seconds, and soon afterwards the cluster software locked up.

ntpd[30917]: time reset -16.332117 s

I need to repeat the failure to ensure that it was not just a coincidence. My intention is to get NTP to step the time back repeatedly until either a) I give up or b) the cluster hangs again.

If ntpd uses the same mechanism as /bin/date to set the time, then this is easy. If it uses a different mechanism and I need to trick ntpd to stepping the clock, then I am stuck.

What is the easiest way to do this testing ?

ntp ntpd ntpdate

1 Answers

  1. Best Answer

    If you want to test how a system reacts to time changes, use date to mess with the clock (this is probably sufficient for your case: My instinct says the cluster software doesn't like time() going backwards...).

    If you want to test how a system reacts to time changes initiated by ntpd set up an NTP server, synchronize to it, then change the time on the NTP server (and let the client daemons do the right thing).
    This isn't a huge amount of effort so it's probably worth doing anyway.

    Backward jumps are usually more likely to cause problems than forward jumps, but both should be tested for completeness.

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