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A most unusual temporal issue

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Most of us have suffered time-related woes, dealing with servers that just can’t keep their clock straight even with NTP. Well we’ve just come across a new one, and NTP isn’t going to save the day – what happens when you have multiple misbehaving clocks? We first noticed the problem when reloading the firewall on the host, a KVM server that had been virtualised from hardware. We use filtergen for ruleset generation, and one of its postreload scripts restarts fail2ban, an anti-bruteforce tool. One part of fail2ban’s initscript makes a call to sleep 1 to give things time to settle. We noticed that the invocation of sleep was taking more than a second, much more. Something wasn’t right and the automatic 15sec rollback was kicking in, having not received explicit…

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