How NTP Keeps the World Synchronized: The Hidden Protocol Behind Every Network Clock
On June 30, 2012, at 23:59:60 UTC, something unusual happened. A single extra second was added to the world’s clocks to account for the Earth’s gradually slowing rotation. Within minutes, Reddit went offline. LinkedIn stopped responding. Mozilla’s servers ground to a halt. Qantas Airways reported that their check-in systems had failed, stranding passengers across Australia. The culprit wasn’t a cyberattack or a hardware failure. It was a bug in how Linux handled leap seconds—a feature that had been tested only a handful of times in the previous decade. The Network Time Protocol (NTP) had warned servers about the incoming leap second, but the kernel’s high-resolution timer subsystem got confused. Applications that were “sleeping” suddenly woke up all at once, overwhelming CPUs. ...