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Understanding Leap Seconds and the 2005 Linux OS Glitch
A leap second is a one-second adjustment made to Coordinated Universal Time (UTC), the global standard for timekeeping, to reconcile the discrepancy between precise timekeeping (based on atomic clocks) and the Earth’s slightly irregular rotation. While this adjustment is intended to keep our clocks aligned with solar time, it has historically caused significant technical challenges, particularly in computer systems. One notable instance of such disruption occurred in 2005, when a leap second led to a massive glitch in the Linux operating system. Below, we explore what a leap second is, why it exists, and the specific reasons behind the Linux glitch in 2005.
What Is a Leap Second?
A leap second is an additional second inserted into (or, in rare cases, removed from) the UTC time scale to account for the gradual slowdown of the Earth’s rotation. The Earth’s rotation is not perfectly constant due to factors like gravitational interactions with the Moon and Sun, atmospheric pressure changes, oceanic currents, and seismic activity. As a result, a day based on Earth’s rotation (solar time) is slightly longer than the 86,400 seconds defined by highly precise atomic clocks, which measure time based on the frequency of vibrations in cesium atoms.
