Falsehoods programmers believe about Unix time

And so our falsehoods go as follows:

Unix time is the number of seconds since 1 January 1970 00:00:00 UTC, minus leap seconds. Here’s what that would look like, in quarter-second increments: If you start at 23:59:58:00 UTC and wait one second, the Unix time advances by two seconds, and the Unix timestamp 101 never gets assigned. Here’s what that would look like, in quarter-second increments: If you start at 23:59:60.50 and wait half a second, the Unix time goes back by half a second, and the Unix timestamp 101 matches two UTC seconds.

Source: alexwlchan.net