Unix time (also known as POSIX time or Epoch time) is a system for describing instants in time, defined as the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, not counting leap seconds. It is used widely in Unix-like and many other operating systems and file formats. Because it does not handle leap seconds, it is neither a linear representation of time nor a true representation of UTC. Unix time may be checked on most Unix systems by typing date +%s on the command line.
At 03:14:08 UTC on Tuesday, 19 January 2038, 32-bit versions of the Unix time stamp will cease to work, as it will overflow the largest value that can be held in a signed 32-bit number (7FFFFFFF16 or 2,147,483,647). Before this moment, software using 32-bit time stamps will need to adopt a new convention for time stamps, and file formats using 32-bit time stamps will need to be changed to support larger time stamps or a different epoch. If unchanged, the next second will be incorrectly interpreted as 20:45:52 Friday 13 December 1901 UTC.
At 06:28:15 UTC on Sunday, 7 February 2106, the Unix time will reach FFFFFFFF16 or 4,294,967,295 seconds which, for systems that hold the time on 32 bit unsigned numbers, is the maximum attainable. For these systems, the next second will be incorrectly interpreted as 00:00:00 Thursday 1 January 1970 UTC.