What is the Unix Epoch?
Simply put it is the number of seconds that have elapsed since January 1, 1970 at 00:00:00 GMT (1970-01-01 00:00:00 GMT). This allows Unix systems and programs that run upon them to measure and coordinate a point in time.
The largest signed integer that can be recorded by 32-bit systems is 2,147,483,647. This date is 03:14:07 Tuesday, 19 January 2038 UTC. Before then all Unix systems and other programs will have to be upgraded to 64-bit, use a different system or lapse back to 20:45:52 Friday, 13 December 1901 UTC the second after the aforementioned date.