The Unix operating system is closely linked to the C programming language. In C the standard structure for representing time is called 'time_t'. In the vast majority of implementations time_t is a 32 bit signed integer.
The number represents the number of seconds since the epoch date of 1970-01-01 00:00:00.
Using a 32 bit signed integer means that the maximum possible date is 2038-01-19 03:14:07.
If the number is unsigned then the maximum possible date is 2106-02-07 06:28:15.
Because of the limitations of a 32 bit time_t there are moves to upgrade the specification to a 64 bit signed integer. As far as I am aware there are currently very few implementations of this standard, however it is included in TimeLord to assist with analysis and to help to future-proof the application.
Be aware that Linux computers can have their hardware clock set to UTC or to a local time.
The way that Unix and Linux deal with time zones is dealt with in: