Unix time, or POSIX time, is a system for describing instants in time, defined as the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of
Thursday, January 1, 1970 (Unix times are defined, but negative, before that date), not counting leap seconds, which are declared by the International Earth Rotation and Reference Systems Service and are not predictable. It is used widely in Unix-like and many other operating systems and file formats. It is neither a linear representation of time nor a true representation of UTC (though it is frequently mistaken for both), as it cannot unambiguously represent UTC leap seconds (e.g.
December 31, 1998 23:59:60), although otherwise the times it represents are UTC. Unix time may be checked on some Unix systems by typing
date +%s on the command line.
Based on that last paragraph I conclude:
When you ask a UNIX computer computer to give you a
timestampit will give you the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of
Thursday, January 1, 1970.
Please read my post about Coordinated Universal Time (UTC).
The UNIX time is synchronize (the same) on all computers. It doesn’t matter where the computer is. At a particular point in time they all have the same UNIX time (timestamp.)