Unix Epoch is the system for describing time in Unix and Unix like systems. It starts on 00:00:00 January 1st; 1970.
Unix time is the number of seconds that have elapsed since the start of the Unix Epoch. This Unix Epoch time is an ever-incrementing counter which goes up every second and shows the number of seconds elapsed since 00:00:00 UTC on January 1, 1970. Such large numbers are pretty useless in their raw form for the tasks of confirming current time and date, but they're perfect for measuring between two points in time – it's easier and quicker to find difference between two Unix timestamps that calculate the same between two human-readable timestamps.
Times and dates you see and work with on your Linux desktop or server are all derived from Unix time: your operating system confirms the Unix Time first and then uses standard library procedures to convert it into commonly used formats we can actually read.
How To Find Out Unix Time
You can get current Unix time using the date command:
$ date +%s 1547311301
Without any parameters, date command will show you a more readable current tkme:
$ date Sat Jan 12 16:41:43 UTC 2019
If you are sporting the recent bash 5.0 release, you don't even need the date command: just use the EPOCHSECONDS variable like this:
$ echo $EPOCHSECONDS 1547318486