tar: Seconds since the Epoch

1 
1 7.9 Seconds since the Epoch
1 ===========================
1 
1 If you precede a number with '@', it represents an internal timestamp as
1 a count of seconds.  The number can contain an internal decimal point
1 (either '.' or ','); any excess precision not supported by the internal
1 representation is truncated toward minus infinity.  Such a number cannot
1 be combined with any other date item, as it specifies a complete
1 timestamp.
1 
1    Internally, computer times are represented as a count of seconds
1 since an epoch--a well-defined point of time.  On GNU and POSIX systems,
1 the epoch is 1970-01-01 00:00:00 UTC, so '@0' represents this time, '@1'
1 represents 1970-01-01 00:00:01 UTC, and so forth.  GNU and most other
1 POSIX-compliant systems support such times as an extension to POSIX,
1 using negative counts, so that '@-1' represents 1969-12-31 23:59:59 UTC.
1 
1    Traditional Unix systems count seconds with 32-bit two's-complement
1 integers and can represent times from 1901-12-13 20:45:52 through
1 2038-01-19 03:14:07 UTC.  More modern systems use 64-bit counts of
1 seconds with nanosecond subcounts, and can represent all the times in
1 the known lifetime of the universe to a resolution of 1 nanosecond.
1 
1    On most hosts, these counts ignore the presence of leap seconds.  For
1 example, on most hosts '@915148799' represents 1998-12-31 23:59:59 UTC,
1 '@915148800' represents 1999-01-01 00:00:00 UTC, and there is no way to
1 represent the intervening leap second 1998-12-31 23:59:60 UTC.
1