timestamp,human-readble time 和epoch time

如果你对标题里面的几个概念已经很了解了。那么请跳过这个文章。

什么是Linux epoch time。 国外网上上这么一段：
The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap seconds (in ISO 8601: 1970-01-01T00:00:00Z). Literally speaking the epoch is Unix time 0 (midnight 1-1-1970), but 'epoch' is often used as a synonym for 'Unix time'. Many Unix systems store epoch dates as a signed 32-bit integer, which might cause problems on January 19, 2038 (known as the Year 2038 problem or Y2038).
注意里面的几个关键字，epoch是从GMT开始计算的，然后是从1970年开始计算的。也就是同一时刻 全球的计算机timestamp输出应该是一致的。但如果在不同区域的机器上使用相同的human-read time，那么他们的timestamp必然不同。