"What time is it?" - "1234567890"
That's how thw answer to one of the most usual questions may be at the moment. 1234567890 is the Unix time at the moment I'm publishing this entry. It the last remarkable number for a long time - 2222222222 will be reached on June 2nd, 2040, on 05:57:02 (CEST).
How do I know what time it is?
date +%s