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Meet the Guy Whose Software Keeps the World's Digital Clocks In Sync (ieee.org)
New submitter Wave723 quotes a story on IEEE: In many cases, the internal clock that ticks away in a laptop or desktop computer is synchronized to an official time service maintained by the U.S. National Institute of Standards and Technology (NIST). This free service shares Coordinated Universal Time with personal devices, web browsers, financial trading software and e-mail programs throughout the world. The service receives 150,000 requests per second (roughly 16 billion a day) from systems that repeatedly ask, 'What time is it?' "If you have a PC, it's probably synchronized to the time service," says Judah Levine, the man who originally built servers and programmed software to send time over the Internet for NIST back in 1993.
Biggest problem is that there can't be anything but 86400 seconds in a POSIX day _and_ it enumerates time as seconds since 1/1/70, two things which are mutually exclusive. "Right" time fixes some things, but can break stuff which expects POSIX time.
But yes, ntpd (the reference implementation) is very broken - it doesn't even follow its own RFC with regard to enumerating time. Of course, anyone who is inclined to produce a correct implementation will bump into the fact that the reference implementation is spewing incorrect timestamps everywhere, and systems expect that. It was developed to keep POSIX time, so just like POSIX, doesn't deal well with leap seconds or UTC.
"National Security is the chief cause of national insecurity." - Celine's First Law
Judah Levine, the gentleman mentioned in the article, built interfaces to existing atomic clocks that allowed other clocks to synchronize with them, which is a worthy achievement.
But today, the vast majority of synchronized clocks are being kept synced by NTP across the Internet, not by radio signals. And although Levine also implemented NTP interfaces at NIST, he didn't invent NTP nor was he responsible for its dominance of Internet timekeeping.
The man who invented NTP and originally wrote the implementation was David L. Mills of the University of Delaware.
Mills is also the man who created the Fuzzballs and EGP, making global-scale internetworking possible.
That's essentially what NTP does. It runs in the background as a daemon and disciplines the local clock to keep it in sync with the upstream servers. It won't jump the time unless you tell it to, choosing instead to slow/speed the passage of time to stay in sync.
IIRC, the amount needed to discipline the local clock is stored in the drift file.
This all works very well as long as your clock crystal is mostly rational and doesn't jitter too much based on temperature variation.