I'ved noticed that munin graphs a few bits of information about timing/kernel statistics that I've never quite understood. Most of my servers seem to stay close to 0, which I presume is good, but one of them is slowly but steadily getting more and more negative on one of the graphs.
Munin graphs the following statistics over time:
- NTP kernel PLL estimated error (secs)
- NTP kernel PLL frequency (ppm + 0)
- NTP kernel PLL offset (secs)
- NTP timing statistics for system peer
Here's an example from munin's docs: http://demo.munin-monitoring.org/time-year.html
Searching around the web for a concise, understandable definition of NTP turns up nothing (except for a bunch of Nagios and Munin graphs), and searching Server Fault turns up a ton of answers that presume the reader knows something about NTP already.
Stack Overflow defines it thusly:
NTP stands for Network Time Protocol, and it is an Internet protocol used to synchronize the clocks of computers to some time reference.
But that seems a little obtuse—does this affect, say, a web server, encryption, or database synchronization?
What is NTP, and why should I care? Are there any stats in particular I should make sure don't get out of control?