[CentOS] System Time Source

Wed May 24 14:52:49 UTC 2017
Chris Adams <linux at cmadams.net>

Once upon a time, Warren Young <warren at etr-usa.com> said:
> a. It’s transmitting from a fixed location in a time zone you probably aren’t in — US Mountain — being the least populous of the lower 48’s four time zones.  You therefore have to configure time zone offset and DST rules, which means additional software if you want it to track changes to these things.  There were 10 batches of such changes last year!

This really has no bearing on time source; none of the commonly-used
time sources (satellite, terrestrial radio, or network) carry time zone
information (although WWVB does carry a bit to indicate if US DST rules
are in effect).  They each use a single global time scale (although
unfortunately, not the _same_ time scale).

> GPS time is a much better solution, but it’s power-hungry, as you probably know from running GPS on your smartphone.  This rules it out for laptops.

Not exactly; laptop batteries' capacity is an order of magnitude larger
than phone batteries.

> The GPS transmitters probably have a higher received signal strength than WWVB, but cinderblock walls and grids of 42U equipment racks block the GPS signal quite well.  This is why data centers with such clocks generally have to run an antenna to the outside for their clock.  That makes it far more expensive than just connecting to an upstream NTP server.

No, GPS is lower signal strength than WWVB, at least for most of the
continental US (although WWVB signal strength varies significantly based
on the time of day, because it is a low frequency signal).
Chris Adams <linux at cmadams.net>