sntpq

== sntpq: a SNTP query program

SNTP is the basic version of NTP that pretty much every NTP server
responds to, even if they don't respond to queries from the venerable
'ntpq' program. There are many SNTP clients that will set your system's
time from one or more (S)NTP servers, but very few programs that will
send a SNTP query to a (S)NTP server and tell you what it responds
with. This is such a query program.

A SNTP query cannot tell you a NTP server's list of peers and time
sources, but it can report the server's current synchronization peer
and various basic information. A typical example:

 ; sntpq ns3.switch.ca
 ns3.switch.ca:
   Stratum:         3
   Time Source:     206.108.0.134 ntp4.torix.ca (ce6c0086)
   Time at xmit:    2018-12-19 19:40:10.247662067 +0000 UTC
   RTT:             64.352066ms
   Precision:       119ns
   MinError:        0s
   Clock updated:   2018-12-19 19:32:49.043288485 +0000 UTC
   Root delay:      36.102294ms
   Root dispersion: 500.656127ms
   local root distance: 550.883307ms (via this server)
   local adjustment:    -1.971151ms (based on this server's time)

Interpreting many of these fields requires knowing something about NTP,
which is out of scope for this README. Note that the 'Time Source' field
only works for IPv4 time sources, because NTP transmits this information
in a 32-bit field and there is no way to fully encode an IPv6 address
into 32 bits. Chris Siebenmann doesn't know what shows up in this field
for IPv6 time sources, so sntpq right now will try to treat them as IPv4
addresses which will probably not work very well.

sntpq has a convenient '-f' option that will follow the chain of
time sources until they run out (or you hit a time source that you can't
query). You can do this by hand, but -f takes the tedium out of it.

	- Chris Siebenmann, December 19 2018