Friday, 14 March 2014

NTP the *#x+ does that mean?

Linux command ntpq should have defined it's columns within a man page but left it to the Internet to remember, so this page is dedicated to me staying sane:

The character in front of server hostnames from ntpq -p
" " Unresponsive peer, high stratum, Local
* The peer currently being used for time sync
# Fail over peers ready to take over in case one of the first six + peers fail
o Good peer using PPS
+ Good peer and has been included in the final set
Out of threshold, usage discarded
x Out of threshold, usage discarded

refid - how does the remote peer sync time? Popular options:

LOCL - This local host
GPS - GPS satellites, atomic clock source
PPS - Pulses Per Second, mostly from applicable GPS receivers
CDMA - Mobile phone networks using CDMA

st column - stratum of the remote peer

t column:
l = local time source
u = unicast (almost always this is true)
m = multicast
b = broadcast

when - last polled, default in seconds (h - hours, d - days)
poll – how often to poll peer
reach – 8-bit left-shift register - 377 for a perfect peer, 0 for a useless one
delay – Round trip time in milliseconds
offset – The difference for this peer between the local time and the weighted average of our set of peers
jitter – The variance in latency on the network to peer

Hope the above helps someone!

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