Check manual page of ntp.time
NTP time synchronization using ntpd
This check uses the output of ntpq -p as sent by the agent in order
to check the quality of the NTP time synchronization of the client.
If more than one peer is available, NTP chooses the "best" of them
as "system peer". This check only measures the time difference to
that system peer.
The check is CRIT or WARN, if the time supplied by the
system peer is not good enough (see below for parameters). It
is UNKNOWN if no system peer is present or the system peer is
The check is CRIT, when there are NTP peers reachable but non
of those is used by the NTP daemon. That is the case if the time
provided by those peers is too bad.
Note: If you want to check the health of the peers, you might
want to use ntp, which creates one individual check per NTP peer.
If at least one peer is present, exactly one check is created, if
ntp_inventory_mode is set to "summary" or "both".