Nagios, 2nd Edition

13.4 Reacting to Out-of-Date Information of Passive Checks

It lies in the nature of passive checks that Nagios is content with the information delivered. Nagios has no influence over when and at what intervals the remote host delivers them. It may even be the case that the information does not arrive at all.

In order to classify the "knowledge state" of the server as out of date, Nagios has the ability to become active itself, with a freshness check. Like passive checks, freshness checking must be enabled both globally and in the relevant serviceable host object. To do this, you need to set the following global parameters in the file nagios.cfg:

# /etc/nagios/nagios.cfg ... check_service_freshness=1 service_freshness_check_interval=60 check_host_freshness=0 ...