what is the relation between nrpe and nagios?

[Santosh Kumar Balasubramani]

when this exception occurs "Connection refused by host".

[Peter Johnson]

Connection refused by host usually means that the port you are attempting to access is not open.

If you would provide some more details about what you are doing and when/where the error shows up we could be more helpful.
TellTheDetails

[Tim Holloway]

"Connection refused by host" means literally what it says. The client (nrpe), attempted to connect to the host (nagios listener) and the host rejected the attempt.

This can happen for 2 primary reasons:

1. There's nothing listening on the host port - the nrpe server isn't running either as a daemon or under the (x)inetd super-server.

2. There's a firewall blocking access to the host port.

Linux firewalls would normally be blocking the nrpe port by default, so if the nrpe server is functioning, it's probably the firewall.

[Santosh Kumar Balasubramani]

Hi Tim,
Linux firewalls would normally be blocking the nrpe port by default. How would i know that Linux firewall is blocking the nrpe port..?
Is there any way that i will overcome from this issue.

[Tim Holloway]

I normally add this iptables predicate to a rule right before the final REJECT/DROP rule in my firewall:

"-j LOG"

That will show all the blocked traffic in the system log, including the nrpe traffic, if it's being blocked.

Most Linux systems will setup their rules to block anything that wasn't specifically approved.