[Nagiosplug-help] check_by_ssh Host key verification failed

[Michael Markstaller]

> > I've some problems with check_by_ssh: I've setup things 
> with a id_rsa 
> > without password and everything works fine from shell as 
> root and with 
> > "su nagios"; added the hosts to the ~/.ssh/known_hosts and 
> copied the 
> > same file to nagios' home, I still get "Host key 
> verification failed" in 
> > the service output.. Any hint where to search further or 
> how to find out 
> > where check_by_ssh looks for known_hosts when run from 
> within nagios ?
> 
> Do the "su" routine again, but instead of specifying a 
> hostname, specify 
> the machine's IP address.
> 
> Thanks,
> 
> Charles

Just tried that, it worked also fine with specifiying IP's instead of the hostname but you pushed me in the right direction: 
adding the FQDN which nagios has in hosts.cfg solved the problem.
I've now added all three hostname,FQDN&IP in the global /etc/ssh/ssh_known_hosts for checked hosts to make sure it works in future and only root can maintain it..

Thanks, Michael