I have setup Nagios on one of the RHEL Server.As of now, its only monitoring local Machine.
Just want to ask you - Say, I have Nagios running in RHEL4. I have three Machine - fedora 9, fedora 10 and fedora 11. I want to monitor these fedora Machine. Do I need to add up anything into those Fedora's to monitor the servers?if Yes, Can't it be without disturbing the remote boxes?

Yes. NRPE will do what you want. http://www.nagios.org/download/addons

No, you'll have to install NRPE on each machine, unless all you want to know is if they answer a PING.

Hello,

There are several checks that can be performed without installing the NRPE on the servers you want to check. Examples are, like AKviking stated, icmp_ping_alive, checking http, https ports, mysql ports and so on. Of course if you want to monitor more in-depth then you'll have to compile and install the NRPE daemon and the Nagios Plugins which is pretty easy, straigthforward and doesn't have implications on the performance of the remote systems.

Kind regards,

Eric

Is there any monitoring tool which fetches the data without disturbing the remote server?

Maybe there is but I doubt it would be useful. I think that you'll get the best response with the least 'disturbance' on the remote server using the Nagios plugins and NRPE. If you want to control more than just availability using 'external' tools then you'll have to provide access to let's say a database directly to the outside world which includes possible security risks. With Nagios you run everything through the NRPE daemon and you can configure it to only accept connections from the Nagios server, so very little security risk.

And believe me, I have Nagios running in a high availability production environment with offices in 6 European countries without any problem.

Kind regards,

Eric

Wouldn't that violate the security we expect Linux to maintain?

How do you define "disturbed"? If you mean: w/o software
installations: you can extract a fair amount of info by
SNMP (if it's installed) or ssh remote commands.
If you mean: w/o using any CPU and/or RAM - no, that can't be
done at all.