hi all,
i am new to nagios and am trying to decide whether or not to use it. from what i have read so far, it seems that it is necessary to install an application on the client where is service is running in order to monitor that service. is this true?
also, are there different installations required to monitor services on different OSs?
thanks for the help.
Yes, you’ll have to install probes on your clients if you want to supervise other services than PING.
This will of course depend on the OS of your client. I know of several ways to do that:
-NRPE: it’s an agent on the client listening for incoming requests. It will execute a plug in and return the result to the nagios server
-NSCA: an agent on the client that will execute plug ins and send the results to the nagios server, without requests
-snmp: you can install an snmp manager that will send traps to the nagios server; or that will accept incoming traps, execute a plugin and send the result via snmp
-ssh: same as NRPE
anyway, you’ll have to install something…
Under NT, the agents (NSCA and NRPE) are pre-compiled and should work on every versions.
if you have unix/linux, you’ll have to compile the agents for each version. I’ve done it for 400 servers with 8 different versions; it’s quite tedious, but manageable…
hope this helps 
Maybe I am reading the question incorrectly; but it is not necessary to install client on each machines. Read the documentation for Add on (nagios proxy monitoring).