Nagios Support Forum

I'm an absolute Nagios newbie (first time working with it). The company I'm working for is using Nagios 3.5, and most web content is out of date, sadly. It's also my first time working this "seriously" with Linux, so it's still a little foreign to me.

I somewhat understand the concept of Nagios plugins, but if someone could explain to me with more beginner-friendly terms what exactly is happening, and how I install a Nagios plugin and use it with the clients (NSClient++).

The clients (they're all Windows machines), right now, are just running the basic check_nt package that monitors the hardware. It only monitors the C:\ drive of the machines, however, and the company wants to monitor all the drives. This has proven to me to be way more difficult than I anticipated, or maybe I'm just tackling the problem wrong.

The Nagios server is running CentOS 6.

The check_nt plugin can check all disks or just one depending on arguments. It can also check memory usage, CPU service states, etc.
There are plugins that come as part of nsclient so check if one that does what you want isn't already there. To install a plugin you copy it to the (if I recall) scripts dir, and add the command definition to nsclient.ini and restart the nsclient service. Then on the nagios host, define a nagios service to run the check.
Using your disk check as a start, you might look at the check_nt file location, and check_nt in nsclient.ini on windows, and the disk check service in nagios.