Another way to communicate with NSClient++ is over NRPE (described in more detail in Chapter 8). UNIX machines offer a way to run external commands via NRPE. In this case, the protocol can be used for querying internal functions as well as running external commands or scripts.

NSClient++ requires the modification of the NSC.ini configuration file in order to offer querying data over NRPE. The first thing that needs to be done is to enable NRPEListener.dll and CheckExternalScripts.dll entries in the modules section. The first one is responsible for handling NRPE protocol, while the second module allows the creation of aliases for internal commands and external scripts.

NSClient++ can be configured to use both internal commands and external scripts to perform actual checks. Internal commands define aliases for checks that will be done internally, without launching external applications. NSClient++ allows the definition of aliases that are used later on when...