In this recipe, we'll learn how to check that the SSH daemon on a remote host is responding to requests using the
check_ssh plugin and the command of the same name. This will allow us to be notified as soon as there are problems connecting to the SSH service.
You should have a Nagios Core 4.0 or newer server with at least one host configured already. We'll use the example of
troy.example.net, a host defined in its own file. You should also understand the basics of how hosts and services relate, which is covered in the recipes in Chapter 1, Understanding Hosts, Services, and Contacts.
It may be a good idea to verify first that the host for which you want to add monitoring is presently running the SSH service ...