Nagios Core Administration Cookbook - Second Edition

Checking an alternative SSH port

In this recipe, we'll learn how to deal with the common situation of a machine running an SSH daemon that is running on an alternative port; in this case, a service definition that uses check_ssh as used in the recipe Monitoring SSH for any host fails, because the plugin defaults to using the standard SSH TCP port number 22.

This kind of setup is common in situations where an SSH server should not be open to the general public and is often employed as a "security by obscurity" method to reduce automated attacks against the server. The SSH daemon is, therefore, configured to listen on a different port, usually with a much higher number, and the administrators who need to use it are told what the port number is.