nagios-plugins (Plugins for the Nagios network monitoring server)

Unlike many other monitoring tools, Nagios does not include any internal
mechanisms for checking the status of hosts and services on your
network. Instead, Nagios relies on external programs (called plugins) to
do all the dirty work. Plugins are compiled executables or scripts (Perl
scripts, shell scripts, etc.) that can be run from a command line to check
the status or a host or service.

Remember to install the Nagios::Plugin perl module and its dependencies to
ensure all functionality of perl plugins.

Remember to install the applications you plan to use plugins with before
installation of nagios-plugins as some plugins are compiled using the relevant
libraries installed on your system for the application being probed.