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.