Nagios

Nagios offers complete monitoring and alerting for servers, switches, applications, and services.

Install Nagios
Decide whether you want to use lighttpd or apache2 as the nagios frontend, and enable the preferred webserver USE flag for nagios.

Apache Web Server Configuration
Follow the instructions within the PHP Gentoo Wiki.

You'll need to enable the NAGIOS and PHP modules and test PHP works.

Specify Allowed Users
Edit the /etc/groups file and add the user name(s) to the nagios group, whom are allowed access to the Nagios service.

Once done, completely log-out from all shells and relogin for the update to /etc/groups to occur.

Navigate to the Nagios Web Page
Open your browser and navigate to "http://localhost/nagios"