Nagios is a popular open source computer system monitor, network monitoring and infrastructure monitoring software application. Nagios offers complete monitoring and alerting for servers, switches, applications, and services.
Nagios, originally created under the name NetSaint, was written and is currently maintained by Ethan Galstad, along with a group of developers actively maintaining both official and unofficial plugins. N.A.G.I.O.S. is a recursive acronym: “Nagios Ain’t Gonna Insist On Sainthood”, “Sainthood” being a reference to the original name NetSaint, which was changed in response to a legal challenge by owners of a similar trademark. “Agios” is also a transliteration of the Greek word which means “saint”.
Nagios was originally designed to run under Linux, but also runs well on other Unix variants. It is free software, licensed under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.
To install the newest version on an Ubuntu server turns out to be quite trivial, thanks to a greatly streamlined installer. To grab for your server, run:
sudo apt-get install -y nagios3
Follow the prompts when asked, and when the final bits and pieces have been pulled down and installed, you should have a working Nagios installation accessible on your webserver http://localhost/nagios3/ with the username nagiosadmin and whatever password you had selected during the install process.
Config files which you can alter can be found in /etc/nagios3/conf.d/ and to start and stop nagios, you can make use of the service command:
sudo service nagios3 stop sudo service nagios3 start
Related Link: http://www.nagios.org