====== Install Nagios Server ======

Nagios is an enterprise class, open source software that can be used for network and infrastructure monitoring. You can monitor servers, switches, applications and services etc. It will alert the System Administrator or other groups when something goes wrong and also alerts back when the issues have been rectified.

First, make sure that all of the latest patches are installed.

<code bash>
sudo apt-get update
sudo apt-get dist-upgrade
sudo reboot
</code>

Install dependencies<code bash>
sudo apt-get install build-essential libgd2-xpm-dev openssl libssl-dev apache2-utils unzip snmp
</code>

Create Nagios User and Group<code bash>
sudo useradd nagios
sudo groupadd nagcmd
sudo usermod -a -G nagcmd nagios
sudo usermod -G nagcmd www-data
</code>

Install Nagios Core<code bash>
cd /tmp
curl -L -O https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.3.4.tar.gz

tar xvf nagios-*.tar.gz

cd nagios-*

./configure --with-nagios-group=nagios --with-command=nagcmd

make all

sudo make install
sudo make install-commandmode
sudo make install-init
sudo make install-config
sudo /usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf

chown nagios:nagcmd /usr/local/nagios/var/rw 
chown nagios:nagcmd /usr/local/nagios/var/rw/nagios.cmd
</code>

Install Nagios Plugins:<code bash>
cd /tmp
curl -L -O http://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz

tar xvf nagios-plugins-*.tar.gz

cd nagios-plugins-*

./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl
make
sudo make install
</code>

====== Create Web UI Admin Account ======

Create a nagiosadmin account fro logging into the Nagios web interface:<code bash>
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
</code>
then restart the web server software:<code bash>
sudo systemctl restart apache2
</code>

====== Configure Nagios ======

Once the software is installed, you should configure Nagios to your enviornment. There are many good web sites out there that cover this. I will not cover it here specifically since every environment is different.