How to Install Nagios 4 on Ubuntu 16.04

Installing Nagios 4

There are multiple ways to install Nagios, but we'll install Nagios and its components from source to ensure we get the latest features, security updates, and bug fixes.

Log into your Ubuntu Server that runs Apache.

sshusername@your_nagios_server_ip

sudo useradd nagios

sudo groupadd nagcmd

Then add the user to the group:

sudo usermod -a -G nagcmd nagios

Since we are building Nagios and its components from source, we must install a few development libraries to complete the build, including compilers, development headers, and OpenSSL.

Update package lists to ensure we can download the latest versions of the prerequisites:

sudo apt-get update

Now install the required packages:

sudo apt-get install build-essential libgd2-xpm-dev openssl libssl-dev unzip

Download the source code for the latest stable release of Nagios Core. Go to the Nagios downloads page, and click the Skip to download link below the form. Copy the link address for the latest stable release so you can download it to your Nagios server.

Download the release to your home directory with the curl command:

cd ~
curl -L -O https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.3.4.tar.gz

Extract the Nagios archive:

tar zxf nagios-*.tar.gz

Then change to the extracted directory:

cd nagios-*

Before building Nagios, run the configure script to specify the user and group you want Nagios to use. Use the nagios user and nagcmd group you created:

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

You'll see the following output from the configure command:

Output
*** Configuration summary for nagios 4.3.4 2017-11-09 ***:

 General Options:
 -------------------------
        Nagios executable:  nagios
        Nagios user/group:  nagios,nagios
       Command user/group:  nagios,nagcmd
             Event Broker:  yes
        Install ${prefix}:  /usr/local/nagios
    Install ${includedir}:  /usr/local/nagios/include/nagios
                Lock file:  /run/nagios.lock
   Check result directory:  ${prefix}/var/spool/checkresults
           Init directory:  /etc/init.d
  Apache conf.d directory:  /etc/apache2/sites-available
             Mail program:  /bin/mail
                  Host OS:  linux-gnu
          IOBroker Method:  epoll

 Web Interface Options:
 ------------------------
                 HTML URL:  http://localhost/nagios/
                  CGI URL:  http://localhost/nagios/cgi-bin/
 Traceroute (used by WAP):


Review the options above for accuracy.  If they look okay,
type 'make all' to compile the main program and CGIs.

Now compile Nagios with below command:

make all

Now run these make commands to install Nagios, its init scripts, and its default configuration files:

sudo make install
sudo make install-commandmode
sudo make install-init
sudo make install-config

You'll use Apache to serve Nagios' web interface, so copy the sample Apache configuration file to the /etc/apache2/sites-available folder:

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

In order to issue external commands via the web interface to Nagios, add the web server user, www-data, to the nagcmd group:

sudo usermod -G nagcmd www-data

Nagios is now installed.

Now we'll install a plugin which will allow Nagios to collect data from various hosts.

Installing the check_nrpe Plugin

Nagios monitors remote hosts using the Nagios Remote Plugin Executor, or NRPE. It consists of two pieces:

1.The check_nrpe plugin which is used by Nagios server.
2.The NRPE daemon, which runs on the remote hosts and sends data to the Nagios server.

Let's install the check_nrpe plugin on our Nagios server.

Find the download URL for the latest stable release of NRPE at the Nagios Exchange site.

Download it to your home directory with curl:

cd ~curl -L -O https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.1/nrpe-3.2.1.tar.gz

Extract the NRPE archive:

tar zxf nrpe-*.tar.gz

Then change to the extracted directory:

cd nrpe-*

Configure the check_nrpe plugin:

./configure

Now build and install check_nrpe:

make check_nrpe
sudo make install-plugin

Let's configure the Nagios server next.

Configuring Nagios

Now let's perform the initial Nagios configuration, which involves editing some configuration files and configuring Apache to serve the Nagios web interface. You only need to perform this step once on your Nagios server.

Open the main Nagios configuration file in your text editor:

sudo nano /usr/local/nagios/etc/nagios.cfg

Find this line in the file:

#cfg_dir=/usr/local/nagios/etc/servers

Save the file and exit the editor.

Now create the directory that will store the configuration file for each server that you will monitor:

sudo mkdir /usr/local/nagios/etc/servers

Open the Nagios contacts configuration in your text editor:

sudo nano /usr/local/nagios/etc/objects/contacts.cfg

define contact{
        contact_name                    nagiosadmin             ; Short name of user
        use                             generic-contact         ; Inherit default values from generic-contact template (defined above)
        alias                           Nagios Admin            ; Full name of user
emailyour_email@your_domain.com        ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******

Next, add a new command to your Nagios configuration that lets you use the check_nrpe command in Nagios service definitions. Open the file /usr/local/nagios/etc/objects/commands.cfg in your editor:

sudo nano /usr/local/nagios/etc/objects/commands.cfg

...
define command{
        command_name check_nrpe
        command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}

sudo a2enmod rewrite
sudo a2enmod cgi

sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

sudo ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/ 

sudo nano /etc/apache2/sites-available/nagios.conf 

#  SSLRequireSSL

Order allow,deny
Allow from all

# Order allow,deny
# Allow from all

#  Order deny,allow
#  Deny from all
#  Allow from 127.0.0.1

Order deny,allow
Deny from all
Allow from 127.0.0.1 your_ip_address

sudo systemctl restart apache2 

sudo nano /etc/systemd/system/nagios.service 

[Unit]
Description=Nagios
BindTo=network.target

[Install]
WantedBy=multi-user.target

[Service]
Type=simple
User=nagios
Group=nagios
ExecStart=/usr/local/nagios/bin/nagios /usr/local/nagios/etc/nagios.cfg

sudo systemctl enable /etc/systemd/system/nagios.service
sudo systemctl start nagios