How to Install Nagios 4 on Ubuntu 16.04

This step by step guide will walk you through the steps to install and configure Nagios 4 on Ubuntu 16.04 Server.

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.

ssh username@your_nagios_server_ip

Create a nagios user and nagcmd group. You'll use these to run the Nagios process.

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:

/usr/local/nagios/etc/nagios.cfg

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

Uncomment this line by deleting the # character from the front of the line:

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

Find the email directive and replace its value with your own email address:

/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
        email                           your_email@your_domain.com        ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******

Save and exit the editor.

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

Add the following to the end of the file to define a new command called check_nrpe:

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

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

This defines the name and specifies the command-line options to execute the plugin. You'll use this command in Step 5.

Save and exit the editor.

Now configure Apache to serve the Nagios user interface. Enable the

Apache rewrite and cgimodules with the a2enmod command:

sudo a2enmod rewrite
sudo a2enmod cgi

Use the htpasswd command to create an admin user called nagiosadmin that can access the Nagios web interface:

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

Enter a password at the prompt. Remember this password, as you will need it to access the Nagios web interface.

Note: If you create a user with a name other than nagiosadmin, you will need to edit /usr/local/nagios/etc/cgi.cfg and change all the nagiosadmin references to the user you created.

Now create a symbolic link for nagios.conf to the sites-enabled directory. This enables the Nagios virtual host.


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

Next, open the Apache configuration file for Nagios.


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

If you've configured Apache to serve pages over HTTPS, locate both occurrances of this line: