Nagios is a very popular open source monitoring system. In this tutorial, we will cover the installation of Nagios 4 and some basic configuration to to monitor host resources via the web interface.
To follow this tutorial, you must have superuser privileges on the Ubuntu server that will run Nagios and a fully working LAMP stack.
First, update your apt-get package lists:
apt-get update
Then install the required packages:
Because we are building Nagios Core from source, we must install a few development libraries that will allow us to complete the build.
apt-get install build-essential libgd2-xpm-dev openssl libssl-dev xinetd apache2-utils unzip
We must create a user and group that will run the Nagios process. Create a “nagios” user and “nagcmd” group, then add the user to the group with these commands:
useradd nagios groupadd nagcmd usermod -a -G nagcmd nagios
In order to issue external commands via the web interface to Nagios, we must add the web server user, www-data, to the nagcmd group:
usermod -G nagcmd www-data
Install Nagios Core
Create a folder called nagios-installer in the home directory and download the source code for the latest stable release of Nagios Core (nagios-4.1.1 at this time).
mkdir ~/nagios-installer cd ~/nagios-installer wget https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.1.1.tar.gz
Extract the Nagios archive with this command:
tar xvf nagios-*.tar.gz
Then change to the extracted directory:
cd nagios-*
Run the following commands one by one from the Terminal to compile and install nagios.
./configure --with-command-group=nagcmd make all make install make install-init make install-config make install-commandmode /usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
Create a nagiosadmin account for logging into the Nagios web interface. Remember the password you assign to this account. You’ll need it while logging in to nagios web interface.
htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
Now create a symbolic link of nagios.conf to the sites-enabled directory:
ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/
Restart Apache to make the new settings take effect.
service apache2 restart
Download and Install Nagios Plugins
cd ~/nagios-installer wget http://www.nagios-plugins.org/download/nagios-plugins-2.1.1.tar.gz tar xvf nagios-plugins-*.tar.gz cd nagios-plugins-* ./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl make make install
Configure Nagios
The default configuration files will work fine for getting started with Nagios. But you need to put your actual email ID to receive alerts.
Edit /usr/local/nagios/etc/objects/contacts.cfg config file and change the email addres
vi /usr/local/nagios/etc/objects/contacts.cfg
Enable Apache’s rewrite and cgi modules:
a2enmod rewrite a2enmod cgi
Restart apache
service apache2 restart
Check nagios conf file for any syntax errors:
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
If there are no errors, start nagios service and make it to start automatically on every boot.
service nagios start
you may see the following error message while starting nagios service.
Failed to start nagios.service: Unit nagios.service failed to load: No such file or directory.
To fix this error, copy /etc/init.d/skeleton to /etc/init.d/nagios using the following command:
cp /etc/init.d/skeleton /etc/init.d/nagios
Edit file /etc/init.d/nagios
vi /etc/init.d/nagios
Add the following lines:
DESC="Nagios" NAME=nagios DAEMON=/usr/local/nagios/bin/$NAME DAEMON_ARGS="-d /usr/local/nagios/etc/nagios.cfg" PIDFILE=/usr/local/nagios/var/$NAME.lock
Save and close the file.
change the permissions of the file
chmod +x /etc/init.d/nagios
start nagios service
service nagios start OR /etc/init.d/nagios start
To start nagios automatically on every boot, run the following command.
sudo ln -s /etc/init.d/nagios /etc/rcS.d/S99nagios
Access Nagios Web Interface
Open up your web browser and navigate to http://nagios-server-ip/nagios and enter the username as nagiosadmin and its password which we created in the earlier steps.
Click on the “Hosts” section in the left pane of the console. You will see there the no of hosts being monitored by Nagios server. We haven’t added any hosts yet. So it simply monitors the localhost itself only.
Let’s see how to monitor another host with Nagios in next post.
