Nagios installation and configuration

Nagios Installation

Install Build Dependencies:

#sudo yum install gcc glibc glibc-common gd gd-devel make net-snmp openssl-devel xinetd unzip

Create Nagios User and Group:

Create a “nagios” user and “nagcmd” group, then add the user to the group with these commands

#sudo useradd nagios

#sudo groupadd nagcmd

#sudo usermod -a -G nagcmd nagios

Install Nagios

#cd /opt

#curl -L -O https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.6.tar.gz

#ls

nagios-4.4.6.tar.gz

Extract the Nagios archive with this command

#tar xvf nagios-*.tar.gz

#cd nagios-*

Before building Nagios, we must configure it with this command:

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

Now compile Nagios with this command:

#make all

Now we can run these make commands to install Nagios, init scripts, and sample configuration files:

#sudo make install

#sudo make install-commandmode

#sudo make install-init

#sudo make install-config

#sudo make install-webconf

In order to issue external commands via the web interface to Nagios, we must add the web server user, apache, to the nagcmd group:

#sudo usermod -G nagcmd apache

Install Nagios Plugins

#cd /opt/

#curl -L -O http://nagios-plugins.org/download/nagios-plugins-2.1.1.tar.gz

#tar xvf nagios-plugins-*.tar.gz

#cd nagios-plugins-*

Before building Nagios Plugins, we must configure it. Use this command:

#./configure --with-nagios-user=nagios --with-nagios-group=nagios --with-openssl

Now compile Nagios Plugins with this command:

#make

#sudo make install

Install NRPE

#cd /opt

#curl -L -O http://downloads.sourceforge.net/project/nagios/nrpe-2.x/nrpe-2.15/nrpe-2.15.tar.gz

Extract the NRPE archive with this command

#tar xvf nrpe-*.tar.gz

#cd nrpe-*

Configure NRPE with these commands

#./configure --enable-command-args --with-nagios-user=nagios --with-nagios-group=nagios --with-ssl=/usr/bin/openssl --with-ssl-lib=/usr/lib/x86_64-linux-gnu

Now build and install NRPE and its xinetd startup script with these commands:

#make all

#sudo make install

#sudo make install-xinetd

#sudo make install-daemon-config

Open the xinetd startup script in an editor:

#sudo vi /etc/xinetd.d/nrpe

only_from = 127.0.0.1 192.168.4.29

Modify the only_from line by adding the private IP address of the your Nagios server to the end

Restart the xinetd service to start NRPE:

#sudo service xinetd restart

Configure Nagios:

Organize Nagios Configuration

#sudo vi /usr/local/nagios/etc/nagios.cfg

Now find an uncomment this line by deleting the #:

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

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

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

Configure Nagios Contacts

email nagios@localhost ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******

Find the email directive, and replace its value (the highlighted part) with your own email address:

Configure check_nrpe Command

#sudo vi /usr/local/nagios/etc/objects/commands.cfg

Add the following to the end of the file:

define command{

command_name check_nrpe

command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$

}

Configure Apache

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

Note: If you create a user that is not named “Nagiosadmin”, you will need to edit /usr/local/nagios/etc/cgi.cfg and change all the “Nagiosadmin” references to the user you created.

#sudo systemctl daemon-reload

#sudo systemctl start nagios.service

#sudo systemctl restart httpd.service

#sudo chkconfig nagios on

Optional: Restrict Access by IP Address

#sudo vi /etc/httpd/conf.d/nagios.conf

Find and comment the following two lines by adding # symbols in front of them:

Order allow,deny

Allow from all

Then uncomment the following lines, by deleting the # symbols, and add the IP addresses or ranges (space-delimited) that you want to allow to in the Allow from the line:

# Order deny,allow

# Deny from all

# Allow from 127.0.0.1

Now start Nagios and restart Apache to put the change into effect:

#sudo systemctl restart nagios.service

#sudo systemctl restart httpd.service

Accessing the Nagios Web Interface

#http://nagios_server_public_ip/nagios