Below we give a brief description of how to install and configure Nagios.

To install Nagios make sure the following are installed and working properly in your machine

* httpd
* php
* gcc
* glibc
* glibc-common
* gd
* gd-devel
* png
* png-devel
* jpeg
* jpeg-devel
* zlib
* zlib-devel

Install Steps

1) Create a new user and group as root

Create a new user nagios.

useradd -m nagios

passwd nagios 

Create a new nagcmd group for allowing external commands to be submitted through the web interface. Add both the nagios user and the apache user to the group.

/usr/sbin/groupadd nagcmd

/usr/sbin/usermod -a -G nagcmd nagios

/usr/sbin/usermod -a -G nagcmd apache 

2) Download Nagios and the Nagios Plugins

Download the source code tarballs of both Nagios and the Nagios plugins.

wget http://sourceforge.net/projects/nagios/files/nagios-3.x/nagios-3.2.0/nagios-3.2.0.tar.gz/download
wget http://sourceforge.net/projects/nagiosplug/files/nagiosplug/1.4.14/nagios-plugins-1.4.14.tar.gz/download

3) Compile and Install Nagios

Extract the Nagios source code.

tar xzf nagios-3.2.0.tar.gz
cd nagios-3.2.0

make sure that these libraries are already installed in the system .Otherwise install them using YUM

   * gd
    * gd-devel
    * png
    * png-devel
    * jpeg
    * jpeg-devel
    * zlib
    * zlib-devel 

Run the Nagios configure script, passing the name of the group:

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

Compile the Nagios source code.

 make all 

Install binaries, init script, sample config files and set permissions on the external command directory.

make install

make install-init

make install-config

make install-commandmode 

4) Customize Configuration

After installation the default configuration file can be found in the directory /usr/local/nagios/etc/. Also edit your contact information

 vi /usr/local/nagios/etc/objects/contacts.cfg

5) Configure the Web Interface

Install the Nagios web config file in the Apache conf.d directory.

 make install-webconf 

Create a nagiosadmin account for logging into the Nagios web interface.

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

Restart Apache to make the new settings take effect.

 /etc/init.d/httpd restart 

6) Compile and Install the Nagios Plugins

Extract the Nagios plugins source code.

 tar xzf nagios-plugins-1.4.14.tar.gz

cd nagios-plugins-1.4.14 

Compile and install the plugins.

 ./configure --with-nagios-user=nagios --with-nagios-group=nagios
make

make install

7) Start Nagios

Add Nagios to the list of system services and have it automatically start when the system boots.

 chkconfig --add nagios

chkconfig nagios on 

Verify the default Nagios configuration files.

 /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg 

If there are no errors, start Nagios.

 service nagios start

8) Modify SELinux Settings

This step is important if the Selinux is not in the Permissive mode it shows error like this

See if SELinux is in Enforcing mode.

getenforce

Put SELinux into Permissive mode.

setenforce 0

To make this change permanent, you’ll have to modify the settings in /etc/selinux/config and reboot.

9) Login to the Web Interface
You should now be able to access the Nagios web interface at the URL below. You’ll be prompted for the username (nagiosadmin) and password(nagios) you specified earlier.

http://localhost/nagios/ 

10) Add hosts to be monitored

There are object configuration files in which you can define hosts, host groups, contacts, contact groups, services, etc. You can split your object definitions across several config files if you wish, or keep them all in a single config file.

For convinience we created two files hosts.cfg and services.cfg under the directory /usr/local/nagios/etc/objects/ and add the file path to /usr/local/nagios/etc/nagios.cfg as

cfg_file=/usr/local/nagios/etc/objects/hosts.cfg
cfg_file=/usr/local/nagios/etc/objects/services.cfg 

Then create a simple script to add hosts, named add_host_service.sh by adding the following lines.

## script begins here
#!/bin/bash
echo "Enter Host Name"
read name
echo "Enter IP Address of $name"
read ip_add

echo "
define host{
        use                     linux-server
        host_name               $name
        alias                   $name
        address                 $ip_add
        }
" >> /usr/local/nagios/etc/objects/hosts.cfg

echo "
define service {
host_name                       $name
service_description             HTTP
check_command                   check_http
use                             generic-service
notification_interval           1
}
define service {
host_name                       $name
service_description             POP
check_command                   check_pop
use                             generic-service
notification_interval           1
}
define service {
host_name                       $name
service_description             SMTP
check_command                   check_smtp!-t 20
use                             generic-service
notification_interval           1
}
" >> /usr/local/nagios/etc/objects/services.cfg 

##script ends here

The above script will monitor three services HTTP, SMTP and POP. To monitor a new service add a new define service entry as shown above.

execute the above script by the command

sh add_host_service.sh

While the execution it will ask for the host name and the IP Address of the host to be added. After execution it will add a new host to nagios. To verify the nagios configuration for errors use the command

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

For the changes to take effect we must restart the nagios as follows.

killall nagios
/usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg

Now you can find the newly added hosts under the link Hosts in Nagios interface.

Happy Monitoring

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