Okey i been planning to do this long back.on rhel5 box here is a simple guide i have made which lets you compile nagio3 from source and install in RHEL5 box. Make sure you have these packages installed:--

1.Apache

2. GCC compiler

3.GD development libraries

You can use "yum" to install these packages by running the following commands (as root):

yum install httpd gcc glibc glibc-common gd gd-devel

Create a new nagios user account and give it a password.

/usr/sbin/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 Plugins Create a directory for storing the downloads.

mkdir ~/downloads

cd ~/downloads

Download the source code tarballs of both Nagios and the Nagios plugins (visit http://www.nagios.org/download/ for links to the latest versions).The latest versions of Nagios and the Nagios plugins were 3.0.3 and 1.4.11, respectively.

wget http://osdn.dl.sourceforge.net/sourceforge/nagios/nagios-3.0.6.tar.gz

wget http://osdn.dl.sourceforge.net/sourceforge/nagiosplug/nagios-plugins-1.4...

3) Compile and Install Nagios Extract the Nagios source code tarball.

cd ~/downloads tar xzf nagios-3.0.6.tar.gz cd nagios-3.0.6

Run the Nagios configure script, passing the name of the group you created earlier like so:

./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

Don't start Nagios yet - there's still more that needs to be done...

4) Customize Configuration Sample configuration files have now been installed in the /usr/local/nagios/etc directory. These sample files should work fine for getting started with Nagios. You'll need to make just one change before you proceed...

Edit the /usr/local/nagios/etc/objects/contacts.cfg config file with your favorite editor and change the email address associated with the nagiosadmin contact definition to the address you'd like to use for receiving alerts. 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.

Remember the password you assign to this account - you'll need it later.

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

users nagiosadmin Restart Apache to make the new settings take effect.

service httpd restart

Implementing Digest Authentication The implementation of Digest Authentication is simple. You will have to create the new type of password file using the 'htdigest' tool, then modify the Apache configuration for nagios (typically /etc/httpd/conf.d/nagios.conf).

Create a new passwords file using the 'htdigest' tool.

The difference that you will notice if you are familiar with 'htpasswd' tools is the requirement to supply a 'realm' argument. Where 'realm' in this case refers to the value of the 'AuthName' directive in the Apache configuration. htdigest -c /usr/local/nagios/etc/.digest_pw "Nagios Access" nagiosadmin Next, edit the Apache configuration file for Nagios (typically /etc/httpd/conf.d/nagios.conf) using the following example.

## BEGIN APACHE CONFIG SNIPPET - NAGIOS.CONF ScriptAlias /nagios/cgi-bin "/usr/local/nagios/sbin"

Options ExecCGI AllowOverride None Order allow,deny Allow from all AuthType Digest AuthName "Nagios Access" AuthUserFile /usr/local/nagios/etc/.digest_pw Require valid-user Alias /nagios "/usr/local/nagios/share" Options None AllowOverride None Order allow,deny Allow from all AuthType Digest AuthName "Nagios Access" AuthUserFile /usr/local/nagios/etc/.digest_pw Require valid-user

## END APACHE CONFIG SNIPPETS

Then, restart the Apache service so the new settings can take effect.

/etc/init.d/httpd restart

6) Compile and Install the Nagios Plugins Extract the Nagios plugins source code tarball.

     cd ~/downloads tar xzf nagios-plugins-1.4.11.tar.gz

     cd nagios-plugins-1.4.11

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 sample 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

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 you specified earlier.

http://localhost/nagios/

Click on the "Service Detail" navbar link to see details of what's being monitored on your local machine.

It will take a few minutes for Nagios to check all the services associated with your machine, as the checks are spread out over time.

refernce :-- nagios manual