Nagios installation

Install Ubuntu with LAMP & postfix & Build essentials

Nagios User Setup

useradd -m -s /bin/bash nagios

passwd nagios

usermod -G nagios nagios

groupadd nagcmd

usermod -a -G nagcmd nagios

Download And Unzip Nagios And Nagios Plugins

cd /downloads

wget http://prdownloads.sourceforge.net/nagios/nagios-3.2.3.tar.gz

wget http://prdownloads.sourceforge.net/nagiosplug/nagios-plugins-1.4.15.tar.gz

tar -zxf /downloads/nagios-3.2.3.tar.gz

tar -zxf /downloads/nagios-plugins-1.4.15.tar.gz

Install Nagios

cd /downloads/nagios-3.2.3

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

make all

make install

make install-init

make install-config

make install-commandmode

make install-webconf

Nagios Password

This is the password you will need to look at the nagios pages. If you install Nagios to a different directory please change this command to where the Nagios etc. folder will be.

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

Enter your password when prompted.
Now we will restart Apache to make sure all of the changes take effect:

/etc/init.d/apache2 restart

Nagios Plugins

cd /downloads/nagios-plugins-1.4.15/

make

make install

Now we need to make Nagios start at bootup:

ln -s /etc/init.d/nagios /etc/rcS.d/S99nagios

Change Default Email Address For Nagios Admin

Open your favorite editor and open /usr/local/nagios/etc/objects/contacts.cfg

Once you have saved your changes to the contacts.cfg we need to verify that there are no errors in the configuration of Nagios.

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

Now we are going to start nagios:

/etc/init.d/nagios start

Postfix Configuration For A Smarthost Relay

postconf -e 'relayhost=yourmailserver.com'

postconf -e 'smtp_sasl_auth_enabled = yes'

postconf -e 'smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd'

postconf -e 'smtp_sasl_security_options ='

echo "yourmailserver.com emailusername:emailpassword" > /etc/postfix/sasl_passwd

Now we will need to change the password file attributes so only root has access to read it.

chown root:root /etc/postfix/sasl_passwd

chmod 600 /etc/postfix/sasl_passwd

postmap /etc/postfix/sasl_passwd

Now we are going to set the map that will change your outbound messages from nagios to your email server username/email address.

echo "nagios mailusername@yourmailserver.com" /etc/postfix/canonical

echo "canonical_maps = hash:/etc/postfix/canonical" >> /etc/postfix/main.cf

postmap /etc/postfix/canonical

/etc/init.d/postfix restart

Now that this all has been completed you can restart your system.
Once your system has come back up you will be able to login to the website and look at your first Nagios installation.

http://yourserver/nagios/

 source: http://www.howtoforge.com/nagios-installation-on-ubuntu-10.04-lucid-lynx-p3