Download latest Ioncube loader for your OS from

http://www.ioncube.com/loaders.php

For CentOS 64 bit

cd /usr/local/src
wget http://downloads2.ioncube.com/loader_downloads/ioncube_loaders_lin_x86-64.tar.gz
tar zxvf ioncube_loaders_lin_x86-64.tar.gz
cd  ioncube
mkdir /usr/local/ioncube
cp ioncube_loader_lin_5.2.so /usr/local/ioncube

I coped ioncube_loader_lin_5.2.so as PHP version installed on the server was PHP 5.2

Now edit php.ini file. To find location of php.ini, run

php -i| grep php.ini

In my case, php.ini was in /etc/php.ini folder

Add following line to end on php.ini

zend_extension = /usr/local/ioncube/ioncube_loader_lin_5.2.so