wget http://downloads.ioncube.com/loader_downloads/ioncube_loaders_lin_x86-64.tar.gz
tar zxvf ioncube_loaders_lin_x86-64.tar.gz
mv ioncube /usr/local/
zend_extension = /usr/local/ioncube/ioncube_loader_lin_5.2.so
There are a few versions of the loader in the tar archive and you can choose the one that suites your needs
/etc/init.d/apache2 restart