CentOS 5.x comes with PHP in version 5.1.6 which is pretty old those days. There are already quite some web applications that have dropped PHP 5.1.x support which makes it impossible to install them on a CentOS 5.x installation. With the release of CentOS 5.6 additional packages called php53, php53-common, php53-ldap, etc. have been released which could replace the 5.1.6 default version of PHP if you don't have other RPM packages that depend on the original php packages. Since the php and the new php53 packages do install their resources into the same directories you can't install both of them in parallel. Instead of faking empty php packages to be able to install all php53 packages without conflicts and missing dependencies I decided to go for a third party PHP installation provided by AtomiCorp.