PHP 5.2 and PHP 5.3 has tons of functionalities which are not provided by PHP 5.1 and PHP 5.1 is the most recent version of PHP available in CentOS 5.1 and RHEL 5.1 via updates. Also, its difficult for people to upgrade OS(s) on production servers frequently and especially if the servers are running absolutely fine, it doesn’t really make sense to upgrade just for the heck of it. One more reason for no upgrades is the OS choices provided by many hosting companies. But a lot of CMS(s) and softwares are now recommending at least PHP 5.2 for an extended feature set.
I tried a lot of repos for CentOS including RPM Fusion, RPM Forge, EPEL etc., but none of them could provide even PHP 5.2. In some corner of my mind, I had a faint idea of Remi Collet publishing updates about Remi repository. Did a quick google search and found out that PHP 5.3 is actually available in the repository 😀
So, if you are really in need of PHP5.3 on your CentOS/RHEL 5.1 or lesser, head over to Repository Configuration Page and follow the instructions.
Note: The repository is not enabled on install (enabled=0). You need to enable it in /etc/yum.repos.d/remi.repo.
Once installed and enabled, you can update PHP, MySQL from remi repository using the following command
[root@fedora ~]$ yum update php php-* mysql-*
Warning: Drupal is still not totally compatible with PHP5.3 and if you run Drupal sites, be sure to investigate things before upgrading.