NOTE: these information were originally provided in a post I wrote on the Joomla forum
Many CentOS and Joomla users had a bad surprise lately: while Joomla 3.2 happily run on CentOS provided PHP packages (5.3.3), the 3.3 update strongly refuse to run on anything that PHP 5.3.10, citing security issues as the main reason. In my opinion, this is not a wise move - after all, the long-term distribution all apply custom patches and backports to their PHP version and, in this specific case, CentOS packages provide absolutely comparable security to the target 5.3.10 PHP version.
Anyway, we can do very little to change this situation: Joomla developer stated that the will not support older PHP version. So, how can we use Joomla on our beloved CentOS 6.x installations? While custom-patching Joomla's version-check functions can be tempting, this is not the best thing to do: any custom patching increase the risk of future problems, especially when updating your Joomla installation. On the other side, simply using a more up-to-date repository featuring PHP 5.4+ can not be practical: maybe you have other sites on hosted on your server, and (correctly) you don't want to introduce any possible problems for this sites, or you simply want to stick with default repositories.
Fortunately, the solution exists: say hello to "Software collections" or SCL in short.