My shiny new VPS* runs Ubuntu 12.10 (official subtitle: Quantal Queztal. Local nickname: Quirky Kestrel) and therefore has PHP 5.4 installed. It's very new so every command I type is missing, and today I realised that included a PECL module (pecl_http, of course). [...] What's happened here is that all debian-flavoured unixes have adopted this standard for their PHP 5.4 packages, so if you're using debian, ubuntu, or any of their relatives with PHP 5.4, you'll see a directory structure like this. When you add a module to PHP, you'll add a file to the mods-available directory enabling the module and adding any config specific to it.

She points out that the "phpenmod" command, accompanied by the PECL extension to install, is the newer way to correctly get these extensions downloaded and configured correctly.