I am trying to use the Piwik PHP API for the Piwik Wordpress Plugin as discussed here.
The webspace still runs on Ubuntu 12.04 LTS which features PHP 5.3, so I updated PHP to 5.4 manually as described here.
Now running PHP Version 5.4.40-1+deb.sury.org~precise+4 on Ubuntu 12.04 LTS and...