Virtualization technology has been a key driver for cloud computing, and is also being widely applied to server environments. The technology provides a software based separation of logic within a system. This allows server consolidation, i.e. running several operating systems in parallel on a single hardware platform. A hyper visor is used as middleware between the hardware and the virtual machines running on top. Hyper visor schedulers are aimed at high throughput, while some applications however have real-time requirements. This means they come with timing constraints, which do not virtualize well in current schedulers. In this paper we present a taxonomy of current hyper visor schedulers which aim to virtualize real-time systems. We have chosen different techniques applied to general purpose systems, based on two popular open-source hyper visors: KVM and Xen. We conclude with an overview of real-time schedulers for other platforms.