For all those who ever wanted to install Ubuntu or needed a Linux environment for running their specific software, I can really recommend following instruction video. This video clearly shows in an easy understandable and step-by-step way how to install Xubuntu (a lighter version of Ubuntu) on a VirtualBox. So this makes it possible to run an Ubuntu-flavor OS within your normal OS (e.g. Windows or Mac). I followed this video to create an OS-basis for installing GRASS GIS and FIDIMO for modelling fish dispersal in rivers.