Hi Robert,
This post sets out the minimum recommended hardware to run Roon. Unfortunately the Raspberry Pi 2B is under spec.
The good news however is that Raspberry Pi will run RoonSpeakers (when released) enabling it to operate as an inexpensive network endpoint. This post contains information about support for Raspberry Pi as an endpoint. There are some pretty interesting photos towards the end of that thread.
A Linux version of Roon has not yet been released. It is hoped that RoonSpeakers may be released during November.