Steam Won't open on Ubuntu 15.04

[joshtheimpaler]

When I try to open stream on Ubuntu nothing happens. Running from the terminal gives this message:

Running Steam on ubuntu 15.04 64-bit
STEAM_RUNTIME is enabled automatically
Installing breakpad exception handler for appid(steam)/version(1431729692)
libGL error: unable to load driver: radeonsi_dri.so
libGL error: driver pointer missing
libGL error: failed to load driver: radeonsi
libGL error: unable to load driver: swrast_dri.so
libGL error: failed to load driver: swrast

and then the program hangs.

Any ideas as to how to fix this?