Xenial Xerus - Ubuntu 16.04 LTS

word for the wary:

Ubuntu 16.04 LTS does not have a fglrx driver, nor will it work when you try to install the AMD fglrx driver of a previous version.
Ubuntu 16.04 LTS now works with an open source driver.
The good: it recognizes the GPU and it's OpenCL capabilities upon boot.
The bad: it will -for the moment- only crunch when using GCN 1.2 and later -the very latest in Radeon.
My Athlon 5350s have a GCN 1.1 IGP (Kalindi, aka AMD RAdeon HD 8400) and give CL file build failures.
OpenCL-wise the open source driver is a -hopefully temporary- step back, from OpenCL 2.0 under the fglrx driver to OpenCL 1.1 under Mesa.
At least Boinc can now be started right away, and with the latest generation GCN cards, GPU crunch right away too. No re-starts are needed anymore in order to make Boinc 'see' your GPU.