As initially reported by Michael Larabel from Phoronix, Canonical has recently updated the release notes of the forthcoming Ubuntu 16.04 LTS (Xenial Xerus) operating system with new info on the proprietary AMD Catalyst driver.
Long story short, Ubuntu 16.04 LTS will not support the AMD Catalyst proprietary graphics driver for AMD GPUs (Graphics Processing Units), which is known to the community as the fglrx driver. Instead, Canonical recommends users using the open-source Radeon and AMDGPU alternatives.
According to the Ubuntu developers, who go to all the trouble of backporting the latest kernel code from the upstream Linux 4.5 kernel branch for the open-source AMDGPU and xf86-video-ati AMD Radeon graphics drivers into Ubuntu 16.04 LTS' Linux kernel packages, AMD has put a lot of effort into the video drivers.
"The fglrx driver is now deprecated in 16.04, and we recommend its open source alternatives (radeon and amdgpu). AMD put a lot of work into the drivers, and we backported kernel code from Linux 4.5 to provide a better experience," reads the preliminary release notes for Ubuntu 16.04 LTS.
What you need to know if you're upgrading from a previous release
Those of you making a fresh install of the Ubuntu 16.04 LTS (Xenial Xerus) after its official release date of April 21, 2016, need not worry about anything, but they should test to see if their AMD Radeon graphics cards are supported by first running the Live CD and then install the operating system if everything is OK.
On the other hand, if you are upgrading from a previously supported release of Ubuntu Linux, such as Ubuntu 15.10 (Wily Werewolf) or Ubuntu 14.04 LTS (Trusty Tahr), you should be aware of the fact that the fglrx driver will be automatically purged from your system, including the xorg.conf configuration file.
After removing the proprietary AMD Catalyst driver, Ubuntu 16.04 LTS will try to assign one of the supported open-source Radeon or AMDGPU video drivers that corresponds to your hardware, but if something goes wrong, you can file a bug report on the Launchpad website.
Update: We've been informed by Oliver Grawert from Canonical that the proprietary AMD Catalyst (fglrx) driver has been temporarily removed the Ubuntu 16.04 LTS repositories, as it is not yet ported to X.Org Server 1.8. It will be added again as part of the first point release, Ubuntu 16.04.1 LTS.
