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[Bug 1568211] Re: no UMS support in radeon module


I am facing the same issue. I have upgraded from Xubuntu 14.04 to
Xubuntu 16.04 and I was greeted with a black screen just after my first

I use a Radeon HD 5430 card with two monitors. Incidentally, I had to
switch off one of them so that the Live USB from which I installed the
upgrade would work. The problem, though, started with the reboot.

This is the output of my uname -a:

Linux tiramisu 4.4.0-21-generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC
2016 x86_64 x86_64 x86_64 GNU/Linux

There are three ways in which I can "start" my computer:

* Normal boot, which ends in a black screen.
* Recovery mode, which, after selecting "continue boot", generates errors such as "*ERROR* no UMS support in radeon module!" above, defaults to VESA module (and poor resolution), and cannot manage two screens. I enclose the Xorg.1.log file for this method.
* Recovery method and deleting the nomodesetting kernel option. After selecting "continue boot", I get a perfectly working environment: radeon module works, etc. I enclose the Xorg.0.log file for this method.

** Attachment added: "Corresponds to a "clean" boot"

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  no UMS support in radeon module

Status in linux package in Ubuntu:

Bug description:
  I upgraded overnight from Wily to Xenial. The system will not boot.
  Only a blank screen after grub loads the kernel.

  The recovery kernel loads fine and I was able to find the following

  [drm] VGACON disable radeon kernel modesetting
  [drm:radeon_init [radeon]] *ERROR* no UMS support in radeon module!

  The recovery kernel command line had a nomodeset parameter that was
  not in the main kernel command line.

  Adding the nomodeset parameter the main kernel command line finally
  booted the system. It's kind of ugly but it seems to work.

  Note: For what it's worth I reported a similar issue against several
  Utopic kernels (bug #1407505). There was a back and forth with
  jsalisbury until a kernel finally worked. I have had no problems until

  Hope that helps.

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