Comment 0 for bug 1516216

System: Ubuntu 14.04
Graphics Card: Geforce GTX 670
Graphics Driver: nvidia-352.55

Starting with kernel 3.13.0-66, the start of X / default display manager results in a black screen. My observations are:
- When I get this black screen, I cannot CTRL+ALT+F1 into a text console
- Pressing the power button in this state leads to a proper shutdown (which I guess means that it is not a complete kernel panic).
- When using these latest kernel, the graphics behavior during boot-up also has changed. Instead of a graphical animation, the system boots in text mode (I can see the syslog output), and at the moment I should get the display manager, the screen goes black.

My work-around so far has been to boot kernel 3.13.0-65 instead of 3.13.0-66, 3.13.0-67, or 3.13.0-68. So far this has worked reliably. However today, booting kernel 3.13.0-65 has resulted in a black screen as well. Fortunately, I found a new work-around: I can boot kernel 3.13.0-68 in recovery mode, and chose simply "continue" in the recovery console. With this modification of the boot process, X will start.

In the syslog, I can see some suspicious messages, around the time X should start: "BUG: unable to handle kernel NULL pointer dereference at (null)". I have attached a syslog contain some failed starts as well as a successful one.

Another suspicion is that the problem is related having an Oculus Rift DK2 connected. In particular, this requires to use a custom Xorg.conf which runs individual X screens for the main display and the Oculus Rift.