Gfilui

Two days ago the software updater did its usual thing then asked for a reboot. I rebooted into a black screen with a blinking cursor.

Dropping into ctrl-alt-f1 I learned that lightdm was failing to start with an error. I could still startx or startxfce4 to bring up the gui. But once in, I couldn't and still can't get any browsers to open. Some things will open, most of the settings windows, but not Mousepad or other native xfce apps.

So far I've tried removing lightdm by replacing it with xdm, which solved the blinking cursor but makes no difference once I'm in xfce4

Journalctl output and /var/log/lightdm logs don't tell me much. Firefox logs a segfault error, Vivaldi, chromium, and brave just do nothing. Starting from the terminal just exits with no error message.

I've tried dpkg-reconfigure on the Nvidia drivers, on xfce, lightdm, and booting into several kernels. Nothing.

I'm not even sure what update did it since my dpkg logs aren't showing me. All I know is it would have been an update for Ubuntu 16.04 on around the 27-28 of March

Can't give terminal output since I'm having to type this out on a tablet. But this system specs:

Kernel is 4.13.0.37-generic, Ubuntu 16.04.4, lightdm 1.18.3, xfce4 latest version of 4.12, using an Nvidia GeForce card running the nvidia-current package (nvidia-304)

Can add any more details needed

EDIT: Still no success here. I've tried with the previous kernel, 4.13.0.36, and with 4.4.0-116

Have replaced lightdm with xdm and tried lxde instead of xfce. XDM will load a GUI but I cannot get any browser windows or native xfce apps to open. LXDE's text editor and other apps will open but nothing else.

Right now this is looking like screwy library or a video driver issue... but I'm out of ideas.

Any thoughts at all?

After four days I finally found the solution to this, so here it is just in case anybody else runs into this problem.

It turns out I was right about the video driver problem. When I dug around in the output of journalctl I noticed that there was a problem with the gpu-manager service.

update-alternatives: error: no alternatives for x86_64-linux-gnu_gfxcore_conf

Which was leading to this error:

Failed to start Detect the available GPUs and deal with any system changes.

And this was causing the error I originally found in lightdm as well as the GUI problems.

I found the solution in this thread. What I had to do was install the HWE package for the Xserver:

apt-get install xserver-xorg-hwe-16.04

Once that upgraded I was able to reboot and lightdm started up into the GUI as normal.

Hope that'll help someone else out.