After the upgrade to 17.10 I only get a black screen. How do I fix this?

This happened to several users of NVidia or AMD binary drivers (Bug #1705369). You need to re-install the drivers:

1. Switch to a different terminal (TTY) by pressing CTRL+ALT+F2 and login with your user.
2. Remove the binary driver by running sudo apt-get purge ^nvidia. AMD users can run amdgpu-pro-uninstall to remove the AMD graphics stack.
3. If /etc/X11/xorg.conf exists, rename (e.g. sudo mv /etc/X11/xorg.conf{,.bak}).
4. Disable Wayland completely: edit /etc/gdm3/custom.conf and uncomment the following line # WaylandEnable=false
5. Reboot Ubuntu with sudo shutdown -r now and you should see the login screen.

You can now install your binary drivers again, either manually (see How do I install the Nvidia drivers) or with the Software Properties GUI. AMD users should refer to the official installation guide for instructions.

After rebooting everything should work as expected.

Note: The new Wayland display server doesn't work with binary drivers, yet, which is why we disabled it in step 4. In the future, when Wayland is fully supported by the binary drivers, you should comment this line again.