Comment 21 for bug 1663926

As a side note, you can rescue your system if it is currently not booting.

Press esc during boot to bring grub options and select safe mode (I think this is the name, it should be the last boot option), it may be tricky to get the correct timing for pressing esc, and some people say shift is the correct key, YMMV. In safe mode, select root from the menu. Then run the following:

mount -o rw,remount /
prime-select nvidia
reboot