Jtdcftul

I added the graphics-drivers PPA and installed the 415 driver, but it seemed that in doing so my 940MX was no longer being utilised. So, I attempted to revert to the 390. I made the mistake of removing the PPA before switching away, though. When I tried to switch back to the 390 driver, Ubuntu spat out an error - I can't remember the exact message, though I believe it mentioned something not being found in cache.

After restarting my system, the boot process got stuck on a screen flooded with countless "Starting NVIDIA persistence daemon" and "Stopping NVIDIA persistence daemon" messages. To get the system to boot, I had to enter recovery mode and use prime-select intel. If I use the Nouveau driver the system can boot, but my laptop doesn't seem to use my GPU.

Running nvidia-smi produces the following:

NVIDIA-SMI has failed because it couldn't communicate with the NVIDIA driver. Make sure that the latest NVIDIA driver is installed and running.

I followed the advice here, but it unfortunately didn't help. I've attempted to remove any remnants that the 415 driver may have left behind. Initially I looked this thread, but regarding the page linked by it the directory /usr/local/cuda-X.Y does not exist (as in, theres no cuda-related directory), and the link /usr/bin/nvidia-uninstall points to nvidia-installer, but that doesn't exist. So, I removed the packages as recommended in accordance with this answer. I then set the driver to NVIDIA's 390 in the software settings, so it re-installed everything. Still, restarting with the NVIDIA GPU selected stops me from being able to boot.

The result of dpkg -l | grep nvidia at the time of writing is the following:

ii  libnvidia-cfg1-390:amd64                   390.77-0ubuntu0.18.04.1                           amd64        NVIDIA binary OpenGL/GLX configuration library

ii  libnvidia-common-390                       390.87-0ubuntu0~gpu18.04.1                        all          Shared files used by the NVIDIA libraries

ii  libnvidia-compute-390:amd64                390.77-0ubuntu0.18.04.1                           amd64        NVIDIA libcompute package

ii  libnvidia-compute-390:i386                 390.77-0ubuntu0.18.04.1                           i386         NVIDIA libcompute package

ii  libnvidia-decode-390:amd64                 390.77-0ubuntu0.18.04.1                           amd64        NVIDIA Video Decoding runtime libraries

ii  libnvidia-decode-390:i386                  390.77-0ubuntu0.18.04.1                           i386         NVIDIA Video Decoding runtime libraries

ii  libnvidia-encode-390:amd64                 390.77-0ubuntu0.18.04.1                           amd64        NVENC Video Encoding runtime library

ii  libnvidia-encode-390:i386                  390.77-0ubuntu0.18.04.1                           i386         NVENC Video Encoding runtime library

ii  libnvidia-fbc1-390:amd64                   390.77-0ubuntu0.18.04.1                           amd64        NVIDIA OpenGL-based Framebuffer Capture runtime library

ii  libnvidia-fbc1-390:i386                    390.77-0ubuntu0.18.04.1                           i386         NVIDIA OpenGL-based Framebuffer Capture runtime library

ii  libnvidia-gl-390:amd64                     390.77-0ubuntu0.18.04.1                           amd64        NVIDIA OpenGL/GLX/EGL/GLES GLVND libraries and Vulkan ICD

ii  libnvidia-gl-390:i386                      390.77-0ubuntu0.18.04.1                           i386         NVIDIA OpenGL/GLX/EGL/GLES GLVND libraries and Vulkan ICD

ii  libnvidia-ifr1-390:amd64                   390.77-0ubuntu0.18.04.1                           amd64        NVIDIA OpenGL-based Inband Frame Readback runtime library

ii  libnvidia-ifr1-390:i386                    390.77-0ubuntu0.18.04.1                           i386         NVIDIA OpenGL-based Inband Frame Readback runtime library

ii  nvidia-compute-utils-390                   390.77-0ubuntu0.18.04.1                           amd64        NVIDIA compute utilities

ii  nvidia-dkms-390                            390.77-0ubuntu0.18.04.1                           amd64        NVIDIA DKMS package

ii  nvidia-driver-390                          390.77-0ubuntu0.18.04.1                           amd64        NVIDIA driver metapackage

ii  nvidia-kernel-common-390                   390.87-0ubuntu0~gpu18.04.1                        amd64        Shared files used with the kernel module

ii  nvidia-kernel-source-390                   390.77-0ubuntu0.18.04.1                           amd64        NVIDIA kernel source package

ii  nvidia-prime                               0.8.8.2                                           all          Tools to enable NVIDIA's Prime

ii  nvidia-settings                            390.77-0ubuntu0.18.04.1                           amd64        Tool for configuring the NVIDIA graphics driver

ii  nvidia-utils-390                           390.77-0ubuntu0.18.04.1                           amd64        NVIDIA driver support binaries

ii  xserver-xorg-video-nvidia-390              390.77-0ubuntu0.18.04.1                           amd64        NVIDIA binary Xorg driver