Ubuntu – Ubuntu 18.04 + Radeon RX 580 Drivers

The Issue:

I don't seem to be able to install the Radeon Drivers on Ubuntu 18.04.

Attempt One:

Downloaded drivers from AMD's page here.

Ran the following commands:

sudo ./amdgpu-install -y
sudo reboot

Once back into Ubuntu, the desktop and even youtube video's were rendering slowly. As if the CPU was being used instead of the GPU.

Attempt Two:

Ran the following commands:

sudo apt-add-repository -r ppa:graphics-drivers/ppa && \
sudo apt update && \
sudo apt upgrade && \
sudo apt autoremove && \
sudo apt autoclean
sudo add-apt-repository ppa:oibaf/graphics-drivers
sudo apt-get update
sudo apt upgrade
sudo apt install --reinstall xserver-xorg-video-amdgpu
sudo dpkg --configure -a
sudo dpkg-reconfigure gdm3 ubuntu-session xserver-xorg-video-amdgpu
sudo apt-get install mesa-vdpau-drivers
sudo reboot

Once back into the desktop, the whole desktop and even youtube videos were still rendering slowly, as if the CPU was being used instead of the GPU.

Attempt Three:

Ran the following commands:

sudo ./amdgpu-pro-install -y
sudo reboot

Ubuntu no longer gets to the login screen. Shows the following message:

WARNING: Failed to connect to lvmetad. Falling back to device scanning.
Volume group "ubuntu-vg" not found
Cannot process volume group ubuntu-vg
WARNING: Failed to connect to lvmetad. Falling back to device scanning.
Reading all physical volumes.  This may take a while...
Found volume group "ubuntu-vg" using metadata type lvm2
WARNING: Failed to connect to lvmetad. Falling back to device scanning.
2 logical volume(s) in volume group "ubuntu-vg" now active
/dev/mapper/ubuntu--vg-root: clearn, 428119/15155200 files, 35460694/60609536 blocks

Other Info:

Before I got the RX 580, I had an old Nvidia GT 520 and I had to have nomodeset in the grub config file. When installing the Radeon drivers, I get a message saying:

WARNING: nomodeset detected in kernel parameters, amdgpu requires KMS

So I remove nomodeset from the grub, reboot, and then I am no longer able to access the desktop. If I put the nomodeset back into the grub config file, I can then get back into the desktop.

The Question:

Now that I have managed to get back into Ubuntu, how do I remove any residue of the amdgpu-pro driver and anything else that I should not have done from the above attempts, remove the nvidia drivers for the previously installed gpu, and then try installing the amd drivers again to get the RX 580 working on Ubuntu 18.04? Tried and tested on Windows 10 (used bios boot options to boot into a second SSD which has Windows 10 installed) and the GPU works perfectly after installing the drivers on Windows 10. So it's not a hardware problem with the GPU.