Xorg not starting

Question

I recently tried to install some new graphics drivers on my laptop running Ubuntu 18.04.4 LTS, but upon rebooting I ended up on a log screen (like you'd see in recovery) constantly flashing back and forth to a black screen. I have discerned that this is due to the Xorg server being unable to start. In the Xorg.0.log there are several notable error lines:

(EE) systemd-logind: failed to get session: PID 12463 does not belong to any known session
...
(II) RADEON: Driver for ATI/AMD Radeon chipsets:
    (long list of GPUs)
(EE) No devices detected.
...
(EE) open /dev/dri/card0: no such file or directory
(WW) Falling back to old probe method for modesetting
(EE) open /dev/dri/card0: no such file or directory
...
(EE) Screen 0 deleted because of no matching config section.
...
(EE) AIGLX: reverting to software rendering

The server ends up terminating, then restarting, etc. My computer uses an AMD Ryzen 5 3500U with integrated graphics. lspci indicates that:

...
03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Picasso (rev c2)
...

Note: I'm performing these commands from the recovery mode root shell.

Answer 1

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(EE) open /dev/dri/card0: no such file or directory

It looks like your kernel does not currently have the appropriate DRI/modesetting drivers for your GPU.

(EE) No devices detected.

... and the Xorg X server's driver module for Radeons does not support your GPU either.

You're using the LTS version of Ubuntu from early 2018, but your processor with its integrated GPU was introduced in 2019. You might have easier time with an OS version that is not older than your hardware model.