I have just finished upgrading to 18.04 from 17.10 using
sudo do-release-upgrade
then rebooted only to find that it cannot boot up again.
When I try to boot, it goes well until the systemd message:
Started Dispatcher daemon for systemd-networkd.files...tem changes.pp link was shut down...
where it starts flickering and stays there.
I tried older kernel versions, but the same thing happened. I also tried adding some boot parameters amdgpu.dc=0(from this answer) and nomodeset, but those only stopped the backlight from flickering with the display.
GPUs:
0:Intel HD Graphics 520
1:AMD Radeon R5 M330
UPDATE:
I was able to disable gdm3 and make lightdm the default DM. Now it gets to LightDM, but it will never get to GNOME; it just loops (login loop).
At least now I am sure the cause of the flickering is gdm3.
Note: I tried gdm3 under both Wayland and X11, by editing /etc/gdm3/custom.conf, but the only difference was that with X11 I couldn't even see the systemd messages.
