Kubuntu 24.04 LTS display bug

I recently installed Kubuntu 24.04 LTS (Noble Numbat) on a laptop and all was well. I had been using flavours of Ubuntu 20.04 LTS, but when I was creating a new boot media this time round, the default Ubuntu download was 24.04 so I went with that. Maybe it would have been wiser to wait for 24.04.4.

The first and second boots were fine. However, on one of the subsequent boots, after the GRUB menu, the Kubuntu splash logo never showed up, and there was just a black screen. Trying to get to an alternative TTY via Ctrl-Alt-F2, F3, etc. didn't work either. The only way out was to do a hard shutdown by holding the power button.

Interestingly, booting into recovery mode, and then resuming normal boot allowed me to boot to desktop, although then I had a second issue — external monitors were not detected in the KDE settings app and also not via xrandr -q.

It turns out that many other people have encountered this rather serious bug:

• /r/Kubuntu — Beware: Kubuntu 24.04 Is Presenting Display/Graphics Driver Issues For Some Users (26 April 2024)
• /r/Kubuntu — Heads up: I hit a serious bug while testing Kubuntu 24.04!

It also looks like the bug has already been reported on Launchpad and GitHub as a bug in ssdm:

• sddm/simpledrm race conditions leads to frequent black display on bootup
• Kubuntu 24.04 Second boot always black screen
• ssdm/ssdm — SDDM races with DRM GPU drivers

In the meantime, there is a fairly simple workaround — simply skip the splash screen by editing the kernel options to remove 'splash':

sudo vim /etc/default/grub

# Remove 'splash' from the `GRUB_CMDLINE_LINUX_DEFAULT`
# so that the line looks like this:
# GRUB_CMDLINE_LINUX_DEFAULT='quiet'

sudo update-grub

Reboot, and all should be well again.