No video on Ubuntu 20.04 minimal VM via virt-manager

Question

Environment: Ubuntu 18.04 Server running KVM. Guests managed via Virtual Machine Manager installed on a separate Lubuntu 20.04 machine. All guests running 18.04 up to now, all accessible via SSH and also via the console window in Virtual Machine Manager.

Problem: I upgraded a KVM guest running a working 18.04 minimal installation, to 20.04. The minimal installation is just about as bare as possible, just SSH selected in tasksel. Since the upgrade I get no console video output in Virtual Machine Manager for this guest. The VM appears to be working fine otherwise and I can SSH into it. Am using Spice channel for video and settings appear unchanged following the upgrade, but spice channel is now showing disconnected for this guest in virtual machine manager. Have also tried a clean install of a new 20.04 minimal guest on the same KVM host. Same problem, no video output. Spice channel disconnected.

18.04 minimal guests do not exhibit this problem. I am assuming therefore this is a missing/broken configuration in the 20.04 minimal guest. What can be done to restore video via the VMM console?

Answer 1

I had the same problem with the black screen after installing Ubuntu 20.04 Minimal with the absolute minimum.

In /etc/default/grub you will find this line:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

Edit this file (you need root priviledges, so use sudo) and remove the word "splash". Then rebuild the grub config and reboot:

sudo update-grub
reboot

The "splash" parameter ultimately leads to the vt.handoff=7 being passed to the kernel as well, but this functionality seems to malfunction.

An explanation of what it is supposed to do can be found in this thread. As I understand it, the output of the boot sequence is maintained on virtual terminal 7 and when the boot sequence is finished and the login prompt is ready (on VT 1-6), the display switch to VT 1 and VT 7 is destroyed.

But the switching seems to fail with the minimal install and nothing is displayed. When the boot sequence completed, you can select "Send Key" --> "Ctrl+Alt+7" in the Virtual Machine Manager menu to switch to VT 7 (even though there are only supposed to be 6 virtual terminals) and you will see the first few lines of the boot sequence.

You can similarly switch to VT 1 (or 2-6) using "Ctrl+Alt+1" (or 2-6) and you will see the boot prompt.