virtualbox.org

Thanks ftho, that explains it.

The interesting thing is that this message:
appears when the screen goes black and there are no other Display::i_handleDisplayResize log lines until I use Host+F to toggle full-screen mode off.

Recently I faced the same issue. Black screen after boot linux guests.
I used different linux guests - Emmabuntus and MX, 32 and 64 versions. All of them Debian based. All of them use lightdm and vmsvga enabled driver. My host PC is i3 Win10 64 based. After booting I am getting black screen with cursor. The cursor lives. Keyboard lives too. I can switch between VT-s (Ctrl+Alt+Fn where n is virtual terminal number). By default KVM uses VT7 in localhost seat in linux. I notice, when I switch to another VT and then back to VT7 I see normal operation guest linux system. Sometimes guests systems have been loaded correctly, very rare. I compared logs successful and unsuccessful attempts. Only one thing I found out - LightDM is waiting for response from choosen Seat but got nothing and X system stopped. I made changes in lightdm.conf to disable seat's liberty. I provided waiting script before X starts and some other things... But I not got desired stability. So, I shure, I faced Debian kernel level bug.
Ordinary user can't fix it up, relax

Today I tried Xubuntu 20.04 with the similar result. Black screen, keyboard lives, mouse no lives. Switching between VT comes normal functionality back.

Since 'zova' brought this topic back to life, there is one thing I just noticed in the OP:

adi5 wrote:I was using my Lubuntu 20.04 virtualbox guest OS just this morning and it was running fine. .... I attempted to install an update, I remember it said there was some error with installing it but I can't recall exactly what it said.

If this error was a "Disk Full" error, Ubuntu et al is known to fail to open a GUI desktop with a full disk, whether on real hardware or in a VM. Fixing as one would do on a real PC with the problem is needed. Web-search how to fix this through Ubuntu's help channels.

Just an FYI for future readers.

Hi!

Old post, but i think that my solution might be useful. I was having the same issue (Lubuntu ISO in VirtualBox starts in black screen), and I solved it updating the permissions of the VBoxGuestAdditions.iso in C:\Program Files\Oracle\VirtualBox - after gaving permissions to all users the problem dissapeared and can use Lubuntu with no hiccups.

Before this, I had updated video RAM to 128 MB with 3D hardware acceleration on, although I think this setup has no impact in the black screen issue.

Good luck!

JaimeAlba wrote:I solved it updating the permissions of the VBoxGuestAdditions.iso in C:\Program Files\Oracle\VirtualBox

Thanks for posting what worked for you! However, I have to respectfully point out that, knowing what that ISO does, I see no way that changing host permissions on that ISO can influence how the VM OS would boot. That is an installer ISO. It has no function unless it's mounted in the VM's CD drive and the executable on it is being run inside the already-booted-to-desktop VM OS. Since the Ubuntu OS isn't booting to the desktop yet, I'm not certain how the host's permissions for the container file holding the data could help the VM OS to boot.

Additionally, Windows hosts already have enough permissions for Virtualbox to use that ISO, unless someone had been footling with the permissions ahead of time and manually restricted them. Some folks seem to like editing permissions like cooks play in the spice rack in the kitchen...

I suspect this was a coincidence on your PC.

I take the liberty to join this thread to report on my observations with this issue. Host Windows 10, Guest Linux Mint Mate 20.3.

VirtualBox version older than 6.1.28 with Guest Additions 6.1.6:

When VM was quit while in Full Screen mode, next start of VM brings a black screen. Toggling out of and back into Full Screen Mode by pressing HOST-F twice fixes this.

VirtualBox version from 6.1.28 with Guest Additions 6.1.6:

Works as expected: When VM was quit while in Full Screen Mode, it starts back in Full Screen Mode.

Any VirtualBox version after 6.1.6 with corresponding Guest Additions (e.g. GA 6.1.28 for VBox 6.1.28) installed:

VM starts garbled; see screenshot 1. Going out of and back into Full Screen mode fixes that... somewhat. An area on the bottom of the screen remains unusable (e.g., you can't drag anything in there); see screenshot 2. This can be fixed by re-setting the VM's screen size, e.g. with the xrandr commands indicated in an earlier post. However, the next time you go out of, and back into, Full Screen mode, you have the same situation again.

Log included.

It's not a catastrophic situation since there are workkarounds; still, would be nice if it "just worked".

Additional information: Setting Preferences / Maximum Guest Screen Size to "None" or to "Hint / 1920 / 1200" (my monitor resolution) doesn't seem to make a difference.