virtualbox.org

I just upgraded virtualbox from 5.2.6. to 5.2.8. The host is macOS 10.13.3 and the guest is Xubuntu 16.04 LTS.
After the upgrade, Xubuntu boots, but does not react to any mouse or keyboard inputs. It is completely unresponsive.
I powered-off the guest and booted it again a few times, no change of the situation.
The mouse pointer seems to be captured when I hover over the guest window area, I see that it changes form the macOS shape to the Xubuntu shape, but mouse clicks do not register, I can not select or do anything. System completely unusable as it is.

We're going to need to see a VM log from a complete VM run:

• Start the VM from cold-boot (not from a paused or saved state) / Observe error / Shutdown the VM (force close it if you have to).
• With the VM completely shut down (not paused or saved), right-click on the VM in the VirtualBox Manager and select "Show Log".
• Save only the first "VBox.log", ZIP it and attach it to your response. See the "Upload attachment" tab below the reply form.

log attached.

00:00:01.552154 Host RAM: 4096MB (4.0GB) total, 1176MB available
00:00:01.673108 RamSize   <integer> = 0x0000000080000000 (2 147 483 648, 2 048 MB)

You are assigning memory to your guest, that you do not have available. Either close some applications on the host, buy more RAM for the host, or reduce the amount of RAM assigned to the guest.

00:00:01.673583 VRamSize <integer> = 0x0000000001000000 (16 777 216, 16 MB)

At the same time the amount of vRAM assigned seems a little too small. I would bump it to 32 or 64 MB at least.

00:00:01.673105 NumCPUs   <integer> = 0x0000000000000002 (2)
00:00:01.839585 CPUM: Physical host cores: 2

You have assigned all your CPUs to the VM. The host is going to run low on resources, since VirtualBox cares about physical processors (cores), not logical ones (threads). And yes, your i5-4258U CPU has 2 cores / 4 threads.

Remember that simple rule:

• Total CPUs for your guests + 1 ≤ Host CPUs.
• Total RAM+vRAM+overhead for your guests ≤ Host available RAM + some.

Here are a couple of applications, so that you know what's available on your system at any given time:

• MenuMeters (for OSX > 10.10).
• X Resource Graph.
• Memory Monitor.
• Built-in Activity monitor.

This did not help. I increased the guest VRAM, decreased guest RAM, freed up RAM on host, no change. Besides may I stress that it did work before and stopped working with the upgrade, so I believe problems are probably more related to the fact that I updated instead of generic points regarding RAM usage. To test, I made a fresh Xubuntu 16.04 LTS guest machine on the same Virtual Box instance - works without problems! But I do not know how to repair / rescue my original Xubuntu guest installation on that same Virtual Box instance, which (Xubuntu) is now broken. Original Xubuntu instance simply boots into the Xubuntu desktop and is "dead" in the sense that I can move the mouse, but mouse clicks do not register, keyboard does not register. The usual tricks (Alt-F4) show no effect, I guess because the keyboard is unresponsive in that instance. Regret to have updated! New Xubuntu guest instance works without problems, not clear where the problems even originate from - Virtual Box or Xubuntu.

Resolved!
The issue might not be caused by Virtual Box but by ubuntu.
The solution for me was to follow these instructions: https://askubuntu.com/a/910211
Solution is basically to update/install xserver-xorg-input-all
As keyboard / mouse do not work, this needs to be done from root fallback console (press shift during boot, enable networking, fall back to root shell, apt install the package).
I did this for two installations of Xubuntu 16.04 under VirtualBox, versions described as above, and it resolved the issue in both cases.

anton.kratz, first of all, a big thanks for letting us know about the problem. Second, the solution that you linked to, talked about an update from 16.04 to 16.10. Did you update you Xubuntu as well?

No, I did not update Xubuntu, only Virtual Box. Xubuntu at 16.04 LTS. Virtual Box and host versions please see my original post above.