I came across an interesting effect with VirtualBox (Version 3.2.6 r63112 running on a CentOS 5.4 host) wherein a VM without Guest Additions can negatively impact the host if a screen saver is set to blank. No other hosts have been tested, and the symptoms are intermittent. I have not gotten this work using an active screen saver.

Here's how it works:

When the VM is running and has the mouse captured, after the screen fades the host will no longer respond to mouse or keyboard input. Pressing the host key to release the mouse has no effect.

At first I recovered by by pressing CTRL-ALT-BKSP to forcibly restart X, but this aborts all other VMs and GUI applications, which is undesirable.

A better work around I've found was to press CTRL-ALT-F1 to log into a separate console. Then, find the VM of interest:

[roger@localhost ~]$ ps aux | grep virtual

roger 10096 0.1 0.6 301912 26240 ? Sl 15:52 0:04 /usr/lib/virtualbox/VirtualBox

roger 10110 0.0 0.0 92900 1856 ? S 15:52 0:01 /usr/lib/virtualbox/VBoxXPCOMIPCD

roger 10117 0.1 0.1 168896 6152 ? Sl 15:52 0:04 /usr/lib/virtualbox/VBoxSVC --pipe 11 --auto-shutdown

roger 10154 24.5 1.4 979564 58708 ? SLl 15:52 13:58 /usr/lib/virtualbox/VirtualBox --comment XP --startvm 45ed30a2-3028-48ea-86c4-99425d5a3d48 --no-startvm-errormsgbox

roger 10467 36.5 0.8 916800 35320 ? SLl 16:48 0:19 /usr/lib/virtualbox/VirtualBox --comment LFS_Tiny --startvm 5972dc92-02bb-4912-9fcf-0382b2437efc --no-startvm-errormsgbox

roger 10489 0.0 0.0 61184 740 pts/2 R+ 16:49 0:00 grep virtual

Tiny Core was the VM to have the mouse captured, so:

[roger@localhost ~]$kill 10467

After this you can press CTRL-ALT-F7 to get back to the GUI to unlock the screen. The VM that was killed will show as aborted in the VM Virtual Box Manager.

I didn't like abruptly killing Tiny Core though, so I found an alternative. The best solution in this situation would be to use VirtualBox's own command line, wherein you can do just about anything that you could with VM Virtual Box Manager. Being that we cannot interact with the guest to save any data, the best way to shut the process down is by saving the state using “VBoxManage controlvm <uuid>|<name> savestate”.

Or in my case...

[roger@localhost ~]$VBoxManage controlvm LFS_Tiny savestate
Oracle VM VirtualBox Command Line Management Interface Version 3.2.6
(C) 2005-2010 Oracle Corporation
All rights reserved.

0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
[roger@localhost ~]$

Thanks,
Roger Heslop

Nice write up, thanks.

You might improve it further by putting the code in "Code:" blocks.