Unity7 and Gnome 3: How to disable "lock was blocked by an application", so that Gnome3 always locks the screen?

Question

When I have virtualbox in full screen, on Unity it always locks after 5 minutes, but in Gnome3 (and even Unity7) it shows a popup message: lock was blocked by an application.

Can I force Unity or Gnome3 to always lock regardless of FULL-SCREENED applications?

Solution

To enable screen lock when VirtualBox guest is in full screen, go to VirtualBox Manager -> File -> Preferences -> Input and switch off "Auto Capture Keyboard".

Click OK and run guest OS in full screen mode. Screen should auto lock now, and without annoying notification "lock was blocked by application". I'm using Ubuntu 20.04 LTS with VirtualBox 6.1.26.

PS: Is security issue fixed? - Yes, screen lock is working now. Whether usability is lowered? - Yes, a little. This is a kind of trade-off between security and usability. You choose.

Comments

[robocat]

I found a commit that implies a code fix "XXX: another option is to kick the user into the gdm loginscreen, where we're not affected by grabs". Grepping the journal using journalctl -rb | grep -n3 "Lock was" shows "gnome-shell[1980]: pushModal: invocation of begin_modal failed".

[Nir]

I also get this message, what does lock mean?

[Michael]

it started doing this to me recently - it didn't before, and I can't think what i would have changed that would have caused this!

[Phil]

That bug is closed, and was closed when this answer was posted.

[Chris S.]

Is there an option in virtual box to disable this feature?