Multiple Monitors on Full Screen MAC do not work

[tinpotnick]

I started a discussion regarding this on ​https://forums.virtualbox.org/viewtopic.php?f=8&t=82004&p=386615#p386615

I have tested in on 5.1.15 (pre-release) and 5.0.32. The matching Guest additions were installed from the iso in all tests.

When trying to use multiple monitors on a MAC (Sierra) with a Linux client (tested Debian 8 and Mint (17 & 18)) they work in normal mode. Set monitor count to 2, you get 2 Windows and it all works well.

Clicking any of the Windows to full screen, the primary screen maximises, the second screen disappears. It is not shown in mission control or available anywhere I can find. I checked with Apple support to ensure I was not doing anything silly!

If you enable 3D support for those guests and you get an unusual window for the second display. i.e. when you first click full screen, the primary goes full screen, the second disappears. Go to mission control, and you see a small icon with an image fragment next to it. Click on this and you get the second monitor back. But this second monitor does not work, most of the window is white with a tiny bit (top left) shows a small amount of the second screen.

Image attached of the second window. If you try to full-screen this window, it bounces up, and straight back down to a window (maintaining what you see in the image).

Revert from full screen and both monitors start to work again. All other applications on this computer use multiple full screens without problems.

[tinpotnick]

Image of second window

[tinpotnick]

Debian virtualbox log

[tinpotnick]

Mint 18 Virtualbox log

[Socratis]

I was about to reply "You didn't like my analysis? Did you try to fix the issues that I raised?", when I realized that my analysis/answer was nowhere to be found! I definitely replied to that message of yours in the forums, I simply don't know what on earth happened. Maybe I closed the window before posting it?

Anyway I re-posted my ​answer in the forums, full analysis. I'll briefly summarize here as well, but please let's keep the discussion going in the forums, where a lot more people are going to benefit:

• Quite old VirtualBox version (5.0.32) for OSX 10.12.
• Wrong template for the guest selected: Linux26_64 instead of Ubuntu_64.
• Old version and Mint-forked distribution of the Guest Additions.
• 3D acceleration is disabled (I don't think it plays a big role).