Virtualbox Ubuntu guest + 5K resolution host

[DavidDobrigkeitChinellato]

I've installed the latest version of virtualbox in a computer running Windows 10 Professional and a Dell UP2715K with a resolution of 5120x2880, and have been using it to run Ubuntu 15.10 in a virtual machine rather successfully. However, when attempting to use the full resolution of the host also in the guest, it seems I am getting a malfunction of the Virtualbox-additions video driver inside the guest operating system... It seems that, when I pass 4000 pixels in the horizontal axis, the linux guest display reverts to (width of virtualbox window minus 4000 pixels) as actual display width, i.e. when trying to occupy nearly the full 5000 pixels I get a super "slim and tall" virtual display of only ~1000 pixels in size, and when I resize to ~4500 pixels in width in the host, I get ~500 pixels width in the guest.... Has anybody ever faced a similar difficulty?

I've tried allocating the maximum possible video memory to the guest OS, as well as enabling 3D acceleration, but haven't had success so far. Could it be that it is simply a shortcoming of the software in the additions driver, which is not yet OK with horizontal display widths exceeding 4000 pixels?

For the time being, I am resorting to 200% scaling, and that allows me to use the linux guest full-screen, but of course then I only use part of the resolution that I could be using

Many thanks in advance for any input!

[socratis]

1) Have you installed the Guest Additions (GAs) in your guest?
2) How are you trying to resize your guest? Manually? With VBoxManage?
3) Did you try to go directly to full-screen (Host+F)? What happened?
4) What is the setting for HiDPI in the VM Settings?
5) Post a VBox.log for the guest. With the VM shut down, right-click on the VM, show log, save it, zip it, attach it. Mind you, post the log after you've tried to change the resolution.

[DavidDobrigkeitChinellato]

Many thanks for your answer! Here are the answers to your points:

1) Yes, GAs are there.
2) I've tried only via GUIs so far (resizing window and going full-screen).
3) Yes, I tried, same result: very thin and tall display (actually seen as 1024x2880 by the guest)
4) If by this you mean the scaling factor, it's set at 100% (pixel-for-pixel matchup). At 200%, all these issues disappear since the guest never sees anything close to 4000 pixels.
5) I've started the VM, attempted full screen mode (which resulted in the 1024x2880 issue), powered down and saved the log file that is attached. I am of course unsure of what any of this means but an interesting part, confirming that the guest sees 1024x2880 instead of 5120x2880, is copy-pasted below...

00:00:55.419843 GUI: UIMachineViewFullscreen::adjustGuestScreenSize: Adjust guest-screen size if necessary.
00:00:55.419859 GUI: UIMachineView::sltPerformGuestResize: Sending guest size-hint to screen 0 as 5120x2880
00:00:55.419895 VMMDev: SetVideoModeHint: Got a video mode hint (5120x2880x32)@(0x0),(1;0) at 0
00:00:55.422918 VBVA: InfoScreen: [0] @0,0 1024x2880, line 0x1000, BPP 32, flags 0x1
00:00:55.422975 Display::handleDisplayResize: uScreenId=0 pvVRAM=0000000010e80000 w=1024 h=2880 bpp=32 cbLine=0x1000 flags=0x1
00:00:55.423109 GUI: UIFrameBufferPrivate::NotifyChange: Screen=0, Origin=0x0, Size=1024x2880, Sending to async-handler
00:00:55.428444 VBVA: InfoScreen: [0] @0,0 1024x2880, line 0x1000, BPP 32, flags 0x1
00:00:55.444490 VBVA: InfoScreen: [0] @0,0 1024x2880, line 0x1000, BPP 32, flags 0x1

[loukingjr]

From your log…

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00:00:12.003249 VMMDev: Guest Additions information report: Version 5.0.0 r101573 '5.0.0_Ubuntu'

Remove the 5.0.0 version of the GAs and install the correct version by choosing "Insert Guest Additions CD Image…" from the VirtualBox Devices menu.

[DavidDobrigkeitChinellato]

Thanks for the suggestion! I reinstalled the GA and I still got 5.0.0 as version number, but I noticed there was a warning that the kernel headers were not found. I then noticed that I actually had linux-headers-generic installed but not linux-headers-virtual, which I promptly installed.

Now I think the additions are correctly reported as 5.0.14:

00:00:13.832678 VMMDev: Guest Additions information report: Version 5.0.14 r105127 '5.0.14'

....however, the problem with the max width of the guest display not being able to go over 4000 pixels still persists unchanged, and a full-screen mode still results in a guest display of only 1024x2880 (as also visible in the attached log...)

[socratis]

Can you try a couple of things?
- Go in the VirtualBox Preferences, Display. What's the value of "Maximum Guest Screen Size"?
- Go in the VM Preferences and lower the RAM to 4GB and the vCPUs to 2.

And generally speaking, it's a good practice to shut down the VM instead of suspending it...

[DavidDobrigkeitChinellato]

Thanks for the input, socratis! I looked at the "Maximum Guest Screen Size" and it was set to auto. I then tried "none" and also "suggest" (and suggested 5120x2880, the monitor's native resolution) but none of this helped.

I also tried changing the VM preferences to 4GB RAM and 2 vCPUs , but that too made no difference...

As for suspending vs shutdown, actually I thought I always asked for shutdown. I will check and be sure to do shutdown (I always have this latent fear of suspend under linux since it often has issues)...

[loukingjr]

If you've ever used the display settings in your Ubuntu guest, it creates a monitor.xml file inside the /Home/<user>/.config folder that will override the virtualbox settings. See if one exists in your guest and delete it. Restart the guest.

just to be sure your guest is set up correctly, run…

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sudo apt-get install dkms build-essential

then reinstall the guest additions.

[mv1]

Did this ever get resolved? I have the same issue with a 4k Dell display (Dell P2715Q). Strangely, on one boot of the virtual machine the problem went away. But, after shutting down virtualbox and restarting it later, the issue came back. I've tried the suggestions here to no avail. This is Ubuntu Xenial as the guest, Windows 10 as the host, guest additions installed, and reinstalled as per the suggestions in this thread.