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Investigating problems with dynamic resizing

  • The basic mechanisms of dynamic resizing are described on another wiki page<1>. The short summary is that the host sends "size hints" to the virtual machine (which consist of an interrupt on the virtual graphics card or the "guest" device and a way for the guest to ask for the details) and special "driver" modules from the Guest Additions ask the guest operating system to resize its virtual displays to match the hints.
  • The first requirement for dynamic resizing to work is for the Guest Additions to support it. If you are using the normal user interface, you can check that the menu option to enable dynamic resizing can be enabled (meaning the Additions provide that support) and is enabled.
  • Every time the host sends a hint there will be a matching entry in the machine log file on the host ("VMMDev: SetVideoModeHint: Got a video mode hint (...)" VMMDev is the "guest" device. A matching hint may be sent to the graphics device). The next thing to check is whether these entries are appearing when you expect the guest to resize.
  • If for whatever reason the guest operating system chooses to modify the requested size the host windows will try to follow that. If the host window manager refuses the usual result is that the guest display will not fit the host window perfectly. The guest drivers may also (Windows guests only) modify resize requests from the guest operating system to fit the size policy chosen by the user.

Connecting to guests with VRDP

(To do.)

Guests running X.Org or Wayland

  • See the description of how the drivers work on the Guest Resizing page<1>. If your guest is running X.Org or XFree86 as its main windowing system (not just XWayland) then the log file Xorg.0.log should show that it is using either the vboxvideo driver or the modesetting driver. You should see lines starting with "vboxvideo" or "modeset" near the end of the file, not just at the beginning. If not that is probably where the problem lies.
  • If you are running a Wayland compositor, the kernel vboxvideo driver should be running: type "lsmod| grep vboxvideo" into a terminal in the guest.
  • If you are not sure if the kernel driver was set up correctly, see the information page about investigating that<2>.
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