The Guest Additions provide services for controlling the guest system's monitor topology. Monitor topology means the resolution of each virtual monitor and its state (disabled/enabled). The resolution of a virtual monitor can be modified from the host side either by resizing the window that hosts the virtual monitor, by using the View menu or the VBoxManage controlvm vmname setscreenlayout command. On guest operating systems with X11/Wayland desktops this is put into effect by either of the following two services:

        VBoxClient --vmsvga
        VBoxDRMClient
      

The following are some details about guest screen resolution control functionality:

• On X11/Wayland desktops the resizing service is started during desktop session initialization, that is desktop login. On X11 desktops VBoxClient --vmsvga handles screen topology through the RandR extension. On Wayland clients VBoxDRMClient is used. The decision is made automatically at each desktop session start.

• On 32-bit guest operating systems VBoxDRMClient is always used, in order to work around bugs.

• Since the monitor topology control services are initialized during the desktop session start, it is impossible to control the monitor resolution of display managers such as GDM or LightDM. This default behavior can be changed by setting the guest property /VirtualBox/GuestAdd/DRMResize of the virtual machine to any value. See for details of how to update guest properties. When this guest property is set then VBoxDRMClient is started during the guest OS boot and stays active all the time, for both the display manager login screen and the desktop session.