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, through the view menu or through VBoxManage controlvm "vmname" setscreenlayout. On guest operating systems with X11/Wayland desktops this is put into effect by either of two following services:
VBoxClient --vmsvga
VBoxDRMClient
Here are some details about guest screen resolution control functionality:
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On X11/Wayland desktops the resizing service is started during desktop session initialization, that is desktop login. On X11 desktops
VBoxClient --vmsvgahandles screen topology through the RandR extension. On Wayland clientsVBoxDRMClientis used. The decision is made automatically at each desktop session start. -
On 32 bit guest operating systems
VBoxDRMClientis always used, in order to work around bugs. -
Since the mentioned 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, lightdm. This default behavior can be changed by setting the guest property
/VirtualBox/GuestAdd/DRMResizeof the virtual machine to any value. Please refer to Section 4.7, "Guest Properties" for updating guest properties. When this guest property is set thenVBoxDRMClientis started during the guest OS boot and stays active all the time, for both ithe display manager login screen and the desktop session.
VBoxDRMClient is not able to handle arbitrary guest monitor topologies. Specifically, disabling a guest monitor (except the last one) invalidates the monitor topology due to limitations in the Linux kernel module vmwgfx.ko. iFor example, when the guest is configured to have 4 monitors it is not recommended to disable the 2nd or 3rd monitor.