Crie um arquivo chamado /etc/X11/xorg.conf.d/10-monitor.conf
com o seguinte conteúdo:
Section "Monitor"
Identifier "Monitor0"
EndSection
Section "Device"
Identifier "Device0"
Driver "vboxvideo" # Choose the driver
EndSection
Section "Screen"
Identifier "Screen0"
Device "Device0"
Monitor "Monitor0"
DefaultDepth 24 # Choose the depth (16||24)
SubSection "Display"
Depth 24
Modes "1280x720" # Choose the resolution
EndSubSection
EndSection