In the VM Window menu, go to View and make sure that the Auto-resize Guest Display option is enabled
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sudo apt-get install virtualbox-ose-guest-utils virtualbox-ose-guest-x11 virtualbox-ose-guest-dkms
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follow the steps:
It is recommended that you set 128 MB of video memory, as when a video mode with higher resolution is used, more video memory is needed. You can also enable 2D and 3D acceleration.
open cmd:
cd "c:\Program Files\oracle\virtualbox"
VBoxManage setextradata "NAMEOFVM" VBoxInternal2/EfiGraphicsResolution 1920x1080
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sudo apt-get install virtualbox-guest-utils virtualbox-guest-x11 virtualbox-guest-dkms