In older Linux and Oracle Solaris guests, graphics and mouse integration goes through the X Window System. can use the X.Org variant of the system, or XFree86 version 4.3 which is identical to the first X.Org release. During the installation process, the X.Org display server will be set up to use the graphics and mouse drivers that come with the Guest Additions.

After installing the Guest Additions into a fresh installation of most Linux distributions or Oracle Solaris systems, the guest's graphics mode will change to fit the size of the window on the host when it is resized. You can also ask the guest system to switch to a particular resolution by sending a video mode hint using the VBoxManage tool.

Multiple guest monitors are supported in guests using the X.Org server version 1.3, which is part of release 7.3 of the X Window System version 11, or a later version. The layout of the guest screens can be adjusted as needed using the tools which come with the guest operating system.

The Guest Additions includes drivers for X.Org. You should not need to change these. By default these drivers are in the following directory:

/opt/VBoxGuestAdditions-version/other/

The correct versions for the X server are symbolically linked into the X.Org driver directories.

For graphics integration to work correctly, the X server must load the vboxvideo driver. Many recent X server versions look for it automatically if they see that they are running in . For an optimal user experience, the guest kernel drivers must be loaded and the Guest Additions tool VBoxClient must be running as a client in the X session.

For mouse integration to work correctly, the guest kernel drivers must be loaded. In addition, for legacy X servers the correct vboxmouse driver must be loaded and associated with /dev/mouse or /dev/psaux. For most guests, a driver for a PS/2 mouse must be loaded and the correct vboxmouse driver must be associated with /dev/vboxguest.

The guest graphics driver can use any graphics configuration for which the virtual resolution fits into the virtual video memory allocated to the virtual machine, minus a small amount used by the guest driver, as described in Display Settings. The driver will offer a range of standard modes at least up to the default guest resolution for all active guest monitors. The default mode can be changed by setting the output property VBOX_MODE to "<width>x<height>" for any guest monitor. When VBoxClient and the kernel drivers are active this is done automatically when the host requests a mode change. The driver for older versions can only receive new modes by querying the host for requests at regular intervals.

With legacy X Servers before version 1.3, you can also add your own modes to the X server configuration file. Add them to the "Modes" list in the "Display" subsection of the "Screen" section. For example, the following section has a custom 2048x800 resolution mode added:

Section "Screen"
        Identifier    "Default Screen"
        Device        "VirtualBox graphics card"
        Monitor       "Generic Monitor"
        DefaultDepth  24
        SubSection "Display"
                Depth         24
                Modes         "2048x800" "800x600" "640x480"
        EndSubSection
EndSection