4 Guest Additions
For Linux and Solaris guests, the Xorg server version 1.3 or later is required for automatic resizing (the feature has been disabled on Fedora 9 guests due to a bug in the X server they supply). The server version can be checked with Xorg
Finally, if the Guest Additions are installed, 3D graphics for guest applications can be accelerated; see chapter 4.9, Hardware 3D acceleration (OpenGL and Di- rect3D 8/9), page 72.
Time synchronization With the Guest Additions installed, VirtualBox can ensure that the guest’s system time is better synchronized. This fixes the problem that an operating system normally expects to have 100% of a computer’s time for itself without interference, which is no longer the case when your VM runs together with your host operating system and possibly other applications on your host. As a result, your guest operating system’s timing will soon be off significantly. The Guest Additions will
Shared folders These provide an easy way to exchange files between the host and the guest. Much like ordinary Windows network shares, you can tell VirtualBox to treat a certain host directory as a shared folder, and VirtualBox will make it available to the guest operating system as a network share. For details, please refer to chapter 4.7, Folder sharing, page 68.
Seamless windows With this feature, the individual windows that are displayed on the desktop of the virtual machine can be mapped on the host’s desktop, as if the underlying application was actually running on the host. See chapter 4.8, Seamless windows, page 71 for details.
Shared clipboard With the Guest Additions installed, the clipboard of the guest op- erating system can optionally be shared with your host operating system; see chapter 3.3, General settings, page 46.
Automated Windows logons (Credentials passing; Windows guests only) For de- tails, please see chapter 9.2, Automated Windows guest logons, page 137.
4.2 Versions
Each version of VirtualBox, even minor releases, ship with their own version of the Guest Additions. While the interfaces through which the VirtualBox core communi- cates with the Guest Additions are kept stable so that Guest Additions already installed in a VM should continue to work when VirtualBox is upgraded on the host, for best results, it is recommended to keep the Guest Additions at the same version.
Starting with VirtualBox 3.1, the Windows and Linux Guest Additions therefore check automatically whether they have to be updated. If the host is running a newer VirtualBox version than the Guest Additions, a notification with with further instruc- tions is displayed in the guest.
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