The previous chapter covered getting started with VirtualBox and installing operating systems in a virtual machine. For any serious and interactive use, the VirtualBox Guest Additions will make your life much easier by providing closer integration between host and guest and improving the interactive performance of guest systems. This chapter describes the Guest Additions in detail. As said in , the Guest Additions are designed to be installed inside a virtual machine after the guest operating system has been installed. They consist of device drivers and system applications that optimize the guest operating system for better performance and usability. Please see for details on what guest operating systems are fully supported with Guest Additions by VirtualBox. The VirtualBox Guest Additions for all supported guest operating systems are provided as a single CD-ROM image file which is called VBoxGuestAdditions.iso. This image file is located in the installation directory of VirtualBox. To install the Guest Additions for a particular VM, you mount this ISO file in your VM as a virtual CD-ROM and install from there. The Guest Additions offer the following features: Mouse pointer integration To overcome the limitations for mouse support that were described in , this provides you with seamless mouse support. You will only have one mouse pointer and pressing the Host key is no longer required to "free" the mouse from being captured by the guest OS. To make this work, a special mouse driver is installed in the guest that communicates with the "real" mouse driver on your host and moves the guest mouse pointer accordingly. Better video support While the virtual graphics card which VirtualBox emulates for any guest operating system provides all the basic features, the custom video drivers that are installed with the Guest Additions provide you with extra high and non-standard video modes as well as accelerated video performance. In addition, with Windows and recent Linux, Solaris and OpenSolaris guests, if the Guest Additions are installed, you can resize the virtual machine's window, and the video resolution in the guest will be automatically adjusted (as if you had manually entered an arbitrary resolution in the guest's display settings). Finally, if the Guest Additions are installed, 3D graphics for guest applications can be accelerated; see . Time synchronization With the Guest Additions installed, VirtualBox can ensure that the guest's system time is better synchronized with that of the host. For various reasons, the time in the guest might run at a slightly different rate than the time on the host. The host could be receiving updates via NTP and its own time might not run linearly. A VM could also be paused, which stops the flow of time in the guest for a shorter or longer period of time. When the wall clock time between the guest and host only differs slightly, the time synchronization service attempts to gradually and smoothly adjust the guest time in small increments to either "catch up" or "lose" time. When the difference is too great (e.g., a VM paused for hours or restored from saved state), the guest time is changed immediately, without a gradual adjustment. The Guest Additions will re-synchronize the time regularly. See for how to configure the parameters of the time synchronization mechanism. 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 . 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 for details. Shared clipboard With the Guest Additions installed, the clipboard of the guest operating system can optionally be shared with your host operating system; see . Automated logons (credentials passing) For details, please see . Each version of VirtualBox, even minor releases, ship with their own version of the Guest Additions. While the interfaces through which the VirtualBox core communicates 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 further instructions is displayed in the guest. To disable this update check for the Guest Additions of a given virtual machine, set the value of its /VirtualBox/GuestAdd/CheckHostVersion guest property to 0; see for details. Guest Additions are available for virtual machines running Windows, Linux, Solaris or OS/2. The following sections describe the specifics of each variant in detail. The VirtualBox Windows Guest Additions are designed to be installed in a virtual machine running a Windows operating system. The following versions of Windows guests are supported: Microsoft Windows NT 4.0 (any service pack) Microsoft Windows 2000 (any service pack) Microsoft Windows XP (any service pack) Microsoft Windows Server 2003 (any service pack) Microsoft Windows Server 2008 Microsoft Windows Vista (all editions) Microsoft Windows 7 (all editions) In the "Devices" menu in the virtual machine's menu bar, VirtualBox has a handy menu item named "Install guest additions", which mounts the Guest Additions ISO file inside your virtual machine. A Windows guest should then automatically start the Guest Additions installer, which installs the Guest Additions into your Windows guest. For Direct 3D acceleration to work in a Windows Guest, you must install the Guest Additions in "Safe Mode"; see for details. If you prefer to mount the additions manually, you can perform the following steps: Start the virtual machine in which you have installed Windows. Select "Mount CD/DVD-ROM" from the "Devices" menu in the virtual machine's menu bar and then "CD/DVD-ROM image". This brings up the Virtual Media Manager described in . In the Virtual Media Manager, press the "Add" button and browse your host file system for the VBoxGuestAdditions.iso file: On a Windows host, you can find this file in the VirtualBox installation directory (usually under C:\Program files\Oracle\VirtualBox ). On Mac OS X hosts, you can find this file in the application bundle of VirtualBox. (Right click on the VirtualBox icon in Finder and choose Show Package Contents. There it is located in the Contents/MacOS folder.) On a Linux host, you can find this file in the additions folder under where you installed VirtualBox (normally /opt/VirtualBox/). On Solaris hosts, you can find this file in the additions folder under where you installed VirtualBox (normally /opt/VirtualBox). Back in the Virtual Media Manager, select that ISO file and press the "Select" button. This will mount the ISO file and present it to your Windows guest as a CD-ROM. Unless you have the Autostart feature disabled in your Windows guest, Windows will now autostart the VirtualBox Guest Additions installation program from the Additions ISO. If the Autostart feature has been turned off, choose VBoxWindowsAdditions.exe from the CD/DVD drive inside the guest to start the installer. The installer will add several device drivers to the Windows driver database and then invoke the hardware detection wizard. Depending on your configuration, it might display warnings that the drivers are not digitally signed. You must confirm these in order to continue the installation and properly install the Additions. After installation, reboot your guest operating system to activate the Additions. Windows Guest Additions can be updated by running the installation program again, as previously described. This will then replace the previous Additions drivers with updated versions. Alternatively, you may also open the Windows Device Manager and select "Update driver..." for two devices: the VirtualBox Graphics Adapter and the VirtualBox System Device. For each, choose to provide your own driver and use "Have Disk" to point the wizard to the CD-ROM drive with the Guest Additions. In order to allow for completely unattended guest installations, you can specify a command line parameter to the install launcher: VBoxWindowsAdditions.exe /S This automatically installs the right files and drivers for the corresponding platform (32- or 64-bit). Because of the drivers are not yet WHQL certified, you still might get some driver installation popups, depending on the Windows guest version. For more options regarding unattended guest installations, consult the command line help by using the command: VBoxWindowsAdditions.exe /? If you would like to install the files and drivers manually, you can extract the files from the Windows Guest Additions setup by typing: VBoxWindowsAdditions.exe /extract To explicitly extract the Windows Guest Additions for another platform than the current running one (e.g. 64-bit files on a 32-bit system), you have to execute the appropriate platform installer (VBoxWindowsAdditions-x86.exe or VBoxWindowsAdditions-amd64.exe) with the /extract parameter. Earlier versions of VirtualBox provided a virtual AMD PCNet Ethernet card to guests by default. Since Microsoft no longer ships a driver for that card with Windows (starting with Windows Vista), if you select Windows Vista or newer as the guest operating system for a virtual machine, VirtualBox will instead present a virtual Intel network controller to the guest (see ). However, if for any reason you have a 32-bit Windows Vista VM that is configured to use an AMD PCNet card, you will have no networking in the guest initially. As a convenience, VirtualBox ships with a 32-bit driver for the AMD PCNet card, which comes with the Windows Guest Additions. If you install these in a 32-bit Vista guest, the driver will automatically be installed as well. If, for some reason, you would like to install the driver manually, you can extract the required files from the Windows Guest Additions setup. Please consult on how to achieve this. You will then find the AMD PCNet driver files in the x86\Network\AMD\netamd.inf subdirectory of the default install directory. Alternatively, change the Vista guest's VM settings to use an Intel networking card instead of the default AMD PCNet card; see for details. Unfortunately, there is no 64-bit driver available for the AMD PCNet card. So for 64-bit Windows VMs, you should always use the Intel networking devices. Like the Windows Guest Additions, the VirtualBox Guest Additions for Linux take the form of a set of device drivers and system applications which may be installed in the guest operating system. The following Linux distributions are officially supported: Fedora as of Fedora Core 4; Redhat Enterprise Linux as of version 3; SUSE and openSUSE Linux as of version 9; Ubuntu as of version 5.10. Many other distributions are known to work with the Guest Additions. The version of the Linux kernel supplied by default in SUSE and openSUSE 10.2, Ubuntu 6.10 (all versions) and Ubuntu 6.06 (server edition) contains a bug which can cause it to crash during startup when it is run in a virtual machine. The Guest Additions work in those distributions. Note that some Linux distributions already come with VirtualBox Guest Additions or a part thereof. You may keep the distribution's version of the Guest Additions but often, these are not up to date and limited in functionality. Therefore, you can choose the install the Guest Additions that come with VirtualBox, overriding the already installed version. The VirtualBox Linux Guest Additions installer tries to detect existing installation and replace them but depending on how the distribution integrates the Guest Additions, they may require some manual interaction. It is highly recommended to take a snapshot of the virtual machine before overriding the installation. The VirtualBox Guest Additions for Linux are provided on the same ISO CD-ROM as the Additions for Windows described above. They also come with an installation program guiding you through the setup process, although, due to the significant differences between Linux distributions, installation may be slightly more complex. Installation generally involves the following steps: Before installing the Guest Additions, you will have to prepare your guest system for building external kernel modules. This works similarly as described in , except that this step must now be performed in your Linux guest instead of on a Linux host system, as described there. Again, as with Linux hosts, we recommend using DKMS for Linux guests as well. If it is not installed, use this command for Ubuntu/Debian systems:sudo apt-get install dkms or for Fedora systems: yum install dkms Make sure to nstall DKMS before installing the Linux Guest Additions. Mount the VBoxGuestAdditions.iso file as your Linux guest's virtual CD-ROM drive, exactly the same way as described for a Windows guest in . Change to the directory where your CD-ROM drive is mounted and execute as root: sh ./VBoxLinuxAdditions-x86.run In a 64-bit Linux guest, use VBoxLinuxAdditions-amd64.run instead. For your convenience, the following step-by-step instructions have been verified to work for freshly installed copies of the most popular Linux distributions. After these preparational steps, you can execute the VirtualBox Guest Additions installer as described above. In order to update your system to the latest version of the packets, open a terminal and as root, execute apt-get update followed by apt-get upgrade Install DKMS using apt-get install dkms Reboot your guest system in order to activate the updates and then proceed as described above. In order to update your system to the latest version of the packets, open a terminal and as root, execute yum update Install DKMS and the GNU C compiler using yum install dkms followed by yum install gcc Reboot your guest system in order to activate the updates and then proceed as described above. In order to update your system to the latest version of the packets, open a terminal and as root, execute zypper update Install the make tool and the GNU C compiler using zypper install make gcc Reboot your guest system in order to activate the updates. Find out which kernel you are running using uname -a An example would be 2.6.31.12-0.2-default which refers to the "default" kernel. Then install the correct kernel development package. In the above example this would be zypper install kernel-default-devel Make sure that your running kernel (uname -a) and the kernel packages you have installed (rpm -qa kernel\*) have the exact same version number. Proceed with the installation as described above. In order to update your system to the latest version of the packets, open a terminal and as root, execute zypper update Install the GNU C compiler using zypper install gcc Reboot your guest system in order to activate the updates. Find out which kernel you are running using uname -a An example would be 2.6.27.19-5.1-default which refers to the "default" kernel. Then install the correct kernel development package. In the above example this would be zypper install kernel-syms kernel-source Make sure that your running kernel (uname -a) and the kernel packages you have installed (rpm -qa kernel\*) have the exact same version number. Proceed with the installation as described above. Mandrake ships with the VirtualBox Guest Additions which will be replaced if you follow these steps. In order to update your system to the latest version of the packets, open a terminal and as root and execute urpmi --auto-update Reboot your system in order to activate the updates. Install DKMS using urpmi dkms and make sure the choose the correct kernel-devel package when asked by the installer (use uname -a to compare). Add divider=10 to the kernel boot options in /etc/grub.conf to reduce the idle CPU load. To update your system to the latest version of the packets, open a terminal and as root, execute yum update Install the GNU C compiler and the kernel development packages using yum install gcc followed by yum install kernel-devel Reboot your guest system in order to activate the updates and then proceed as described above. Note that OpenGL support is not available unless you update to a later Linux kernel. In case Oracle Enterprise Linux does not find the required packages, you either have to install them from a different source (e.g. DVD) or use Oracle's public Yum server located at http://public-yum.oracle.com. In order to update your system to the latest version of the packets, open a terminal and as root, execute apt-get update followed by apt-get upgrade Install the make tool and the GNU C compiler using apt-get install make gcc Reboot your guest system in order to activate the updates. Determine the exact version of your kernel using uname -a and install the correct version of the linux-headers package, e.g. using apt-get install linux-headers-2.6.26-2-686 Note that OpenGL support is not available unless you update to a later Linux kernel. The VirtualBox Guest Additions contain several different drivers. If for any reason you do not wish to set them all up, you can install the Guest Additions using the following command: sh ./VBoxLinuxAdditions-x86.run no_setup (substituting VBoxLinuxAdditions-amd64 on a 64-bit guest). After this, you will need to at least compile the kernel modules by running the command /usr/lib/VBoxGuestAdditions/vboxadd setup as root (you will need to replace lib by lib64 on some 64bit guests), and on older guests without the udev service you will need to add the vboxadd service to the default runlevel to ensure that the modules get loaded. To setup the time synchronization service, run the command /usr/lib/VBoxGuestAdditions/vboxadd-service setup and add the service vboxadd-service to the default runlevel. To set up the X11 and OpenGL part of the Guest Additions, run the command /usr/lib/VBoxGuestAdditions/vboxadd-x11 setup (you do not need to enable any services for this). To recompile the guest kernel modules, use this command: /usr/lib/VBoxGuestAdditions/vboxadd setup After compilation you should reboot your guest to ensure that the new modules are actually used. In Linux guests, VirtualBox video acceleration is available through the X Window System. Typically, in today's Linux distributions, this will be the X.Org server. During the installation process, X will be set up to use the VirtualBox video driver shipped with the Guest Additions. For Linux and Solaris guests, the X.org 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 -version. You can also send video mode hints using the VBoxManage tool. If you are only using recent Linux guests systems, you can skip the rest of this section. On older guest systems, whatever graphics modes were set up before the installation will be used. If these modes do not suit your requirements, you can change your setup by editing the configuration file of the X server, usually found in /etc/X11/xorg.conf. VirtualBox can use any default X graphics mode which fits into the virtual video memory allocated to the virtual machine, as described in . You can also add your own modes to the X server configuration file. You simply need to add them to the "Modes" list in the "Display" subsection of the "Screen" section. For example, the section shown here 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 The Guest Additions can simply be updated by going through the installation procedure again with an updated CD-ROM image. This will replace the drivers with updated versions. You should reboot after updating the Guest Additions. If you have a version of the Guest Additions installed on your virtual machine and wish to remove it without installing new ones, you can do so by inserting the Guest Additions CD image into the virtual CD-ROM drive as described above and running the installer for the current Guest Additions with the "uninstall" parameter from the path that the CD image is mounted on in the guest: sh ./VBoxLinuxAdditions-x86.run uninstall (substituting VBoxLinuxAdditions-amd64 on a 64-bit guest). While this will normally work without issues, you may need to do some manual clean up of the guest (particularly of the XFree86Config or xorg.conf file) in some cases, particularly if the Additions version installed or the guest operating system were very old, or if you made your own changes to the Guest Additions setup after you installed them. Starting with version 3.1.0, you can uninstall the Additions by invoking /opt/VBoxGuestAdditions-$VBOX_VERSION_STRING/uninstall.sh substituting /opt/VBoxGuestAdditions-$VBOX_VERSION_STRING with the Guest Additions installation directory. Like the Windows Guest Additions, the VirtualBox Guest Additions for Solaris take the form of a set of device drivers and system applications which may be installed in the guest operating system. The following Solaris distributions are officially supported: OpenSolaris Nevada (Build 82 and higher; this includes OpenSolaris 2008.05, 2008.11 and 2009.06); OpenSolaris Indiana (Developer Preview 2 and higher); Solaris 10 (u5 and higher). Other distributions may work if they are based on comparable software releases. The VirtualBox Guest Additions for Solaris are provided on the same ISO CD-ROM as the Additions for Windows and Linux described above. They also come with an installation program guiding you through the setup process. Installation involves the following steps: Mount the VBoxGuestAdditions.iso file as your Solaris guest's virtual CD-ROM drive, exactly the same way as described for a Windows guest in . If in case the CD-ROM drive on the guest doesn't get mounted (observed on some versions of Solaris 10), execute as root: svcadm restart volfs Change to the directory where your CD-ROM drive is mounted and execute as root: pkgadd -G -d ./VBoxSolarisAdditions.pkg Choose "1" and confirm installation of the Guest Additions package. After the installation is complete, re-login to X server on your guest to activate the X11 Guest Additions. The Solaris Guest Additions can be safely removed by removing the package from the guest. Open a root terminal session and execute: pkgrm SUNWvboxguest The Guest Additions should be updated by first uninstalling the existing Guest Additions and then installing the new ones. Attempting to install new Guest Additions without removing the existing ones is not possible. VirtualBox also ships with a set of drivers that improve running OS/2 in a virtual machine. Due to restrictions of OS/2 itself, this variant of the Guest Additions has a limited feature set; see for details. The OS/2 Guest Additions are provided on the same ISO CD-ROM as those for the other platforms. As a result, mount the ISO in OS/2 as described previously. The OS/2 Guest Additions are located in the directory \32bit\OS2. As we do not provide an automatic installer at this time, please refer to the readme.txt file in that directory, which describes how to install the OS/2 Guest Additions manually. With the "shared folders" feature of VirtualBox, you can access files of your host system from within the guest system. This is similar how you would use network shares in Windows networks -- except that shared folders do not need require networking, so long as the Guest Additions are installed. Shared Folders are supported with Windows (2000 or newer), Linux and Solaris guests. Shared folders must physically reside on the host and are then shared with the guest; sharing is accomplished using a special service on the host and a file system driver for the guest, both of which are provided by VirtualBox. For Windows guests, shared folders are implemented as a pseudo-network redirector; for Linux and Solaris guests, the Guest Additions provide a virtual filesystem driver which handles communication with the host. To share a host folder with a virtual machine in VirtualBox, you must specify the path of that folder and choose for it a "share name" that the guest can use to access it. Hence, first create the shared folder on the host; then, within the guest, connect to it. There are several ways in which shared folders can be set up for a particular virtual machine: In the graphical user interface of a running virtual machine, you can select "Shared folders" from the "Devices" menu, or click on the folder icon on the status bar in the bottom right corner of the virtual machine window. If a virtual machine is not currently running, you can configure shared folders in each virtual machine's "Settings" dialog. From the command line, you can create shared folders using the VBoxManage command line interface; see . The command is as follows: VBoxManage sharedfolder add "VM name" --name "sharename" --hostpath "C:\test" There are two types of shares: VM shares which are only available to the VM for which they have been defined; transient VM shares, which can be added and removed at runtime and do not persist after a VM has stopped; for these, add the --transient option to the above command line. Shared folders have read/write access to the files at the host path by default. To restrict the guest to have read-only access, create a read-only shared folder. This can either be achieved using the GUI or by appending the parameter --readonly when creating the shared folder with VBoxManage. You can mount the shared folder from inside a VM the same way as you would mount an ordinary network share: In a Windows guest, starting with VirtualBox 1.5.0, shared folders are browseable and are therefore visible in Windows Explorer. So, to attach the host's shared folder to your Windows guest, open Windows Explorer and look for it under "My Networking Places" -> "Entire Network" -> "VirtualBox Shared Folders". By right-clicking on a shared folder and selecting "Map network drive" from the menu that pops up, you can assign a drive letter to that shared folder. Alternatively, on the Windows command line, use the following: net use x: \\vboxsvr\sharename While vboxsvr is a fixed name (note that vboxsrv would also work), replace "x:" with the drive letter that you want to use for the share, and sharename with the share name specified with VBoxManage. In a Linux guest, use the following command: mount -t vboxsf [-o OPTIONS] sharename mountpoint To mount a shared folder during boot, add the following entry to /etc/fstab: sharename mountpoint vboxsf defaults 0 0 In a Solaris guest, use the following command: mount -F vboxfs [-o OPTIONS] sharename mountpoint Replace sharename (use lowercase) with the share name specified with VBoxManage or the GUI, and mountpoint with the path where you want the share to be mounted on the guest (e.g. /mnt/share). The usual mount rules apply, that is, create this directory first if it does not exist yet. Here is an example of mounting the shared folder for the user "jack" on OpenSolaris: $ id uid=5000(jack) gid=1(other) $ mkdir /export/home/jack/mount $ pfexec mount -F vboxfs -o uid=5000,gid=1 jackshare /export/home/jack/mount $ cd ~/mount $ ls sharedfile1.mp3 sharedfile2.txt $ Beyond the standard options supplied by the mount command, the following are available: iocharset CHARSET to set the character set used for I/O operations (utf8 by default) and convertcp CHARSET to specify the character set used for the shared folder name (utf8 by default). The generic mount options (documented in the mount manual page) apply also. Especially useful are the options uid, gid and mode, as they allow access by normal users (in read/write mode, depending on the settings) even if root has mounted the filesystem. Starting with version 3.3.0, VirtualBox supports automatic mounting support for shared folders. The installed Guest Additions will then take care of all shared folders which are marked as being auto-mounted as soon as a user is logged in to the guest OS. This makes it more convenient instead of mounting shared folders manually described in . Auto-mounting currently is only supported on Windows, Linux and Solaris guests. On Windows guests an auto-mounted shared folder will be represented by an own drive letter (e.g. E:), depending on the remaining free drive letters of the system. On Linux and Solaris guests auto-mounted shared folders get mounted into the /media directory, along with the prefix sf_, so the shared folder myfiles would be mounted to /media/sf_myfiles on Linux and /mnt/sf_myfiles on Solaris. To change the prefix sf_ of a given virtual machine, set the value of its /VirtualBox/GuestAdd/SharedFolders/MountPrefix guest property to another value; see for details. To get a user full access to the auto-mounted shared folders on the guest this user needs to be part of the newly create group "vboxsf", which is created by the VirtualBox Guest Additions installer. Without being in that group read-only access is provided. To get changes applied, for example by adding new or deleting auto-mounted shared folders while a VM is running, the guest OS needs to be rebooted. However, this does not affect . With the "seamless windows" feature of VirtualBox, you can have the windows that are displayed within a virtual machine appear side by side next to the windows of your host. This feature is supported for the following guest operating systems (provided that the Guest Additions are installed): Windows guests (support added with VirtualBox 1.5); Linux or Solaris/OpenSolaris guests with an X.org server version 1.3 or higher The X server version is not the same as the version of the entire X.org suite. You can type X -version in a terminal to find out about the X.org server version level that is currently installed. (support added with VirtualBox 1.6). The exception is Fedora 9, due to a bug in its X server. After seamless windows are enabled (see below), VirtualBox suppresses the display of the Desktop background of your guest, allowing you to run the windows of your guest operating system seamlessly next to the windows of your host: To enable seamless mode, after starting the virtual machine, press the Host key (normally the right control key) together with "L". This will enlarge the size of the VM's display to the size of your host screen and mask out the guest operating system's background. To go back to the "normal" VM display (i.e. to disable seamless windows), press the Host key and "L" again. The VirtualBox Guest Additions contain experimental hardware 3D support for Windows, Linux and Solaris guests. OpenGL support for Windows guests was added with VirtualBox 2.1; support for Linux and Solaris followed with VirtualBox 2.2. With VirtualBox 3.0, Direct3D 8/9 support was added for Windows guests. OpenGL 2.0 is now supported as well. With this feature, if an application inside your virtual machine uses 3D features through the OpenGL or Direct3D 8/9 programming interfaces, instead of emulating them in software (which would be slow), VirtualBox will attempt to use your host's 3D hardware. This works for all supported host platforms (Windows, Mac, Linux, Solaris), provided that your host operating system can make use of your accelerated 3D hardware in the first place. The 3D acceleration currently has the following preconditions: It is only available for certain Windows, Linux and Solaris guests. In particular: For Windows guests, support is restricted to 32-bit versions of XP and Vista. Both OpenGL and Direct3D 8/9 are supported (experimental). OpenGL on Linux requires kernel 2.6.27 and higher as well as X.org server version 1.5 and higher. Ubuntu 8.10 and Fedora 10 have been tested and confirmed as working. OpenGL on Solaris guests requires X.org server version 1.5 and higher. The Guest Additions must be installed. For Direct 3D acceleration to work in a Windows Guest, VirtualBox needs to replace Windows system files in the virtual machine. As a result, the Guest Additions installation program offers Direct 3D acceleration as an option that must be explicitly enabled. Also, you must install the Guest Additions in "Safe Mode"; see for details. Because 3D support is still experimental at this time, it is disabled by default and must be manually enabled in the VM settings (see ). Enabling 3D acceleration may expose security holes to malicious software running the guest. The third-party code that VirtualBox uses for this purpose (Chromium) is not hardened enough to prevent every risky 3D operation on the host. Technically, VirtualBox implements this by installing an additional hardware 3D driver inside your guest when the Guest Additions are installed. This driver acts as a hardware 3D driver and reports to the guest operating system that the (virtual) hardware is capable of 3D hardware acceleration. When an application in the guest then requests hardware acceleration through the OpenGL or Direct3D programming interfaces, these are sent to the host through a special communication tunnel implemented by VirtualBox, and then the host performs the requested 3D operation via the host's programming interfaces. Starting with version 3.1, the VirtualBox Guest Additions contain experimental hardware 2D video acceleration support for Windows guests. With this feature, if an application (e.g. a video player) inside your Windows VM uses 2D video overlays to play a movie clip, then VirtualBox will attempt to use your host's video acceleration hardware instead of performing overlay stretching and color conversion in software (which would be slow). This currently works for Windows, Linux and Mac host platforms, provided that your host operating system can make use of 2D video acceleration in the first place. The 2D video acceleration currently has the following preconditions: It is only available for Windows guests (XP or later). The Guest Additions must be installed. Because 2D support is still experimental at this time, it is disabled by default and must be manually enabled in the VM settings (see ). Technically, VirtualBox implements this by exposing video overlay DirectDraw capabilities in the Guest Additions video driver. The driver sends all overlay commands to the host through a special communication tunnel implemented by VirtualBox. On the host side, OpenGL is then used to implement color space transformation and scaling Starting with version 2.1, VirtualBox allows for requesting certain properties from a running guest, provided that the VirtualBox Guest Additions are installed and the VM is running. This is good for two things: A number of predefined VM characteristics are automatically maintained by VirtualBox and can be retrieved on the host, e.g. to monitor VM performance and statistics. In addition, arbitrary string data can be exchanged between guest and host. This works in both directions. To accomplish this, VirtualBox establishes a private communication channel between the VirtualBox Guest Additions and the host, and software on both sides can use this channel to exchange string data for arbitrary purposes. Guest properties are simply string keys to which a value is attached. They can be set (written to) by either the host and the guest, and they can also be read from both sides. In addition to establishing the general mechanism of reading and writing values, a set of predefined guest properties is automatically maintained by the VirtualBox Guest Additions to allow for retrieving interesting guest data such as the guest's exact operating system and service pack level, the installed version of the Guest Additions, users that are currently logged into the guest OS, network statistics and more. These predefined properties are all prefixed with /VirtualBox/ and organized into a hierarchical tree of keys. Some of this runtime information is shown when you select "Session Information Dialog" from a virtual machine's "Machine" menu. A more flexible way to use this channel is via the VBoxManage guestproperty command set; see for details. For example, to have all the available guest properties for a given running VM listed with their respective values, use this:$ VBoxManage guestproperty enumerate "Windows Vista III" VirtualBox Command Line Management Interface Version $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILD (C) 2005-$VBOX_C_YEAR $VBOX_VENDOR All rights reserved. Name: /VirtualBox/GuestInfo/OS/Product, value: Windows Vista Business Edition, timestamp: 1229098278843087000, flags: Name: /VirtualBox/GuestInfo/OS/Release, value: 6.0.6001, timestamp: 1229098278950553000, flags: Name: /VirtualBox/GuestInfo/OS/ServicePack, value: 1, timestamp: 1229098279122627000, flags: Name: /VirtualBox/GuestAdd/InstallDir, value: C:/Program Files/Oracle/VirtualBox Guest Additions, timestamp: 1229098279269739000, flags: Name: /VirtualBox/GuestAdd/Revision, value: 40720, timestamp: 1229098279345664000, flags: Name: /VirtualBox/GuestAdd/Version, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILD, timestamp: 1229098279479515000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxControl.exe, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279651731000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxHook.dll, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279804835000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxDisp.dll, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279880611000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxMRXNP.dll, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279882618000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxService.exe, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279883195000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxTray.exe, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279885027000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxGuest.sys, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279886838000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxMouse.sys, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279890600000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxSF.sys, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279893056000, flags: Name: /VirtualBox/GuestAdd/Components/VBoxVideo.sys, value: $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILDr40720, timestamp: 1229098279895767000, flags: Name: /VirtualBox/GuestInfo/OS/LoggedInUsers, value: 1, timestamp: 1229099826317660000, flags: Name: /VirtualBox/GuestInfo/OS/NoLoggedInUsers, value: false, timestamp: 1229098455580553000, flags: Name: /VirtualBox/GuestInfo/Net/Count, value: 1, timestamp: 1229099826299785000, flags: Name: /VirtualBox/HostInfo/GUI/LanguageID, value: C, timestamp: 1229098151272771000, flags: Name: /VirtualBox/GuestInfo/Net/0/V4/IP, value: 192.168.2.102, timestamp: 1229099826300088000, flags: Name: /VirtualBox/GuestInfo/Net/0/V4/Broadcast, value: 255.255.255.255, timestamp: 1229099826300220000, flags: Name: /VirtualBox/GuestInfo/Net/0/V4/Netmask, value: 255.255.255.0, timestamp: 1229099826300350000, flags: Name: /VirtualBox/GuestInfo/Net/0/Status, value: Up, timestamp: 1229099826300524000, flags: Name: /VirtualBox/GuestInfo/OS/LoggedInUsersList, value: username, timestamp: 1229099826317386000, flags: To query the value of a single property, use the "get" subcommand like this:$ VBoxManage guestproperty get "Windows Vista III" "/VirtualBox/GuestInfo/OS/Product" VirtualBox Command Line Management Interface Version $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILD (C) 2005-$VBOX_C_YEAR $VBOX_VENDOR All rights reserved. Value: Windows Vista Business Edition To add or change guest properties from the guest, use the tool VBoxControl. This tool is included in the Guest Additions of VirtualBox 2.2 or later. When started from a Linux guest, this tool requires root privileges for security reasons:$ sudo VBoxControl guestproperty enumerate VirtualBox Guest Additions Command Line Management Interface Version $VBOX_VERSION_MAJOR.$VBOX_VERSION_MINOR.$VBOX_VERSION_BUILD (C) 2009-$VBOX_C_YEAR $VBOX_VENDOR All rights reserved. Name: /VirtualBox/GuestInfo/OS/Release, value: 2.6.28-18-generic, timestamp: 1265813265835667000, flags: <NULL> Name: /VirtualBox/GuestInfo/OS/Version, value: #59-Ubuntu SMP Thu Jan 28 01:23:03 UTC 2010, timestamp: 1265813265836305000, flags: <NULL> ... For more complex needs, you can use the VirtualBox programming interfaces; see . Starting with version 3.2, the Guest Additions of VirtualBox allow starting applications inside a VM from the host system. For this to work, the application needs to be installed inside the guest; no additional software needs to be installed on the host. Additionally, text mode output (to stdout and stderr) can be shown on the host for further processing along with options to specify user credentials and a timeout value (in milliseconds) to limit time the application is able to run. This feature can be used to automate deployment of software within the guest. On Windows guests, a process lauched via the guest control execute support is only able to display a graphical user interface if the user account it is started under, is currently logged in and has a desktop session. Otherwise, the process will not be able to display its user interface. Also, for using accounts without or with an empty password specified, the group policy needs to be changed on the guest. To do so, open the group policy editor on the command line by typing gpedit.msc, open the key Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options and change the value of Accounts: Limit local account use of blank passwords to console logon only to Disabled. To use this feature, use the VirtualBox command line. See for details. Starting with version 3.2, the Guest Additions of VirtualBox can change the amount of memory of a virtual machine while the machine is running. Because of how this is implemented, this feature is called "memory ballooning". Normally, to change the amount of memory allocated to a virtual machine, one has to shut down the virtual machine entirely and change the virtual machine's settings. With memory ballooning, memory that was allocated for a virtual machine can be given to another virtual machine without having to shut the machine down. This can be useful to temporarily start another virtual machine, or in more complicated environments for sophisticated memory management of many virtual machines that may be running in parallel depending on how memory is used by the guests. When memory ballooning is requested, the VirtualBox Guest Additions (which run inside the guest) allocate physical memory from the guest operating system on the kernel level and lock this memory down in the guest. This ensures that the guest will not use that memory any longer: no guest applications can allocate it, and the guest operating system will not use it either. VirtualBox can then re-use this memory and give it to a second virtual machine. The memory made available through the ballooning mechanism is only available for re-use by VirtualBox. It is not returned as free memory to the host. Requesting balloon memory from a running guest will therefore not increase the amount of free, unallocated memory on the host. Effectively, memory ballooning is therefore a memory overcommitment mechanism for multiple virtual machines while they are running. At this time, memory ballooning is only supported in VBoxManage, the VirtualBox command-line utility. Use the following command to increase or decrease the size of the memory balloon within a running virtual machine that has Guest Additions installed: VBoxManage controlvm "VM name" guestmemoryballoon <n> where "VM name" is the name or UUID of the virtual machine in question and <n> is the amount of memory to allocate from the guest in megabytes; see for more information. You can also set a default balloon that will automatically be requested from the VM every time after it has started up with the following command: VBoxManage modifyvm "VM name" --guestmemoryballoon <n> By default, no balloon memory is allocated. This is a VM setting, like other modifyvm settings, and therefore can only be set while the machine is shut down; see . VirtualBox supports memory ballooning only on 64-bit hosts, memory ballooning is not supported on Mac OS X hosts. Page Fusion is a novel technique to further improve VM density on the host, i.e. a way of overcommitting resources. It was first introduced with VirtualBox 3.2 and is currently limited to VMs running Windows 2000 and later. In a typical scenario, dozens, up to hundreds of very similar VMs are consolidated on a powerful host computer and the level of consolidation is most often limited by the amount of RAM that can be installed in a system at reasonable cost. Often, due to RAM exhaustion, additional VMs cannot be started even though the host's CPUs still provide capacity. To circumvent this restriction, hypervisors can benefit from the fact that often, VMs are very similar (e.g. multiple VMs running Windows XP Service Pack 2) and therefore contain a number of identical RAM cells. The hypervisor can look for such duplicate data in memory, eliminate the redundancy (deduplication) and thereby free additional memory. Traditional hypervisors use a technique often called "page sharing" or "same page merging" where they go through all memory and compute checksums (hashes) for each memory page. Then, they look for pages with identical hashes and compare the content of the pages (if two pages produce the same hash, it is very likely that the pages are identical in content). Identical pages get eliminated so that all VMs point to the same page as long as none of the VMs tries to modify the page. If such a page gets modified, the previously eliminated duplicates get allocated again. All this is fully transparent to the virtual machine. However, the classical algorithm has several drawbacks. First of all, it takes rather long to scan the complete memory (esp. when the system is not idling) so the additional memory only becomes available after some time (this can be hours or even days!). Also, the whole page sharing algorithm generally consumes significant CPU resources and increases the virtualization overhead by 10-20%. Page Fusion in VirtualBox uses the VirtualBox Guest Additions to identify memory cells that are most likely identical across VMs and therefore achieves most of the possible savings of page sharing almost immediately and with almost no overhead. Page Fusion is also much less likely to be tricked by identical memory that it will eliminate just to learn seconds later that the memory will now change and having to perform a highly expensive and often service disrupting reallocation. Page Fusion can be enabled for a VM using: VBoxManage modifyvm "VM name" --pagefusion on You can observe Page Fusion operation using some metrics. RAM/VMM/Shared shows the total amount of fused pages whereas the per VM metric Guest/RAM/Usage/Shared will return the amount of fused memory for a given VM. Please refer to for information on how to query metrics. VirtualBox supports Page Fusion only on 64-bit host operating systems. Mac OS X hosts are currently not supported. Page Fusion is only available for Windows 2000 and later guests with current Guest Additions.