# Known limitations

This sections describes known problems with VirtualBox $VBOX_VERSION_STRING. Unless marked otherwise, these issues are planned to be fixed in later releases.

- The following Guest SMP (multiprocessor) limitations exist:

  - Poor performance with 32-bit guests on AMD CPUs. This affects mainly Windows and Solaris guests, but possibly also some Linux kernel revisions. Partially solved in 3.0.6 for 32 bits Windows NT, 2000, XP and 2003 guests. Requires 3.0.6 or higher Guest Additions to be installed.

  - Poor performance with 32-bit guests on certain Intel CPU models that do not include virtual APIC hardware optimization support. This affects mainly Windows and Solaris guests, but possibly also some Linux kernel revisions. Partially solved in 3.0.12 for 32 bits Windows NT, 2000, XP and 2003 guests. Requires 3.0.12 or higher Guest Additions to be installed.

- 64-bit guests on some 32-bit host systems with VT-x can cause instabilities to your system. If you experience this, do not attempt to execute 64-bit guests. Refer to the VirtualBox user forum for additional information.

- Direct 3D support in Windows guests. For this to work, the Guest Additions must be installed in Windows "safe mode". Press F8 when the Windows guest is booting and select "Safe mode", then install the Guest Additions. Otherwise Windows' file protection mechanism will interfere with the replacement DLLs installed by VirtualBox and keep restoring the original Windows system DLLs.

- Guest control. 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.

- Guest multi-monitor support. This feature is currently only supported with Windows guests.

- Deleting the only snapshot with a running VM is not implemented. Trying to perform this operation will result in an error message. This feature will be added in one of the next maintenance releases. It is possible to delete the only snapshot when the VM is not running, e.g. in "poweroff" or "saved" state.

- Disabled host I/O caches. Disabling the host I/O cache (see ) will yield poor performance with VHD and sparse VMDK files as these do not currently support asynchronous I/O. This does not apply to VDI files and raw disk/partition VMDK files, which do support async I/O. This restriction will be lifted in a future maintenance update.

- Compacting virtual disk images is limited to VDI files. The `VBoxManage modifyhd --compact` command is currently only implemented for VDI files. At the moment the only way to optimize the size of a virtual disk images in other formats (VMDK, VHD) is to clone the image and then use the cloned image in the VM configuration.

- OVF import/export:

  - When importing an OVF that was previously exported by VirtualBox 3.2 or higher which contains a complete VirtualBox machine configuration in the <vbox:Machine> element, some of the import customizations that can be specified (in either the GUI or on the VBoxManage command line) are presently ignored. In particular, customizations of the imported storage configuration are ignored. This will be fixed in the next release.

  - OVF localization (multiple languages in one OVF file) is not yet supported.

  - Some OVF sections like StartupSection, DeploymentOptionSection and InstallSection are ignored.

  - OVF environment documents, including their property sections and appliance configuration with ISO images, are not yet supported.

  - OVA archives (TAR containers) are not yet supported.

  - Remote files via HTTP or other mechanisms are not yet supported.

- Seamless mode does not work correctly with Linux guests that have 3D effects enabled (such as with compiz-enabled window managers).

- Mac OS X hosts. The following restrictions apply (all of which will be resolved in future versions):

  - The numlock emulation has not yet been implemented.

  - The CPU frequency metric is not supported.

  - 3D OpenGL acceleration, in particular with Linux guests that have 3D effects enabled (such as with compiz-enabled window managers).

  - Memory ballooning is not supported.

- Mac OS X Server guests.

  - Mac OS X Server guests can only run on a certain host hardware. For details about license and host hardware limitations, please see .

  - VirtualBox does not provide Guest Additions for Mac OS X Server at this time.

  - The graphics resolution currently defaults to 1024x768 as Mac OS X Server falls back to the built-in EFI display support. See for more information on how to change EFI video modes.

  - Even when idle, Mac OS X Server guests currently burn 100% CPU. This is a power management issue that will be addressed in a future release.

  - Mac OS X Server guests only work with one CPU assigned to the VM. Support for SMP will be provided in a future release.

  - Depending on your system and version of Mac OS X Server, you might experience guest hangs after some time. This can be fixed by turning off energy saving (set timeout to "Never") in the system preferences.

  - By default, the VirtualBox EFI enables debug output of the Mac OS X Server kernel to help you diagnose boot problems. Note that there is a lot of output and not all errors are fatal (they would also show on your physical Mac). You can turn off these messages by issuing this command:

        VBoxManage setextradata "VM name" "VBoxInternal2/EfiBootArgs" "  "

    To revert to the previous behavior, use:

        VBoxManage setextradata "VM name" "VBoxInternal2/EfiBootArgs" ""

- Solaris hosts. The following restrictions apply for OpenSolaris and Solaris 10:

  - There is no support for USB devices connected to Solaris 10 hosts.

  - USB support on OpenSolaris hosts requires version snv_124 or higher. Webcams and other isochronous devices are known to have poor performance.

  - No ACPI information (battery status, power source) is reported to the guest.

  - No support for using wireless adapters with bridged networking.

- Guest Additions for OS/2. Shared folders are not yet supported with OS/2 guests. In addition, seamless windows and automatic guest resizing will probably never be implemented due to inherent limitations of the OS/2 graphics system.