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<chapter id="KnownIssues">
<title>Known limitations</title>
<sect1 id="ExperimentalFeatures">
<title>Experimental Features</title>
<para>Some VirtualBox features are labeled as experimental. Such
features are provided on an "as-is" basis and are not formally
supported. However, feedback and suggestions about such features are
welcome. A comprehensive list of experimental features follows:</para>
<itemizedlist>
<listitem>
WDDM Direct3D video driver for Windows guests
</listitem>
<listitem>
Hardware 3D acceleration support for Windows, Linux, and Solaris
guests
</listitem>
<listitem>
Hardware 2D video playback acceleration support for Windows
guests
</listitem>
<listitem>
PCI pass-through (Linux hosts only)
</listitem>
<listitem>
Mac OS X guests (Mac hosts only)
</listitem>
<listitem>
ICH9 chipset emulation
</listitem>
<listitem>
EFI firmware
</listitem>
<listitem>
</listitem>
<listitem>
Support of iSCSI via internal networking
</listitem>
<listitem>
Synthetic CPU reporting
</listitem>
</itemizedlist>
</sect1>
<sect1 id="KnownProblems">
<title>Known Issues</title>
<para>The following section describes known problems with VirtualBox
$VBOX_VERSION_STRING. Unless marked otherwise, these issues are planned to
be fixed in later releases.</para>
<itemizedlist>
<listitem>
<para>The following <emphasis role="bold">Guest SMP (multiprocessor)
limitations</emphasis> exist:<itemizedlist>
<listitem>
<para><emphasis role="bold">Poor performance</emphasis> 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.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Poor performance</emphasis> 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.</para>
</listitem>
</itemizedlist></para>
</listitem>
<listitem>
<para><emphasis role="bold">NX (no execute, data execution
prevention)</emphasis> only works for guests running on 64-bit hosts
or guests running on 32-bit hosts with PAE enabled and requires that
hardware virtualization be enabled.</para>
</listitem>
<listitem>
<para>For <emphasis role="bold">basic Direct3D support in Windows
guests</emphasis> 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. <note>
<para>This does <emphasis role="bold">not</emphasis> apply to the
experimental WDDM Direct3D video
driver available for Vista and Windows 7 guests shipped with
VirtualBox 4.1.</para>
</note></para>
</listitem>
<listitem>
<para><emphasis role="bold">Guest control.</emphasis> On Windows guests,
a process lauched via the guest control execute support will not be able
to display a graphical user interface <emphasis>unless</emphasis> the
user account under which it is running is currently logged in and has a
desktop session.</para>
<para>Also, to use accounts without or with an empty password, the
guest's group policy must be changed. To do so, open the group policy
editor on the command line by typing
<emphasis>Computer Configuration\Windows Settings\Security
Settings\Local Policies\Security Options</emphasis> and change the value
of <emphasis>Accounts: Limit local account use of blank passwords to
console logon only</emphasis> to <emphasis>Disabled</emphasis>.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Compacting virtual disk images is limited to
VDI files.</emphasis> The <code>VBoxManage modifyhd --compact</code>
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.</para>
</listitem>
<listitem>
<listitem>
<para>OVF localization (multiple languages in one OVF file) is not
yet supported.</para>
</listitem>
<listitem>
<para>Some OVF sections like StartupSection,
DeploymentOptionSection and InstallSection are ignored.</para>
</listitem>
<listitem>
<para>OVF environment documents, including their property sections
and appliance configuration with ISO images, are not yet
supported.</para>
</listitem>
<listitem>
<para>Remote files via HTTP or other mechanisms are not yet
supported.</para>
</listitem>
</itemizedlist></para>
</listitem>
<listitem>
<para>Neither <emphasis role="bold">scale mode</emphasis> nor <emphasis
role="bold">seamless mode</emphasis> work correctly with guests using
OpenGL 3D features (such as with compiz-enabled window managers).</para>
</listitem>
<listitem>
<para>The RDP server in the VirtualBox extension pack supports only
audio streams in format 22.05kHz stereo 16 bit. If the RDP client
requests any other audio format there will be no audio.</para>
</listitem>
<listitem>
<para>Preserving the aspect ratio in scale mode works only on Windows
hosts and on Mac OS X hosts.</para>
</listitem>
<listitem>
<para>On <emphasis role="bold">Mac OS X hosts,</emphasis> the following
features are not yet implemented:</para>
<para><itemizedlist>
<listitem>
<para>Numlock emulation</para>
</listitem>
<listitem>
<para>CPU frequency metric</para>
</listitem>
<listitem>
<para>Memory ballooning</para>
</listitem>
</itemizedlist></para>
</listitem>
<listitem>
<para><emphasis role="bold">Mac OS X guests:</emphasis>
<itemizedlist>
<listitem>
<para>Mac OS X guests can only run on a certain host hardware.
For details about license and host hardware limitations, please
see <xref linkend="intro-macosxguests" /> and check the Apple
software license conditions.</para>
</listitem>
<listitem>
<para>VirtualBox does not provide Guest Additions for Mac OS X
at this time.</para>
</listitem>
<listitem>
<para>The graphics resolution currently defaults to 1024x768 as
Mac OS X falls back to the built-in EFI display support. See
<xref linkend="efividmode" /> for more information on how to
change EFI video modes.</para>
</listitem>
<listitem>
<para>Mac OS X guests only work with one CPU assigned to the
VM. Support for SMP will be provided in a future release.</para>
</listitem>
<listitem>
<para>Depending on your system and version of Mac OS X, 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.</para>
</listitem>
<listitem>
<para>By default, the VirtualBox EFI enables debug output of the
Mac OS X 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:<screen>VBoxManage setextradata "VM name" "VBoxInternal2/EfiBootArgs" " "</screen>To
revert to the previous behavior, use:<screen>VBoxManage setextradata "VM name" "VBoxInternal2/EfiBootArgs" ""</screen></para>
</listitem>
<listitem>
<para>It is currently not possible to start a Mac OS X guest in safe mode by specifying "-x" option
</listitem>
</itemizedlist></para>
</listitem>
<listitem>
<para><emphasis role="bold">Solaris hosts:</emphasis> <itemizedlist>
<listitem>
<para>There is no support for USB devices connected to Solaris 10
hosts.</para>
</listitem>
<listitem>
<para>USB support on Solaris hosts requires Solaris 11 version
snv_124 or higher. Webcams and other isochronous devices are known
to have poor performance.</para>
</listitem>
<listitem>
<para>Host Webcam passthrough is restricted to 640x480 frames at
20 frames per second due to limitations in the Solaris V4L2 API.
This may be addressed in a future Solaris release.</para>
</listitem>
<listitem>
<para>No ACPI information (battery status, power source) is
reported to the guest.</para>
</listitem>
<listitem>
<para>No support for using wireless adapters with bridged
networking.</para>
</listitem>
<listitem>
<para>Crossbow-based bridged networking on Solaris 11 hosts does
not work directly with aggregate links. However, you can manually
create a VNIC (using <computeroutput>dladm</computeroutput>) over
the aggregate link and use that with a VM. This limitation does
not exist in Solaris 11u1 build 17 and newer.</para>
</listitem>
</itemizedlist></para>
</listitem>
<listitem>
<para><emphasis role="bold">Guest Additions of version 4.1, 4.1.2 and 4.1.4 for Windows</emphasis>
Thus VirtualBox WDDM Video driver may be installed and kept in guest system
if Guest additions uninstallation is performed.
This is caused by a bug in Guest Additions uninstaller.
<note>
<para>This does <emphasis role="bold">not</emphasis> apply to Guest Additions update,
i.e. installing a one version of Guest Additions on top of another works correctly.</para>
</note>
To solve this problem, one should uninstall the VirtualBox WDDM Video driver manually.
To do that open Device Manager, and check whether the Display Adapter is named
"VirtualBox Graphics Adapter ..". If no - there is nothing to be done. If yes - right-click
the VirtualBox Graphics Adapter in Device Manager, select "Uninstall", check "Delete the driver software for this device"
and click "OK". Once uninstallation is done - in Device Manager go to menu "Action" and select
"Scan for hardware changes" to make the propper (Windows default) driver be picked up for the Graphics adapter.
</para>
</listitem>
<listitem>
</emphasis> drivers for <emphasis role="bold">Windows XP guests
</emphasis> support segmentation offloading. Therefore
Windows XP guests have slower transmission rates comparing to other
guest types. Refer to MS Knowledge base article 842264 for additional
information.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Guest Additions for OS/2.</emphasis> 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.</para>
</listitem>
</itemizedlist>
</sect1>
</chapter>