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<chapter id="KnownIssues">
<title>Known limitations</title>
<para>This sections 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">64-bit guests on some 32-bit host systems
with VT-x</emphasis> 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.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Direct 3D support in Windows
guests.</emphasis> 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.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Guest control.</emphasis> 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. </para>
<para>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
<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">Guest multi-monitor support.</emphasis> This
feature is currently only supported with Windows guests.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Deleting the only snapshot with a running VM
is not implemented.</emphasis> 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.</para>
</listitem>
<listitem>
<para><emphasis role="bold">Disabled host I/O caches.</emphasis>
Disabling the host I/O cache (see <xref linkend="iocaching" />) 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
restriction will be lifted in a future maintenance update.</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>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.</para>
</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>OVA archives (TAR containers) 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><emphasis role="bold">Seamless mode</emphasis> does not work
correctly with Linux guests that have 3D effects enabled (such as with
compiz-enabled window managers).</para>
</listitem>
<listitem>
<para><emphasis role="bold">Mac OS X hosts.</emphasis> The following
restrictions apply (all of which will be resolved in future
versions):<itemizedlist>
<listitem>
<para>The numlock emulation has not yet been implemented.</para>
</listitem>
<listitem>
<para>The CPU frequency metric is not supported.</para>
</listitem>
<listitem>
<para>3D OpenGL acceleration, in particular with Linux guests that
have 3D effects enabled (such as with compiz-enabled window
managers).</para>
</listitem>
<listitem>
<para>Memory ballooning is not supported.</para>
</listitem>
</itemizedlist></para>
</listitem>
<listitem>
<para><emphasis role="bold">Mac OS X Server guests.</emphasis>
<itemizedlist>
<listitem>
<para>Mac OS X Server guests can only run on a certain host
hardware. For details about license and host hardware limitations,
please see <xref linkend="intro-macosxguests" />.</para>
</listitem>
<listitem>
<para>VirtualBox does not provide Guest Additions for Mac OS X
Server at this time.</para>
</listitem>
<listitem>
<para>The graphics resolution currently defaults to 1024x768 as
Mac OS X Server 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>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.</para>
</listitem>
<listitem>
<para>Mac OS X Server 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 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.</para>
</listitem>
<listitem>
<para>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:<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>
</itemizedlist></para>
</listitem>
<listitem>
<para><emphasis role="bold">Solaris hosts.</emphasis> The following
restrictions apply for OpenSolaris and Solaris 10:<itemizedlist>
<listitem>
<para>There is no support for USB devices connected to Solaris 10 hosts.</para>
</listitem>
<listitem>
<para>USB support on OpenSolaris hosts requires version snv_124 or
higher. Webcams and other isochronous devices are known to have
poor performance.</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>
</itemizedlist></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>
</chapter>