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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>
                <para>WDDM Direct3D video driver for Windows guests</para>
            </listitem>
            <listitem>
                <para>Hardware 3D acceleration support for Windows, Linux, and Solaris 
                guests</para>
            </listitem>
            <listitem>
                <para>Hardware 2D video playback acceleration support for Windows 
                guests</para>
            </listitem>
            <listitem>
                <para>PCI pass-through (Linux hosts only)</para>
            </listitem>
            <listitem>
                <para>Mac OS X guests (Mac hosts only)</para>
            </listitem>
            <listitem>
                <para>ICH9 chipset emulation</para>
            </listitem>
            <listitem>
                <para>EFI firmware</para>
            </listitem>
            <listitem>
                <para>Host CD/DVD drive pass-through</para>
            </listitem>
            <listitem>
                <para>Support of iSCSI via internal networking</para>
            </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
          <computeroutput>gpedit.msc</computeroutput>, open the key
          <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>
          <para><emphasis role="bold">OVF import/export:</emphasis><itemizedlist>
              <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
                in "VBoxInternal2/EfiBootArgs" extradata.</para>
              </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>
          <para>Neither <emphasis>virtio</emphasis> nor <emphasis>Intel PRO/1000
            </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>
