source: vbox/trunk/doc/manual/en_US/user_Frontends.xml@ 42510

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<chapter>
  <title>Remote virtual machines</title>

  <sect1>
    <title id="vrde">Remote display (VRDP support)</title>

    <para>VirtualBox can display virtual machines remotely, meaning that a
    virtual machine can execute on one machine even though the machine will be
    displayed on a second computer, and the machine will be controlled from
    there as well, as if the virtual machine was running on that second
    computer.</para>

    <para>For maximum flexibility, starting with VirtualBox 4.0, VirtualBox
    implements remote machine display through a generic extension interface,
    the VirtualBox Remote Desktop Extension (VRDE). The base open-source
    VirtualBox package only provides this interface, while implementations can
    be supplied by third parties with VirtualBox extension packages, which
    must be installed separately from the base package. See <xref
    linkend="intro-installing" /> for more information.</para>

    <para>Oracle provides support for the <emphasis role="bold">VirtualBox
    Remote Display Protocol (VRDP)</emphasis> in such a VirtualBox extension
    package. When this package is installed, VirtualBox versions 4.0 and later
    support VRDP the same way as binary (non-open-source) versions of
    VirtualBox before 4.0 did.</para>

    <para>VRDP is a backwards-compatible extension to Microsoft's Remote
    Desktop Protocol (RDP). Typically graphics updates and audio are sent from
    the remote machine to the client, while keyboard and mouse events are sent
    back. As a result, you can use any standard RDP client to control the
    remote VM.</para>

    <para>Even when the extension is installed, the VRDP server is disabled by
    default. It can easily be enabled on a per-VM basis either in the
    VirtualBox Manager in the "Display" settings (see <xref
    linkend="settings-display" />) or with
    <computeroutput>VBoxManage</computeroutput>:<screen>VBoxManage modifyvm "VM name" --vrde on</screen></para>

    <para>If you use <computeroutput>VBoxHeadless</computeroutput> (described
    further below), VRDP support will be automatically enabled since
    VBoxHeadless has no other means of output.</para>

    <sect2 id="rdp-viewers">
      <title>Common third-party RDP viewers</title>

      <para>Since VRDP is backwards-compatible to RDP, you can use any
      standard RDP viewer to connect to such a remote virtual machine
      (examples follow below). For this to work, you must specify the
      <emphasis role="bold">IP address</emphasis> of your
      <emphasis>host</emphasis> system (not of the virtual machine!) as the
      server address to connect to, as well as the <emphasis role="bold">port
      number</emphasis> that the RDP server is using.</para>

      <para>By default, VRDP uses TCP port
      <computeroutput>3389</computeroutput>. You will need to change the
      default port if you run more than one VRDP server, since the port can
      only be used by one server at a time; you might also need to change it
      on Windows hosts since the default port might already be used by the RDP
      server that is built into Windows itself. Ports 5000 through 5050 are
      typically not used and might be a good choice.</para>

      <para>The port can be changed either in the "Display" settings of the
      graphical user interface or with
      <computeroutput>--vrdeport</computeroutput> option of the
      <computeroutput>VBoxManage modifyvm</computeroutput> command. You can
      specify a comma-separated list of ports or ranges of ports. Use a dash
      between two port numbers to specify a range. The VRDP server will bind
      to <emphasis role="bold">one</emphasis> of available ports from the
      specified list. For example, <computeroutput>VBoxManage modifyvm "VM
      name" --vrdeport 5000,5010-5012</computeroutput> will configure the
      server to bind to one of the ports 5000, 5010, 5011 or 5012. See <xref
      linkend="vboxmanage-modifyvm" /> for details.</para>

      <para>The actual port used by a running VM can be either queried with
      <computeroutput>VBoxManage showvminfo</computeroutput> command or seen
      in the GUI on the "Runtime" tab of the "Session Information Dialog",
      which is accessible via the "Machine" menu of the VM window.</para>

      <para>Here follow examples for the most common RDP viewers:<itemizedlist>
          <listitem>
            <para>On Windows, you can use the Microsoft Terminal Services
            Connector (<computeroutput>mstsc.exe</computeroutput>) that ships
            with Windows. You can start it by bringing up the "Run" dialog
            (press the Windows key and "R") and typing "mstsc". You can also
            find it under "Start" -&gt; "All Programs" -&gt; "Accessories"
            -&gt; "Remote Desktop Connection". If you use the "Run" dialog,
            you can type in options directly:<screen>mstsc 1.2.3.4[:3389]</screen></para>

            <para>Replace "1.2.3.4" with the host IP address, and 3389 with a
            different port if necessary.</para>

            <note>
              <para>When connecting to localhost in order to test the
              connection, the addresses
              <computeroutput>localhost</computeroutput> and
              <computeroutput>127.0.0.1</computeroutput> might not work using
              <computeroutput>mstsc.exe</computeroutput>. Instead, the address
              <computeroutput>127.0.0.2[:3389]</computeroutput> has to be
              used.</para>
            </note>
          </listitem>

          <listitem>
            <para>On other systems, you can use the standard open-source
            <computeroutput>rdesktop</computeroutput> program. This ships with
            most Linux distributions, but VirtualBox also comes with a
            modified variant of rdesktop for remote USB support (see <xref
            linkend="usb-over-rdp" /> below).</para>

            <para>With rdesktop, use a command line such as the
            following:<screen>rdesktop -a 16 -N 1.2.3.4:3389</screen></para>

            <para>As said for the Microsoft viewer above, replace "1.2.3.4"
            with the host IP address, and 3389 with a different port if
            necessary. The <computeroutput>-a 16</computeroutput> option
            requests a color depth of 16 bits per pixel, which we recommend.
            (For best performance, after installation of the guest operating
            system, you should set its display color depth to the same value).
            The <computeroutput>-N</computeroutput> option enables use of the
            NumPad keys.</para>
          </listitem>

          <listitem>
            <para>If you run the KDE desktop, you might prefer
            <computeroutput>krdc</computeroutput>, the KDE RDP viewer. The
            command line would look like this:<screen>krdc --window --high-quality rdp:/1.2.3.4[:3389]</screen></para>

            <para>Again, replace "1.2.3.4" with the host IP address, and 3389
            with a different port if necessary. The "rdp:/" bit is required
            with krdc to switch it into RDP mode.</para>
          </listitem>

          <listitem>
            <para>With Sun Ray thin clients you can use
            <computeroutput>uttsc</computeroutput>, which is part of the
            Sun Ray Windows Connector package. See the corresponding
            documentation for details.</para>
          </listitem>
        </itemizedlist></para>
    </sect2>

    <sect2 id="vboxheadless">
      <title>VBoxHeadless, the remote desktop server</title>

      <para>While any VM started from the VirtualBox Manager is capable of
      running virtual machines remotely, it is not convenient to have to run
      the full-fledged GUI if you never want to have VMs displayed locally in
      the first place. In particular, if you are running server hardware whose
      only purpose is to host VMs, and all your VMs are supposed to run
      remotely over VRDP, then it is pointless to have a graphical user
      interface on the server at all -- especially since, on a Linux or
      Solaris host, the VirtualBox manager comes with dependencies on the Qt
      and SDL libraries. This is inconvenient if you would rather not have the
      X Window system on your server at all.</para>

      <para>VirtualBox therefore comes with yet another front-end called
      <computeroutput>VBoxHeadless</computeroutput>, which produces no visible
      output on the host at all, but instead only delivers VRDP data. This
      front-end has no dependencies on the X Window system on Linux and
      Solaris hosts.<footnote>
          <para>Before VirtualBox 1.6, the headless server was called
          <computeroutput>VBoxVRDP</computeroutput>. For the sake of backwards
          compatibility, the VirtualBox installation still installs an
          executable with that name as well.</para>
        </footnote></para>

      <para>To start a virtual machine with
      <computeroutput>VBoxHeadless</computeroutput>, you have two
      options:</para>

      <itemizedlist>
        <listitem>
          <para>You can use <screen>VBoxManage startvm "VM name" --type headless</screen>The
          extra <computeroutput>--type</computeroutput> option causes
          VirtualBox to use <computeroutput>VBoxHeadless</computeroutput> as
          the front-end to the internal virtualization engine instead of the
          Qt front-end.</para>
        </listitem>

        <listitem>
          <para>The alternative is to use
          <computeroutput>VBoxHeadless</computeroutput> directly, as
          follows:<screen>VBoxHeadless --startvm &lt;uuid|name&gt;</screen></para>

          <para>This way of starting the VM helps troubleshooting problems
          reported by <computeroutput>VBoxManage startvm ...</computeroutput>
          because you can see sometimes more detailed error messages,
          especially for early failures before the VM execution is started.
          In normal situations <computeroutput>VBoxManage startvm</computeroutput>
          is preferred since it runs the VM directly as a background process
          which has to be done explicitly when directly starting
          <computeroutput>VBoxHeadless</computeroutput>.</para>
        </listitem>
      </itemizedlist>

      <para>Note that when you use
      <computeroutput>VBoxHeadless</computeroutput> to start a VM, since the
      headless server has no other means of output, the VRDP server will
      <emphasis>always</emphasis> be enabled, regardless of whether you had
      enabled the VRDP server in the VM's settings. If this is undesirable
      (for example because you want to access the VM via
      <computeroutput>ssh</computeroutput> only), start the VM like
      this:<screen>VBoxHeadless --startvm &lt;uuid|name&gt; --vrde=off</screen>To
      have the VRDP server enabled depending on the VM configuration, as the
      other front-ends would, use this:<screen>VBoxHeadless --startvm &lt;uuid|name&gt; --vrde=config</screen></para>

      <para>If you start the VM with <computeroutput>VBoxManage startvm ...</computeroutput>
      then the configuration settings of the VM are always used.</para>
    </sect2>

    <sect2>
      <title>Step by step: creating a virtual machine on a headless
      server</title>

      <para>The following instructions may give you an idea how to create a
      virtual machine on a headless server over a network connection. We will
      create a virtual machine, establish an RDP connection and install a
      guest operating system -- all without having to touch the headless
      server. All you need is the following:</para>

      <para><orderedlist>
          <listitem>
            <para>VirtualBox on a server machine with a supported host
            operating system. The VirtualBox extension pack for the VRDP
            server must be installed (see the previous section). For the
            following example, we will assume a Linux server.</para>
          </listitem>

          <listitem>
            <para>An ISO file accessible from the server, containing the
            installation data for the guest operating system to install (we
            will assume Windows XP in the following example).</para>
          </listitem>

          <listitem>
            <para>A terminal connection to that host through which you can
            access a command line (e.g. via
            <computeroutput>ssh</computeroutput>).</para>
          </listitem>

          <listitem>
            <para>An RDP viewer on the remote client; see <xref
            linkend="rdp-viewers" /> above for examples.</para>
          </listitem>
        </orderedlist>Note again that on the server machine, since we will
      only use the headless server, neither Qt nor SDL nor the X Window system
      will be needed.</para>

      <para><orderedlist>
          <listitem>
            <para>On the headless server, create a new virtual machine:</para>

            <screen>VBoxManage createvm --name "Windows XP" --ostype WindowsXP --register</screen>

            <para>Note that if you do not specify
            <computeroutput>--register</computeroutput>, you will have to
            manually use the <computeroutput>registervm</computeroutput>
            command later.</para>

            <para>Note further that you do not need to specify
            <computeroutput>--ostype</computeroutput>, but doing so selects
            some sane default values for certain VM parameters, for example
            the RAM size and the type of the virtual network device. To get a
            complete list of supported operating systems you can use</para>

            <screen>VBoxManage list ostypes</screen>
          </listitem>

          <listitem>
            <para>Make sure the settings for this VM are appropriate for the
            guest operating system that we will install. For example:<screen>VBoxManage modifyvm "Windows XP" --memory 256 --acpi on --boot1 dvd --nic1 nat</screen></para>
          </listitem>

          <listitem>
            <para>Create a virtual hard disk for the VM (in this case, 10GB in
            size):<screen>VBoxManage createhd --filename "WinXP.vdi" --size 10000</screen></para>
          </listitem>

          <listitem>
            <para>Add an IDE Controller to the new VM:<screen>VBoxManage storagectl "Windows XP" --name "IDE Controller"
      --add ide --controller PIIX4</screen></para>
          </listitem>

          <listitem>
            <para>Set the VDI file created above as the first virtual hard
            disk of the new VM:<screen>VBoxManage storageattach "Windows XP" --storagectl "IDE Controller"
      --port 0 --device 0 --type hdd --medium "WinXP.vdi"</screen></para>
          </listitem>

          <listitem>
            <para>Attach the ISO file that contains the operating system
            installation that you want to install later to the virtual
            machine, so the machine can boot from it:<screen>VBoxManage storageattach "Windows XP" --storagectl "IDE Controller"
      --port 0 --device 1 --type dvddrive --medium /full/path/to/iso.iso</screen></para>
          </listitem>

          <listitem>
            <para>Start the virtual machine using VBoxHeadless:<screen>VBoxHeadless --startvm "Windows XP"</screen></para>

            <para>If everything worked, you should see a copyright notice. If,
            instead, you are returned to the command line, then something went
            wrong.</para>
          </listitem>

          <listitem>
            <para>On the client machine, fire up the RDP viewer and try to
            connect to the server (see <xref linkend="rdp-viewers" /> above
            for how to use various common RDP viewers).</para>

            <para>You should now be seeing the installation routine of your
            guest operating system remotely in the RDP viewer.</para>
          </listitem>
        </orderedlist></para>
    </sect2>

    <sect2 id="usb-over-rdp">
      <title>Remote USB</title>

      <para>As a special feature on top of the VRDP support, VirtualBox
      supports remote USB devices over the wire as well. That is, the
      VirtualBox guest that runs on one computer can access the USB devices of
      the remote computer on which the VRDP data is being displayed the same
      way as USB devices that are connected to the actual host. This allows
      for running virtual machines on a VirtualBox host that acts as a server,
      where a client can connect from elsewhere that needs only a network
      adapter and a display capable of running an RDP viewer. When USB devices
      are plugged into the client, the remote VirtualBox server can access
      them.</para>

      <para>For these remote USB devices, the same filter rules apply as for
      other USB devices, as described with <xref linkend="settings-usb" />.
      All you have to do is specify "Remote" (or "Any") when setting up these
      rules.</para>

      <para>Accessing remote USB devices is only possible if the RDP client
      supports this extension. On Linux and Solaris hosts, the VirtualBox
      installation provides a suitable VRDP client called
      <computeroutput>rdesktop-vrdp</computeroutput>. Recent versions of
      <computeroutput>uttsc</computeroutput>, a client tailored for the use
      with Sun Ray thin clients, also support accessing remote USB devices.
      RDP clients for other platforms will be provided in future VirtualBox
      versions.</para>

      <para>To make a remote USB device available to a VM,
      <computeroutput>rdesktop-vrdp</computeroutput> should be started as
      follows:<screen>rdesktop-vrdp -r usb -a 16 -N my.host.address</screen>Note
      that <computeroutput>rdesktop-vrdp</computeroutput> can access USB
      devices only through <computeroutput>/proc/bus/usb</computeroutput>.
      Please refer to <xref linkend="ts_usb-linux" /> for further details on how
      to properly set up the permissions. Furthermore it is advisable to
      disable automatic loading of any host driver on the remote host which
      might work on USB devices to ensure that the devices are accessible by
      the RDP client. If the setup was properly done on the remote host,
      plug/unplug events are visible on the VBox.log file of the VM.</para>
    </sect2>

    <sect2 id="vbox-auth">
      <title>RDP authentication</title>

      <para>For each virtual machine that is remotely accessible via RDP, you
      can individually determine if and how client connections are
      authenticated. For this, use <computeroutput>VBoxManage
      modifyvm</computeroutput> command with the
      <computeroutput>--vrdeauthtype</computeroutput> option; see <xref
      linkend="vboxmanage-modifyvm" /> for a general introduction. Three
      methods of authentication are available:<itemizedlist>
          <listitem>
            <para>The "null" method means that there is no authentication at
            all; any client can connect to the VRDP server and thus the
            virtual machine. This is, of course, very insecure and only to be
            recommended for private networks.</para>
          </listitem>

          <listitem>
            <para>The "external" method provides external authentication
            through a special authentication library. VirtualBox ships with
            two such authentication libraries:<orderedlist>
                <listitem>
                  <para>The default authentication library,
                  <computeroutput>VBoxAuth</computeroutput>, authenticates
                  against user credentials of the hosts. Depending on the host
                  platform, this means:<itemizedlist>
                      <listitem>
                        <para>On Linux hosts,
                        <computeroutput>VBoxAuth.so</computeroutput>
                        authenticates users against the host's PAM
                        system.</para>
                      </listitem>

                      <listitem>
                        <para>On Windows hosts,
                        <computeroutput>VBoxAuth.dll</computeroutput>
                        authenticates users against the host's WinLogon
                        system.</para>
                      </listitem>

                      <listitem>
                        <para>On Mac OS X hosts,
                        <computeroutput>VBoxAuth.dylib</computeroutput>
                        authenticates users against the host's directory
                        service.<footnote>
                            <para>Support for Mac OS X was added in version
                            3.2.</para>
                          </footnote></para>
                      </listitem>
                    </itemizedlist></para>

                  <para>In other words, the "external" method per default
                  performs authentication with the user accounts that exist on
                  the host system. Any user with valid authentication
                  credentials is accepted, i.e. the username does not have to
                  correspond to the user running the VM.</para>
                </listitem>

                <listitem>
                  <para>An additional library called
                  <computeroutput>VBoxAuthSimple</computeroutput> performs
                  authentication against credentials configured in the
                  "extradata" section of a virtual machine's XML settings
                  file. This is probably the simplest way to get
                  authentication that does not depend on a running and
                  supported guest (see below). The following steps are
                  required:<orderedlist>
                      <listitem>
                        <para>Enable
                        <computeroutput>VBoxAuthSimple</computeroutput> with
                        the following command:</para>

                        <para><screen>VBoxManage setproperty vrdeauthlibrary "VBoxAuthSimple"</screen></para>
                      </listitem>

                      <listitem>
                        <para>To enable the library for a particular VM, you
                        must then switch authentication to external:<screen>VBoxManage modifyvm &lt;vm&gt; --vrdeauthtype external</screen></para>

                        <para>Replace
                        <computeroutput>&lt;vm&gt;</computeroutput> with the
                        VM name or UUID.</para>
                      </listitem>

                      <listitem>
                        <para>You will then need to configure users and
                        passwords by writing items into the machine's
                        extradata. Since the XML machine settings file, into
                        whose "extradata" section the password needs to be
                        written, is a plain text file, VirtualBox uses hashes
                        to encrypt passwords. The following command must be
                        used:<screen>VBoxManage setextradata &lt;vm&gt; "VBoxAuthSimple/users/&lt;user&gt;" &lt;hash&gt;</screen></para>

                        <para>Replace
                        <computeroutput>&lt;vm&gt;</computeroutput> with the
                        VM name or UUID,
                        <computeroutput>&lt;user&gt;</computeroutput> with the
                        user name who should be allowed to log in and
                        <computeroutput>&lt;hash&gt;</computeroutput> with the
                        encrypted password. As an example, to obtain the hash
                        value for the password "secret", you can use the
                        following command:<screen>VBoxManage internalcommands passwordhash "secret"</screen></para>

                        <para>This will print
                        <screen>2bb80d537b1da3e38bd30361aa855686bde0eacd7162fef6a25fe97bf527a25b</screen>
                        You can then use VBoxManage setextradata to store this
                        value in the machine's "extradata" section.</para>

                        <para>As example, combined together, to set the
                        password for the user "john" and the machine "My VM"
                        to "secret", use this command:<screen>VBoxManage setextradata "My VM" "VBoxAuthSimple/users/john"
    2bb80d537b1da3e38bd30361aa855686bde0eacd7162fef6a25fe97bf527a25b</screen></para>
                      </listitem>
                    </orderedlist></para>
                </listitem>
              </orderedlist></para>
          </listitem>

          <listitem>
            <para>Finally, the "guest" authentication method performs
            authentication with a special component that comes with the Guest
            Additions; as a result, authentication is not performed on the
            host, but with the <emphasis>guest</emphasis> user
            accounts.</para>

            <para>This method is currently still in testing and not yet
            supported.</para>
          </listitem>
        </itemizedlist></para>

      <para>In addition to the methods described above, you can replace the
      default "external" authentication module with any other module. For
      this, VirtualBox provides a well-defined interface that allows you to
      write your own authentication module. This is described in detail in the
      VirtualBox Software Development Kit (SDK) reference; please see <xref
      linkend="VirtualBoxAPI" /> for details.</para>
    </sect2>

    <sect2 id="vrde-crypt">
      <title>RDP encryption</title>

      <para>RDP features data stream encryption, which is based on the RC4
      symmetric cipher (with keys up to 128bit). The RC4 keys are being
      replaced in regular intervals (every 4096 packets).</para>

      <para>RDP provides different authentication methods:<orderedlist>
          <listitem>
            <para>Historically, RDP4 authentication was used, with which the
            RDP client does not perform any checks in order to verify the
            identity of the server it connects to. Since user credentials can
            be obtained using a "man in the middle" (MITM) attack, RDP4
            authentication is insecure and should generally not be
            used.</para>
          </listitem>

          <listitem>
            <para>RDP5.1 authentication employs a server certificate for which
            the client possesses the public key. This way it is guaranteed
            that the server possess the corresponding private key. However, as
            this hard-coded private key became public some years ago, RDP5.1
            authentication is also insecure.</para>
          </listitem>

          <listitem>
            <para>RDP5.2 authentication uses the Enhanced RDP Security, which
            means that an external security protocol is used to secure the
            connection. RDP4 and RDP5.1 use Standard RDP Security.
            The VRDP server supports Enhanced RDP Security with TLS protocol and,
            as a part of TLS handshake, sends the server certificate to the
            client.</para>

            <para>The <computeroutput>Security/Method</computeroutput> VRDE
            property sets the desired security method, which is used for a
            connection. Valid values are:<itemizedlist>
              <listitem>
                <para>
                  <computeroutput>Negotiate</computeroutput> - both Enhanced (TLS)
                  and Standard RDP Security connections are allowed. The security
                  method is negotiated with the client. This is the default setting.
                </para>
              </listitem>

              <listitem>
                <para>
                  <computeroutput>RDP</computeroutput> - only Standard RDP Security
                  is accepted.</para>
              </listitem>

              <listitem>
                <para>
                  <computeroutput>TLS</computeroutput> - only Enhanced RDP Security
                  is accepted. The client must support TLS.</para>
                </listitem>
            </itemizedlist>
            For example the following command allows a client to use either Standard
            or Enhanced RDP Security connection:
            <screen>vboxmanage modifyvm "VM name" --vrdeproperty "Security/Method=negotiate"</screen>
            </para>

            <para>If the <computeroutput>Security/Method</computeroutput> property is
            set to either <computeroutput>Negotiate</computeroutput> or
            <computeroutput>TLS</computeroutput>, the TLS protocol will be automatically
            used by the server, if the client supports TLS. However, in order to use TLS
            the server must possess the Server Certificate, the Server Private Key and the
            Certificate Authority (CA) Certificate. The following example shows how to
            generate a server certificate.<orderedlist>
                <listitem>
                Create a CA self signed certificate:
                <screen>openssl req -new -x509 -days 365 -extensions v3_ca \
  -keyout ca_key_private.pem -out ca_cert.pem</screen>
                </listitem>

                <listitem>
                Generate a server private key and a request for signing:
                <screen>openssl genrsa -out server_key_private.pem
openssl req -new -key server_key_private.pem -out server_req.pem</screen>
                </listitem>

                <listitem>
                Generate the server certificate:
                <screen>openssl x509 -req -days 365 -in server_req.pem \
  -CA ca_cert.pem -CAkey ca_key_private.pem -set_serial 01 -out server_cert.pem</screen>
                </listitem>
            </orderedlist>
            The server must be configured to access the required files:
            <screen>vboxmanage modifyvm "VM name" \
  --vrdeproperty "Security/CACertificate=path/ca_cert.pem"</screen>
            <screen>vboxmanage modifyvm "VM name" \
  --vrdeproperty "Security/ServerCertificate=path/server_cert.pem"</screen>
            <screen>vboxmanage modifyvm "VM name" \
  --vrdeproperty "Security/ServerPrivateKey=path/server_key_private.pem"</screen>
            </para>
          </listitem>
        </orderedlist></para>

      <para>As the client that connects to the server determines what type
      of encryption will be used, with rdesktop, the Linux RDP viewer, use the
      <computeroutput>-4</computeroutput> or
      <computeroutput>-5</computeroutput> options.</para>
    </sect2>

    <sect2 id="vrde-multiconnection">
      <title>Multiple connections to the VRDP server</title>

      <para>The VRDP server of VirtualBox supports multiple simultaneous
      connections to the same running VM from different clients. All connected
      clients see the same screen output and share a mouse pointer and
      keyboard focus. This is similar to several people using the same
      computer at the same time, taking turns at the keyboard.</para>

      <para>The following command enables multiple connection mode: <screen>VBoxManage modifyvm "VM name" --vrdemulticon on</screen></para>
    </sect2>

    <sect2 id="vrde-multimonitor">
      <title>Multiple remote monitors</title>

      <para>To access two or more remote VM displays you have to enable the
      VRDP multiconnection mode (see <xref
      linkend="vrde-multiconnection" />).</para>

      <para>The RDP client can select the virtual monitor number to connect to
      using the <computeroutput>domain</computeroutput> logon parameter
      (<computeroutput>-d</computeroutput>). If the parameter ends with
      <computeroutput>@</computeroutput> followed by a number, VirtualBox
      interprets this number as the screen index. The primary guest screen is
      selected with <computeroutput>@1</computeroutput>, the first secondary
      screen is <computeroutput>@2</computeroutput>, etc.</para>

      <para>The Microsoft RDP6 client does not let you specify a separate
      domain name. Instead, use
      <computeroutput>domain\username</computeroutput> in the
      <computeroutput>Username:</computeroutput> field -- for example,
      <computeroutput>@2\name</computeroutput>.
      <computeroutput>name</computeroutput> must be supplied, and must be the
      name used to log in if the VRDP server is set up to require credentials.
      If it is not, you may use any text as the username.</para>
    </sect2>

    <sect2 id="vrde-videochannel">
      <title>VRDP video redirection</title>

      <para>Starting with VirtualBox 3.2, the VRDP server can redirect video
      streams from the guest to the RDP client. Video frames are compressed
      using the JPEG algorithm allowing a higher compression ratio than
      standard RDP bitmap compression methods. It is possible to increase the
      compression ratio by lowering the video quality.</para>

      <para>The VRDP server automatically detects video streams in a guest as
      frequently updated rectangular areas. As a result, this method works
      with any guest operating system without having to install additional
      software in the guest; in particular, the Guest Additions are not
      required.</para>

      <para>On the client side, however, currently only the Windows 7 Remote
      Desktop Connection client supports this feature. If a client does not
      support video redirection, the VRDP server falls back to regular bitmap
      updates.</para>

      <para>The following command enables video redirection: <screen>VBoxManage modifyvm "VM name" --vrdevideochannel on</screen></para>

      <para>The quality of the video is defined as a value from 10 to 100
      percent, representing a JPEG compression level (where lower numbers mean
      lower quality but higher compression). The quality can be changed using
      the following command: <screen>VBoxManage modifyvm "VM name" --vrdevideochannelquality 75</screen></para>
    </sect2>

    <sect2 id="vrde-customization">
      <title>VRDP customization</title>

      <para>With VirtualBox 4.0 it is possible to disable display output,
      mouse and keyboard input, audio, remote USB or clipboard individually in
      the VRDP server.</para>

      <para>The following commands change corresponding server
      settings:</para>

      <screen>VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableDisplay=1
VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableInput=1
VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableUSB=1
VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableAudio=1
VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableClipboard=1
VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableUpstreamAudio=1</screen>

      <para>To reenable a feature use a similar command without the trailing
      1. For example: <screen>VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableDisplay=</screen></para>

      <para>These properties were introduced with VirtualBox 3.2.10. However,
      in the 3.2.x series, it was necessary to use the following commands to
      alter these settings instead:</para>

      <screen>VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableDisplay" 1
VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableInput" 1
VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableUSB" 1
VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableAudio" 1
VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableClipboard" 1</screen>

      <para>To reenable a feature use a similar command without the trailing
      1. For example: <screen>VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableDisplay"</screen></para>
    </sect2>
  </sect1>

  <sect1 id="teleporting">
    <title>Teleporting</title>

    <para>Starting with version 3.1, VirtualBox supports "teleporting" -- that
    is, moving a virtual machine over a network from one VirtualBox host to
    another, while the virtual machine is running. This works regardless of
    the host operating system that is running on the hosts: you can teleport
    virtual machines between Solaris and Mac hosts, for example.</para>

    <para>Teleporting requires that a machine be currently running on one
    host, which is then called the <emphasis role="bold">"source"</emphasis>.
    The host to which the virtual machine will be teleported will then be
    called the <emphasis role="bold">"target"</emphasis>; the machine on the
    target is then configured to wait for the source to contact the target.
    The machine's running state will then be transferred from the source to
    the target with minimal downtime.</para>

    <para>Teleporting happens over any TCP/IP network; the source and the
    target only need to agree on a TCP/IP port which is specified in the
    teleporting settings.</para>

    <para>At this time, there are a few prerequisites for this to work,
    however:<orderedlist>
        <listitem>
          <para>On the target host, you must configure a virtual machine in
          VirtualBox with exactly the same hardware settings as the machine on
          the source that you want to teleport. This does not apply to
          settings which are merely descriptive, such as the VM name, but
          obviously for teleporting to work, the target machine must have the
          same amount of memory and other hardware settings. Otherwise
          teleporting will fail with an error message.</para>
        </listitem>

        <listitem>
          <para>The two virtual machines on the source and the target must
          share the same storage (hard disks as well as floppy and CD/DVD
          images). This means that they either use the same iSCSI targets or
          that the storage resides somewhere on the network and both hosts
          have access to it via NFS or SMB/CIFS.</para>

          <para>This also means that neither the source nor the target machine
          can have any snapshots.</para>
        </listitem>
      </orderedlist></para>

    <para>Then perform the following steps:<orderedlist>
        <listitem>
          <para>On the <emphasis>target</emphasis> host, configure the virtual
          machine to wait for a teleport request to arrive when it is started,
          instead of actually attempting to start the machine. This is done
          with the following VBoxManage command:<screen>VBoxManage modifyvm &lt;targetvmname&gt; --teleporter on --teleporterport &lt;port&gt;</screen></para>

          <para>where <computeroutput>&lt;targetvmname&gt;</computeroutput> is
          the name of the virtual machine on the target host and
          <computeroutput>&lt;port&gt;</computeroutput> is a TCP/IP port
          number to be used on both the source and the target hosts. For
          example, use 6000. For details, see <xref
          linkend="vboxmanage-modifyvm-teleport" />.</para>
        </listitem>

        <listitem>
          <para>Start the VM on the target host. You will see that instead of
          actually running, it will show a progress dialog. indicating that it
          is waiting for a teleport request to arrive.</para>
        </listitem>

        <listitem>
          <para>Start the machine on the <emphasis>source</emphasis> host as
          usual. When it is running and you want it to be teleported, issue
          the following command on the source host:<screen>VBoxManage controlvm &lt;sourcevmname&gt; teleport --host &lt;targethost&gt; --port &lt;port&gt;</screen></para>

          <para>where <computeroutput>&lt;sourcevmname&gt;</computeroutput> is
          the name of the virtual machine on the source host (the machine that
          is currently running),
          <computeroutput>&lt;targethost&gt;</computeroutput> is the host or
          IP name of the target host on which the machine is waiting for the
          teleport request, and <computeroutput>&lt;port&gt;</computeroutput>
          must be the same number as specified in the command on the target
          host. For details, see <xref
          linkend="vboxmanage-controlvm" />.</para>
        </listitem>
      </orderedlist></para>

    <para>For testing, you can also teleport machines on the same host; in
    that case, use "localhost" as the hostname on both the source and the
    target host.<note>
        <para>In rare cases, if the CPUs of the source and the target are very
        different, teleporting can fail with an error message, or the target
        may hang. This may happen especially if the VM is running application
        software that is highly optimized to run on a particular CPU without
        correctly checking that certain CPU features are actually present.
        VirtualBox filters what CPU capabilities are presented to the guest
        operating system. Advanced users can attempt to restrict these virtual
        CPU capabilities with the <computeroutput>VBoxManage --modifyvm
        --cpuid</computeroutput> command; see <xref
        linkend="vboxmanage-modifyvm-teleport" />.</para>
      </note></para>
  </sect1>
</chapter>