Chapter 7. Remote virtual machines

Table of Contents

Remote display (VRDP support)
Common third-party RDP viewers
VBoxHeadless, the remote desktop server
Step by step: creating a virtual machine on a headless server
Remote USB
RDP authentication
RDP encryption
Multiple connections to the VRDP server
Multiple remote monitors
VRDP video redirection
VRDP customization

Remote display (VRDP support)

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.

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 the section called “Installing VirtualBox and extension packs” for more information.

Oracle provides support for the VirtualBox Remote Display Protocol (VRDP) 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.

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.

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 the section called “Display settings”) or with VBoxManage:

VBoxManage modifyvm "VM name" --vrde on

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

Common third-party RDP viewers

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 IP address of your host system (not of the virtual machine!) as the server address to connect to, as well as the port number that the RDP server is using.

By default, VRDP uses TCP port 3389. 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.

The port can be changed either in the "Display" settings of the graphical user interface or with --vrdeport option of the VBoxManage modifyvm 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 one of available ports from the specified list. For example, VBoxManage modifyvm "VM name" --vrdeport 5000,5010-5012 will configure the server to bind to one of the ports 5000, 5010, 5011 or 5012. See the section called “VBoxManage modifyvm” for details.

The actual port used by a running VM can be either queried with VBoxManage showvminfo 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.

Here follow examples for the most common RDP viewers:

  • On Windows, you can use the Microsoft Terminal Services Connector (mstsc.exe) 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" -> "All Programs" -> "Accessories" -> "Remote Desktop Connection". If you use the "Run" dialog, you can type in options directly:


    Replace "" with the host IP address, and 3389 with a different port if necessary.


    When connecting to localhost in order to test the connection, the addresses localhost and might not work using mstsc.exe. Instead, the address[:3389] has to be used.

  • On other systems, you can use the standard open-source rdesktop program. This ships with most Linux distributions, but VirtualBox also comes with a modified variant of rdesktop for remote USB support (see the section called “Remote USB” below).

    With rdesktop, use a command line such as the following:

    rdesktop -a 16 -N

    As said for the Microsoft viewer above, replace "" with the host IP address, and 3389 with a different port if necessary. The -a 16 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 -N option enables use of the NumPad keys.

  • If you run the KDE desktop, you might prefer krdc, the KDE RDP viewer. The command line would look like this:

    krdc --window --high-quality rdp:/[:3389]

    Again, replace "" 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.

VBoxHeadless, the remote desktop server

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.

VirtualBox therefore comes with yet another front-end called VBoxHeadless, 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.[30]

To start a virtual machine with VBoxHeadless, you have two options:

  • You can use

    VBoxManage startvm "VM name" --type headless

    The extra --type option causes VirtualBox to use VBoxHeadless as the front-end to the internal virtualization engine instead of the Qt front-end.

  • The alternative is to use VBoxHeadless directly, as follows:

    VBoxHeadless --startvm <uuid|name>

    This way of starting the VM is preferred because you can see more detailed error messages, especially for early failures before the VM execution is started. If you have trouble with VBoxManage startvm, it can help greatly to start VBoxHeadless directly to diagnose the problem cause.

Note that when you use VBoxHeadless to start a VM, since the headless server has no other means of output, the VRDP server will always 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 ssh only), start the VM like this:

VBoxHeadless --startvm <uuid|name> --vrde=off

To have the VRDP server enabled depending on the VM configuration, as the other front-ends would, use this:

VBoxHeadless --startvm <uuid|name> --vrde=config

Step by step: creating a virtual machine on a headless server

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:

  1. 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.

  2. 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).

  3. A terminal connection to that host through which you can access a command line (e.g. via ssh).

  4. An RDP viewer on the remote client; see the section called “Common third-party RDP viewers” above for examples.

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.

  1. On the headless server, create a new virtual machine:

    VBoxManage createvm --name "Windows XP" --ostype WindowsXP --register

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

    Note further that you do not need to specify --ostype, 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

    VBoxManage list ostypes
  2. Make sure the settings for this VM are appropriate for the guest operating system that we will install. For example:

    VBoxManage modifyvm "Windows XP" --memory 256 --acpi on --boot1 dvd --nic1 nat
  3. Create a virtual hard disk for the VM (in this case, 10GB in size):

    VBoxManage createhd --filename "WinXP.vdi" --size 10000
  4. Add an IDE Controller to the new VM:

    VBoxManage storagectl "Windows XP" --name "IDE Controller"
          --add ide --controller PIIX4
  5. Set the VDI file created above as the first virtual hard disk of the new VM:

    VBoxManage storageattach "Windows XP" --storagectl "IDE Controller"
          --port 0 --device 0 --type hdd --medium "WinXP.vdi"
  6. 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:

    VBoxManage storageattach "Windows XP" --storagectl "IDE Controller"
          --port 0 --device 1 --type dvddrive --medium /full/path/to/iso.iso
  7. Start the virtual machine using VBoxHeadless:

    VBoxHeadless --startvm "Windows XP"

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

  8. On the client machine, fire up the RDP viewer and try to connect to the server (see the section called “Common third-party RDP viewers” above for how to use various common RDP viewers).

    You should now be seeing the installation routine of your guest operating system remotely in the RDP viewer.

Remote USB

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.

For these remote USB devices, the same filter rules apply as for other USB devices, as described with the section called “USB settings”. All you have to do is specify "Remote" (or "Any") when setting up these rules.

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 rdesktop-vrdp. RDP clients for other platforms will be provided in future VirtualBox versions.

To make a remote USB device available to a VM, rdesktop-vrdp should be started as follows:

rdesktop-vrdp -r usb -a 16 -N

Note that rdesktop-vrdp can access USB devices only through /proc/bus/usb. Please refer to the section called “USB not working” 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.

RDP authentication

For each virtual machine that is remotely accessible via RDP, you can individually determine if and how client connections are authenticated. For this, use VBoxManage modifyvm command with the --vrdeauthtype option; see the section called “VBoxManage modifyvm” for a general introduction. Three methods of authentication are available:

  • 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.

  • The "external" method provides external authentication through a special authentication library. VirtualBox ships with two such authentication libraries:

    1. The default authentication library, VBoxAuth, authenticates against user credentials of the hosts. Depending on the host platform, this means:

      • On Linux hosts, authenticates users against the host's PAM system.

      • On Windows hosts, VBoxAuth.dll authenticates users against the host's WinLogon system.

      • On Mac OS X hosts, VBoxAuth.dylib authenticates users against the host's directory service.[31]

      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.

    2. An additional library called VBoxAuthSimple 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:

      1. Enable VBoxAuthSimple with the following command:

        VBoxManage setproperty vrdeauthlibrary "VBoxAuthSimple"
      2. To enable the library for a particular VM, you must then switch authentication to external:

        VBoxManage modifyvm <vm> --vrdeauthtype external

        Replace <vm> with the VM name or UUID.

      3. 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:

        VBoxManage setextradata <vm> "VBoxAuthSimple/users/<user>" <hash>

        Replace <vm> with the VM name or UUID, <user> with the user name who should be allowed to log in and <hash> with the encrypted password. As an example, to obtain the hash value for the password "secret", you can use the following command:

        VBoxManage internalcommands passwordhash "secret"

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

        As example, combined together, to set the password for the user "john" and the machine "My VM" to "secret", use this command:

        VBoxManage setextradata "My VM" "VBoxAuthSimple/users/john"
  • 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 guest user accounts.

    This method is currently still in testing and not yet supported.

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 Chapter 11, VirtualBox programming interfaces for details.

RDP encryption

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).

RDP provides three different authentication methods:

  1. 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.

  2. 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 and cannot be recommended.

  3. RDP5.2 authentication is based on TLS 1.0 with customer-supplied certificates. The server supplies a certificate to the client which must be signed by a certificate authority (CA) that the client trusts (for the Microsoft RDP Client 5.2, the CA has to be added to the Windows Trusted Root Certificate Authorities database). VirtualBox allows you to supply your own CA and server certificate and uses OpenSSL for encryption.

While VirtualBox supports all of the above, only RDP5.2 authentication should be used in environments where security is a concern. As the client that connects to the server determines what type of encryption will be used, with rdesktop, the Linux RDP viewer, use the -4 or -5 options.

Multiple connections to the VRDP server

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.

The following command enables multiple connection mode:

VBoxManage modifyvm "VM name" --vrdemulticon on

Multiple remote monitors

To access two or more remote VM displays you have to enable the VRDP multiconnection mode (see the section called “Multiple connections to the VRDP server”).

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

The Microsoft RDP6 client does not let you specify a separate domain name. Instead, use domain\username in the Username: field -- for example, @2\name. name 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.

VRDP video redirection

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.

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.

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.

The following command enables video redirection:

VBoxManage modifyvm "VM name" --vrdevideochannel on

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:

VBoxManage modifyvm "VM name" --vrdevideochannelquality 75

VRDP customization

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.

The following commands change corresponding server settings:

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

To reenable a feature use a similar command without the trailing 1. For example:

VBoxManage modifyvm "VM name" --vrdeproperty Client/DisableDisplay=

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:

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

To reenable a feature use a similar command without the trailing 1. For example:

VBoxManage setextradata "VM name" "VRDP/Feature/Client/DisableDisplay"


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.

Teleporting requires that a machine be currently running on one host, which is then called the "source". The host to which the virtual machine will be teleported will then be called the "target"; 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.

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.

At this time, there are a few prerequisites for this to work, however:

  1. 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.

  2. 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.

    This also means that neither the source nor the target machine can have any snapshots.

Then perform the following steps:

  1. On the target 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:

    VBoxManage modifyvm <targetvmname> --teleporter on --teleporterport <port>

    where <targetvmname> is the name of the virtual machine on the target host and <port> is a TCP/IP port number to be used on both the source and the target hosts. For example, use 6000. For details, see the section called “Teleporting settings”.

  2. 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.

  3. Start the machine on the source host as usual. When it is running and you want it to be teleported, issue the following command on the source host:

    VBoxManage controlvm <sourcevmname> teleport --host <targethost> --port <port>

    where <sourcevmname> is the name of the virtual machine on the source host (the machine that is currently running), <targethost> is the host or IP name of the target host on which the machine is waiting for the teleport request, and <port> must be the same number as specified in the command on the target host. For details, see the section called “VBoxManage controlvm”.

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.


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 VBoxManage --modifyvm --cpuid command; see the section called “Teleporting settings”.

[30] Before VirtualBox 1.6, the headless server was called VBoxVRDP. For the sake of backwards compatibility, the VirtualBox installation still installs an executable with that name as well.

[31] Support for Mac OS X was added in version 3.2.