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I am am running Kubuntu Hardy Heron, with a dual monitor setup, and have VirtualBox on it running Windows XP in seamless mode.

My problem is, I can't get virtualbox to extend to the second monitor. Has anyone been able to achieve this or know if it can be achieved?

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Of course if you have the guest additions installed, you could make the window as large as you like. Obviously this won't make Virtualbox use multiple displays, but it will expand across as many monitors as your host machine supports. –  willoller Sep 2 '10 at 5:10
    
    
@David: For your bounty to be useful, better explain what is missing in the accepted answer. –  harrymc Jun 19 '13 at 5:38
    
@harrymc the step in the accepted answer that says perform the standard "Extend the desktop onto this display" method based on the Guest OS is vague, and it is not clear how to perform this on a Ubuntu Guest. Is there some program, driver, or specific configuration to do this? Also, there are three sections. How do they differ and in which context would I choose one over the other? –  David Jun 19 '13 at 15:06

5 Answers 5

up vote 46 down vote accepted

VirtualBox 3.2.1 supports multiple guest monitors. The documentation was not clear on how to enable this.

Basic Setup:

  1. Power off your virtual machine if it's on.
  2. From the main VirtualBox window, select your VM and choose Settings.
  3. Choose display.
  4. Below "Video Memory" is Monitor Count. Slide it to 2, and adjust your video memory if VirtualBox complains.
  5. Start your guest and perform the standard "Extend the desktop onto this display" method based on the Guest OS. (Guest Additions need to be installed.)
  6. A second "Oracle VM VirtualBox" window will appear with the second display. You can resize it however you want.

Seamless/Fullscreen

  1. Enter Seamless or Fullscreen. I'll assume your HostKey is the default RightCtrl.
  2. If the screens are on the wrong displays, hit RightCtrl+Home.
  3. From the View Menu, choose Virtual Display 1 and set it to the Host display you want. The other displays will shuffle around to accommodate this. If you have more than 2 virtual displays, repeat with Virtual Display 2 and so on.

Headless

  1. Set the number of monitors with VBoxManage modifyvm "vm name" --monitorcount X
  2. Enable multiple vrdp connections with VBoxManage modifyvm "VM name" --vrdpmulticon on
  3. Use VBoxHeadless to launch as normal.
  4. connect to monitor 1 with rdesktop -d \@1 ip-address-of-host and monitor 2 with rdesktop -d \@2 ip-address-of-host. This is explained in lomaxx's answer. (You might be able to use @ instead of \@, depending on your shell)
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Silly me, messing with this for two hours before googling it. Forgot to install VM additions; thx. –  tsilb Mar 29 '11 at 19:44

Start your guest and perform the standard "Extend the desktop onto this display" method based on the Guest OS. (Guest Additions need to be installed.)

This one confused me. I looked all over the Guest Additions and couldn't find it. In the hopes that it might help someone else, it is talking about the Control Panel in Windows itself. In the Control Panel click on Display -> Setting and there you will see the "Extend the desktop onto this display".

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I found that if I moved the Virtual Box VM Launcher on to the secondary monitor, and THEN pressed "Start" I was able to resize the window that appeared to fit onto my secondary monitor. If I started it from my primary monitor, I could not resize it any larger than my primary monitor.

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AFAIK you can only use multiple monitors in the following instances:

  1. Multiple monitors currently work only with Windows XP guests, and Guest Additions must be installed, as the implementation resides in the Guest Additions video driver.

  2. Multiple monitors work only with the VBoxHeadless frontend. You must also enable VRDP multiconnection mode (see chapter 7.4.6, VRDP multiple connections, page 94) to access two or more VM displays when the guest is using multiple monitors.

From the Manual

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I am running Debian Sid and i was able to get windows 7 and xp to run in seamless in dual monitor mode, with 3D acceleration, you need to install your guest additions in safe mode.

the steps i took were:

install os with dual screens enabled already, if your o/s is already installed i am unsure if you will get support, though i would recommend following the below to do so.

after install hit F8 while booting up windows

select run in safemode with networking (networking isnt really needed, but thats the step i took)

then install guest additions 32bit (dual screens works in 64 but 3D does not) reboot and you should have dual screens available with 3D support on One monitor (:1)

i couldn't get it to work on both. I did Not have vrdp enabled to do this and it worked just fine.

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