Version 76 (modified by klaus, 14 years ago) (diff)


Frequently Asked Questions for end users (User FAQ)

Here you can find common questions, frequently asked on the VirtualBox mailing lists and IRC channel, along with their answers. Please consult this list every time you run into a problem that is not described in the User Manual.

Note that we update the User Manual on a regular basis, and information that first shows up on this page is moved to the User Manual regularly. As a result, please do check the User Manual also, especially the "Troubleshooting" section.

Also make sure to check whether you are running the latest version of VirtualBox.

This particular FAQ is for end-user issues only; you may want to look at the Developer FAQ and Licensing FAQ for additional topics.


  • Sometimes VirtualBox fails to start with a message on the lines of
    Failed to create VirtualBox COM object
     Callee RC: 0x80470007
    This usually means that the VirtualBox COM server was unable to start up, and is often a sign of problems in your installation of VirtualBox. In many cases this problem can be solved simply by reinstalling VirtualBox. Reinstalling will simply set up the VirtualBox program files again, and will not affect any virtual machines which you have created.

If this does not help, and you wish to investigate the problem further yourself, try starting the VirtualBox COM server (the program VBoxSVC in the VirtualBox program folder) from a command prompt or a DOS box. You may be able to see what is going wrong from error messages when the server starts.

Please do not open bug reports when you get this error before you have tried the other available support channels ( forums, mailing lists and IRC).

  • "How come it doesn't detect my nVidia/ATI/whatever graphics card?"

Because the guest sees a virtual graphics card, not the host graphics card. The virtual graphics card provides the necessary VESA and VGA features to make the guest operative systems work OK. Additional features, like higher resolutions, is provided by the graphics driver included with the guest additions. More details on how to install guest additions and features of the virtual graphics card can be found in the manual.

  • I use VirtualBox 1.5.0 and one of my VMs has become inaccessible. I get the following error message: "Hard disk X is already attached to a machine Y." But I'm sure I didn't attach this hard disk to any other VM or anything like that.

Most likely, you have defined one or more shared folders for this VM but later deleted these folders on the host (or made them inaccessible in some other way). This was a known issue of version 1.5.0, but it's been fixed with VirtualBox 1.5.2. If you can't upgrade, you can try to re-create the inaccessible shared folders. You may find these shared folders in the .xml file mentioned in the error message -- open it in any text editor, search for the text <SharedFolder and then look at the path that immediately follows the text hostPath=. Alternatively, open this .xml in any text editor and delete all such SharedFolder elements.

(Fixed with VirtualBox 1.5.2)

Linux hosts

  • CD/DVD support: VirtualBox uses hal to detect available CD/DVD/floppy drives. Version 1.5.0 and 1.5.2 requires that the file is available. This is a bug, future versions of VirtualBox will look for Until this just install the hal-devel or hal-dev package depending on your distribution.
    (Fixed with VirtualBox 1.5.4)
  • USB on Ubuntu/Gutsy: Ubuntu removed support for /proc/bus/usb/*. We will address this issue in the future. Until this, edit the script `/etc/init.d/ and activate the four lines around line 40 (Magic to make /proc/bus/usb work). Then execute
    /etc/init.d/ start
    From now on, there should be a directory /proc/bus/usb/ and the device entries below should be accessible by any user.
  • USB on openSUSE: See the  this on the openSUSE support pages.
  • Tickless Linux timer: VirtualBox currently does not work well on Linux kernels with tickless timer support (CONFIG_NO_HZ enabled). We are investigating the problem but in the meantime you should disable the tickless timer by disabling that config option or by adding nohz=off to the Linux kernel command line.
    Starting with VirtualBox 1.5.6 the Linux kernel module knows the parameter force_async_tsc. Try loading the kernel module with
    modprobe vboxdrv force_async_tsc=1
    and see if that helps to improve things for you.
  • If you get a message saying "VirtualBox kernel driver not accessible, permission problem" when starting VirtualBox immediately after installation, make sure that your user account is a member of the vboxusers group. This group is created when VirtualBox is installed, but you will need to manually add all users to it who are to be allowed to run VirtualBox. The documentation accompanying your Linux distribution should provide information about how to do this. If not, the following should also work on most Linux systems. These commands should be run as the Administrator user from the command line.
    # groups <login name>
    [Shows a list of groups for that login name]
    # useradd <login name> -g <first group in list> -G <second group>,<third group>,...,vboxusers
    These changes will only take effect after the users have logged out and back in again.
  • If the kernel module refuses to load with a message saying "Error inserting vboxdrv: Invalid argument", check (as root) the output of the "dmesg" command, and see "Troubleshooting" -> "Linux hosts" in the User Manual for solutions.
  • If USB doesn't work, check your usbfs permissions. See "Troubleshooting" -> "Linux hosts" in the User Manual for a solution.

Windows hosts

  • If you configure a VM to use NAT networking (the default), the DNS relay in VirtualBox forwards all DNS queries to the first configured DNS server. Unfortunately on Windows the first configured DNS server is frequently not working (e.g. because it corresponds to a currently not connected interface). To work around this problem, configure a working DNS server in the network configuration inside the VM.
  • Windows Vista hosts might show an error about a COM server not being accessible. This is a problem of our installation routine which we have not figured out yet. To fix the problem, open a command prompt shell and enter:
    cd \Programs\InnoTek VirtualBox
    VBoxSVC.exe /ReRegServer
    regsvr32.exe VBoxC.dll
    (Should not occur with current versions anymore)
  • Installing the guest on fixed size disk images. Until version 1.5.4, VirtualBox creates a sparse file if the user selects 'fixed size' when creating a virtual disk image. That means that the file is created and its length on the real hard disk is defined but the file content is still not allocated. When trying to install a guest OS on this image, the first write accesses to a sector in the middle of the image will be delayed for a long time on Windows hosts. This might confuse the guest and make installing a guest impossible (for example, creating a partition fails). Starting with VirtualBox 1.5.6 we will write the whole file once during creation. Users of current versions should select a dynamically expanding image which does not have this limitation. (Will be fixed in VirtualBox 1.5.6)

Windows Vista guests

  • There is no networking in Windows Vista guests initially because, unfortunately, with Vista, Microsoft dropped driver support for the virtual AMD PCnet card that we are providing. See "Troubleshooting" -> "Windows guests" in the User Manual for a solution. The VirtualBox Guest Additions contain the AMD PCnet driver.

Windows 98 guests

  • High CPU load while running Windows 98 Windows 98 does not execute the 'hlt' instruction, which temporarily turns off the CPU, when it has no work to do. Download and install rain20 from  here.
  • Poor graphical output in Windows 98 Unlike more modern systems, Windows 98 does not come with a driver which will work with the VirtualBox graphics card, so it falls back to using it as a 16 color VGA card. While innotek do not provide Guest Additions for Windows 98, the Display Doctor 7 Beta suite by the company SciTech does contain a driver which will allow you to use higher color and resolution graphics modes. Please note that neither innotek nor SciTech support nor accept liability for the use of this program.

Display Doctor 7 Beta requires activation codes to work. We understand that the free activation code for Display Doctor 6 also applies to version 7 Beta:

You might also want to look at the following site pointed out by users of VirtualBox, which also provides VESA drivers for Windows 98: Please be aware that innotek provides this link in good faith, but cannot take responsibility for the site or the software which it refers to.
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