You can customize the Windows guest operating systems of the virtual machines when you deploy a new virtual machine from a template or clone an existing virtual machine. Customizing the guest operating system helps prevent conflicts that might result if you or other users deploy virtual machines with identical settings, such as duplicate computer names.

You can prevent Windows from assigning new virtual machines or templates with the same Security IDs (SIDs) as the original virtual machine. Duplicate SIDs do not cause problems when the computers are part of a domain and only domain user accounts are used. However, if the computers are part of a Workgroup or local user accounts are used, duplicate SIDs can compromise file access controls. For more information, see the documentation for your Microsoft Windows operating system.

Important: After customization, the default administrator password is not preserved for Windows Server 2008. During customization, the Windows Sysprep utility deletes and recreates the administrator account on Windows Server 2008. You must reset the administrator password when the virtual machine starts the first time after customization.



  1. Right-click any vSphere Client inventory object that is a valid parent object of a virtual machine, such as data center, cluster, vApp, resource pool, or host, and select New Virtual Machine.
  2. On the Select a creation page, select Clone an existing virtual machine or Deploy from template.
  3. Click Next.
  4. Follow the prompts until you reach the Select clone options page.
  5. On the Select clone options page, select the Customize the operating system check box and click Next.
  6. On the Customize guest OS page, apply a customization specification to the virtual machine, and click Next.
    Option Action
    Select an existing specification Select a customization specification from the list.
    Override To change the guest customization specification for this deployment only, click Override, complete the steps in the Override VM Customization Specification wizard, and click OK.
  7. On the User settings page, specify the required settings for the virtual machine.
    This page of the wizard appears only if the selected specification requires additional customization.
  8. On the Ready to complete page, review the details and click Finish.


When the new virtual machine starts for the first time, the guest operating system runs finalization scripts to complete the customization process. The virtual machine might restart several times during this process.

If the guest operating system pauses when the new virtual machine starts, it might be waiting for you to correct errors, such as an incorrect product key or an invalid user name. To determine whether the system is waiting for information, open the virtual machine console.

What to do next

After you deploy certain Windows operating systems that are not volume licensed, you might need to reactivate your operating system on the new virtual machine.

If the new virtual machine encounters customization errors while it is starting, the errors are logged to %WINDIR%\temp\vmware-imc. To view the error log file, from the Windows Start menu navigate to Programs > Administrative Tools > Event Viewer.