Resolving “duplicate SID” errors in a Windows domain

Please see Running a Windows domain in Skytap for more information.


When you join a Windows VM or physical machine to a domain, a unique identifier or SID is generated when the machine boots for the first time. The SID is used to uniquely identify the machine to the domain.

However, the ability to replicate and deploy copies of individual machines or entire networks can cause unexpected behavior. For example, if you save a Windows VM to a template, and then redeploy another copy with the intention of adding both machines to the same domain, a “duplicate SID” error displays.

This error only occurs when you copy a VM in an environment to the same environment. If you copy the VM to a different environment or add a VM from a different environment, this error doesn’t occur.

Best practices

To have multiple copies of a VM run simultaneously in the same environment:

For a VM that isn’t part of a domain
  1. Save the VM as a template before you add it to the domain.
  2. When you add a copy of the machine to the domain, make sure it has a unique hostname.

    Choose a generic hostname for the template VM. When you add the template VM to an environment, change the hostname, before you power it on. After the VM is running with the new hostname, you can join it to your corporate domain or domain in Skytap.

For a VM that is already joined to a domain

If a machine is already a member of a domain and you need multiple copies of it, use Sysprep to clear the SID for the machine.