Windows activation - duplicate Client Machine ID

Applies to: ✔️ Windows VMs

We generally recommend using Azure Key Management Services (KMS) servers to activate Azure Windows virtual machines (VMs), even when Azure Hybrid Benefit is enabled. However, in specific cases, because network restrictions might prevent VMs from communicating with Azure KMS servers, you can use a self-hosted KMS server for activation. This article discusses an issue of duplicate Client Machine ID that occurs when you use a self-hosted KMS server for Windows activation, and provides a solution.

Symptoms

When you use a self-hosted KMS server for activation and try to activate more than one Windows Server VM, the activation fails after the evaluation period, and your self-hosted KMS server reports the following error in the Duplicate Client Machine ID Report:

The Duplicate Client Machine ID Report helps identify machines in the environment which are running images that were not properly generalized by using the Sysprep tool before deployment.
Note:
- Multiple Volume Activation Clients with the same CMID will be counted as a single client by KMS. If this causes the KMS Client Count to fall below the minimum threshold, KMS activation will fail in your environment.

Cause

• The Client Machine ID (CMID) is cleared during the Sysprep process of the original source image. However, if the Sysprep process is triggered with the parameter SkipRearm set to 1 instead of the default value of 0, the CMID won't be cleared. In this case, all VMs created from this image will have the same CMID.

• When you create VMs from Azure Marketplace, Azure Marketplace images for Windows Server have been generalized with the parameter SkipRearm set to 1. Therefore, the VMs created from the same Windows Server image will have the same CMID.

Confirm duplicate CMID

Check if the VMs have the same CMID based on the source image and version:

1. Run the following command on the problematic VMs:

   cscript C:\Windows\System32\slmgr.vbs /dlv
   

   Here's a command output sample:

   Most recent activation information:
   Key Management Service client information
       Client Machine ID (CMID): <client-machine-ID>
       Registered KMS machine name: <KMS-machine-name>
   

2. Compare the command outputs on the problematic VMs and confirm if the VMs have the same CMID.

Solution

• For the problematic VMs created from a custom image, generalize/sysprep the original VM with the parameter SkipRearm set to 0 to make sure the CMID is cleared from the image.

• For the problematic VMs that are already deployed, follow these steps:

  1. Run the slmgr /rearm command from an elevated command prompt.

  2. Restart the VM.

  3. Once the VM is online after the restart, run the following command to confirm that the CMID has been changed:

     cscript C:\Windows\System32\slmgr.vbs /dlv
     

  4. Trigger the activation again.

Contact us for help

If you have questions or need help, create a support request, or ask Azure community support. You can also submit product feedback to Azure feedback community.