Multiple instances of the Unknown computers collection occur when you reinstall a primary site

This article provides a workaround for the issue that multiple instances of the Unknown computers collection are shown in Microsoft System Center 2012 Configuration Manager.

Original product version:   Microsoft System Center 2012 Configuration Manager
Original KB number:   2688121

Symptoms

Consider this scenario in Microsoft System Center 2012 Configuration Manager:

• You install a central administration site.
• You install a primary site and then uninstall the primary site.
• You reinstall the primary site by using the same server name and site name.

In this scenario, you may notice multiple instances of the Unknown computers collection.

Workaround

To work around this problem, create a collection that includes all Unknown Computer objects. This method creates a collection that contains both active and inactive objects. Then, advertise a task sequence to this collection to make sure that it becomes associated with the inactive GUID that is being used by the Pre-Boot Execution Environment (PXE) image.

To do this, run the following query for the collection, and then retarget advertisements to the new collection:

Select SMS_R_UNKNOWNSYSTEM.ResourceID,SMS_R_UNKNOWNSYSTEM.ResourceType,SMS_R_UNKNOWNSYSTEM.Name,SMS_R_UNKNOWNSYSTEM.Name,SMS_R_UNKNOWNSYSTEM.Name from SMS_R_UnknownSystem where Decommissioned = "0"