Users encounter errors that refer to the need to run Adprep, or they experience an error when they try to run it. And this seems to be common because the the most frequently viewed thread on the AD DS forum on TechNet is DC promotion and adprep /forestprep . So this article is intended to briefly summarize how to run Adprep.exe and to cover common errors. If you experience an error that is not covered here, please edit the article and add information about your error and if possible, how you resolved it.

Adprep.exe is a command-line utility that performs operations that must be completed in an existing Active Directory environment before you can add a domain controller that runs that version of Windows Server. The TechNet article titled Running Adprep.exe covers everything you need to know about it.

How to run Adprep

The TechNet article I mentioned covers all this in much greater detail, but the short story is that you need to locate Adprep.exe (or Adprep32.exe) on the Windows Server operating system disk and run the Adprep commands before you can add a domain controller that runs that version of Windows Server to an existing Active Directory environment. Specifically, you need to run:

  • Adprep /forestprep on the schema master
  • Adprep /domainprep on the infrastructure master of each domain in the forest
  • Adprep /rodcprep on any computer (this is optional, only required if you intend to install a read-ony domain controller)

Each command has specific credential requirements so refer to the TechNet topic for that.


The rest of this topic summarizes the problems and questions that users are citing on the TechNet Forum thread and how to resolve them.

ADPrep vs Schema master DC

Problem: Adprep /forestprep returns an error "Adprep cannot run on this platform because it is not an Active Directory Domain Controller."

Resolution: Run adprep/ forestprep on the schema master domain controller. If you don't know which server is the schema master, at the command line run netdom query fsmo.

ADPrep on all DC?

Problem: Do I need to run Adprep on all DCs?

Resolution: No. Adprep only has to be run on the computers mentioned earlier in this topic.


Problem: I have successfully run Adprep /forestprep, but now when I try to run dcpromo to install a new domain controller, Adprep returns an error "To install a domain controller into this active directory domain, you must first prepare the domain using "adprep /domainprep". The adprep utility is available on the windows server 2008 installation media in the \sources\adprep folder."

Resolution: After you run adprep /forestprep and that change has replicated to all the DCs in the forest, you need to run adprep /domainprep on the infrastructure master in the domain where you are adding the new DC. If you don't know which server is the infrastructuremaster, at the command line run netdom query fsmo.

ADPrep success message

Problem: I don't really know if Forestprep succeeded because it seems to run and run and run until I press return to get a new prompt.

Resolution: Adprep returns a success message at the command line when it finishes. There is also an objectVersion attribute of the Schema container that you can check to verify if adprep /forestprep completed successfully. For Windows Server 2008, the value of the objectVersion attribute will be 44 after you successfully run adprep /forestprep; for Windows Server 2008 R2, the value will be 47. See http://technet.microsoft.com/en-us/library/dd464018(WS.10).aspx#BKMK_VerifyForestPrep 

ADPrep wrong version?

Problem: If I have a Windows Server 2003 Enterprise DC and want to introduce a Windows Server 2008 Standard DC, then running adprep does not work from the Windows Server 2008 DVD because it's the wrong version.

Resolution: It will work. The SKU edition has no affect on running Adprep.exe.


Question: Will Adprep commands require a reboot of the DC the operation is performed on?

Answer: No.

Functional level?

Question: What is the functional level requirement to run Adprep? 

Answer: Adprep /domainprep requires a Windows 2000 native or higher domain functional level in each target domain. The other Adprep commands do not have any functional level requirement.

From DVD or copy the files?

Question: Can I run the Adprep commands from the DVD on the appropriate operations master or do I need to copy Adprep.exe to the local server?

Answer: Either. It is not required to copy the utility to the operations master in order to run it. But if you do copy it, be sure to copy the entire Adprep folder.

Machine type issue

Problem: Running adprep /forestprep on a Windows 2003 Server from a Windows 2008 R2 DVD results in the error "The image file adprep.exe is valid, but is for a machine type other than the current machine"

Answer: The adprep.exe file on the Windows 2008 R2 DVD is a 64bit application. Use adprep32.exe instead.


Item Description
DVD  Digital Versatile Disk
DC Domain Controller
AD DS  Active Directory Domain Services
FSMO  Flexible single master operation