Extending Active Directory Schema
To extend Schema (Extending Active Directory), use an account that is a member of the Schema Admins security group. Be signed in to the schema master domain controller.
E:\SC2012_SP2_Configmgr_SCEP\SMSSETUP\BIN\X64
Locate the extadsch which can be found in SMSSETUP\BIN\X64 of the configuration manager setup DVD.
Hold the shift key on your keyboard and right click extadsch and click on Copy as Path.
Launch the Window PowerShell using run as administrator. Right click and click paste and hit enter.
You should see the line Successfully extended the Active Directory Schema.
Open the log file extadsch.log located in the root of the system drive. You should see the line Successfully extended the Active Directory Schema.
Now that we have created the system management container, we must grant the site server’s computer account the permissions that are required to publish site information to the container. The primary site server computer account must be granted Full Control permissions to the System Management container and all its child objects.
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How to Install Prerequisites for SCCM 2012 R2 – SCCM