Here is how I have done it in Redhat 8.0
In order for a Samba-2 server to join an NT domain, you must add the NetBIOS name of the Samba server to the NT domain on the PDC using Server Manager for Domains. This creates the computer account in the domain. Only add the Samba server as a member server, not as a PDC or BDC.
Let's assume you have a Samba-2 server with a NetBIOS name of SERV1 and are joining an NT domain called DOM, which has a PDC with a NetBIOS name of DOMPDC and two backup domain controllers with NetBIOS names DOMBDC1 and DOMBDC2.
For you to join the domain, you will first have to stop all Samba (SMB) daemons and then run the following command:
smbpasswd -j DOM -r DOMPDC
....as we are joining the domain DOM and the PDC for that domain (the only machine that has write access to the domain SAM database) is DOMPDC. If this is successful you will see the message:
smbpasswd: Joined domain DOM.
Hope this helps
OH.........and Welcome to LinuxQuestions.org