Joining an NT Domain with Samba 2.0

Jeremy Allison, Samba Team

11th November 1998

In order for a Samba-2 server to join an NT domain, you must first add the NetBIOS name of the Samba server to the NT domain on the PDC using Server Manager for Domains. This creates the machine account in the domain (PDC) SAM.

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.

In order to join the domain, first stop all Samba daemons and run the 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). If this is successful you will see the message:

smbpasswd: Joined domain DOM.

in your terminal window. See the smbpasswd man page for more details.

This command goes through the machine account password change protocol, then writes the new (random) machine account password for this Samba server into the a file in the same directory in which an smbpasswd file would be stored (normally :

/usr/local/samba/private

The filename looks like this:

<NT DOMAIN NAME>.<Samba Server Name>.mac

The .mac suffix stands for machine account password file. So in our example above, the file would be called:

DOM.SERV1.mac

This file is created and owned by root and is not readable by any other user. It is the key to the domain-level security for your system, and should be treated as carefully as a shadow password file.

Now, before restarting the Samba daemons you must edit your smb.conf file to tell Samba it should now use domain security.

Change (or add) your

"security ="

line in the [global] section of your smb.conf to read:

security = domain

Next change the

"workgroup ="

line in the [global] section to read:

workgroup = DOM

as this is the name of the domain we are joining.

You must also have the parameter "encrypt passwords" set to "yes" in order for your users to authenticate to the NT PDC.

Finally, add (or modify) a:

"password server ="

line in the [global] section to read:

password server = DOMPDC DOMBDC1 DOMBDC2

These are the primary and backup domain controllers Samba will attempt to contact in order to authenticate users. Samba will try to contact each of these servers in order, so you may want to rearrange this list in order to spread out the authentication load among domain controllers.

Currently, Samba requires that a defined list of domain controllers be listed in this parameter in order to authenticate with domain-level security. NT does not use this method, and will either broadcast or use a WINS database in order to find domain controllers to authenticate against.

Originally, I considered this idea for Samba, but dropped it because it seemed so insecure. However several Samba-2 alpha users have requested that this feature be added to make Samba more NT-like, so I'll probably add a special name of '*' (which means: act like NT when looking for domain controllers) in a future release of the code. At present, however, you need to know where your domain controllers are.

Finally, restart your Samba daemons and get ready for clients to begin using domain security!

Currently, domain security in Samba doesn't free you from having to create local Unix users to represent the users attaching to your server. This means that if domain user DOM\fred attaches to your domain security Samba server, there needs to be a local Unix user fred to represent that user in the Unix filesystem. This is very similar to the older Samba security mode "security=server", where Samba would pass through the authentication request to a Windows NT server in the same way as a Windows 95 or Windows 98 server would.

The advantage to domain-level security is that the authentication in domain-level security is passed down the authenticated RPC channel in exactly the same way that an NT server would do it. This means Samba servers now participate in domain trust relationships in exactly the same way NT servers do (i.e., you can add Samba servers into a resource domain and have the authentication passed on from a resource domain PDC to an account domain PDC.

In addition, with "security=server" every Samba daemon on a server has to keep a connection open to the authenticating server for as long as that daemon lasts. This can drain the connection resources on a Microsoft NT server and cause it to run out of available connections. With "security =domain", however, the Samba daemons connect to the PDC/BDC only for as long as is necessary to authenticate the user, and then drop the connection, thus conserving PDC connection resources.

And finally, acting in the same manner as an NT server authenticating to a PDC means that as part of the authentication reply, the Samba server gets the user identification information such as the user SID, the list of NT groups the user belongs to, etc. All this information will allow Samba to be extended in the future into a mode the developers currently call appliance mode. In this mode, no local Unix users will be necessary, and Samba will generate Unix uids and gids from the information passed back from the PDC when a user is authenticated, making a Samba server truly plug and play in an NT domain environment. Watch for this code soon.

NOTE: Much of the text of this document was first published in the Web magazine "LinuxWorld" as the article "Doing the NIS/NT Samba".