security = domain in Samba 2.x

Joining an NT Domain with Samba 2.2

Assume you have a Samba 2.x 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:

root# smbpasswd -j DOM -r DOMPDC -UAdministrator%password

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. The Administrator%password is the login name and password for an account which has the necessary privilege to add machines to the domain. If this is successful you will see the message:

smbpasswd: Joined domain DOM.

in your terminal window. See the smbpasswd(8) man page for more details.

There is existing development code to join a domain without having to create the machine trust account on the PDC beforehand. This code will hopefully be available soon in release branches as well.

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


In Samba 2.0.x, 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:


In Samba 2.2, this file has been replaced with a TDB (Trivial Database) file named secrets.tdb.

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(5) 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.

Alternatively, if you want smbd to automatically determine the list of Domain controllers to use for authentication, you may set this line to be :

password server = *

This method, which was introduced in Samba 2.0.6, allows Samba to use exactly the same mechanism that NT does. This method either broadcasts or uses a WINS database in order to find domain controllers to authenticate against.

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

Samba and Windows 2000 Domains

Many people have asked regarding the state of Samba's ability to participate in a Windows 2000 Domain. Samba 2.2 is able to act as a member server of a Windows 2000 domain operating in mixed or native mode.

There is much confusion between the circumstances that require a "mixed" mode Win2k DC and a when this host can be switched to "native" mode. A "mixed" mode Win2k domain controller is only needed if Windows NT BDCs must exist in the same domain. By default, a Win2k DC in "native" mode will still support NetBIOS and NTLMv1 for authentication of legacy clients such as Windows 9x and NT 4.0. Samba has the same requirements as a Windows NT 4.0 member server.

The steps for adding a Samba 2.2 host to a Win2k domain are the same as those for adding a Samba server to a Windows NT 4.0 domain. The only exception is that the "Server Manager" from NT 4 has been replaced by the "Active Directory Users and Computers" MMC (Microsoft Management Console) plugin.

Why is this better than security = server?

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.

Please refer to the Winbind paper for information on a system to automatically assign UNIX uids and gids to Windows NT Domain users and groups. This code is available in development branches only at the moment, but will be moved to release branches soon.

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.