The first step in manually creating a Machine Trust Account is to manually create the corresponding UNIX account in /etc/passwd. This can be done using vipw or another “adduser” command that is normally used to create new UNIX accounts. The following is an example for a Linux-based Samba server:

root# /usr/sbin/useradd -g machines -d /var/lib/nobody \
   -c "machine nickname" \
   -s /bin/false machine_name$ 

root# passwd -l machine_name$

In the example above there is an existing system group “machines” which is used as the primary group for all machine accounts. In the following examples the “machines” group numeric GID is 100.

On *BSD systems, this can be done using the chpass utility:

root# chpass -a \
'machine_name$:*:101:100::0:0:Windows machine_name:/dev/null:/sbin/nologin'

The /etc/passwd entry will list the machine name with a “$” appended, and will not have a password, will have a null shell and no home directory. For example, a machine named “doppy” would have an /etc/passwd entry like this:

doppy$:x:505:100:machine_nickname:/dev/null:/bin/false

in which machine_nickname can be any descriptive name for the client, such as BasementComputer. machine_name absolutely must be the NetBIOS name of the client to be joined to the domain. The “$” must be appended to the NetBIOS name of the client or Samba will not recognize this as a Machine Trust Account.

Now that the corresponding UNIX account has been created, the next step is to create the Samba account for the client containing the well-known initial Machine Trust Account password. This can be done using the smbpasswd command as shown here:

root# smbpasswd -a -m machine_name

where machine_name is the machine's NetBIOS name. The RID of the new machine account is generated from the UID of the corresponding UNIX account.

A working add machine script is essential for machine trust accounts to be automatically created. This applies no matter whether you use automatic account creation or the NT4 Domain Server Manager.

If the machine from which you are trying to manage the domain is an MS Windows NT4 workstation or MS Windows 200x/XP Professional, the tool of choice is the package called SRVTOOLS.EXE. When executed in the target directory it will unpack SrvMgr.exe and UsrMgr.exe (both are domain management tools for MS Windows NT4 workstation).

If your workstation is a Microsoft Windows 9x/Me family product, you should download the Nexus.exe package from the Microsoft Web site. When executed from the target directory, it will unpack the same tools but for use on this platform.

Further information about these tools may be obtained from Knowledge Base articles 173673, and 172540

Launch the srvmgr.exe (Server Manager for Domains) and follow these steps:

The third (and recommended) way of creating Machine Trust Accounts is simply to allow the Samba server to create them as needed when the client is joined to the domain.

Since each Samba Machine Trust Account requires a corresponding UNIX account, a method for automatically creating the UNIX account is usually supplied; this requires configuration of the add machine script option in smb.conf. This method is not required; however, corresponding UNIX accounts may also be created manually.

Here is an example for a Red Hat Linux system:

The procedure for making an MS Windows workstation or server a member of the domain varies with the version of Windows.

Assumptions lists names that are used in the remainder of this chapter.

First, 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:

Note that if the parameter security = user is used, this machine would function as a standalone server and not as a domain member server. Domain security mode causes Samba to work within the domain security context.

Next change the workgroup line in the [global] section to read:

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. This is the default setting if this parameter is not specified. There is no need to specify this parameter, but if it is specified in the smb.conf file, it must be set to Yes.

Finally, add (or modify) a password server line in the [global] section to read:

These are the PDC and BDCs 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 determine automatically the list of domain controllers to use for authentication, you may set this line to be:

This method allows Samba to use exactly the same mechanism that NT does. The method either uses broadcast-based name resolution, performs a WINS database lookup in order to find a domain controller against which to authenticate, or locates the domain controller using DNS name resolution.

To join the domain, run this command:

root# net rpc join -S DOMPDC -UAdministrator%password

If the -S DOMPDC argument is not given, the domain name will be obtained from smb.conf and the NetBIOS name of the PDC will be obtained either using a WINS lookup or via NetBIOS broadcast based name look up.

The machine is joining the domain DOM, and the PDC for that domain (the only machine that has write access to the domain SAM database) is DOMPDC; therefore, use the -S option. The Administrator%password is the login name and password for an account that has the necessary privilege to add machines to the domain. If this is successful, you will see the following message in your terminal window. Where the older NT4-style domain architecture is used:

Joined domain DOM.

Where Active Directory is used, the command used to join the ADS domain is:

root#  net ads join -UAdministrator%password

And the following output is indicative of a successful outcome:

Joined SERV1 to realm MYREALM.

Refer to the net man page and to the chapter on remote administration for further information.

This process joins the server to the domain without separately having to create the machine trust account on the PDC beforehand.

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 a smbpasswd file would be normally stored. The trust account information that is needed by the DMS is written into the file /usr/local/samba/private/secrets.tdb or /etc/samba/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.

Finally, restart your Samba daemons and get ready for clients to begin using domain security. The way you can restart your Samba daemons depends on your distribution, but in most cases the following will suffice:

root# /etc/init.d/samba restart

Currently, domain security in Samba does not 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 file system. This is 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 Winbind: Use of Domain Accounts, for information on a system to automatically assign UNIX UIDs and GIDs to Windows NT domain users and groups.

The advantage of 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 or BDC only for as long as is necessary to authenticate the user and then drop the connection, thus conserving PDC connection resources.

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, and so on.

You must use at least the following three options in smb.conf:

In case samba cannot correctly identify the appropriate ADS server using the realm name, use the password server option in smb.conf:

The most common reason for which Samba may not be able to locate the ADS domain controller is a consequence of sites maintaining some DNS servers on UNIX systems without regard for the DNS requirements of the ADS infrastructure. There is no harm in specifying a preferred ADS domain controller using the password server.

With both MIT and Heimdal Kerberos, it is unnecessary to configure the /etc/krb5.conf, and it may be detrimental.

Microsoft ADS automatically create SRV records in the DNS zone _kerberos._tcp.REALM.NAME for each KDC in the realm. This is part of the installation and configuration process used to create an Active Directory domain. A KDC is a Kerberos Key Distribution Center and forms an integral part of the Microsoft active directory infrastructure.

UNIX systems can use kinit and the DES-CBC-MD5 or DES-CBC-CRC encryption types to authenticate to the Windows 2000 KDC. For further information regarding Windows 2000 ADS kerberos interoperability please refer to the Microsoft Windows 2000 Kerberos Interoperability guide. Another very useful document that may be referred to for general information regarding Kerberos interoperability is RFC1510. This RFC explains much of the magic behind the operation of Kerberos.

MIT's, as well as Heimdal's, recent KRB5 libraries default to checking for SRV records, so they will automatically find the KDCs. In addition, krb5.conf only allows specifying a single KDC, even there if there may be more than one. Using the DNS lookup allows the KRB5 libraries to use whichever KDCs are available.

When manually configuring krb5.conf, the minimal configuration is:

[libdefaults]
	default_realm = YOUR.KERBEROS.REALM

[realms]
	YOUR.KERBEROS.REALM = {
	kdc = your.kerberos.server
	}

[domain_realms]
	.kerberos.server = YOUR.KERBEROS.REALM

When using Heimdal versions before 0.6, use the following configuration settings:

[libdefaults]
	default_realm      = YOUR.KERBEROS.REALM
	default_etypes     = des-cbc-crc des-cbc-md5
	default_etypes_des = des-cbc-crc des-cbc-md5

[realms]
        YOUR.KERBEROS.REALM = {
        kdc = your.kerberos.server
	}

[domain_realms]
        .kerberos.server = YOUR.KERBEROS.REALM

Test your config by doing a kinit USERNAME@REALM and making sure that your password is accepted by the Win2000 KDC.

With Heimdal versions earlier than 0.6.x you can use only newly created accounts in ADS or accounts that have had the password changed once after migration, or in case of Administrator after installation. At the moment, a Windows 2003 KDC can only be used with Heimdal releases later than 0.6 (and no default etypes in krb5.conf). Unfortunately, this whole area is still in a state of flux.

Clock skew limits are configurable in the Kerberos protocols. The default setting is five minutes.

You also must ensure that you can do a reverse DNS lookup on the IP address of your KDC. Also, the name that this reverse lookup maps to must either be the NetBIOS name of the KDC (i.e., the hostname with no domain attached) or it can be the NetBIOS name followed by the realm.

The easiest way to ensure you get this right is to add a /etc/hosts entry mapping the IP address of your KDC to its NetBIOS name. If you do not get this correct, then you will get a local error when you try to join the realm.

If all you want is Kerberos support in smbclient, then you can skip directly to Testing with smbclient now. Create the Computer Account and Testing Server Setup are needed only if you want Kerberos support for smbd and winbindd.

As a user who has write permission on the Samba private directory (usually root), run:

root#  net ads join -U Administrator%password

The Administrator account can be any account that has been designated in the ADS domain security settings with permission to add machines to the ADS domain. It is, of course, a good idea to use an account other than Administrator. On the UNIX/Linux system, this command must be executed by an account that has UID=0 (root).

When making a Windows client a member of an ADS domain within a complex organization, you may want to create the machine trust account within a particular organizational unit. Samba-3 permits this to be done using the following syntax:

root#  kinit Administrator@your.kerberos.REALM
root#  net ads join "organizational_unit"

Your ADS manager will be able to advise what should be specified for the "organizational_unit" parameter.

For example, you may want to create the machine trust account in a container called “Servers” under the organizational directory “Computers\BusinessUnit\Department,” like this:

root#  net ads join "Computers\BusinessUnit\Department\Servers"

This command will place the Samba server machine trust account in the container Computers\BusinessUnit\Department\Servers. The container should exist in the ADS directory before executing this command.

If the join was successful, you will see a new computer account with the NetBIOS name of your Samba server in Active Directory (in the “Computers” folder under Users and Computers.

On a Windows 2000 client, try net use * \\server\share. You should be logged in with Kerberos without needing to know a password. If this fails, then run klist tickets. Did you get a ticket for the server? Does it have an encryption type of DES-CBC-MD5?

On your Samba server try to log in to a Windows 2000 server or your Samba server using smbclient and Kerberos. Use smbclient as usual, but specify the -k option to choose Kerberos authentication.

You must change the administrator password at least once after installing a domain controller, to create the right encryption types.

Windows 200x does not seem to create the _kerberos._udp and _ldap._tcp in the default DNS setup. Perhaps this will be fixed later in service packs.

“A Windows workstation was reinstalled. The original domain machine trust account was deleted and added immediately. The workstation will not join the domain if I use the same machine name. Attempts to add the machine fail with a message that the machine already exists on the network I know it does not. Why is this failing?”

The original name is still in the NetBIOS name cache and must expire after machine account deletion before adding that same name as a domain member again. The best advice is to delete the old account and then add the machine with a new name. Alternately, the name cache can be flushed and reloaded with current data using the nbtstat command on the Windows client:

C:\>  nbtstat -R

“Adding a Windows 200x or XP Professional machine to the Samba PDC Domain fails with a message that says, "The machine could not be added at this time, there is a network problem. Please try again later." Why?”

You should check that there is an add machine script in your smb.conf file. If there is not, please add one that is appropriate for your OS platform. If a script has been defined, you will need to debug its operation. Increase the log level in the smb.conf file to level 10, then try to rejoin the domain. Check the logs to see which operation is failing.

Possible causes include:

The add machine script does not create the machine account in the Samba backend database; it is there only to create a UNIX system account to which the Samba backend database account can be mapped.

Windows 2003 requires SMB signing. Client-side SMB signing has been implemented in Samba-3.0. Set client use spnego = yes when communicating with a Windows 2003 server. This will not interfere with other Windows clients that do not support the more advanced security features of Windows 2003 because the client will simply negotiate a protocol tha both it and the server suppport. This is a well-known fall-back facility that is built into the SMB/CIFS protocols.