&author.jerry; &author.jht; DavidBannon Samba Team

dbannon@samba.org

(26 Apr 2001) There are many who approach MS Windows networking with incredible misconceptions. That's OK, because it give the rest of us plenty of opportunity to help someone. Those who really want help would be well advised to be informed of information that is in fact already available. The reader is well advised NOT to tackle this section without having first understood and mastered some basics. MS Windows networking is not particularly forgiving of misconfiguration. Users of MS Windows networking are likely to complain bitterly of persistent niggles that may be caused by broken network or system configuration. To a great many people however, MS Windows networking starts with a domain controller that in some magical way is expected to solve all ills. From the Samba mailing list one can readilly identify many common networking issues. If you are not clear on the following subjects, then it will do much good to read the sections of this HOWTO that deal with it. These are the most common causes of MS Windows networking problems: Basic TCP/IP configuration NetBIOS name resolution Authentication configuration User and Group configuration Basic File and Directory Permission Control in Unix/Linux Understanding of how MS Windows clients interoperate in a network environment Do not be put off too much, on the surface of it MS Windows networking seems so simple that any fool can do it. In fact, only a fool would set up an MS Windows network with inadequate training and preparation. So let's get our first indelible principle out of the way: It is perfectly OK to make mistakes! In the right place and at the right time, mistakes are the essence of learning. It is very much not Ok to make mistakes that cause loss of productivity and impose an avoidable financial burden on an organisation. Where is the right place to make mistakes? Only out of harms' way! If you are going to make mistakes, then please do this on a test network, away from users and in such a way as to not inflict pain on others. Do your learning on a test network. The following functionalities are new to the Samba-3 release: Windows NT4 domain trusts Adding users via the User Manager for Domains The following functionalities are NOT provided by Samba 3.0: SAM replication with Windows NT4 Domain Controllers (i.e. a Samba PDC and a Windows NT BDC or vice versa) Acting as a Windows 2000 Domain Controller (i.e. Kerberos and Active Directory) Please note that Windows 9x / Me / XP Home clients are not true members of a domain for reasons outlined in this article. Therefore the protocol for support of Windows 9x-style domain logons is completely different from NT4 / Win2k type domain logons and has been officially supported for some time. MS Windows XP Home edition is NOT able to join a domain and does not permit the use of domain logons. Samba-3 offers a complete implementation of group mapping between Windows NT groups and Unix groups (this is really quite complicated to explain in a short space). A Samba-3 PDC also has to store machine trust account information in a suitable backend data store. With Samba-3 there can be multiple back-ends for this including: smbpasswd - the plain ascii file stored used by earlier versions of Samba. This file configuration option requires a Unix/Linux system account for EVERY entry (ie: both for user and for machine accounts). This file will be located in the private directory (default is /usr/local/samba/lib/private or on linux /etc/samba). tdbsam - a binary database backend that will be stored in the private directory in a file called passwd.tdb. The key benefit of this binary format file is that it can store binary objects that can not be accomodated in the traditional plain text smbpasswd file. ldapsam - An LDAP based back-end. Permits the LDAP server to be specified. eg: ldap://localhost or ldap://frodo.murphy.com Read the chapter about the User Database for details. The new tdbsam and ldapsam account backends store vastly more information than smbpasswd is capable of. The new backend database includes capacity to specify per user settings for many parameters, over-riding global settings given in the smb.conf file. eg: logon drive, logon home, logon path, etc. Over the years public perceptions of what Domain Control really is has taken on an almost mystical nature. Before we branch into a brief overview of Domain Control there are three basic types of domain controllers: Primary Domain Controller Backup Domain Controller ADS Domain Controller The Primary Domain Controller or PDC plays an important role in the MS Windows NT4 and Windows 200x Domain Control architecture, but not in the manner that so many expect. There is a form of folk lore that dictates that because of it's role in the MS Windows network that the PDC should be the most powerful and most capable machine in the network. As corny as it may seem to say this here, where good over all network performance is desired the entire infrastructure needs to be balanced. It may be more advisable to invest more in the Backup Domain Controllers and Stand-Alone (or Domain Member) servers than in the PDC. In the case of MS Windows NT4 style domaines it is the PDC seeds the Domain Control database, a part of the Windows registry called the SAM (Security Accounts Management). It plays a key part in NT4 type domain user authentication and in synchronisation of the domain authentication database with Backup Domain Controllers. New to Samba-3 is the ability to use a back-end database that holds the same type of data as the NT4 style SAM (Security Account Manager) database (one of the registry files). The samba-3 SAM can be specified via the smb.conf file parameter passwd backend and valid options include smbpasswd, tdbsam, ldapsam, nisplussam, xmlsam, mysqlsam, plugin, guest. The Backup Domain Controller or BDC plays a key role in servicing network authentication requests. The BDC is biased to answer logon requests in preference to the PDC. On a network segment that has a BDC and a PDC the BDC will be most likely to service network logon requests. The PDC will answer network logon requests when the BDC is too busy (high load). A BDC can be promoted to a PDC. If the PDC is on line at the time that the BDC is promoted to PDC the previous PDC is automatically demoted to a BDC. With Samba-3 this is NOT an automatic operation, the PDB and BDC must be manually configured and changes need to be made likewise. With MS Windows NT4 it is an install time decision what type of machine the server will be. It is possible to change the promote a BDC to a PDC and vica versa only, but the only way to convert a domain controller to a domain member server or a stand-alone server is to reinstall it. The install time choices offered are: Primary Domain Controller - The one that seeds the domain SAM Backup Domain Controller - One that obtains a copy of the domain SAM Stand-Alone Server - One that plays NO part is SAM synchronisation With MS Windows 2000 the configuration of domain control is done after the server has been installed. Samba-3 is capable of acting fully as a native member of a Windows 200x server Active Directory domain. New to Samba-3 is the ability to function fully as an MS Windows NT4 style Domain Controller, excluding the SAM replication components. However, please be aware that Samba-3 support the MS Windows 200x domain control protcols also. At this time Samba-3 is capable of acting as an ADS Domain Controller but in only a limited and experimental manner. This functionality should not be depended upon until the samba-team offers formal support for it. At such a time, the documentation will be revised to duely reflect all configuration and management requirements. The first step in creating a working Samba PDC is to understand the parameters necessary in &smb.conf;. Here we attempt to explain the parameters that are covered in the &smb.conf; man page. Here is an example &smb.conf; for acting as a PDC: [global] ; Basic server settings netbios name = POGO workgroup = NARNIA ; User and Machine Account Backends ; Choices are: tdbsam, smbpasswd, ldapsam, mysqlsam, xmlsam, guest passdb backend = ldapsam, guest ; we should act as the domain and local master browser os level = 64 preferred master = yes domain master = yes local master = yes ; security settings (must user security = user) security = user ; encrypted passwords are a requirement for a PDC encrypt passwords = yes ; support domain logons domain logons = yes ; where to store user profiles? logon path = \\%N\profiles\%u ; where is a user's home directory and where should it be mounted at? logon drive = H: logon home = \\homeserver\%u ; specify a generic logon script for all users ; this is a relative **DOS** path to the [netlogon] share logon script = logon.cmd ; necessary share for domain controller [netlogon] path = /usr/local/samba/lib/netlogon read only = yes write list = ntadmin ; share for storing user profiles [profiles] path = /export/smb/ntprofile read only = no create mask = 0600 directory mask = 0700 The above parameters make for a full set of parameters that may define the server's mode of operation. The following parameters are the essentials alone: workgroup = NARNIA domain logons = Yes security = User The additional parameters shown in the longer listing above just makes for a more complete environment. There are a couple of points to emphasize in the above configuration. Encrypted passwords must be enabled. For more details on how to do this, refer to the User Database chapter. The server must support domain logons and have a [netlogon] share The server must be the domain master browser in order for Windows client to locate the server as a DC. Please refer to the various Network Browsing documentation included with this distribution for details. A machine trust account is an account that is used to authenticate a client machine (rather than a user) to the Domain Controller server. In Windows terminology, this is known as a "Computer Account." The password of a machine trust account acts as the shared secret for secure communication with the Domain Controller. This is a security feature to prevent an unauthorized machine with the same NetBIOS name from joining the domain and gaining access to domain user/group accounts. Windows NT, 200x, XP Professional clients use machine trust accounts, but Windows 9x / Me / XP Home clients do not. Hence, a Windows 9x / Me / XP Home client is never a true member of a domain because it does not possess a machine trust account, and thus has no shared secret with the domain controller. A Windows NT4 PDC stores each machine trust account in the Windows Registry. The introduction of MS Windows 2000 saw the introduction of Active Directory, the new repository for machine trust accounts. A Samba PDC, however, stores each machine trust account in two parts, as follows: A Samba account, stored in the same location as user LanMan and NT password hashes (currently smbpasswd). The Samba account possesses and uses only the NT password hash. A corresponding Unix account, typically stored in /etc/passwd. (Future releases will alleviate the need to create /etc/passwd entries.) There are two ways to create machine trust accounts: Manual creation. Both the Samba and corresponding Unix account are created by hand. "On-the-fly" creation. The Samba machine trust account is automatically created by Samba at the time the client is joined to the domain. (For security, this is the recommended method.) The corresponding Unix account may be created automatically or manually. 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 other 'add user' 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 100 -d /dev/null -c "machine nickname" -s /bin/false machine_name$ root# passwd -l machine_name$ On *BSD systems, this can be done using the 'chpass' utility: root# chpass -a "machine_name$:*:101:100::0:0:Workstation machine_name:/dev/null:/sbin/nologin" The /etc/passwd entry will list the machine name with a "$" appended, won't 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$:x:505:501:machine_nickname:/dev/null:/bin/false Above, machine_nickname can be any descriptive name for the client, i.e., BasementComputer. machine_name absolutely must be the NetBIOS name of the client to be joined to the domain. The "$" 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(8) 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. Manually creating a machine trust account using this method is the equivalent of creating a machine trust account on a Windows NT PDC using the "Server Manager". From the time at which the account is created to the time which the client joins the domain and changes the password, your domain is vulnerable to an intruder joining your domain using a machine with the same NetBIOS name. A PDC inherently trusts members of the domain and will serve out a large degree of user information to such clients. You have been warned! The second (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. Below is an example for a RedHat Linux system. [global] # <...remainder of parameters...> add machine script = /usr/sbin/useradd -d /dev/null -g 100 -s /bin/false -M %u The procedure for joining a client to the domain varies with the version of Windows. Windows 2000 When the user elects to join the client to a domain, Windows prompts for an account and password that is privileged to join the domain. A Samba administrative account (i.e., a Samba account that has root privileges on the Samba server) must be entered here; the operation will fail if an ordinary user account is given. The password for this account should be set to a different password than the associated /etc/passwd entry, for security reasons. The session key of the Samba administrative account acts as an encryption key for setting the password of the machine trust account. The machine trust account will be created on-the-fly, or updated if it already exists. Windows NT If the machine trust account was created manually, on the Identification Changes menu enter the domain name, but do not check the box "Create a Computer Account in the Domain." In this case, the existing machine trust account is used to join the machine to the domain. If the machine trust account is to be created on-the-fly, on the Identification Changes menu enter the domain name, and check the box "Create a Computer Account in the Domain." In this case, joining the domain proceeds as above for Windows 2000 (i.e., you must supply a Samba administrative account when prompted). Samba Joining a samba client to a domain is documented in the Domain Member chapter. Not yet Freddie! A domain and a workgroup are exactly the same thing in terms of network browsing. The difference is that a distributable authentication database is associated with a domain, for secure login access to a network. Also, different access rights can be granted to users if they successfully authenticate against a domain logon server. Samba-3 does this now in the same way that MS Windows NT/2K. The SMB client logging on to a domain has an expectation that every other server in the domain should accept the same authentication information. Network browsing functionality of domains and workgroups is identical and is explained in this documentation under the browsing discussions. It should be noted, that browsing is totally orthogonal to logon support. Issues related to the single-logon network model are discussed in this section. Samba supports domain logons, network logon scripts, and user profiles for MS Windows for workgroups and MS Windows 9X/ME clients which are the focus of this section. When an SMB client in a domain wishes to logon it broadcast requests for a logon server. The first one to reply gets the job, and validates its password using whatever mechanism the Samba administrator has installed. It is possible (but very stupid) to create a domain where the user database is not shared between servers, i.e. they are effectively workgroup servers advertising themselves as participating in a domain. This demonstrates how authentication is quite different from but closely involved with domains. Using these features you can make your clients verify their logon via the Samba server; make clients run a batch file when they logon to the network and download their preferences, desktop and start menu. Before launching into the configuration instructions, it is worthwhile to look at how a Windows 9x/ME client performs a logon: The client broadcasts (to the IP broadcast address of the subnet it is in) a NetLogon request. This is sent to the NetBIOS name DOMAIN<1c> at the NetBIOS layer. The client chooses the first response it receives, which contains the NetBIOS name of the logon server to use in the format of \\SERVER. The client then connects to that server, logs on (does an SMBsessetupX) and then connects to the IPC$ share (using an SMBtconX). The client then does a NetWkstaUserLogon request, which retrieves the name of the user's logon script. The client then connects to the NetLogon share and searches for this and if it is found and can be read, is retrieved and executed by the client. After this, the client disconnects from the NetLogon share. The client then sends a NetUserGetInfo request to the server, to retrieve the user's home share, which is used to search for profiles. Since the response to the NetUserGetInfo request does not contain much more then the user's home share, profiles for Win9X clients MUST reside in the user home directory. The client then connects to the user's home share and searches for the user's profile. As it turns out, you can specify the user's home share as a sharename and path. For example, \\server\fred\.profile. If the profiles are found, they are implemented. The client then disconnects from the user's home share, and reconnects to the NetLogon share and looks for CONFIG.POL, the policies file. If this is found, it is read and implemented. The main difference between a PDC and a Windows 9x logon server configuration is that Password encryption is not required for a Windows 9x logon server. Windows 9x/ME clients do not possess machine trust accounts. Therefore, a Samba PDC will also act as a Windows 9x logon server. There are a few comments to make in order to tie up some loose ends. There has been much debate over the issue of whether or not it is ok to configure Samba as a Domain Controller in security modes other than USER. The only security mode which will not work due to technical reasons is SHARE mode security. DOMAIN and SERVER mode security is really just a variation on SMB user level security. Actually, this issue is also closely tied to the debate on whether or not Samba must be the domain master browser for its workgroup when operating as a DC. While it may technically be possible to configure a server as such (after all, browsing and domain logons are two distinctly different functions), it is not a good idea to do so. You should remember that the DC must register the DOMAIN#1b NetBIOS name. This is the name used by Windows clients to locate the DC. Windows clients do not distinguish between the DC and the DMB. For this reason, it is very wise to configure the Samba DC as the DMB. Now back to the issue of configuring a Samba DC to use a mode other than "security = user". If a Samba host is configured to use another SMB server or DC in order to validate user connection requests, then it is a fact that some other machine on the network (the "password server") knows more about the user than the Samba host. 99% of the time, this other host is a domain controller. Now in order to operate in domain mode security, the "workgroup" parameter must be set to the name of the Windows NT domain (which already has a domain controller, right?) Therefore configuring a Samba box as a DC for a domain that already by definition has a PDC is asking for trouble. Therefore, you should always configure the Samba DC to be the DMB for its domain. A 'machine name' in (typically) /etc/passwd of the machine name with a '$' appended. FreeBSD (and other BSD systems?) won't create a user with a '$' in their name. The problem is only in the program used to make the entry. Once made, it works perfectly. Create a user without the '$' using vipw to edit the entry, adding the '$'. Or create the whole entry with vipw if you like, make sure you use a unique User ID! This happens if you try to create a machine trust account from the machine itself and already have a connection (e.g. mapped drive) to a share (or IPC$) on the Samba PDC. The following command will remove all network drive connections: C:\WINNT\> net use * /d Further, if the machine is already a 'member of a workgroup' that is the same name as the domain you are joining (bad idea) you will get this message. Change the workgroup name to something else, it does not matter what, reboot, and try again. I joined the domain successfully but after upgrading to a newer version of the Samba code I get the message, "The system can not log you on (C000019B), Please try again or consult your system administrator" when attempting to logon. This occurs when the domain SID stored in the secrets.tdb database is changed. The most common cause of a change in domain SID is when the domain name and/or the server name (netbios name) is changed. The only way to correct the problem is to restore the original domain SID or remove the domain client from the domain and rejoin. The domain SID may be reset using either the net or rpcclient utilities. The reset or change the domain SID you can use the net command as follows: net getlocalsid 'OLDNAME' net setlocalsid 'SID' When I try to join the domain I get the message "The machine account for this computer either does not exist or is not accessible". What's wrong? This problem is caused by the PDC not having a suitable machine trust account. If you are using the add machine script method to create accounts then this would indicate that it has not worked. Ensure the domain admin user system is working. Alternatively if you are creating account entries manually then they have not been created correctly. Make sure that you have the entry correct for the machine trust account in smbpasswd file on the Samba PDC. If you added the account using an editor rather than using the smbpasswd utility, make sure that the account name is the machine NetBIOS name with a '$' appended to it ( i.e. computer_name$ ). There must be an entry in both /etc/passwd and the smbpasswd file. Some people have reported that inconsistent subnet masks between the Samba server and the NT client have caused this problem. Make sure that these are consistent for both client and server. At first be ensure to enable the useraccounts with smbpasswd -e %user%, this is normally done, when you create an account.