Samba-3 introduces a number of new password backend capabilities.

The UNIX and SMB password encryption techniques seem similar on the surface. This similarity is, however, only skin deep. The UNIX scheme typically sends clear-text passwords over the network when logging in. This is bad. The SMB encryption scheme never sends the clear-text password over the network but it does store the 16 byte hashed values on disk. This is also bad. Why? Because the 16 byte hashed values are a “password equivalent.” You cannot derive the user's password from them, but they could potentially be used in a modified client to gain access to a server. This would require considerable technical knowledge on behalf of the attacker but is perfectly possible. You should thus treat the data stored in whatever passdb backend you use (smbpasswd file, LDAP, MYSQL) as though it contained the clear-text passwords of all your users. Its contents must be kept secret and the file should be protected accordingly.

Ideally, we would like a password scheme that involves neither plain text passwords on the network nor on disk. Unfortunately, this is not available as Samba is stuck with having to be compatible with other SMB systems (Windows NT, Windows for Workgroups, Windows 9x/Me).

Windows NT 4.0 Service Pack 3 changed the default setting so plaintext passwords are disabled from being sent over the wire. This mandates either the use of encrypted password support or editing the Windows NT registry to re-enable plaintext passwords.

The following versions of Microsoft Windows do not support full domain security protocols, although they may log onto a domain environment:

The following versions of MS Windows fully support domain security protocols.

All current releases of Microsoft SMB/CIFS clients support authentication via the SMB Challenge/Response mechanism described here. Enabling clear-text authentication does not disable the ability of the client to participate in encrypted authentication. Instead, it allows the client to negotiate either plain text or encrypted password handling.

MS Windows clients will cache the encrypted password alone. Where plain text passwords are re-enabled through the appropriate registry change, the plain text password is never cached. This means that in the event that a network connections should become disconnected (broken), only the cached (encrypted) password will be sent to the resource server to effect an auto-reconnect. If the resource server does not support encrypted passwords the auto-reconnect will fail. Use of encrypted passwords is strongly advised.

Every operation in UNIX/Linux requires a user identifier (UID), just as in MS Windows NT4/200x this requires a Security Identifier (SID). Samba provides two means for mapping an MS Windows user to a UNIX/Linux UID.

First, all Samba SAM (Security Account Manager database) accounts require a UNIX/Linux UID that the account will map to. As users are added to the account information database, Samba will call the add user script interface to add the account to the Samba host OS. In essence all accounts in the local SAM require a local user account.

The second way to effect Windows SID to UNIX UID mapping is via the idmap uid and idmap gid parameters in smb.conf. Please refer to the man page for information about these parameters. These parameters are essential when mapping users from a remote SAM server.

Samba-3 has a special facility that makes it possible to maintain identical UIDs and GIDs on all servers in a distributed network. A distributed network is one where there exists a PDC, one or more BDCs and/or one or more Domain Member servers. Why is this important? This is important if files are being shared over more than one protocol (e.g., NFS) and where users are copying files across UNIX/Linux systems using tools such as rsync.

The special facility is enabled using a parameter called idmap backend. The default setting for this parameter is an empty string. Technically it is possible to use an LDAP based idmap backend for UIDs and GIDs, but it makes most sense when this is done for network configurations that also use LDAP for the SAM backend. Following example shows that.

A network administrator who wants to make significant use of LDAP backends will sooner or later be exposed to the excellent work done by PADL Software. PADL http://www.padl.com have produced and released to open source an array of tools that might be of interest. These tools include:

Samba doesn't provide a turnkey solution to LDAP. It is best to deal with the design and configuration of an LDAP directory prior to integration with Samba. A working knowledge of LDAP makes Samba integration easy and the lack of a working knowledge of LDAP can make it one a frustrating experience.

Computer (machine) accounts can be placed where ever you like in an LDAP directory subject to some constraints that are described in this chapter.

The POSIX and SambaSAMAccount components of computer (machine) accounts are both used by Samba. i.e.: Machine accounts are treated inside Samba in the same way that Windows NT4/200X treats them. A user account and a machine account are indistinquishable from each other, except that the machine account ends in a '$' character, as do trust accounts.

The need for Windows user, group, machine, trust, etc. accounts to be tied to a valid UNIX uid is a design decision that was made a long way back in the history of Samba development. It is unlikely that this decision will be reversed of changed during the remaining life of the Samba-3.x series.

The resolution of a UID from the Windows SID is achieved within Samba through a mechanism that must refer back to the host operating system on which Samba is running. The Name Service Switcher (NSS) is the preferred mechanism that shields applications (like Samba) from the need to know everything about every host OS it runs on.

Samba asks the host OS to provide a UID via the “passwd”, “shadow” and “group” facilities in the NSS control (configuration) file. The best tool for achieving this is left up to the UNIX administrator to determine. It is not imposed by Samba. Samba provides winbindd together with its support libraries as one method. It is possible to do this via LDAP - and for that Samba provides the appropriate hooks so that all account entities can be located in an LDAP directory.

For many the weapon of choice is to use the PADL nss_ldap utility. This utility must be configured so that computer accounts can be resolved to a POSIX/UNIX account UID. That is fundamentally an LDAP design question. The information provided on the Samba list and in the documentation is directed at providing working examples only. The design of an LDAP directory is a complex subject that is beyond the scope of this documentation.

The smbpasswd utility is similar to the passwd or yppasswd programs. It maintains the two 32 byte password fields in the passdb backend.

smbpasswd works in a client-server mode where it contacts the local smbd to change the user's password on its behalf. This has enormous benefits.

smbpasswd has the capability to change passwords on Windows NT servers (this only works when the request is sent to the NT Primary Domain Controller if changing an NT Domain user's password).

smbpasswd can be used to:

To run smbpasswd as a normal user just type:

$ smbpasswd
Old SMB password: secret

For secret, type old value here or press return if there is no old password.

New SMB Password: new secret
Repeat New SMB Password: new secret

If the old value does not match the current value stored for that user, or the two new values do not match each other, then the password will not be changed.

When invoked by an ordinary user, the command will only allow the user to change his or her own SMB password.

When run by root, smbpasswd may take an optional argument specifying the user name whose SMB password you wish to change. When run as root, smbpasswd does not prompt for or check the old password value, thus allowing root to set passwords for users who have forgotten their passwords.

smbpasswd is designed to work in the way familiar to UNIX users who use the passwd or yppasswd commands. While designed for administrative use, this tool provides essential User Level password change capabilities.

For more details on using smbpasswd, refer to the man page (the definitive reference).

pdbedit is a tool that can be used only by root. It is used to manage the passdb backend. pdbedit can be used to:

The pdbedit tool is the only one that can manage the account security and policy settings. It is capable of all operations that smbpasswd can do as well as a super set of them.

One particularly important purpose of the pdbedit is to allow the migration of account information from one passdb backend to another. See the XML password backend section of this chapter.

The following is an example of the user account information that is stored in a tdbsam password backend. This listing was produced by running:

$ pdbedit -Lv met
UNIX username:        met
NT username:
Account Flags:        [UX         ]
User SID:             S-1-5-21-1449123459-1407424037-3116680435-2004
Primary Group SID:    S-1-5-21-1449123459-1407424037-3116680435-1201
Full Name:            Melissa E Terpstra
Home Directory:       \\frodo\met\Win9Profile
HomeDir Drive:        H:
Logon Script:         scripts\logon.bat
Profile Path:         \\frodo\Profiles\met
Domain:               MIDEARTH
Account desc:
Workstations:         melbelle
Munged dial:
Logon time:           0
Logoff time:          Mon, 18 Jan 2038 20:14:07 GMT
Kickoff time:         Mon, 18 Jan 2038 20:14:07 GMT
Password last set:    Sat, 14 Dec 2002 14:37:03 GMT
Password can change:  Sat, 14 Dec 2002 14:37:03 GMT
Password must change: Mon, 18 Jan 2038 20:14:07 GMT

The pdbedit tool allows migration of authentication (account) databases from one backend to another. For example: To migrate accounts from an old smbpasswd database to a tdbsam backend:

Older versions of Samba retrieved user information from the UNIX user database and eventually some other fields from the file /etc/samba/smbpasswd or /etc/smbpasswd. When password encryption is disabled, no SMB specific data is stored at all. Instead all operations are conducted via the way that the Samba host OS will access its /etc/passwd database. Linux systems For example, all operations are done via PAM.

Traditionally, when configuring encrypt passwords = yes in Samba's smb.conf file, user account information such as username, LM/NT password hashes, password change times, and account flags have been stored in the smbpasswd(5) file. There are several disadvantages to this approach for sites with large numbers of users (counted in the thousands).

As a result of these deficiencies, a more robust means of storing user attributes used by smbd was developed. The API which defines access to user accounts is commonly referred to as the samdb interface (previously this was called the passdb API, and is still so named in the Samba CVS trees).

Samba provides an enhanced set of passdb backends that overcome the deficiencies of the smbpasswd plain text database. These are tdbsam, ldapsam and xmlsam. Of these, ldapsam will be of most interest to large corporate or enterprise sites.

Samba can store user and machine account data in a “TDB” (Trivial Database). Using this backend does not require any additional configuration. This backend is recommended for new installations that do not require LDAP.

As a general guide, the Samba Team does not recommend using the tdbsam backend for sites that have 250 or more users. Additionally, tdbsam is not capable of scaling for use in sites that require PDB/BDC implementations that require replication of the account database. Clearly, for reason of scalability, the use of ldapsam should be encouraged.

The recommendation of a 250 user limit is purely based on the notion that this would generally involve a site that has routed networks, possibly spread across more than one physical location. The Samba Team has not at this time established the performance based scalability limits of the tdbsam architecture.

There are a few points to stress that the ldapsam does not provide. The LDAP support referred to in this documentation does not include:

The second item can be accomplished by using LDAP NSS and PAM modules. LGPL versions of these libraries can be obtained from PADL Software. More information about the configuration of these packages may be found at LDAP, System Administration; Gerald Carter by O'Reilly; Chapter 6: Replacing NIS."

This document describes how to use an LDAP directory for storing Samba user account information traditionally stored in the smbpasswd(5) file. It is assumed that the reader already has a basic understanding of LDAP concepts and has a working directory server already installed. For more information on LDAP architectures and directories, please refer to the following sites:

Two additional Samba resources which may prove to be helpful are:

ObjectClass (1.3.6.1.4.1.7165.2.2.6 NAME 'sambaSamAccount' SUP top AUXILIARY
    DESC 'Samba-3.0 Auxiliary SAM Account'
    MUST ( uid $ sambaSID )
    MAY  ( cn $ sambaLMPassword $ sambaNTPassword $ sambaPwdLastSet $
          sambaLogonTime $ sambaLogoffTime $ sambaKickoffTime $
          sambaPwdCanChange $ sambaPwdMustChange $ sambaAcctFlags $
          displayName $ sambaHomePath $ sambaHomeDrive $ sambaLogonScript $
          sambaProfilePath $ description $ sambaUserWorkstations $
          sambaPrimaryGroupSID $ sambaDomainName ))

root# cp samba.schema /etc/openldap/schema/

## /etc/openldap/slapd.conf

## schema files (core.schema is required by default)
include	           /etc/openldap/schema/core.schema

## needed for sambaSamAccount
include            /etc/openldap/schema/cosine.schema
include            /etc/openldap/schema/inetorgperson.schema
include            /etc/openldap/schema/nis.schema
include            /etc/openldap/schema/samba.schema
....

# Indices to maintain
## required by OpenLDAP
index objectclass             eq

index cn                      pres,sub,eq
index sn                      pres,sub,eq
## required to support pdb_getsampwnam
index uid                     pres,sub,eq
## required to support pdb_getsambapwrid()
index displayName             pres,sub,eq

## uncomment these if you are storing posixAccount and
## posixGroup entries in the directory as well
##index uidNumber               eq
##index gidNumber               eq
##index memberUid               eq

index   sambaSID              eq
index   sambaPrimaryGroupSID  eq
index   sambaDomainName       eq
index   default               sub

root# ./sbin/slapindex -f slapd.conf

root# /etc/init.d/slapd restart

# Organization for Samba Base
dn: dc=quenya,dc=org
objectclass: dcObject
objectclass: organization
dc: quenya
o: Quenya Org Network
description: The Samba-3 Network LDAP Example

# Organizational Role for Directory Management
dn: cn=Manager,dc=quenya,dc=org
objectclass: organizationalRole
cn: Manager
description: Directory Manager

# Setting up container for users
dn: ou=People,dc=quenya,dc=org
objectclass: top
objectclass: organizationalUnit
ou: People

# Setting up admin handle for People OU
dn: cn=admin,ou=People,dc=quenya,dc=org
cn: admin
objectclass: top
objectclass: organizationalRole
objectclass: simpleSecurityObject
userPassword: {SSHA}c3ZM9tBaBo9autm1dL3waDS21+JSfQVz

# Setting up container for groups
dn: ou=Groups,dc=quenya,dc=org
objectclass: top
objectclass: organizationalUnit
ou: Groups

# Setting up admin handle for Groups OU
dn: cn=admin,ou=Groups,dc=quenya,dc=org
cn: admin
objectclass: top
objectclass: organizationalRole
objectclass: simpleSecurityObject
userPassword: {SSHA}c3ZM9tBaBo9autm1dL3waDS21+JSfQVz

# Setting up container for computers
dn: ou=Computers,dc=quenya,dc=org
objectclass: top
objectclass: organizationalUnit
ou: Computers

# Setting up admin handle for Computers OU
dn: cn=admin,ou=Computers,dc=quenya,dc=org
cn: admin
objectclass: top
objectclass: organizationalRole
objectclass: simpleSecurityObject
userPassword: {SSHA}c3ZM9tBaBo9autm1dL3waDS21+JSfQVz

$ slapadd -v -l initldap.dif

root# smbpasswd -w secret

## allow the "ldap admin dn" access, but deny everyone else
access to attrs=SambaLMPassword,SambaNTPassword
     by dn="cn=Samba Admin,ou=People,dc=quenya,dc=org" write
     by * none

	dn: uid=guest2, ou=People,dc=quenya,dc=org
	sambaLMPassword: 878D8014606CDA29677A44EFA1353FC7
	sambaPwdMustChange: 2147483647
	sambaPrimaryGroupSID: S-1-5-21-2447931902-1787058256-3961074038-513
	sambaNTPassword: 552902031BEDE9EFAAD3B435B51404EE
	sambaPwdLastSet: 1010179124
	sambaLogonTime: 0
	objectClass: sambaSamAccount
	uid: guest2
	sambaKickoffTime: 2147483647
	sambaAcctFlags: [UX         ]
	sambaLogoffTime: 2147483647
	sambaSID: S-1-5-21-2447931902-1787058256-3961074038-5006
	sambaPwdCanChange: 0

	dn: uid=gcarter, ou=People,dc=quenya,dc=org
	sambaLogonTime: 0
	displayName: Gerald Carter
	sambaLMPassword: 552902031BEDE9EFAAD3B435B51404EE
	sambaPrimaryGroupSID: S-1-5-21-2447931902-1787058256-3961074038-1201
	objectClass: posixAccount
	objectClass: sambaSamAccount
	sambaAcctFlags: [UX         ]
	userPassword: {crypt}BpM2ej8Rkzogo
	uid: gcarter
	uidNumber: 9000
	cn: Gerald Carter
	loginShell: /bin/bash
	logoffTime: 2147483647
	gidNumber: 100
	sambaKickoffTime: 2147483647
	sambaPwdLastSet: 1010179230
	sambaSID: S-1-5-21-2447931902-1787058256-3961074038-5004
	homeDirectory: /home/moria/gcarter
	sambaPwdCanChange: 0
	sambaPwdMustChange: 2147483647
	sambaNTPassword: 878D8014606CDA29677A44EFA1353FC7

Every so often someone will come along with a great new idea. Storing user accounts in a SQL backend is one of them. Those who want to do this are in the best position to know what the specific benefits are to them. This may sound like a cop-out, but in truth we cannot attempt to document every little detail why certain things of marginal utility to the bulk of Samba users might make sense to the rest. In any case, the following instructions should help the determined SQL user to implement a working system.

$ mysql -uusername -hhostname -ppassword \
	databasename < /path/to/samba/examples/pdb/mysql/mysql.dump

This module requires libxml2 to be installed.

The usage of pdb_xml is fairly straightforward. To export data, use:

$ pdbedit -e xml:filename

(where filename is the name of the file to put the data in)

To import data, use: $ pdbedit -i xml:filename

“I've installed Samba, but now I can't log on with my UNIX account! ”

Make sure your user has been added to the current Samba passdb backend. Read the section Account Management Tools for details.

A few complaints have been received from users that just moved to Samba-3. The following smb.conf file entries were causing problems, new accounts were being added to the old smbpasswd file, not to the tdbsam passdb.tdb file:

Samba will add new accounts to the first entry in the passdb backend parameter entry. If you want to update to the tdbsam, then change the entry to:

When explicitly setting an auth methods parameter, guest must be specified as the first entry on the line, for example, auth methods = guest sam.