Samba and LDAP
 

• The ability to join an Active Directory domain by means of LDAP and Kerberos

• Built in Unicode support for internationalization

• Support for Microsoft Windows XP Professional client connections to Samba servers without needing local registry hacking

• Two new documents developed by the Samba.org team, which include a 400+ page reference manual, and a 300+ page implementation and integration manual. 

Samba is a powerful and versatile server application. Even seasoned system administrators must know its abilities and limitations before attempting installation and configuration.

What Samba can do:

What Samba cannot do:

Figure 19.1. SMB Workgroups in Nautilus

Figure 19.2. SMB Machines in Nautilus

To query the network for Samba servers, use the findsmb command. For each server found, it displays its IP address, NetBIOS name, workgroup name, operating system, and SMB server version.

To connect to a Samba share from a shell prompt, type the following command:

smbclient /// -U 

Replace with the hostname or IP address of the Samba server you want to connect to, with the name of the shared directory you want to browse, and with the Samba username for the system. Enter the correct password or press Enter if no password is required for the user.

If you see the smb:\> prompt, you have successfully logged in. Once you are logged in, type help for a list of commands. If you wish to browse the contents of your home directory, replace sharename with your username. If the -U switch is not used, the username of the current user is passed to the Samba server.

To exit smbclient, type exit at the smb:\> prompt.

Sometimes it is useful to mount a Samba share to a directory so that the files in the directory can be treated as if they are part of the local file system.

To mount a Samba share to a directory, create create a directory to mount it to (if it does not already exist), and execute the following command as root:

mount -t cifs -o , /// /mnt/point/

This command mounts from in the local directory /mnt/point/. For more information about mounting a samba share, refer to man mount.cifs.

Configuring a Samba Server

The default configuration file (/etc/samba/smb.conf) allows users to view their home directories as a Samba share. It also shares all printers configured for the system as Samba shared printers. In other words, you can attach a printer to the system and print to it from the Windows machines on your network.

19.4.1. Graphical Configuration

To configure Samba using a graphical interface, use the Samba Server Configuration Tool. For command line configuration, skip to Section 19.4.2, “Command Line Configuration”.

The Samba Server Configuration Tool is a graphical interface for managing Samba shares, users, and basic server settings. It modifies the configuration files in the /etc/samba/ directory. Any changes to these files not made using the application are preserved.

To use this application, you must be running the X Window System, have root privileges, and have the system-config-samba RPM package installed. To start the Samba Server Configuration Tool from the desktop, go to the System (on the Panel) => Administration => Server Settings => Samba or type the command system-config-samba at a shell prompt (for example, in an XTerm or a GNOME terminal).

Figure 19.3. Samba Server Configuration Tool

Note

The Samba Server Configuration Tool does not display shared printers or the default stanza that allows users to view their own home directories on the Samba server.

Configuring Server Settings

The first step in configuring a Samba server is to configure the basic settings for the server and a few security options. After starting the application, select Preferences => Server Settings from the pulldown menu. The Basic tab is displayed as shown in Figure 19.4, “Configuring Basic Server Settings”.

Figure 19.4. Configuring Basic Server Settings

On the Basic tab, specify which workgroup the computer should be in as well as a brief description of the computer. They correspond to the workgroup and server string options in smb.conf.

Figure 19.5. Configuring Security Server Settings

The Security tab contains the following options:

• Authentication Mode — This corresponds to the security option. Select one of the following types of authentication.

  • ADS — The Samba server acts as a domain member in an Active Directory Domain (ADS) realm. For this option, Kerberos must be installed and configured on the server, and Samba must become a member of the ADS realm using the net utility, which is part of the samba-client package. Refer to the net man page for details. This option does not configure Samba to be an ADS Controller. Specify the realm of the Kerberos server in the Kerberos Realm field.

    Note

    The Kerberos Realm field must be supplied in all uppercase letters, such as EXAMPLE.COM.

    Using a Samba server as a domain member in an ADS realm assumes proper configuration of Kerberos, including the /etc/krb5.conf file.

  • Domain — The Samba server relies on a Windows NT Primary or Backup Domain Controller to verify the user. The server passes the username and password to the Controller and waits for it to return. Specify the NetBIOS name of the Primary or Backup Domain Controller in the Authentication Server field.

    The Encrypted Passwords option must be set to Yes if this is selected.

  • Server — The Samba server tries to verify the username and password combination by passing them to another Samba server. If it can not, the server tries to verify using the user authentication mode. Specify the NetBIOS name of the other Samba server in the Authentication Server field.

  • Share — Samba users do not have to enter a username and password combination on a per Samba server basis. They are not prompted for a username and password until they try to connect to a specific shared directory from a Samba server.

  • User — (Default) Samba users must provide a valid username and password on a per Samba server basis. Select this option if you want the Windows Username option to work. Refer to Section 19.4.1.2, “Managing Samba Users” for details.

• Encrypt Passwords — This option must be enabled if the clients are connecting from a system with Windows 98, Windows NT 4.0 with Service Pack 3, or other more recent versions of Microsoft Windows. The passwords are transfered between the server and the client in an encrypted format instead of as a plain-text word that can be intercepted. This corresponds to the encrypted passwords option. Refer to Section 19.4.3, “Encrypted Passwords” for more information about encrypted Samba passwords.

• Guest Account — When users or guest users log into a Samba server, they must be mapped to a valid user on the server. Select one of the existing usernames on the system to be the guest Samba account. When guests log in to the Samba server, they have the same privileges as this user. This corresponds to the guest account option.

After clicking OK, the changes are written to the configuration file and the daemon is restarted; thus, the changes take effect immediately.

Managing Samba Users

The Samba Server Configuration Tool requires that an existing user account be active on the system acting as the Samba server before a Samba user can be added. The Samba user is associated with the existing user account.

Figure 19.6. Managing Samba Users

To add a Samba user, select Preferences => Samba Users from the pulldown menu, and click the Add User button. In the Create New Samba User window select a Unix Username from the list of existing users on the local system.

If the user has a different username on a Windows machine and needs to log into the Samba server from the Windows machine, specify that Windows username in the Windows Username field. The Authentication Mode on the Security tab of the Server Settings preferences must be set to User for this option to work.

Also, configure a Samba Password for the Samba User and confirm it by typing it again. Even if you opt to use encrypted passwords for Samba, it is recommended that the Samba passwords for all users are different from their system passwords.

To edit an existing user, select the user from the list, and click Edit User. To delete an existing Samba user, select the user, and click the Delete User button. Deleting a Samba user does not delete the associated system user account.

The users are modified immediately after clicking the OK button.

Adding a Share

To create a Samba share, click the Add button from the main Samba configuration window.

Figure 19.7. Adding a Share

The Basic tab configures the following options:

• Directory — The directory to share via Samba. The directory must exist before it can be entered here.

• Share name — The actual name of the share that is seen from remote machines. By default, it is the same value as Directory, but can be configured.

• Descriptions — A brief description of the share.

• Writable — Enables users to read and write to the shared directory

• Visible — Grants read-only rights to users for the shared directory.

On the Access tab, select whether to allow only specified users to access the share or whether to allow all Samba users to access the share. If you select to allow access to specific users, select the users from the list of available Samba users.

The share is added immediately after clicking OK.

workgroup = WORKGROUPNAME 
server string = BRIEF COMMENT ABOUT SERVER

[sharename] 
comment = Insert a comment here 
path = /home/share/ 
valid users = tfox carole 
public = no 
writable = yes 
printable = no 
create mask = 0765

/sbin/service smb start

/sbin/service smb stop

 /sbin/service smb restart 

 /sbin/service smb condrestart 

 /sbin/service smb reload 

The main benefit of using LDAP is that information for an entire organization can be consolidated into a central repository. For example, rather than managing user lists for each group within an organization, LDAP can be used as a central directory accessible from anywhere on the network. And because LDAP supports Secure Sockets Layer (SSL) and Transport Layer Security (TLS), sensitive data can be protected from prying eyes.

LDAP also supports a number of back-end databases in which to store directories. This allows administrators the flexibility to deploy the database best suited for the type of information the server is to disseminate. Because LDAP also has a well-defined client Application Programming Interface (API), the number of LDAP-enabled applications are numerous and increasing in quantity and quality.

• openldap — Contains the libraries necessary to run the OpenLDAP server and client applications.

• openldap-clients — Contains command line tools for viewing and modifying directories on an LDAP server.

• openldap-servers — Contains the servers and other utilities necessary to configure and run an LDAP server.

• slapadd — Adds entries from an LDIF file to an LDAP directory. For example, the command /usr/sbin/slapadd -l ldif-input reads in the LDIF file, ldif-input, containing the new entries.

  Important

  Only the root user may use /usr/sbin/slapadd. However, the directory server runs as the ldap user. Therefore the directory server is unable to modify any files created by slapadd. To correct this issue, after using slapadd, type the following command:

  chown -R ldap /var/lib/ldap
  

• slapcat — Pulls entries from an LDAP directory in the default format, Sleepycat Software's Berkeley DB system, and saves them in an LDIF file. For example, the command /usr/sbin/slapcat -l ldif-output outputs an LDIF file called ldif-output containing the entries from the LDAP directory.

• slapindex — Re-indexes the slapd directory based on the current content. This tool should be run whenever indexing options within /etc/openldap/slapd.conf are changed.

• slappasswd — Generates an encrypted user password value for use with ldapmodify or the rootpw value in the slapd configuration file, /etc/openldap/slapd.conf. Execute the /usr/sbin/slappasswd command to create the password.

Warning

You must stop slapd by issuing the /sbin/service ldap stop command before using slapadd, slapcat or slapindex. Otherwise, the integrity of the LDAP directory is at risk.

• ldapadd — Adds entries to an LDAP directory by accepting input via a file or standard input; ldapadd is actually a hard link to ldapmodify -a.

• ldapdelete — Deletes entries from an LDAP directory by accepting user input at a shell prompt or via a file.

• ldapmodify — Modifies entries in an LDAP directory, accepting input via a file or standard input.

• ldappasswd — Sets the password for an LDAP user.

• ldapsearch — Searches for entries in an LDAP directory using a shell prompt.

• ldapcompare — Opens a connection to an LDAP server, binds, and performs a comparison using specified parameters.

• ldapwhoami — Opens a connection to an LDAP server, binds, and performs a whoami operation.

• ldapmodrdn — Opens a connection to an LDAP server, binds, and modifies the RDNs of entries.

In addition to the OpenLDAP packages, Red Hat Enterprise Linux includes a package called nss_ldap, which enhances LDAP's ability to integrate into both Linux and other UNIX environments.

The nss_ldap package provides the following modules (where refers to the version of libnss_ldap in use):

The nss_ldap package provides the following modules for Itanium or AMD64 architectures:

The libnss_ldap-.so module allows applications to look up users, groups, hosts, and other information using an LDAP directory via the Nameservice Switch (NSS) interface of glibc. NSS allows applications to authenticate using LDAP in conjunction with the NIS name service and flat authentication files.

The pam_ldap module allows PAM-aware applications to authenticate users using information stored in an LDAP directory. PAM-aware applications include console login, POP and IMAP mail servers, and Samba. By deploying an LDAP server on a network, all of these applications can authenticate using the same user ID and password combination, greatly simplifying administration.

For more about configuring PAM, refer to Section 42.4, “Pluggable Authentication Modules (PAM)” and the PAM man pages.

Red Hat Enterprise Linux includes a package containing an LDAP module for the PHP server-side scripting language.

The php-ldap package adds LDAP support to the PHP4 HTML-embedded scripting language via the /usr/lib/php4/ldap.so module. This module allows PHP4 scripts to access information stored in an LDAP directory.

Red Hat Enterprise Linux ships with the mod_authz_ldap module for the Apache HTTP Server. This module uses the short form of the distinguished name for a subject and the issuer of the client SSL certificate to determine the distinguished name of the user within an LDAP directory. It is also capable of authorizing users based on attributes of that user's LDAP directory entry, determining access to assets based on the user and group privileges of the asset, and denying access for users with expired passwords. The mod_ssl module is required when using the mod_authz_ldap module.

There are graphical LDAP clients available which support creating and modifying directories, but they are not included with Red Hat Enterprise Linux. One such application is LDAP Browser/Editor — A Java-based tool available online at https://www.iit.edu/~gawojar/ldap/.

Other LDAP clients access directories as read-only, using them to reference, but not alter, organization-wide information. Some examples of such applications are Sendmail, Mozilla, Gnome Meeting, and Evolution.

Caution

Do not modify schema items defined in the schema files installed by OpenLDAP.