Manual - Samba Active-directory

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Join a Linux server to Active Directory with Samba 3.0By Scott Lowe MCSE, TechRepublic 10/10/2002 URL: http://asia.cnet.com/enterprise/netadmin/0,,39081966,00.htm

As Linux becomes more prevalent in enterprises, the need for interoperability between it and incumbent operating systemsbecomes more important. After all, nobody wants to add a new system if it will require a whole new set of administrationtools and additional user accounts.

One tool that has become ubiquitous in Linux configurations is Samba, the open source file services and authorizationsoftware. The release of Windows 2000 and its use of Active Directory complicated integrating a Linux server in a Microsoftenvironment, which had become a snap with Windows NT and Samba version 2.2.x. Although Samba can still be used as adomain controller, it requires a mixed-mode Windows 2000 domain, in which some Windows NT 4.0 domain controllers arestill present. (Samba is considered a Windows NT 4.0 domain controller.)

In addition, Windows 2000 (and XP) uses Active Directory with the Kerberos authentication protocol, which presents newchallenges for interoperability. Some administrators want to move to a native mode Active Directory domain but still providea central authentication service, so a new way to handle authentication needs to be devised.

Enter Samba 3.0. The Samba team is providing the means to handle this very task in it newest version, which is still underdevelopment. I’m going to show you how to use the latest alpha version of Samba to allow your Linux server toauthenticate against a Windows 2000 domain controller.

From alpha to final codeThis article employs the latest alpha version of Samba 3.0. Although not ready for production networks, the alpha code doeswork and, according to the road map, will not drastically change when the full public release is ready. After a lengthy chatwith the Samba development team, I was reassured that coming changes to Samba 3.0 (from alpha to the final release) willprimarily be the addition of features and the stabilization of the code. The installation and configurations shown in thisarticle are not likely to change.

What you needTo get Samba 3.0 up and running, you must have:

Windows 2000 Server acting as a domain controller.The OpenLDAP development libraries for Linux. As of this writing, version 2.0.23-4 is the latest release and can bedownloaded here.The MIT Kerberos development libraries for Linux. As of this writing, these libraries are at version 1.2.4-1. krb5-develcan be downloaded here; \\krb5-libs can be downloaded here; and krb5-workstation can be downloaded here.The latest version of the Samba alpha code. (I chose not to get the CVS version.) As of this writing, build 17 of theSamba code was the latest and can be downloaded here.

If you’re not sure whether you have these libraries installed, you can use the RPM command to find out. Use the rpm -qa |grep openldap command to see whether you have the openldap-devel library and use rpm – qa | grep krb to check for theKerberos libraries. If you are missing any of these libraries, install them with the rpm – i libraryname command. The only library I was missing in my default Red Hat Linux 7.3 installation was the krb5-workstation library.

IP addressesThe IP addresses of the machines used in this article will be:Win2K - 10.109.10.133Linux - 10.109.10.132

Installing Samba 3.0The installation of Samba 3.0 is fairly straightforward. Follow these steps:

Expand the Samba 3.0 distribution with the command gunzip -cd samba-3.0-alpha17.tar.gz | tar xvf -.1.Switch to the source directory of the newly created directory with the command cd samba-3.0-alpha17/source.2.Run the configuration script, using the command /configure -prefix=/usr/local/samba to instruct the script to install Samba into /usr/local/samba.

3.

Make sure that the lines #define HAVE KRB5 1 and #define HAVE LDAP 1 are present in the include/config.h file.4.


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Compile the application with the make command.5.Install the application with the make install command.6.

Configuring KerberosYou need to configure some parameters to let the Kerberos process know how to handle the Active Directory server. Listing A shows the entire contents of my /etc/krb5.conf file. Make the appropriate modifications to your configuration, keeping inmind that case matters to Kerberos; SLOWE.COM and slowe.com do not match.

You have one more thing to check. While it might sound trivial, I cannot stress enough the importance of clocksynchronization between your Windows 2000 Server and your Linux server. If the time is off by more than five minutes, thetwo servers will be able to communicate, but no ticket information will work. This is easy to troubleshoot because you willbe greeted with kinit(v5): Clock skew too great while getting initial credentials when you test Kerberos.

To make sure that your connection is working, run the command /usr/kerberos/bin/kinit [email protected]. The Kerberos kinit command will test communication between your servers. The syntax is kinit user@REALM, where REALM is yourActive Directory domain name and must be uppercase. If you do not use all uppercase for the realm, you’ll receive thiserror:kinit(v5): Cannot find KDC for requested realm while getting initial credentials.

If communication is working, you’ll be prompted for the user password. When entered correctly, you’ll simply comeback to a bash prompt. If entered incorrectly, you’ll receive the error: kinit(v5): Preauthentication failed while getting initial credentials.

Join a Linux server to Active Directory with Samba 3.0 Page 2 of 2

Configuring SambaOnce installation is complete, you need to create a Samba configuration file. Samba uses the file/usr/local/samba/lib/smb.conf for its configuration parameters. To begin, I’ll set up a very minimal configuration file thatlooks like this:realm = SLOWE.COMads server = 10.109.10.133security = ADSencrypt passwords = yes

In this configuration file, the realm statement sets the Kerberos realm information. This is analogous to a domain name andhas to be all uppercase. The ads server statement is the resolvable name or the IP address of your Windows 2000 domaincontroller server. I chose to use the IP address to remove the possibility of any DNS issues. The security statement tells Samba to use Active Directory security. Finally, the encrypt passwords statement tells Samba that passwords need to beencrypted to work with the Kerberos protocol.

Putting it all togetherWith Samba and Kerberos both configured, you need to create a computer account in the Windows 2000 Active Directory.To do this, you must log in to the Windows 2000 server as a user, such as Administrator, with the rights to do this. To log into the server from your Linux machine, run the /usr/kerberos/bin/kinit [email protected] command, and you’llbe prompted for your Administrator password. To create the computer account, enter the /usr/local/samba/bin/net ads joincommand. If successful, you’ll get a message similar to: Joined ’LDAPS’ to realm ’SLOWE.COM.

To verify that the process worked, go to your Windows 2000 Server, open Active Directory Users And Computers, and lookat the entries. If the previous step worked, you’ll see an entry in this list with the name of your Linux server. My Linuxserver is named ldaps and now appears in the list.

Testing itOn your Linux machine, you should be able to connect to Windows shares using Samba’s smbclient without a password(thanks to Kerberos). To test this, enter the /usr/local/samba/bin/smbclient //w2k/c\$ -k command at the Linux prompt.

Since this is still an alpha version of Samba 3.0, you’ll see a number of errors scroll by, but this command still works.You’ll finally be connected to the C$ administrative share on your Windows 2000 Server.

On my system, this resulted in the output that appears in Listing B. I’ve also included a directory listing to show that it’sactually connected. Notice the line “Doing kerberos session setup.” Samba has come a long way.

And now, the problems!Being alpha code, Samba 3.0 still has bugs, which is to be expected. Among the errors I received were various compilationwarnings, as well as errors when utilities were run. These bugs are due to the drastic changes made in transition from Samba2.x to 3.0 and will all eventually disappear as Samba 3.0 reaches final release. In addition to the standard bug fare, I’m notable to make Kerberos connections to the Samba server, but as you could see from the examples, the server is more thancapable of initiating them. Making the connection from Windows to Linux is one of the major focuses of the Sambadevelopment team, so rest assured that this feature will be in place at some point between the alpha release and the finalrelease.

Stay tuned for more


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One interesting quirk in my trial install was that the Linux server was able to connect to the Win2K server and access anduse the available shares, but the Win2K server was unable to access and use the Linux shared directories. I contacted theSamba team to make sure that they were aware of the inability of Samba 3.0 to allow two-way use of shared directories.

As Samba 3.0 develops into full-release status, they’re confident this problem will be resolved. The Samba teams alsoinformed me that they’ll add the first-ever upgrade wizards to help users and administrators make the migration from theold Samba 2.x smb.conf files to the newer Samba 3.0 smb.conf files. You can be sure that TechRepublic will be coveringthese wizards as they arrive.

If you are interested in staying on top of the development process of Samba 3.0, the best place to keep apprised of news isone of the many Samba mailing lists. For more information on where the Samba 3.0 development is heading, visit the Samba road map.

Editorial disclaimer: The authors and editors have taken care in preparation of the content contained herein but make noexpressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed forany damages. Always have a verified backup before making any changes.

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Manual - Samba Active-directory