Introducing Samba

The whole point of networking is to allow computers to easily share information. Sharing information with other Linux boxes, or any UNIX host, is easy—tools such as FTP and NFS are readily available and frequently set up easily “out of the box”. Unfortunately, even the most die-hard Linux fanatic has to admit the operating system most of the PCs in the world are running is one of the various types of Windows. Unless you use your Linux box in a particularly isolated environment, you will almost certainly need to exchange information with machines running Windows. Assuming you're not planning on moving all of your files using floppy disks, the tool you need is Samba.

Samba is a suite of programs that gives your Linux box the ability to speak SMB (Server Message Block). SMB is the protocol used to implement file sharing and printer services between computers running OS/2, Windows NT, Windows 95 and Windows for Workgroups. The protocol is analogous to a combination of NFS (Network File System), lpd (the standard UNIX printer server) and a distributed authentication framework such as NIS or Kerberos. If you are familiar with Netatalk, Samba does for Windows what Netatalk does for the Macintosh. While running the Samba server programs, your Linux box appears in the “Network Neighborhood” as if it were just another Windows machine. Users of Windows machines can “log into” your Linux server and, depending on the rights they are granted, copy files to and from parts of the UNIX file system, submit print jobs and even send you WinPopup messages. If you use your Linux box in an environment that consists almost completely of Windows NT and Windows 95 machines, Samba is an invaluable tool.

Figure 1. The Network Neighborhood, Showing the Samba Server

Samba also has the ability to do things that normally require the Windows NT Server to act as a WINS server and process “network logons” from Windows 95 machines. A PAM module derived from Samba code allows you to authenticate UNIX logins using a Windows NT Server. A current Samba project seeks to reverse engineer the proprietary Windows NT domain-controller protocol and re-implement it as a component of Samba. This code, while still very experimental, can already successfully process a logon request from a Windows NT Workstation computer. It shouldn't be long before it will act as a full-fledged Primary Domain Controller (PDC), storing user account information and establishing trust relationships with other NT domains. Best of all, Samba is freely available under the GNU public license, just as Linux is. In many environments the Windows NT Server is required only to provide file services, printer spools and access control to a collection of Windows 95 machines. The combination of Linux and Samba provides a powerful low-cost alternative to the typical Microsoft solution.

Understanding how Samba does its job is easier if you know a little about how Windows networking works. Windows clients use file and printer resources on a server by transmitting “Server Message Block” over a NetBIOS session. NetBIOS was originally developed by IBM to define a networking interface for software running on MS-DOS or PC-DOS. It defines a set of networking services and the software interface for accessing those services, but does not specify the actual protocol used to move bits on the network.

Three major flavors of NetBIOS have emerged since it was first implemented, each differing in the transport protocol used. The original implementation was referred to as NetBEUI (NetBIOS Extended User Interface), which is a low-overhead transport protocol designed for single segment networks. NetBIOS over IPX, the protocol used by Novell, is also popular. Samba uses NetBIOS over TCP/IP, which has multiple advantages.

TCP/IP is already implemented on every operating system worth its salt, so it has been relatively easy to port Samba to virtually every flavor of UNIX, as well as OS/2, VMS, AmigaOS, Apple's Rhapsody (which is really NextSTEP) and (amazingly) mainframe operating systems like CMS. Samba is also used in embedded systems, such as stand-alone printer servers and Whistle's InterJet Internet appliance. Using TCP/IP also means that Samba fits in nicely on large TCP/IP networks, such as the Internet. Recognizing these advantages, Microsoft has renamed the combination of SMB and NetBIOS over TCP/IP the Common Internet Filesystem (CIFS). Microsoft is currently working to have CIFS accepted as an Internet standard for file transfer.

Figure 2. SMB's Network View compared to OSI Networking Reference Model