Samba 3.3.0 Final

Samba - Набор программ, реализующих протокол SMB в среде Unix, что позволяет предоставлять файлы и принтеры клиентам Windows, NT, OS/2 и DOS.

Samba is an Open Source/Free Software suite that has, since 1992, provided file and print services to all manner of SMB/CIFS clients, including the numerous versions of Microsoft Windows operating systems. Samba is freely available under the GNU General Public License.

What is Samba?

As the front page at samba.org says, "Samba is an Open Source/Free Software suite that provides seamless file and print services to SMB/CIFS clients." Samba is freely available, unlike other SMB/CIFS implementations, and allows for interoperability between Linux/Unix servers and Windows-based clients.

Samba-3 by Example explains further, saying:

Samba is software that can be run on a platform other than Microsoft Windows, for example, UNIX, Linux, IBM System 390, OpenVMS, and other operating systems. Samba uses the TCP/IP protocol that is installed on the host server. When correctly configured, it allows that host to interact with a Microsoft Windows client or server as if it is a Windows file and print server.

Samba is a software package that gives network administrators flexibility and freedom in terms of setup, configuration, and choice of systems and equipment. Because of all that it offers, Samba has grown in popularity, and continues to do so, every year since its release in 1992.

What Samba Does

Samba consists of two key programs, plus a bunch of other stuff that we'll get to later. The two key programs are smbd and nmbd. Their job is to implement the four basic modern-day CIFS services, which are:
• File & print services
• Authentication and Authorization
• Name resolution
• Service announcement (browsing)

File and print services are, of course, the cornerstone of the CIFS suite. These are provided by smbd, the SMB Daemon. Smbd also handles "share mode" and "user mode" authentication and authorization. That is, you can protect shared file and print services by requiring passwords. In share mode, the simplest and least recommended scheme, a password can be assigned to a shared directory or printer (simply called a "share"). This single password is then given to everyone who is allowed to use the share. With user mode authentication, each user has their own username and password and the System Administrator can grant or deny access on an individual basis.

The Windows NT Domain system provides a further level of authentication refinement for CIFS. The basic idea is that a user should only have to log in once to have access to all of the authorized services on the network. The NT Domain system handles this with an authentication server, called a Domain Controller. An NT Domain (which should not be confused with a Domain Name System (DNS) Domain) is basically a group of machines which share the same Domain Controller.

The NT Domain system deserves special mention because, until the release of Samba version 2, only Microsoft owned code to implement the NT Domain authentication protocols. With version 2, Samba introduced the first non-Microsoft-derived NT Domain authentication code. The eventual goal, of course, it to completely mimic a Windows NT Domain Controller.

The other two CIFS pieces, name resolution and browsing, are handled by nmbd. These two services basically involve the management and distribution of lists of NetBIOS names.

Name resolution takes two forms: broadcast and point-to-point. A machine may use either or both of these methods, depending upon its configuration. Broadcast resolution is the closest to the original NetBIOS mechanism. Basically, a client looking for a service named Trillian will call out "Yo! Trillian! Where are you?", and wait for the machine with that name to answer with an IP address. This can generate a bit of broadcast traffic (a lot of shouting in the streets), but it is restricted to the local LAN so it doesn't cause too much trouble.

The other type of name resolution involves the use of an NBNS (NetBIOS Name Service) server. (Microsoft called their NBNS implementation WINS, for Windows Internet Name Service, and that acronym is more commonly used today.) The NBNS works something like the wall of an old fashioned telephone booth. (Remember those?) Machines can leave their name and number (IP address) for others to see.

Hi, I'm node Voomba. Call me for a good time! 192.168.100.101

It works like this: The clients send their NetBIOS names & IP addresses to the NBNS server, which keeps the information in a simple database. When a client wants to talk to another client, it sends the other client's name to the NBNS server. If the name is on the list, the NBNS hands back an IP address. You've got the name, look up the number.

Clients on different subnets can all share the same NBNS server so, unlike broadcast, the point-to-point mechanism is not limited to the local LAN. In many ways the NBNS is similar to the DNS, but the NBNS name list is almost completely dynamic and there are few controls to ensure that only authorized clients can register names. Conflicts can, and do, occur fairly easily.

Finally, there's browsing. This is a whole 'nother kettle of worms, but Samba's nmbd handles it anyway. This is not the web browsing we know and love, but a browsable list of services (file and print shares) offered by the computers on a network.

On a LAN, the participating computers hold an election to decide which of them will become the Local Master Browser (LMB). The "winner" then identifies itself by claiming a special NetBIOS name (in addition to any other names it may have). The LMBs job is to keep a list of available services, and it is this list that appears when you click on the Windows "Network Neighborhood" icon.

In addition to LMBs, there are Domain Master Browsers (DMBs). DMBs coordinate browse lists across NT Domains, even on routed networks. Using the NBNS, an LMB will locate its DMB to exchange and combine browse lists. Thus, the browse list is propagated to all hosts in the NT Domain. Unfortunately, the synchronization times are spread apart a bit. It can take more than an hour for a change on a remote subnet to appear in the Network Neighborhood.

SMB Filesystems for Linux

One of the cool things that you can do with a Windows box is use an SMB file share as if it were a hard disk on your own machine. The N: drive can look, smell, feel, and act like your own disk space, but it's really disk space on some other computer somewhere else on the network.

Linux systems can do this too, using the smbfs filesystem. Built from Samba code, smbfs (which stands for SMB Filesystem) allows Linux to map a remote SMB share into its directory structure. So, for example, the /mnt/zarquon directory might actually be an SMB share, yet you can read, write, edit, delete, and copy the files in that directory just as you would local files.

The smbfs is nifty, but it only works with Linux. In fact, it's not even part of the Samba suite. It is distributed with Samba as a courtesy and convenience. A more general solution is the new smbsh (SMB shell, which is still under development at the time of this writing). This is a cool gadget. It is run like a Unix shell, but it does some funky fiddling with calls to Unix libraries. By intercepting these calls, smbsh can make it look as though SMB shares are mounted. All of the read, write, etc. operations are available to the smbsh user. Another feature of smbsh is that it works on a per-user, per shell basis, while mounting a filesystem is a system-wide operation. This allows for much finer-grained access controls.

Setup and Management

Samba is configured using the smb.conf file. This is a simple text file designed to look a lot like those *.ini files used in Windows. The goal, of course, is to give network administrators familiar with Windows something comfortable to play with. Over time, though, the number of things that can be configured in Samba has grown, and the percentage of Network Admins willing to edit a Windows *.ini file has shrunk. For some people, that makes managing the smb.conf file a bit daunting.

Still, learning the ins and outs of smb.conf is a worth-while penance. Each of the smb.conf variables has a purpose, and a lot of fine tuning can be accomplished. The file structure contents are fully documented, so as to give administrators a running head start, and smb.conf can be manipulated using swat, which at least makes it nicer to look at.

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