by July 7, 2001 0 comments



The
first time I saw an application called “Samba” on Sunsite many
years back, I wondered what kind of software would be named after a
Brazilian dance. Since then, Samba (who’s name, according to Andrew
Tridgill, was derived from the letters “s”, “m”, and
“b”) has become an integral part of any network I’ve ever set
up. Let’s face it, even the biggest Linux geeks among us, at times will
accept that there are a lot of users who use an operating system called
Windows, and the best way to introduce them to Linux is to do so without
them knowing it, in roles such as file and print, and mail and Web servers.

History of Samba-David
tracking Goliath

For the
uninitiated, Samba is a suite of programs designed to allow Linux machines
to participate and even manage, Windows domains and workgroups. It’s an
incredibly complex piece of software, and yet, surprisingly easy to set up
and configure. Its complexity is a result of not only the extremely complex
SMB protocol itself, but also the fact that almost the entire specification
has been reverse engineered by a few of the original and incomparable
hackers such as Andrew Tridgill and Jeremy Allison (to name just two-there
are many more to whom credit is due).

It’s a task that Microsoft
has succeeded in making more difficult every step of the way, most recently
by “opening” the specifications to their proprietary version of
the open Kerberos protocol, under a cleverly worded license which
effectively prevents the Samba team from using it in their code. Despite the
difficulty and the fact that the Samba team must not only reverse engineer
the protocol, but also reproduce bugs in Microsoft’s implementation of it,
Samba provides one of the most stable and usable network file systems
around. In all my years of running Samba, I’ve never lost data or network
uptime to Samba.

Let’s get into Samba
itself. Most users who use Linux in a networked environment will have set up
basic Samba configurations at one time or the other, usually providing
public shared directories or home directories to Windows users. I won’t
recapitulate the basic setup here. Instead I’ll talk about a few more
advanced concepts, such as adding Win NT machines to a Samba domain, and the
converse, that is adding a Samba machine to a Win NT domain, some
little-understood config options, and future development (it’s steaming
along in the development trees right now). If you want a basic introduction
to Samba, you can view the article “Setting up a Linux office
server”, Page 27, PC Quest, May 1998, also available on this
month’s CD-ROM.

Interacting with NT

You might ask
yourself why adding Win NT or 2000 machines should be any different from
adding Win 9x machines. However, there are significant differences in the
SMB implementations between versions of Microsoft’s own operating systems.
Even the password algorithms used by the two operating systems are
different. Win 9x machines don’t actually participate in a Win NT domain
the way NT does. The domain controller in this case is used purely for
authentication.

If you want to use Win 2000
machines in a Samba domain, you’ll need to upgrade to Samba 2.0.7 (Zoot
ships with 2.0.6, so you’ll have to download the updated RPMs). There are
a few subtle changes in 2000, most of which have been addressed in this
release. There are a few outstanding bugs though, but no show-stoppers. Note
that Win 2000 is currently only supported in the backwards compatibility
(with NT PDC) mode, and not in its native domain controller mode.

Adding a Samba server to a
Win NT domain

To get a
Samba server to join a Win NT domain, you must first create a machine
account for the server in the PDC’s SAM (Security Accounting Manager)
database. You can do this using the “Server Manager for Domains”
utility on the PDC. The machine account is created using the netbios name of
the Samba server, which is usually, but not necessarily, its host name.

Once you’ve created the
machine account, you need to configure the smb.conf file. Apart from the
standard configuration, you need to make the following changes:

workgroup = NTDOM (Assume
that the domain name is NTDOM)

security = domain

password server = NTDOMPDC
NTDOMBDC1 NTDOMBDC2

where NTDOMPDC is the name of
the domain controller, NTDOMBDC[1,2] are the names of the backup domain
controllers, and SAMBA is the netbios name of the samba server.

Now, before restarting the
smbd daemons, give the command

# smbpasswd -j NTDOM -r
NTDOMPDC

This command will create a
file called SAMBA.NTDOM.mac in your /etc/ directory, containing the machine
account password for the Samba server.

Assuming all goes well, you
should get a message saying

smbpasswd :
Joined domain NTDOM

Adding an NT server to a

To add
a Win NT machine to a Samba domain, you need to create a user entry
for it in the password file. This is the Samba equivalent of creating a
machine account in the SAM database. The username should be the name of the
machine, appended with a “$”. Set no password, and set the home
directory to /dev/null, and shell to /bin/false. (You might have to escape
the “$” on the command line with a “\”, if required)

# useradd ntserver$ -s /bin/false -d /dev/null

The next step
is to go to the NT machine, and set the domain name to SAMBADOM (where
SAMBADOM is the domain name). Take care not to check the “create a
machine account” check box. This feature is not yet supported. You
should get a message saying “Welcome
to the SAMBADOM domain”.

Understanding server
configuration options

If you look
at the man page for the smb.conf file (man 5 smb.conf), you’ll find a
number of configuration options that you can use to tweak the performance
and customize your Samba configuration further. Due to the lack of space
here, I’ll take a look at only a few configuration options.

One of the more misunderstood
configuration parameters is the “security=” option. We’ll take a
brief look at what the various options mean.

security=share

This is the conventional, and
most brain-dead option available. Shares exported will be available to any
machine in the workgroup without further authentication. This is commonly
used for machines sharing public shares, CD-ROMs, etc. Use this only when
you have no security concerns whatsoever.

security=server

Server level security is used
when you want the Samba server to authenticate users against another Samba
or Windows NT machine acting as a domain controller. This is a good idea
when you have a number of machines on your network, with users needing to
logon to the domain to be able to access the shares. In this case, you’ll
have to configure the “password server” parameter to specify the
names of the authentication servers (normally the PDC and BDC).

security=user

In this scheme, the Samba
server actually acts as a workgroup controller, authenticating Windows NT
and Win 9x clients. A separate user list has to be maintained, and users are
added using the “smbpasswd” command. In this case, the Samba
server maintains its equivalent of an NT SAM database.

security=domain

Domain level security is used
in the case described above, when adding a Samba server to a Win NT domain.
Here too, you’ll need to specify the “password server”
parameter. So how’s this different to the “security=server”
configuration? For one, when using server level security, the Samba server
will open and maintain a network connection to the domain controller during
the entire session. This can be a significant drain on network resources. In
domain level security, a connection is established for exchanging
authentication information only.

There are some new parameters
in Samba 2.0.7 as well. Most of these deal with the new utmp and wtmp
support (experimental, I might add) included in this version. This will
enable users logged in via Samba to be seen using the “who”
command, and all login information to be recorded in the system logs, not
just the samba logs. You’ll need to specifically compile support for this
using the
“-with-utmp” flag to “configure”.

Samba development

Samba
development is progressing at an extremely hectic pace. There are currently
four trees under active development (For those new to the open source style
of development, a “tree” consists of all the latest source code of
the software, to which developers have access. Developers “check
in” portions of code they are working on, and then “check
out” the new code for others to test and debug when they have
finished).

There is the SAMBA_STABLE
branch, which has the regularly released “stable code”, for you
and me to use. New features are not introduced into this tree until they’ve
been thoroughly tested in unstable versions. The stable Samba tree at this
time doesn’t have the ability to be a domain controller for Win NT
machines.

The second branch is the
SAMBA_TNG branch, which is where the main thrust of development is going on
at the moment. TNG stands for “The Next Generation”, and includes
all the “cool code”, such as domain controller for NT and Win 2000
machines, support for NT- specific administrative tools such as “User
Manager for Domains”, and trust relationships, etc.

The Third branch is the
SAMBA_HEAD branch, which is the successor to the current 2.0.x series. It
contains improved file and print sharing services and NT file permissions
support. However, it contains no NT PDC support.

The last and final branch is
the HEAD_WITH_TNG branch, which is exactly what you might imagine from its
name.

The most interesting of these
branches is the SAMBA_TNG branch, which focuses on Win NT PDC controller
code. It currently suffers from poor file serving ability, but code mergers
with the SAMBA_HEAD branch will take care of this problem in the near
future.

So if you’re a hacker, or
kid with a network and time to spare, download the TNG or HEAD branch and
play with the code. Finding bugs or contributing documentation is the
easiest way to help the development effort, if you’re not a developer
yourself.

Babu Kalakrishnan, a Director at Sankya System & Objects, Bangalore www://www.sankya.com

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