Chapter 8: Linux Servers on the LAN
What Is Linux
• Linux is a UNIX-like open source operating system.
• Open source software is software in which the source code is
available.
• Linux actually refers to the kernel of the operating system. The
kernel is the operating system’s centerpiece.
• Other components of the operating system have their own names
such as X-Windows, Apache and Sendmail. A collection of
components bundled with Linux is known as a distribution.
What Is Linux
• Some versions of Linux are freely available for download off the
Internet.
• Linux use on the LAN is growing as it can perform many of the
functions that a Windows server can, without the associated
licensing costs.
• A drawback of Linux is that often more complicated to configure
than Windows is. What an organization saves in licensing costs,
it might spend on personnel to manage the Linux systems.
• Linux computers generally co-exist on the LAN with Windows
and Novell servers and replace older UNIX servers.
Distribution
A specific collection of Linux and programs that run on Linux is
known as a distribution. Anyone can create their own Linux
distribution with enough time and effort.
Several popular distributions are:
RedHat Enterprise Linux. Subscription-based, includes support. Targeted
at large corporate LANs. Aims to replace traditional UNIX vendors.
RedHat Fedora. Development branch of Redhat Enterprise Linux used to
test new software. Freely available, but less stable than the Enterprise
version.
Debian. Freely available and highly stable Linux distribution. Does not
include the very newest versions of software, only those versions that have
proven stable.
Novell SUSE. Novell’s Linux distribution. Integrated closely with the
Novell network operating system. Subscription based.
Mandrake. Popular beginner distribution of Linux. Freely available.
Source and Packages
• Source code is the program language text, usually written in the
language C, in text file format.
• A binary file is the result of compiled source code.
• A dependency is another component of the operating system that
must already be installed before the new program will function.
Some, but not all, software source code will attempt a
dependency check prior to installation.
• It can be difficult to uninstall software that you have installed from
the source code.
Source and Packages
• Packages are pre-configured binary files for specific distributions.
Package managers keep track of which packages have been
installed.
• When you install software using a package manager, a
dependency check will occur. If the required packages are not
present on the computer, the installation will abort.
• Some distributions offer a tracking service that will notify you
when new versions of installed packages are available.
Command Line Administration
• Because of Linux’s UNIX roots, the primary method by which it
is administered is the command line.
• Commands are often followed by switches, which allow
different options to be used.
• All administrative tasks can be performed from the command
line, either by issuing specific commands or editing text-based
configuration files.
Command Line Administration
• Can be accessed without the need to run the X-Windows graphical
environment, which reduces CPU overhead. Can be accessed from
GUI as well.
• Can be accessed remotely via encrypted SSH session. Extremely
low bandwidth means that servers can be administered over the
slowest modem connections.
• Command line administration can offer a more precise control of
the operating system than GUI-based administration. The down
side is that it requires precise syntax. Use an incorrect command
switch and you may get a very unintended result.
• Scripts are written in languages like Perl to automate
administration tasks.
X-Windows
• Most Linux services and applications do have GUI-based
configuration utilities as well.
• Generally though, the GUI-based configuration utilities lack all
of the options of command line utilities.
• X-Windows can be run remotely, so that you can view graphic
utilities running on remote computers.
• There are some security issues with
running X-Windows remotely, so it
is often better to use a remote desktop
product such as VNC to remotely
connect to a Linux GUI.
Webmin
• Webmin is a Web-based remote administration tool that can be
run via Web browser.
• Offers the ability to configure most Linux services.
• Some tools are better than the Linux GUI versions. Command line
still offers the best functionality.
Single Sign On
• In Windows, you log on and authenticate against a domain
controller. This means that you can use the same logon
account on any computer for the domain.
• Unlike Windows, Linux computers are designed primarily to
be stand alone. To have a single sign on solution means that
you must configure a NIS/NIS+ server.
• A NIS+ (Network Information Service plus) server keeps a
copy of the account database each NIS+ client computer.
• NIS+ is highly complicated to configure compared to Active
Directory.
File and Print Sharing
• Linux files can be shared in several ways. The first is via NFS
and the second is via SAMBA.
• NFS is primarily used to share files with other Linux clients.
Linux clients can mount an NFS share as a directory within their
local file system.
• SAMBA is primarily used to share files
and printers with Windows clients.
• Windows Servers can be configured to
print directly to Linux printers. You create
a shared printer on Windows Server
2003 which points to the Linux printer.
Windows clients then direct print jobs
through the Windows Server 2003
computer.
SAMBA
• Samba allows Windows clients to access resources on Linux
computers.
• When a request is made for a resource, the Linux computer uses a
Windows server to authenticate the user.
• Shared files appear to clients the same
as they would if hosted on a Windows
Server.
Apache Web Server
• The most popular Web server in the world.
• Has been in use since 1995.
• Configuration is performed by editing httpd.conf file.
• Supports multiple Web sites, differentiated by FQDN, IP and TCP
port.
• Can restrict access on basis of IP address, domain name, username,
and password.
• Apache modules can be added to support different features, such
as scripting languages and encryption.
• Modules are add-on components that enhance Apache’s
functionality.
• Apache modules can be added to support restrictions via digital
certificate.
E-Mail Servers
• Almost all Linux distributions come with a built in e-mail
server.
• The most popular is Sendmail. Sendmail supports POP3,
IMAP4, and SMTP.
• Sendmail is configured by editing sendmail.cf. It has a
reputation as being very difficult to fine tune.
• Another popular mail server is Postfix. Postfix was designed
to be a simpler to administer alternative to Sendmail.
Summary
• A Linux distribution is a collection of utilities bundled around the
Linux kernel.
• The most complete administrative interface for Linux is the
command line. GUI and Web based administration are possible,
but don’t always offer the same number of configuration options.
• When sharing files to UNIX or Linux clients, use NFS. When
sharing files to Windows clients, use SAMBA.
• SAMBA allows a Linux computer to use a Windows Server to
authenticate Windows clients.
• Apache Web server is the most deployed Web server in the world.
Add-in modules extend Apache’s functionality.
• Sendmail and Postfix are popular Linux mail servers. Sendmail is
more fully featured, but more complex to configure.
Discussion Questions
 Which mail server was designed as a simpler to administer
alternative to sendmail?
 Describe the difference between source and packages?
 What service should you install to provide single sign on
capabilities to Linux?
 What do Apache modules do?
 What are the disadvantages to command-line
administration?
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