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					Linux Web Servers

Since the framework for the Internet was developed by many of the same people who developed Unix,
it isn't surprising that Unix and Linux platforms enjoy the broadest choice of available Web servers.

As with most things in the Unix world, this same range of Web servers is available for Linux. The majority
of Linux Web servers are free. The best-known Linux Web servers are these:

    •   Nginx

    •   NCSA httpd

    •   Apache

    •   AOLserver

    •   Boa

    •   WN

    •   W3C/Cern

In addition to these free servers, there are several commercial alternatives available for Linux, including
the following:

    •   FastTrack/iPlanet

    •   Java Web Server

    •   Stronghold

    •   Zeus

Apache

By some counts, Apache is the most widely used Web server software. Standing for "A Patchy Server",
Apache grew out of efforts to patch NCSA httpd, one of the original Web servers, to fix some problems
and add functionality.

Since then, Apache has emerged as the non-commercial server of choice for Unix systems. More
recently, it has been ported to Windows and can be used as a Web server on Windows NT/2000
systems.

Apache offers numerous features that make it attractive for Unix/Linux system administrators. Besides
using a configuration based on the original NCSA httpd configuration files, Apache is available in full
source code and is collectively developed, like many other popular applications for the Linux
environment.
Apache offers its own API, which can be used as an alternative to CGI (which is also supported by
Apache). In addition, the API can be used to produce plug-in modules that serve numerous purposes.
Among the available modules are the following:

    •   Alternative authentication systems, including authentication from NIS authentication servers or
        from LDAP (Lightweight Directory Access Protocol) databases.

    •   Server-side scripting environments that serve the same function as Microsoft Active Server
        Pages or Netscape LiveWire, including PHP/FI and HeiTML.

    •   Modules designed to improve the performance of traditional CGI. For instance, the FastCGI
        module uses shortcuts to minimized the time it takes to execute a CGI program and return the
        results. The Perl module allows Perl scripts to run in a single process and to be compiled on first
        execution only, making Perl-based CGI performs almost as fast as compiled CGI programs and
        some API-based Web applications.

The original source code for the latest version of Apache is available from http.apache.org, along with
precompiled binaries for many different systems including Linux. Apache is included as the default Web
server installed with Red Hat Linux 7.1

NCSA httpd

NCSA httpd is one of the two original Web servers (along with the Cern Web server) upon which the
Web was first built. NCSA httpd comes out of the National Center for Supercomputer Applications at the
University of Illinois at Urbana-Champaign, which is also the home of Mosaic, the original graphical Web
browser that launched the Web onto the road to widespread popularity.

NCSA httpd offers a core set of functions designed to meet the needs of all but the most demanding of
Web sites. These features include built-in support for multiple hosts, Basic and Digest authentication,
directory-level access controls, server-side includes, and full CGI support.

While NCSA httpd is no longer under active development, it does provide the background for the current
structure of Apache. The original source code and precompiled binaries for NCSA httpd are available
from hoohoo.ncsa.uiuc.edu.

W3C/Jigsaw

The Jigsaw Web server is the Java-based successor to Cern, which was one of the first Web servers
powering the Internet. As a completely Java-based server, it is designed to run on any operating system
that supports this language, including Unix/Linux and Microsoft Windows.

Jigsaw is set up with several different types of Java objects, including:

       Resources. What is seen on the Web page. This includes static objects such as text or image files,
and dynamic objects such as scripts.
        Frames. What actually handles the resource. A frame includes all of the necessary information
to serve a specific resource; for example, an HTTPframe object serves an HTTP resource.

        Filters. A way to dynamically modify a resource. For example, if a Web site doesn't see that a
user has logged in, it can "filter" in a login page.

        Indexer. The way to classify resources. The two main indexes are directories (to group files) and
extensions (for common files such as TXT or INI).

WN

This chapter's survey of free servers is now moving toward less-commonly used servers. still, these niche
market servers help you to see the diversity possible in Web server technology and features.

WN is another freely available server with unique features that set it apart from other Web servers. For
instance, WN allows full-text searching of what the developer refers to as a logical HTML document: a
document that consists of multiple linked files. In addition, users can search files on the server and easily
obtain matching documents. Users can also download a single logical document made up of multiple
linked documents, making it easy for them to print files that are structured as a series of small
documents.

Another unique feature of the WN server is its ability to serve up conditional documents. that is, it is
possible to create a single document with definitions that cause the correct version to be sent to a client
on the basis of such variable as the IP address of the client or the browser version of the client.

The security model of the WN server as well as its relatively small size also set it apart from the likes of
Apache and the NCSA httpd Web server. In the latter servers, the default action is to server a file unless
permission is specifically denied. With WN, no file is served unless permission is specifically granted for
the file. This potentially makes the server more secure and provides finer-grained control over access to
files. You can get a copy of WN at hopf.math.nwu.edu.



Boa

The last free Web server is the Boa server. Boa is included here to show that servers can be small,
simple, and basic and still server a useful role. Boa offers very basic functionality and less fine-grained
access control than Apache or WN.

But boa is designed in a way that makes it potentially faster than almost any other available Web server
for Linux. In fact, the creators of Boa claim that the server is significantly faster than Apache, although
more real-world testing on large Web sites is needed to prove this claim.

Boa achieves this performance gain through a single-tasking design. Where traditional Web servers
create multiple process to listen for requests and then create a process to handle each request, the Boa
server runs as a single process and handles all the processing and juggling of multiple requests internally
rather than allowing the operating system's multitasking mechanism to do so. Boa spawns a child
process only when a CGI request is made. You can learn more about Boa at www.boa.org




Stronghold

Stronghold is probably one of the best-known commercial Web servers for Linux. Stronghold is a
commercially available version of Apache that offers an extremely secure and fully supported software
package.

Stronghold provides all the tools you need to set up a secure server, including Certificate Authority tools.
With a Certificate Authority you can, if necessary, issue digital certificates approved by third-party
certificate authority such as VeriSign. Other Stronghold security features include support for hardware
cryptographical acceleration, as well as 128-bit data encryption for additional security.

In addition, since Stronghold comes with full source code, you can use it for everything you use Apache
for, including compiling in Apache modules and writing your own modules.

				
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