Apache Web Server

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The Apache Web server is a full-featured free HTTP (Web) server developed and maintained by the Apache Server Project. The aim of the project is to provide a reliable, efficient, and easily extensible Web server, with free Open Source code made available under its own Apache Software License. The server software includes the server daemon, configuration files, management tools, and documentation. The Apache Server Project is maintained by a core group of volunteer programmers and supported by a great many contributors worldwide. The Apache Server Project is one of several projects currently supported by the Apache Software Foundation (formerly known as the Apache Group). This nonprofit organization provides financial, legal, and organizational support for various Apache Open Source software projects, including the Apache HTTPD Server, Java Apache, Jakarta, and XML- Apache. The Web site for the Apache Software Foundation is at www.apache.org. Table 22-1 lists various Apache-related Web sites.

Apache was originally based on the NCSA Web server developed at the National Center for Supercomputing Applications, University of Illinois, Urbana-Champaign. Apache has since emerged as a server in its own right and has become one of the most popular Web servers in use. Although originally developed for Linux and Unix systems, Apache has become a cross-platform application with Windows and OS/2 versions. Apache provides online support and documentation for its Web server at httpd.apache.org. An HTML-based manual is also provided with the server installation. You can use the Apache Configuration Tool to help configure your Apache server easily. It operates on any X Window System window manager, including GNOME and KDE. In addition, you can use the Comanche configuration tool. Webmin and Linuxconf also provide Apache configuration support.

Java: Apache Jakarta Project

The Apache Jarkarta Project supports the development of Open Source Java software; its Web site is located at jakarta.apache.org. Currently, the Jakarta supports numerous projects, including libraries, tools, frameworks, engines, and server applications. Tomcat is an Open Source implementation of the Java Servlet and JavaServer Pages specifications. Tomcat is designed for use in Apache servers. JMeter is a Java desktop tool to test performance of server resources, such as servlets and CGI scripts. Velocity is a template engine that provides easy access to Java objects. Watchdog is a tool that checks the compatibility of serverlet containers. Struts, Cactus, and Tapestry are Java frameworks, established methods for developing Java Web applications.

Linux Apache Installations

Your Linux distribution will normally provide you with the option of installing the Apache Web server during your initial installation of your Linux system. All the necessary directories and configuration files are automatically generated for you. Then, whenever you run Linux, your system is already a fully functional Web site. Every time you start your system, the Web server will also start up, running continuously. On most distributions, the directory reserved for your Web site data files is /var/www/html. Place your Web pages in this directory or in any subdirectories. Your system is already configured to operate as a Web server. All you need to do is perform any needed network server configurations, and then designate the files and directories open to remote users. You needn't do anything else. Once your Web site is connected to a network, remote users can access it.

Table 22-1: Apache-Related Web Sites

Web Site	Description
www.apache.org	Apache Software Foundation
httpd.apache.org	Apache HTTP Server Project
java.apache.org	Java Apache Project
jakarta.apache.org	Jakarta Apache Project
gui.apache.org	Apache GUI Project
www.comanche.org	Comanche (Configuration Manager for Apache)
www.apache-ssl.org	Apache-SSL server
www.openssl.org	OpenSSL project (Secure Socket Layer)
www.modssl.org	The SSL module (mod_ssl) project to add SSL encryption to an Apache Web server
www.php.net	PHP Hypertext PreProcessor, embedded Web page programming language

The Web server normally sets up your Web site in the /var/www directory. It also sets up several directories for managing the site. The /var/www/cgi-bin directory holds the CGI scripts, and /var/www/html/manual holds the Apache manual in HTML format. You can use your browser to examine it. Your Web pages are to be placed in the /var/www/html directory. Place your Web site home page there. Your configuration files are located in a different directory, /etc/httpd/conf. Table 22-2 lists the various Apache Web server directories and configuration files.

To upgrade your Apache server, either use the Red Hat upgrade tool (RHN) or look for recent Apache update files at the Red Hat FTP site. For binary versions for an RPM supported distribution Red Hat, you can download RPM packages containing the latest version of the Apache Web server, specially configured for your Red Hat Linux distribution. For Red Hat, the RPM packages for the Apache Web server are now named httpd instead of apache.

Alternatively, you can download the source code version for the latest Apache Web server directly from Apache and compile it on your system. You must decompress the file and extract the archive. Many of the same directories are created, with added ones for the source code. The server package includes installation instructions for creating your server directories and compiling your software. Make sure the configuration files are set up and installed.

Note 

If you are installing Apache from the source code, notice that versions of the configuration files ending with the extension .conf-dist are provided. You have to make copies of these configuration files with the same prefix, but only with the extension .conf to set up a default configuration. The Web server reads configuration information only from files with a .conf extension.

Table 22-2: Apache Web Server Files and Directories (RPM Installation)

Web Site Directories	Description
/var/www	Directory for Apache Web site files on Red Hat systems
/var/www/html	Web site Web files
/var/www/cgi-bin	CGI program files
/var/www/html/manual	Apache Web server manual
Configuration Files
.htaccess	Directory-based configuration files; an .htaccess file holds directives to control access to files within the directory in which it is located
/etc/httpd/conf	Directory for Apache Web server configuration files
/etc/httpd/conf/httpd.conf	Apache Web server configuration file
/etc/httpd/conf/conf,d	Directory holding module configuration files like ssl.conf for SSL and php.conf for PHP
Startup Scripts
/etc/rc.d/init.d/httpd	Startup script for Web server daemon
Application Files	Description
/usr/sbin	Location of the Apache Web server program file and utilities
/usr/share/doc/	Apache Web server documentation
/var/log/http	Location of Apache log files

Apache Web Server 2.0

Red Hat now uses Apache version 2.0 and up, which replaces the older 1.3. Apache 2.0 (see Red Hat Linux Reference Guide for conversion instructions). Most directives and features for Apache 1.3 still work on Apache 2.0. However, Apache 2.0 has introduced a new architecture that uses Multi-Processing Modules (MPM), which are designed to customize Apache to different operating systems. A Linux system would use the threaded MPM, whereas Windows would use the mpm_winnt MPM. To maintain compatibility with Apache 1.3 configurations, you would use the prefork MPM.

Apache 2.0 has adopted a much more modular architecture than 1.3. Many directives that once resided in the Apache core are now placed in respective modules and MPMs. With this modular design, several directives have been dropped, such as ServerType. Such directives deprecated in Apache 2.0 are noted in Table 22-3.

Note 

A selected MPM is usually integrated into Apache when it is compiled. Future Linux distributions of Apache should use the Linux/Unix default MPM, which is named "threaded."

Table 22-3: Apache Modules (Apache 2.0)

Module	Description
mod_access	Access control based on client hostname or IP address
mod_actions	Executes CGI scripts based on media type or request method
mod_alias	Maps different parts of the host file system in the document tree; performs URL redirection
mod_asis	Sends files that contain their own HTTP headers
mod_auth	User authentication using text files
mod_auth_anon	Anonymous user access to authenticated areas
mod_auth_db	User authentication using Berkeley DB files
mod_auth_dbm	User authentication using DBM files
mod_auth_digest	MD5 authentication
mod_autoindex	Automatic directory listings
mod_cern_meta	Support for HTTP header metafiles
mod_cgi	Invokes CGI scripts
mod_cgid	Invokes CGI scripts using an external daemon
mod_charset_lite	Configures character set translation
mod_dav	Distributed Authoring and Versioning, WebDAV HTTP extensions
mod_dir	Basic directory handling
mod_env	Passes environments to CGI scripts
mod_example	Demonstrates Apache API
mod_expires	Applies Expires: headers to resources
mod_ext_filter	Filters output with external programs
mod_file_cache	Caches files in memory for faster serving
mod_headers	Adds arbitrary HTTP headers to resources
mod_imap	Image-map file handler
mod_include	Server-parsed documents
mod_info	Server configuration information
mod_isapi	Windows ISAPI Extension support
mod_log_config	User-configurable logging replacement for mod_log_common
mod_mime	Determines document types using file extensions
mod_mime_magic	Determines document types using "magic numbers"
mod_negotiation	Content negotiation
mod_proxy	Caches proxy abilities
mod_rewrite	Powerful URI-to-filename mapping using regular expressions
mod_setenvif	Sets environment variables according to client information
mod_so	Support for loading modules at runtime
mod_spelling	Automatically corrects minor typos in URLs
mod_ssl	Interface for SSL encryption supported by OpenSSL
mod_status	Server status display
mod_userdir	User home directories
mod_unique_id	Generates unique request identifier for every request
mod_usertrack	User tracking using cookies (replacement for mod_cookies.c)
mod_vhost_alias	Support for dynamically configured mass virtual hosting

Starting and Stopping the Web Server

On most systems, Apache is installed as a standalone server, continually running. As noted in Chapter 20, in the discussion of init scripts, your system automatically starts up the Web server daemon, invoking it whenever you start your system. On Red Hat, a startup script for the Web server called httpd is in the /etc/rc.d/init.d directory. Symbolic links through which this script is run are located in corresponding runlevel directories. You will usually find the S85httpd link to /etc/rc.d/init.d/httpd in the runlevel 3 and 5 directories, /etc/rc.d/rc3.d and /etc/rc.d/rc5.d.. You can use the chkconfig command or the System V Init Editor to set the runlevels at which the httpd server will start, creating links in appropriate runlevel directories. The following command will set up the Web server (httpd) to start up at runlevels 3 and 5 (see Chapters 20 and 27 for more details on runlevels).

chkconfig --level 35 httpd on

On Red Hat, you can also use service command to start and stop the httpd server manually. This may be helpful when you are testing or modifying your server. The httpd script with the start option starts the server, the stop option stops it, and restart will restart it. Simply killing the Web process directly is not advisable.

service httpd restart

Apache also provides a control tool called apachectl (Apache control) for managing your Web server. With apachectl, you can start, stop, and restart the server from the command line. apachectl takes several arguments: start to start the server, stop to stop it, restart to shut down and restart the server, and graceful to shut down and restart gracefully. In addition, you can use apachectl to check the syntax of your configuration files with the config argument. You can also use apachectl as a system startup file for your server in the /etc/rc.d directory.

Remember, httpd is a script that calls the actual httpd daemon. You could call the daemon directly using its full pathname. This daemon has several options. The -d option enables you to specify a directory for the httpd program if it is different from the default directory. With the -f option, you can specify a configuration file different from httpd.conf. The -v option displays the version.

/usr/sbin/httpd -v

To check your Web server, start your Web browser and enter the Internet domain name address of your system. For the system turtle.mytrek.com, the user enters http://turtle.mytrek.com. This should display the home page you placed in your Web root directory. A simple way to do this is to use Lynx, the command line Web browser. Start Lynx, and type g to open a line where you can enter a URL for your own system. Lynx displays your Web site's home page. Be sure to place an index.html file in the /var/www/html directory first.

Once you have your server running, you can check its performance with the ab benchmarking tool, also provided by Apache. ab shows you how many requests at a time your server can handle. Options include -v, which enables you to control the level of detail displayed, -n, which specifies the number of requests to handle (default is 1), and -t, which specifies a time limit.

Note 

Currently there is no support for running Apache under xinetd. In Apache 2.0, such support is determined by choosing an MPM module designed to run on xinetd.

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