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This chapter is from the book

Compiling Apache

Compilation is the process whereby a computer translates human readable source code into machine executable binary code. Before you can get any use out of the Apache source code files you downloaded, they must be compiled into an executable binary and stored somewhere that the operating system can find them.

Currently, there are two methods for compiling the source code into executables. The first method—which used to be the only method—requires you to edit a script named Configure located in the src directory of the distribution you just unpacked. The second method uses the Apaci configuration utility. The Apaci method generally is considered the easier of the two, as everything is done on the command line and no hand editing of configuration files is required.

Manual Compilation

There should be a subdirectory called src included with the distribution you just unpacked. To compile Apache manually, you must first make that your current working directory.

cd src 

Located in that directory is a file called Configuration.tmpl containing a boilerplate configuration script that you can modify to suit your needs. First, make a copy of the script called Config-uration:

cp Configuration.tmpl Configuration 

The script contains five types of lines:

  • comment lines, which start with a "#"

  • Makefile options, such as "CFLAGS=," and "CC="

  • Rules, which begin with the word "Rule"

  • AddModule lines, which, when uncommented, add the module into the compilation

  • %Module lines, which specify a module that is compiled in but not enabled

The Rules and AddModule lines are preceded by fairly decent descriptions of what modifications are possible and what the consequences might be. If you're not in a hurry, it's a good idea to read through the file just to get an idea of what options are available.

Once you've modified the Configuration script, you create your makefile by sourcing it:

./Configure 

which should yield output like the following:

$ ./Configure 
Using config file: Configuration Creating Makefile 
configured for <your> platform
setting C compiler to <your compiler>
Adding selected modules
doing sanity check on compiler and options
Creating Makefile in support Creating Makefile in main Creating Makefile in os/unix 
Creating Makefile in modules/standard 

Assuming all goes well, you can create your executable by typing

make 

BACKGROUND INFORMATION: MAKE

Unix executables are almost always compiled with the aid of a popular utility called make. The make utility takes as input two things:

  • The source code and libraries you wish to assemble into an executable whole. In the case of Apache, these were either downloaded from the Web site or (God willing) already in place on your machine.

  • A set of rules for assembling the source. These rules take the form of a text file named the Makefile. The Makefile speci-fies such things as the compiler, the source code files and their dependencies, and the goal (such as a compiled executable, a clean directory, or an installed executable) that you want make to achieve for you.

You will see Makefiles pop up in various stages of your creation of Apache. Depending on what kind of server you want to build, you may even have to edit some of them by hand. Consult your system documentation for details.

The APACI Method

The APACI configure script is a relatively new wrinkle in Apache compilation. With the configure script, you can exercise a great deal of control over your compilation from the command line, without doing a hand edit of a configuration file. There still are situations, such as when you're compiling in some third-party modules, in which you have to do your compilation by hand, whether you want to or not. However, for the most part you can accomplish anything you need to with the APACI method.

When you unpack your distribution, there will be a script named configure in the root directory of the distribution.2 The configure script has more than a hundred possible options. You can display them all with:

./configure --help 

Many of those options will be discussed later in the book, but for now let's keep things simple. The configure script will take a single parameter, --prefix, which indicates the name of the directory under which all the Apache information will be stored. For the sake of example, let's say that directory is /apache. If so, you would invoke the configure script as follows:

./configure --prefix= /apache 

If all goes well, you should see output similar to the following:

Configuring for Apache, Version 1.3.14 
+ using installation path layout: Apache (config.layout) 
Creating Makefile Creating 
Configuration.apaci in src Creating Makefile in src 
Configuring for Apache, Version 1.3.14
+ using installation path layout: Apache
(config.layout)
Creating Makefile
Creating Configuration.apaci in src
Creating Makefile in src
+ configured for Linux platform
+ setting C compiler to gcc
+ setting C pre-processor to gcc -E
+ checking for system header files
+ adding selected modules
+ checking sizeof various data types
+ doing sanity check on compiler and options
Creating Makefile in src/support
Creating Makefile in src/regex
Creating Makefile in src/os/unix
Creating Makefile in src/ap
Creating Makefile in src/main

As you can see above, the configure script first pokes around your machine looking for various pieces of information it needs to know about your compiler and operating system environment. Next, it will modify its default configuration based on any command line options you supplied; finally, it will use all that information to build a Makefile. You can compile your new Web server with a one-word command:

make 

You should end up with an executable version of httpd in the src directory of your installation.3 To install the executable on your system, type:

make install 

That will produce another chunk of progress messages, at the end of which you should see a screen like that shown in Figure 1-1.

Figure 1-1FIGURE 1–1 Installing httpd

Congratulations. The worst is over. By default, the httpd you just built will contain the modules shown in Table 1-1.

As I'll show in the next section, the list of modules compiled into the server is variable. For future reference, you can generate a listing of the modules compiled in to your current httpd by typing:

httpd -l 

If not, you will get an error (or a bunch of them) when you attempt to compile. At that point you will have to edit the makefile or perhaps some system library files by hand and change the offending parameters to match your system. This is a process that we will lightheartedly refer to as "nontrivial." The following command may be of use in locating files on your system:

find / -type f -print | grep <missing file> 

where the <missing file> portion of the command is replaced with the actual name of the missing file.

TABLE 1–1 Default Modules

Module

Description

http_core.c

Core functionality of the server

mod_env.c

Enables passing of environment variables to CGI scripts

mod_log_config.c

User configurable logging

mod_mime.c

Enables Apache to determine document types from file extensions

mod_negotiation.c

Negotiates content

mod_status.c

Displays server status information as a Web page

mod_include.c

Enables Apache to provide limited dynamic content

mod_autoindex.c

Automatic directory listing

mod_dir.c

Basic display of directory information

mod_cgi.c

Enables generation of dynamic content

mod_asis.c

Enables transmission of files without http headers

mod_imap.c

Handles image map files

mod_actions.c

Enables Apache to use CGI scripts to handle certain types of files

mod_userdir.c

Enables Apache to server pages from users' home directories

mod_alias.c

Enables URL redirection and forced remapping within the filesystem

mod_access.c

Accesses control

mod_auth.c

Limited authorization

mod_setenvif.c

Enables Apache to set environment variables based on client information


Changing the Default Configuration

If you're not happy with the modules compiled into the default httpd, you can use the configure script to specify which modules to leave in and which to take out. There are two options for this purpose: --enable-module and --disable-module. For example, to build an httpd that contains all the default modules listed above as well as mod_proxy, you would type:

./configure --prefix=/apache --enable-module=proxy 

and then re-make and reinstall the resulting server:

make
make install 

Similarly, you can remove default modules from the configu-ration using the --disable-module option. For example, the following removes the module mod_asis, which is included by default:

./configure --prefix=/apache --disable-module=asis 

Once again, any time you make changes to your configure scripts, you will need to recompile Apache before they take effect. When you have an executable you're happy with, it's time to move on to the last step of the process.

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