Building Software Packages from Source Files

In the previous sections, you have seen how to install software packages distributed in the RPM format. RPM files bundle everything-all the executable binary files and configuration files-needed to install a software package. Many open-source software packages, however, are distributed in source-code form, without executable binaries. Before you can use such software, you have to build the executable binary files by compiling them, and you have to follow some instructions to install the package. This section shows you how to build software packages from source files.

Downloading and Unpacking the Software

Open-source software source files are typically distributed in compressed tar archives. These archives are created by the tar program and compressed with the gzip program. The distribution is in the form of a single large file with the .tar.gz or .tar.Z extension-often referred to as a compressed tarball. If you want the software, you have to download the compressed tarball and unpack it.

Download the compressed tar file by using anonymous FTP or through your Web browser. Typically, this involves no effort on your part beyond clicking a link and saving the file in an appropriate directory on your system.

To try your hand at downloading and building a software package, practice on the X Multimedia System (XMMS)-a graphical X application for playing MP3 and other multimedia files. XMMS is bundled with CentOS Linux and should already be installed on your system if you have selected the Multimedia Support package group during CentOS Linux installation. However, there is no harm in downloading and rebuilding the XMMS package again.

The source files for XMMS are available from http://www.xmms.org/download.html in the form of a compressed tar archive. In addition, you can also download the files from the xmms/1.2.x directory of the anonymous FTP server ftp.xmms.org.

Click the ftp link for the .tar.gz format on the http://www.xmms.org/download.html page and save the compressed source tarball in the /usr/local/src directory in your CentOS Linux system (be sure to log in as root, otherwise you cannot save in the /usr/local/src directory).

After downloading the compressed tar file, examine the contents with the following tar command:

tar ztf xmms*.gz | more

You should see a listing similar to the following:

xmms-1.2.7/
xmms-1.2.7/Makefile.in
xmms-1.2.7/README
xmms-1.2.7/stamp-h1.in
xmms-1.2.7/ABOUT-NLS
xmms-1.2.7/AUTHORS
xmms-1.2.7/COPYING
xmms-1.2.7/ChangeLog
xmms-1.2.7/INSTALL
xmms-1.2.7/Makefile.am
xmms-1.2.7/NEWS
xmms-1.2.7/TODO
xmms-1.2.7/acconfig.h
xmms-1.2.7/acinclude.m4
xmms-1.2.7/aclocal.m4
xmms-1.2.7/config.guess
xmms-1.2.7/config.h.in
xmms-1.2.7/config.sub
xmms-1.2.7/configure
... rest of the output not shown ...

The output of this tar command shows you what's in the archive and gives you an idea of the directories that will be created after you unpack the archive. In this case, a directory named xmms-1.2.7 will be created in the current directory, which, in my case, is /usr/local/src. From the listing, you'll also learn the programming language used to write the package. If you see .c and .h files, which means that the source files are in the C programming language, which is used to write many open-source software packages.

To extract the contents of the compressed tar archive, type the following tar command:

tar zxvf xmms*.gz

You'll again see the long list of files as they are extracted from the archive and copied to the appropriate directories on your hard disk.

Now, you are ready to build the software.

Building the Software from Source Files

After you unpack the compressed tar archive, all source files will be in a directory whose name is usually that of the software package with a version-number suffix. For example, the XMMS version 1.2.7 source files are extracted to the xmms-1.2.7 directory. To start building the software, change directories with the following command:

cd xmms*

You don't have to type the entire name-the shell can expand the directory name and change to the xmms-1.2.7 directory.

Nearly all software packages come with some sort of README or INSTALL file-a text file that tells you how to build and install the package. XMMS is no exception; it comes with a README file you can peruse by typing more README. There is also an INSTALL file, which contains instructions for building and installing XMMS.

Most open-source software packages, including XMMS, also come with a file named COPYING. This file contains the full text of the GNU General Public License (GPL), which spells out the conditions under which you can use and redistribute the software. If you are not familiar with the GNU GPL, read this file and show the license to your legal counsel for a full interpretation and an assessment of applicability to your business.

To build the software package, follow the instructions in the README or INSTALL file. For the XMMS package, the README file lists some of the prerequisites (such as libraries) and tells you what commands to type to build and install the package. In the case of XMMS, the instructions tell you to use the following steps:

Type ./configure to run a shell script that checks your system configuration and creates a file named Makefile-a file the make command uses to build and install the package. (You can type ./configure -help to see a list of options that configure accepts.)
Type make to build the software. This step compiles the source files in all the subdirectories (compiling source code converts each source file into an object file-a file containing binary instructions that your PC's processor can understand).
Type make install to install the software. This step copies libraries and executable binary files to appropriate directories on your system.

Although these steps are specific to XMMS, most other packages follow these steps-configure, make, and install. The configure shell script guesses system-dependent variables and creates a Makefile with commands needed to build and install the software.

Usually, you do not have to do anything but type the commands to build the software, but you must install the software-development tools on your system. This means that you must install the Software Development package when you install CentOS Linux. To build and run XMMS, you must also install the X Software Development package because it's an X application.

Building and Testing XMMS

To begin building XMMS, type the following command to run the configure script (you must be in the xmms-1.2.7 directory when you type this command):

./configure

The configure script starts running and prints lots of messages as it checks various features of your system-from the existence of the C compiler to various libraries needed to build XMMS. Finally, the configure script creates a Makefile you can use to build the software.

Insider Insight

If the configure script displays error messages and fails, review the INSTALL and README files to find any clues to solving the problem. You may be able to circumvent it by providing some information to the configure script through command-line arguments.

After the configure script finishes, build the software by typing make. This command runs the GNU make utility, which reads the Makefile and starts compiling the source files according to information specified in the Makefile. The make command goes through all the source directories, compiles the source files, and creates the executable files and libraries needed to run XMMS. You'll see a lot of messages scroll by as each file is compiled. These messages show the commands used to compile and link the files.

The make command can take 3 to 10 minutes to complete, depending on how fast your PC is. After make is done, you can install the XMMS software with the following command:

make install

This command also runs GNU make, but the install argument instructs GNU make to perform a specific set of commands from the Makefile. These instructions essentially go through all the subdirectories and copy various files to their final locations. For example, the binary executable files xmms, wmxmms, and xmms-config are copied to the /usr/bin directory.

XMMS already comes with CentOS Linux and you can run it by selecting Main Menu>Sound & Video>Audio Player. However, after you build and install XMMS again, you should get the new version of XMMS.

Try running XMMS from the GNOME or KDE desktop by selecting Main Menu>Sound & Video>Audio Player or by typing xmms in a terminal window. From the XMMS window, press L to get the Load File dialog and select an MP3 file to play. Your PC must have a sound card, and that the sound card must be configured correctly for XMMS to work.

Figure 21-4 shows a typical view of XMMS playing an MP3 music clip.

Figure 21-4: Playing MP3 Music with XMMS.

If you get an error message saying that the MPEG support has been removed, select Window menu>Options>Preferences and in the dialog box that appears select MPEG Layer 1/2/3 Placeholder Plugin. Then click off the Enable Plugin check box to disable that plug-in. The XMMS source that downloaded builds a working MP3 plug-in.

Summarizing the Steps in Building Software from Source Code

Now, that you have tried the entire process of downloading and building a software package, here's an overview of the steps you follow to download, unpack, build, and install a typical software package:

Use a Web browser to download the source code, usually in the form of a .tar.gz file, from the anonymous FTP site or website.
Unpack the file with a tar zxvf filename command.
Change the directory to the new subdirectory where the software is unpacked, with a command such as cd software_dir.
Read any README or INSTALL files to learn any specific instructions you must follow to build and install the software.
The details of building the software may differ slightly from one software package to another, but typically you type the following commands to build and install the software:
```
./configure
make
make install
```
Read any other documentation that comes with the software to learn how to use the software and whether you must configure the software further before using it.