Open Source Software

Linux was developed as a cooperative open source effort over the Internet, so no company or institution controls Linux. Software developed for Linux reflects this background. Development often takes place when Linux users decide to work on a project together. The software is posted at an Internet site, and any Linux user can then access the site and download the software. Linux software development has always operated in an Internet environment and is global in scope, enlisting programmers from around the world. The only thing you need to start a Linux-based software project is a Web site.

Most Linux software is developed as open source software. This means that the source code for an application is freely distributed along with the application. Programmers over the Internet can make their own contributions to a software package's development, modifying and correcting the source code. Linux is an open source operating system. Its source code is included in all its distributions and is freely available on the Internet. Many major software development efforts are also open source projects, as are the KDE and GNOME desktops along with most of their applications. The Netscape Communicator Web browser package has also become open source, with its source code freely available. The OpenOffice office suite supported by Sun is an open source project based on the StarOffice office suite (StarOffice is essentially Sun's commercial version of OpenOffice). Many of the open source applications that run on Linux have located their Web sites at SourceForge (sourceforge.net), which is a hosting site designed specifically to support open source projects. You can find more information about the open source movement and recent developments at Linuxcare (www.linuxcare.com) and at www.opensource.org.

Open source software is protected by public licenses. These prevent commercial companies from taking control of open source software by adding a few modifications of their own, copyrighting those changes, and selling the software as their own product. The most popular public license is the GNU General Public License provided by the Free Software Foundation. This is the license that Linux is distributed under. The GNU General Public License retains the copyright, freely licensing the software with the requirement that the software and any modifications made to it always be freely available. Other public licenses have also been created to support the demands of different kinds of open source projects. The GNU Lesser General Public License (LGPL) lets commercial applications use GNU licensed software libraries. The QT Public License (QPL) lets open source developers use the QT libraries essential to the KDE desktop. You can find a complete listing at www.opensource.org.

Linux is currently copyrighted under a GNU public license provided by the Free Software Foundation, and it is often referred to as GNU software (see www.gnu.org). GNU software is distributed free, provided it is freely distributed to others. GNU software has proved both reliable and effective. Many of the popular Linux utilities, such as C compilers, shells, and editors, are GNU software applications. Installed with your Linux distribution are the GNU C++ and Lisp compilers, Vi and Emacs editors, BASH and TCSH shells, as well as Tex and Ghostscript document formatters. In addition, there are many open source software projects that are licensed under the GNU General Public License (GPL). Many of these software applications are available at different Internet sites, and these are listed in Table 1-3. Chapter 4 and Chapter 29 describe in detail the process of downloading software applications from Internet sites and installing them on your system.

Under the terms of the GNU General Public License, the original author retains the copyright, although anyone can modify the software and redistribute it, provided the source code is included, made public, and provided free. Also, no restriction exists on selling the software or giving it away free. One distributor could charge for the software, while another one could provide it free of charge. Major software companies are also providing Linux versions of their most popular applications. A Linux version of Sun's Java Software Development Kit (SDK) is also available through www.blackdown.org. Oracle provides a Linux version of its Oracle database. (At present, no plans seem in the works for Microsoft applications.)