Open Source License

Software falls under copyright law. Written program code is copyrighted, by default, automatically. If anyone uses the code without permission from the owner of the copyright, it's theft. Piracy. The copyright owner can, of course, allow anyone to use the software, setting any conditions the owner chooses. Software licenses provide the conditions under which the copyright owner allows you to use the software.

If you have ever purchased or installed software, you have probably encountered a license. Commercial software usually includes a written license. If you download software, there's usually a screen that requires you to click your agreement to the license before you can actually install/use the software. Such a license is called the end user license agreement, also not so affectionately known as the EULA.

When you read a EULA, you discover that you haven't actually purchased the software. You have, instead, purchased a license to use the software. The EULA specifies the conditions, or terms, under which you can use the software. The EULA may include some restrictive conditions, such as limiting the software to installation on one computer. It's wise to read the EULA so you know your legal rights and responsibilities. The EULA is generally not open for negotiation.

Open source software also comes with a license. The most common open source license is the General Public License (GPL). The GPL is quite unrestricted. It states that you can use the software for any purpose. You can change it if you want. You can redistribute it if you want. However, you cannot redistribute it as proprietary software. It must remain open source. Anyone receiving the software from you has the right to the source and has the right to change it or redistribute it.

The GPL was developed by GNU (discussed later in this chapter). It's often referred to as copyleft, defined by GNU as a general method for making a program free software and requiring all modified and extended versions of the program to be free software as well. You can see the entire text of the GPL, as well as other information regarding its use, at www.gnu.org/licenses/licenses.html#TOCGPL.

Other open source software licenses are available, such as a license for documentation. You can see information about open source licenses at www.gnu.org/licenses/licenses.html.