FOSS Basics

FOSS Basics

An Introduction to Free and Open Source Software for New Developers.
2018, Apr 07    

Free and open source software (“FOSS”) is hard to escape in the modern software development landscape. The majority of the tools I’m using to learn software development are FOSS: GNU/Linux, Atom, Ruby, PostgreSQL, SQLite, Git, Firefox, Bash and so forth and so on. Coming from my background working with FOSS developers I’m familiar with the minutiae of FOSS; for most starting out in software development however, FOSS is somewhat hazy concept that can be hard to distinguish from something like freeware. I thought I’d use this post to provide a brief introduction to the basics of FOSS for new developers.1

“Free” and “Open Source”

It is quite common to assume that FOSS describes software that is both free of cost and for which the source code is available to the public for review. While these characteristics are both common among FOSS, neither is actually a necessary condition to be considered FOSS. Free software and open source software are basically two schools of philosophy for describing the same thing. Most of the time, software which qualifies as “free” is also “open source”: hence “free and open source”. The “free” in free software, contrary to popular belief, does not refer to pricing. Instead, the “free” in free software refers to being free from restriction. Proponents of the free software movement are fond of the sayings “free as in speech not as in beer” or “free as in freedom” to describe free software. In fact, charging for free software is an entirely acceptable practice. The free software movement (also sometimes called the free/libre software movement) is a social movement predicated on ensuring the rights of individuals with respect to the software that they use.

“Open source”, on the other hand, was a term coined in 1998 as an effort to rebrand some of the concepts free software. Open source has come to represent a pragmatic reimagining of free software in a form that emphasizes business advantages and technical-merit over ethical concerns.

The Free Software Foundation (“FSF”) and the Open Source Initiative (“OSI”), are each well-regarded authorities for defining the boundaries of their respective movements. For FSF, free software must provide users with the following four freedoms:


The freedom to run the program as you wish, for any purpose (freedom 0).

The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.

The freedom to redistribute copies so you can help your neighbor (freedom 2).

The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.

For OSI, open source software must be distributed on terms that meet the following criteria:


1. Free Redistribution

The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale.

2. Source Code

The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost, preferably downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed.

3. Derived Works

The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.

4. Integrity of The Author’s Source Code

The license may restrict source-code from being distributed in modified form only if the license allows the distribution of “patch files” with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software.

5. No Discrimination Against Persons or Groups

The license must not discriminate against any person or group of persons.

6. No Discrimination Against Fields of Endeavor

The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.

7. Distribution of License

The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties. 8. License Must Not Be Specific to a Product

The rights attached to the program must not depend on the program’s being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program’s license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution.

9. License Must Not Restrict Other Software

The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software.

10. License Must Be Technology-Neutral

No provision of the license may be predicated on any individual technology or style of interface.

Each group maintains a list of software licenses that meet their standards and, despite their distinct philosophical approaches, FSF’s and OSI’s lists frequently align. Before delving deeper into FOSS licenses lets take a moment to discuss the relevance of licenses to software in general.

A common misconception among developers is that source code one finds on the internet can be used in any way that one wishes. Along with other expressive works like writing, photos, music, and paintings, computer software is automatically protected by copyright which means that permission is required for most use-cases. A public Git repository without a license is, despite appearances, far from an open invitation for reuse. A license, on the other hand, provides permission for using software and defines any limitations on the scope of that permission; using someone else’s software without a license risks infringing copyright as would using that software outside of the scope of what any license for it permits.

FOSS/Cookie Licenses

There are a good selection of established and approved FOSS licenses that software projects can choose from. These licenses typically fall into one of three broad categories:

  1. permissive (ex. 3-clause BSD, MIT, Apache 2.0)
  2. weak copyleft (ex. LGPL, MPL, CDDL); and
  3. strong copyleft (ex. GPL, AGPL).

Rather than speak about these types of licenses in any technical or legal detail I find that an analogy serves as a far better introductory teaching tool even if it glazes over many of the finer points. For this post I’m going to use cookies, my all time favorite FOSS licensing analogy borrowed from Jim Jagielski. As a brief aside it is worth noting that recipes are considered uncopyrightable subject matter but I will kindly ask the reader to suspend disbelief.

To understand the basics of how a permissive FOSS license works, imagine a dedicated baker’s really exceptional chocolate chip cookie recipe. Unlike many home cooks who guard their secret recipes zealously, the creator of this cookie decides to share her recipe with others but isn’t sure what license to choose.

Chocolate Chip Cookies Photo by Gianna Ciaramello

Consider what would occur if the recipe were shared with a permissive license. The main requirement of a permissive license is that future users of the recipe must give credit to the recipe’s creator. Anyone who manages to get a copy of the recipe is otherwise free to do with it as they wish; they could make as many batches of the cookies a they like, and they could even change the recipe or package and sell the cookies in stores.

The cookie’s creator might not be happy with some of the outcomes from using a permissive license for her recipe. Under a permissive license someone could sell the cookies in their bakery but refuse to share the recipe with their customers. Perhaps someone might improve on the recipe by adding a hint of orange zest and it might bother the initial creator of the cookie to go to the store and buy a box of cookies based on her recipe but not be told what changes were made. In fact, the cookie’s original creator might even be prohibited from trying to figure out on her own what changes were made to improve upon her original recipe.

Orange and Chocolate Chip Cookies Photo by Jade Wulfraat

In this case, the cookie creator might opt to choose a weak copyleft license for her recipe instead. Under a weak copyleft license the scope of the permission granted is a little more complex than under a permissive license. Users of the recipe are permitted to make the cookies or modified versions of them freely but they must share the recipe under the same license terms with anyone that they give their cookies to. This reciprocal sharing requirement is the heart of what is known as copyleft.

For some creators, weak copyleft is a step in the right direction but doesn’t quite go far enough. A weak copyleft license ensures that the cookie recipe itself is shared with recipients of the cookie but its requirements do not extend to a greater product which is based upon the cookie recipe. Just as the cookie is made of ingredients, it can also become an ingredient itself in a larger recipe.

Ice Cream Sandwich

Is frosting completely independent from the cookie it tops? What about the ice cream in an ice cream cookie sandwich? A strong copyleft license extends the reciprocal sharing requirement of weak copyleft to cover any and all recipes which are based on the cookie recipe even if the cookie itself is only one part of it.

FOSS in Practice

Now that we’ve got a sense of the broad categories of FOSS licenses lets take a quick look at how a program can be impacted by the preexisting FOSS tools it is based on. For the beginner developer, discovering how to add and use additional libraries in a program is a watershed moment that unlocks a world of potential. Sometimes the excitement of this moment can make it seem as if all of these tools are magical gifts bestowed by fairies or elves.

Keebler Elves This is not the dude to thank for that sweet web framework you just started using

In fact, libraries are created and shared by developers like anyone else under terms of their choosing which can have a real impact on the software we use them in. Let’s take the Ruby gem ecosystem as an example. Ruby gems can be installed from public Git repositories or gem servers in addition to the popular catalog on Even on there is no restriction on a gem’s choice of license terms or even a requirement to have a license in the first place. Gems on frequently use FOSS licenses and provide metadata about their licenses that can be referenced by running “bundle licenses” to display an overview of the licenses for each of the gems installed in a given project. Here is the “bundle licenses” output for a sample program:

Initial Bundle Licenses Output

The licenses here are mostly MIT with a couple of additional libraries licensed under other permissive licenses. Let’s say that I want to make a command-line application with an intuitive and visually rich interface the displays colored console text. I have no idea how to do that but I do know that there is a great gem that can help me out. After requiring the colorize gem, I can check the output of “bundle licenses” to see if anything has changed:

Bundle Licenses Output With Colorize Gem

As you can see, the license of colorize is “GPL-2.0”, a strong copyleft license (technically the license is GPLv2+ but that’s a whole other blog post). As a result of using this gem I’m now accountable for abiding by it’s license including licensing my program to users under the same or compatible license terms.


While I could happily keep writing about this topic for days, I think this post gives a good taste of what FOSS is, the different types of FOSS, and some of the issues to look out for when using FOSS in a program.

FOSS is an incredibly powerful resource for software developers and it is important to have a basic concept of what FOSS is all about and what using it requires of us in return.

  1. DISCLAIMER: Nothing in this post should be construed as legal advice and it is not a substitute for the advice of a competent attorney. This post is intentionally written as introductory material intended for those wholly unfamiliar with concepts such as FOSS and software licensing. It is intentionally over-simplified. TLDR: This stuff is complicated. Talk to your lawyer.