The flip side of permissive licences — FreeBSD, and freedom for whom?

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In the founding article of this series, I recounted how proprietary software ends up abandoning its users. The answer I champion is free software. But “free” is not a single block: there are two great families of licences, with opposing philosophies.

  • Permissive licences (BSD, MIT, Apache…): do whatever you want with the code, including closing it up inside a proprietary product.
  • Copyleft licences: require that any redistributed version stay free. The best known is the GPL, but it is not the only one: the LGPL, the AGPL and the MPL apply the same idea to varying degrees.

This article explores the first family — permissive licences — through the most spectacular case there is: FreeBSD, the operating system you probably use every day without knowing it. The second, copyleft, is the subject of a dedicated article.

What is a permissive licence?#

A permissive licence — the main ones are BSD (2- or 3-clause), MIT and Apache 2.0 — rests on a simple idea: to give whoever receives the code an almost total freedom. In concrete terms, three rights:

  • the right to modify the code;
  • the right to redistribute it;
  • the right to close it — that is, to turn it into a proprietary product, a black box, without publishing your modifications.

In exchange, a single genuine constraint: keep the original copyright and licence notice. That’s all. (Apache 2.0 adds a patent-grant clause and a NOTICE file; BSD-3 forbids using the authors’ names to endorse a derived product — but the spirit remains the same.)

Here lies the whole difference with copyleft (the GPL being its best-known example), which we will look at in detail in a forthcoming article: a copyleft licence requires that any redistributed version stay free, source code included. A permissive licence does not require this. It therefore explicitly allows taking free software and turning it into proprietary software. Remember this sentence: the whole article follows from it.

FreeBSD, a complete operating system, free… and permissive#

To see what this looks like in practice, a good example is FreeBSD. And the first thing to understand is that it is not a “distribution” like Ubuntu or Fedora.

GNU/Linux is a kernel (Linux) assembled with a host of software from separate projects (the GNU userland, etc.), brought together by a distributor. FreeBSD, by contrast, develops the kernel AND the userland (the system’s core tools) together, in a single source tree. The result is a complete, coherent and unified operating system, designed as one whole.

This coherence earned it a reputation for extreme stability, particularly on two fronts: a TCP/IP network stack reckoned among the best in the industry, and native integration of the ZFS file system. That is exactly what makes it a favourite choice for infrastructure — where you have to handle enormous loads for years without flinching. And this is where permissive licences come into play.

How the giants exploit FreeBSD#

Netflix: the invisible infrastructure#

When you watch a Netflix video, it probably does not come from a distant data centre, but from an Open Connect Appliance (OCA) installed directly at your internet provider’s (Free, Orange, etc.). And these boxes run FreeBSD.

The scale is considerable: Netflix has spent more than a billion dollars developing and deploying more than 8,000 of these appliances, installed by more than 1,000 internet providers — which allowed the latter to save 1.25 billion dollars (as of the end of 2021) by avoiding routing all that video traffic over their links. On the performance side, Netflix engineers presented at EuroBSDCon 2022 a single server capable of serving nearly 800 Gb/s of encrypted video.

Netflix illustrates the permissive model in practice: building one of the largest proprietary services in the world on a free base, giving back only what it is in its interest to give back. And that is exactly what Netflix does: it gives back its kernel modifications to FreeBSD, and runs its servers on FreeBSD-CURRENT (the development branch) — not out of generosity, but out of well-understood self-interest: keeping a private fork that diverges from upstream is expensive in “technical debt.” It does, on the other hand, keep its application layer closed — the Open Connect software itself: streaming server, caching and content-placement algorithms.

But let us be honest, because the point matters for what follows: a copyleft licence (GPL) would change almost nothing here. First, because that closed layer runs in user space: even on a copyleft kernel like Linux, an application that merely calls the kernel is not a “derived work” and can stay proprietary (which is why so much closed software runs on Linux). Second, because copyleft is triggered only by the distribution of the software: yet the boxes remain Netflix’s property, operated in-house — and its modified kernel is in any case already public, by choice. For infrastructure operated in-house, the choice of licence therefore carries little weight. Where it becomes decisive is when the software is delivered into the hands of the end user — exactly what the next two cases show.

Sources: Open Connect (Wikipedia) (FreeBSD system; over $1bn for 8,000+ OCAs; $1.25bn saved for ISPs as of end 2021) · Netflix serves nearly 800 Gb/s on FreeBSD (EuroBSDCon 2022) · upstreaming strategy to reduce technical debt: Netflix case study (FreeBSD Foundation), “Netflix and FreeBSD,” J. Looney, FOSDEM 2019 · on copyleft, user space and distribution: GNU GPL FAQ

Sony PlayStation: the locked fortress#

The genealogy of Sony’s consoles is a BSD story. The PS3 already relied on an internal system (CellOS) forked from both FreeBSD and NetBSD. The PS4 switched entirely to a system named Orbis OS, a fork of FreeBSD 9.0. The PS5, for its part, runs an internal system named ProsperoOS, based on FreeBSD 11.

A small point of honesty, because it matters: for the PS5, Sony communicates nothing. The name “ProsperoOS” and the version “FreeBSD 11” are deduced by security researchers who repair and study the console (reverse engineering), not officially confirmed. I flag this all the more readily because one often reads that the PS5 supposedly runs “Orbis OS 2.0” — that is a confusion: Orbis is the PS4’s code name, Prospero the PS5’s.

Why FreeBSD for a console? For two reasons that go together: an industrial-grade, robust x86 OS, and a licence that allows everything to be locked down. Sony closes the essentials — graphics drivers co-developed with AMD, the security hypervisor, the user interface — and designs the machine to run only signed code, in order to block piracy. Logically, the company gives very little back upstream: the hardware is too specific, and secrecy is part of the security.

Sources — PS3: PlayStation 3 system software (Wikipedia) (“a fork of both FreeBSD and NetBSD”) · PS4: PlayStation 4 system software (Wikipedia), “PlayStation 4 runs modified FreeBSD 9.0: Orbis OS” (OSNews) · PS5: PS5 Kernel — FreeBSD 11.0 / __FreeBSD_version 1100122 (PS5 Developer wiki, reverse engineering)

Apple: the technological Frankenstein#

The deepest case is Apple’s, and it goes back a long way. In 1985, Steve Jobs left Apple and founded NeXT, whose NeXTSTEP system (1989) married a Mach kernel with a 4.3BSD Unix subsystem. When Apple bought NeXT in 1996, it was NeXTSTEP that became the foundation of Mac OS X — and therefore, today, of macOS, iOS, watchOS and tvOS.

At the heart of these systems: the XNU kernel, called “hybrid.” It combines the Mach microkernel, a BSD layer (derived from 4.3BSD, then enriched with 4.4BSD and FreeBSD code: networking, POSIX compatibility, file system) and IOKit for drivers. A concrete and amusing consequence: when you type ls or cp in a Mac’s Terminal, you use the BSD versions of those commands, not the GNU versions Linux users know.

But Apple above all illustrates another facet of licences. Be careful not to overstate it: Apple long shipped software under GPLv2 (the GCC compiler, the bash shell…). What it methodically refuses is GPLv3 (published in 2007). Three examples, all at the precise moment the software moved from GPLv2 to GPLv3:

  • The compiler. Apple long used GCC, then froze it at version 4.2.1 — the last one released under GPLv2 — before funding and adopting Clang/LLVM, under a permissive licence. On a Mac, typing gcc actually launches Clang.
  • The shell. Apple likewise kept bash 3.2 (the last version under GPLv2) for years, refusing the later versions that had moved to GPLv3, then made zsh the default shell starting with macOS Catalina (2019).
  • Windows file sharing. When the Samba project moved to GPLv3, Apple simply removed it from macOS (Lion, 2011) to replace it with its own implementation of the SMB protocol.

And yet — this is where it gets delicious — when Apple publishes its own code, it does not choose a permissive licence. The free core of macOS, Darwin, is released under the Apple Public Source License (APSL): a licence the FSF recognises as free, but which is copyleft and incompatible with the GPL — the FSF even compares it to the AGPL for a clause requiring you to publish your modifications as soon as you deploy the software externally. In other words, Apple flees copyleft for the code it consumes, but attaches one to the code it distributes. Proof, if any were needed, that the choice of a licence is not a matter of principle, but of interest — depending on whether you are the one taking or the one giving.

Why this constancy in avoiding GPLv3? Because it contains clauses Apple does not want to accept — in particular its obligations on patents and its “anti-tivoization” clause, which a dedicated article in this series returns to.

Sources: Apple’s Open Source Roots: The BSD Heritage Behind macOS and iOS (FreeBSD Foundation) · Darwin (operating system) (Wikipedia) · bash → zsh and the GPLv3 reason: “Why does macOS Catalina use Zsh instead of Bash? Licensing” (The Next Web), zsh, default shell (Apple docs) · Samba removed because of GPLv3: OSNews, Engadget · APSL: Apple Public Source License (Wikipedia), FSF classification (GNU licence list)

The nuance: what the giants really give back#

The picture would be dishonest if it were purely for the prosecution. Even when the end user is locked in, the free ecosystem draws real benefits from the presence of these giants. Three facts, verified:

  • Funding. Netflix is a regular financial supporter of the FreeBSD Foundation (donations and hardware for developers). (For Apple and Sony, on the other hand, I found no documented direct funding of the FreeBSD Foundation; their major contribution comes from elsewhere — see below.)
  • LLVM/Clang, the most precious counter-gift. By refusing GPLv3 for its tools, Apple propelled a brand-new modern compiler: LLVM/Clang, today under the Apache 2.0 licence (with LLVM exceptions) — originally under a permissive BSD-style licence (NCSA). Apple hired its creator Chris Lattner as early as 2005; and Sony is among Clang’s contributors. Yet this compiler now benefits the whole industry, including Linux and FreeBSD. A tool born of a refusal of the GPL has become a commons.
  • The shared building blocks. WebKit, Apple’s rendering engine, is itself a fork of KHTML (the engine of the free KDE project, under LGPL) — and it redefined the modern web (Chrome itself descends from it). Bonjour/mDNSResponder, Apple’s network service discovery, was published under Apache 2.0.

In other words: permissive licences create a circulation, imperfect but real, between the giants and the communities. It would be a caricature to see nothing in it but plunder.

Sources: FreeBSD Foundation — Record Growth and Partner Investments (2024) · LLVM (Wikipedia) · Clang (Wikipedia) · WebKit (Wikipedia) · Bonjour (Wikipedia)

And copyleft?#

Permissive licences, as we have seen, let the giants build proprietary products on a free base — while giving back to it, out of self-interest, precious counter-gifts. This is consistent with the philosophy of open source: making the best possible software, the most widely reused. The other great family of free licences — copyleft (GPL, LGPL, AGPL) — pursues a very different goal: preventing freedom from being taken back from the user. This will be the subject of a forthcoming article in this series, which will start from a case that has become emblematic, tivoization, and lead to a conclusion common to both our families of licences.

Sources and references#

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By Yanal-Yves FARGIALLA • Updated on July 4, 2026 (AI-assisted writing, final review by the author)
Unless otherwise noted, this content is licensed under CC BY-SA 4.0. CC BY-SA 4.0