2.1.2. Software Licensing and the Open Source Ecosystem
💡 First Principle: Software licenses are legal agreements that define what you can do with software — copy it, modify it, redistribute it, and under what conditions. The choice of license has direct operational consequences: a copyleft license may require you to open-source modifications, while a permissive license may not.
The XK0-006 exam tests whether you can identify license types and their practical implications — particularly the difference between copyleft (GPL) and permissive (MIT, Apache) licenses.
| License Type | Definition | Practical Implication | Example |
|---|---|---|---|
| Open Source | Source code is publicly available | Can inspect, modify, and often redistribute | Linux kernel, Python |
| Free Software (FSF) | Four freedoms: run, study, modify, redistribute | Philosophical distinction from "open source" | GNU tools |
| Proprietary | Source code is not available; usage is licensed | Cannot modify or redistribute; vendor-dependent | Oracle DB, VMware |
| Copyleft (GPL) | Derivatives must use the same license | If you distribute modified GPL code, you must release your modifications | Linux kernel (GPLv2), Bash (GPLv3) |
| Permissive | Few restrictions on use and distribution | Can incorporate into proprietary products | MIT, Apache 2.0, BSD |
The Linux kernel is licensed under GPL v2 — this is why device driver authors who distribute modifications must release source code. The GPL "viral" nature is why companies like Linus Torvalds's kernel team insist on GPLv2: it ensures the commons stays open.
From an administrative perspective, software licensing affects what you can run in production (proprietary licenses may restrict server counts), what you can modify (copyleft code modified for internal use doesn't need to be released, but distributed modifications do), and what software supply chain risks you carry.
⚠️ Exam Trap: "Free software" in the FSF sense means freedom, not price — it's free as in freedom, not free as in beer. A piece of software can be free-as-in-freedom and still cost money. Proprietary software can be distributed at no cost (freeware) but is not free software. The exam may test this distinction.
Reflection Question: Your company wants to take an open-source tool licensed under the GPL, modify it heavily, and distribute it as part of a commercial product. What does the GPL require you to do?
