Table of Contents Link to heading
- The Open Source Philosophy
- Software Licensing Fundamentals
- The Free Software Foundation and Copyleft
- The Open Source Initiative and Permissive Licences
- Creative Commons Licences
- Open Source Business Models
The Open Source Philosophy Link to heading
Open source is the principle that users have the right to obtain, inspect, modify, and redistribute a software program’s source code. This is philosophically and legally distinct from simply getting access to free software — the rights granted to the recipient are what define the open source model.
The historical context matters: Unix was created at AT&T Bell Labs in 1969 and its source code was initially shared with universities, fostering a culture of collaborative development. When AT&T later asserted commercial control over Unix, the open source movement emerged in part as a response — the GNU Project, started by Richard Stallman in 1983, set out to build a complete Unix-compatible operating system from scratch using free software.
Standards bodies like IEEE and POSIX ensure interoperability across implementations, allowing code designed for one POSIX-compliant system to run on another — a practical benefit of the open ecosystem.
Software Licensing Fundamentals Link to heading
When software is distributed, three interrelated questions determine the user’s rights:
- Ownership: Who holds the intellectual property rights to the code?
- Cost: Is there a purchase price or ongoing licence fee?
- Licence terms: What can you do with the software — modify it, redistribute it, use it commercially, inspect the source?
Most proprietary software is covered by an End User Licence Agreement (EULA) — a legal agreement that grants the right to use the compiled program while restricting inspection, modification, or redistribution of the source.
Open source licences invert this by default: the source is provided, and the licence defines the conditions under which it can be used, modified, and shared. The critical variable is whether the licence is copyleft or permissive.
The Free Software Foundation and Copyleft Link to heading
The Free Software Foundation (FSF), founded by Richard Stallman in 1985, advocates for software freedom defined across four dimensions: the freedom to run, study, modify, and distribute software. The FSF’s distinguishing contribution is copyleft — the legal mechanism that requires derived works to be distributed under the same licence as the original.
In practical terms: if you take GPL-licensed code, modify it, and distribute the result, you must also distribute your modifications under the GPL with source code available. This ensures that open source software cannot be incorporated into proprietary products and “closed off.”
FSF-maintained licences:
- GNU General Public Licence v2 (GPLv2): The licence under which the Linux kernel is distributed
- GNU General Public Licence v3 (GPLv3): Adds patent protection and anti-tivoisation provisions
- GNU Lesser General Public Licence (LGPLv2/v3): Allows proprietary software to link against LGPL libraries without triggering full copyleft requirements — designed for library distribution
The Open Source Initiative and Permissive Licences Link to heading
The Open Source Initiative (OSI) defines and certifies open source licences, but takes a broader view than the FSF — certifying both copyleft and permissive licences.
Permissive licences allow the source to be incorporated into proprietary products without requiring the proprietary code to be released. Examples include the MIT Licence, BSD licences, and Apache Licence 2.0. These are common in software that organisations want to be widely adopted, including in commercial products.
Terminology clarifications:
- FOSS (Free and Open Source Software): An umbrella term covering both FSF-aligned and OSI-aligned software
- FLOSS (Free/Libre/Open Source Software): Uses libre (free from restrictions) to distinguish from free (no cost) — a distinction that matters in non-English-speaking contexts where “free” is ambiguous
Creative Commons Licences Link to heading
Creative Commons (CC) licences apply the open-source licensing philosophy to creative works — documentation, images, datasets, and other non-software content. They are constructed from four base elements that can be combined:
| Element | Requirement |
|---|---|
| Attribution (BY) | Must credit the original author |
| ShareAlike (SA) | Derivatives must use the same licence (copyleft equivalent) |
| No-Derivs (ND) | May not create modified versions |
| NonCommercial (NC) | May not use for commercial purposes |
Common licence combinations:
| Licence | Practical Meaning |
|---|---|
| CC BY | Use for any purpose; credit the author |
| CC BY-SA | Use for any purpose; credit the author; share derivatives under the same licence |
| CC BY-ND | Use and redistribute as-is; no modifications; credit the author |
| CC BY-NC | Non-commercial use only; credit the author |
| CC BY-NC-SA | Non-commercial; credit the author; share derivatives under the same licence |
| CC BY-NC-ND | Non-commercial; no modifications; credit the author |
| CC0 | Public domain — no rights reserved |
For technical documentation in systems administration, CC BY and CC BY-SA are the most common licences encountered in community-maintained wikis and reference materials.
Open Source Business Models Link to heading
Open source software is available without a licence fee, which raises the obvious question of sustainability. Several viable business models have emerged:
- Support and services: Red Hat and Canonical distribute their Linux distributions freely but generate revenue from enterprise support contracts, certifications, and consulting. The software is free; the expertise and SLA guarantees are not.
- Open core: A core product is open source; additional enterprise features (clustering, advanced security, analytics) are proprietary and sold commercially. Many SaaS and infrastructure products use this model.
- Hosted services: The software is open source, but operating it at scale is complex. The vendor provides a managed, hosted version (cloud service) and monetises the operational expertise. AWS (Elasticsearch), MongoDB Atlas, and Elastic Cloud follow this model.
- Hardware bundling: Open source software is packaged with specific hardware. Tivo was an early example; network appliance vendors (Ubiquiti, pfSense on commodity hardware) continue this pattern.
- Developer tooling: Wireshark, IntelliJ IDEA (community edition), and similar tools build ecosystem presence through open source, then monetise professional or enterprise editions.