GPL (GNU General Public License)

The GNU General Public License (GPL) is the most widely used strong copyleft software license, authored by the Free Software Foundation for the GNU Project. It guarantees that everyone who receives a covered program also receives the four essential freedoms: to run, study, share, and modify it. Critically, any derivative work that is distributed must itself be licensed under the GPL and ship with corresponding source code, so the freedoms cannot be stripped away downstream. Where a permissive license permits enclosure, the GPL is engineered to prevent it.

How copyleft works legally

The GPL is enforced through ordinary copyright law, used in reverse. Copyright gives an author exclusive rights over copying and derivative works; the GPL grants those rights to everyone, conditionally — accept the obligations (share source, preserve the license, keep notices) and you may redistribute; violate them and you are simply a copyright infringer with no license at all. This judo move is why copyleft needs no new legal machinery: it makes the code and its freedoms legally inseparable using the same statute that proprietary vendors use to lock code down. Importantly, the obligations trigger on distribution — you may modify GPL code privately, or run it internally, without sharing anything.

GPLv2 vs GPLv3 — and why miners should care about tivoization

GPLv2 (1991) is concise and remains common in long-lived projects such as the Linux kernel. GPLv3 (2007) adds explicit patent grants, clearer international language, and — most relevant to mining — anti-tivoization terms: if a vendor ships GPLv3 software on a consumer device, it must also provide whatever keys or installation information are needed to run modified versions on that same hardware. The clause exists because source code you cannot actually install is freedom in name only. Anyone who has fought a locked-down miner control board — signature-checked firmware, refused downgrades, vendor-gated features — has lived the exact problem GPLv3 was written to address. The two versions are not directly compatible unless a project is licensed "GPLv2 or later," a phrase that quietly determines what code can be combined with what.

The GPL in the mining world

Mining runs on GPL foundations at every layer: the Linux kernel inside effectively every miner's control board, and the classic open mining stack — cgminer and its descendants trace to GPL roots — that generations of firmware were built from. The license is why improvements to shared tools flow back to the community rather than being captured by a single vendor, and why a repair tech or home miner can read the code that actually runs their machine. D-Central's own work stands deliberately in this tradition: DCENT_OS is released as free software under GPL-3.0, standing on the shoulders of the open mining projects that came before it, so anyone can inspect, audit, rebuild, and reflash the code that controls their hardware — the whole point of running your own miner in the first place.

What the GPL does not require

Common misconceptions deserve clearing. The GPL does not oblige you to publish private modifications — obligations attach only when you distribute the software to others. It does not forbid selling: charging for GPL software is explicitly permitted, and always has been; the license governs freedom, not price. Running GPL software to provide a network service is not distribution under the GPL itself, a gap the separate AGPL license exists to close. And using a GPL program's ordinary output — documents it produces, blocks it mines — imposes nothing on that output. The license is demanding precisely where it means to be, and quieter than its reputation everywhere else.

For the underlying philosophy see copyleft, and contrast the GPL with a permissive license such as MIT or Apache 2.0, which impose far fewer obligations on reuse — a legitimate choice with a different theory of how freedom spreads.