The GNU General Public License (GPL) is one of the most widely used free software licenses. It was created by the Free Software Foundation (FSF) to ensure that software remains free to use, study, modify, and distribute.
It is commonly used in open-source projects, including the Linux ecosystem.
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What the GPL allows
The GPL grants users four essential freedoms:
- the freedom to run the software for any purpose
- the freedom to access and study the source code
- the freedom to modify the software
- the freedom to redistribute the software
These permissions apply to both original and modified versions of the software.
What “copyleft” means
The GPL is a copyleft license.
This means that:
- any modified version of GPL software must remain under the GPL license
- improvements must also be shared under the same terms
- the software and its derivatives must remain open-source
This ensures that software built on GPL code remains free and accessible to others.
Key conditions of the GPL
When using or distributing GPL-licensed software, certain conditions must be met:
- the license text must be included
- the source code must be made available
- modifications must be clearly documented
- recipients must retain the same usage rights
These conditions apply whenever the software is redistributed.
Compatibility considerations
The GPL is a strong copyleft license, which means it may not be compatible with all other software licenses.
In practice:
- GPL software must remain under GPL when distributed
- combining GPL code with proprietary code may be restricted
- license compatibility must be checked when mixing open-source components
Practical implications
The GPL is designed to preserve openness in software development.
It ensures that:
- users maintain long-term access to source code
- improvements are shared with the community
- software remains freely available
However, developers must understand the licensing rules before integrating GPL code into projects.
Summary
The GNU GPL is a free software license that guarantees users the freedom to use, modify, and share software. Through its copyleft principle, it ensures that all modified versions remain open-source and subject to the same license terms.