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COPYLEFT

Enhanced Definition

Copyleft is a software licensing approach that grants users the freedom to run, study, modify, and distribute software and its modified versions, with the crucial condition that all derivative works must be distributed under the *same* copyleft license. In the mainframe context, while core IBM z/OS components are proprietary, copyleft licenses become relevant when integrating or developing open-source software on the platform.

Key Characteristics

- Reciprocal Licensing: Requires that any modifications or extensions to copyleft-licensed software must also be released under the same license, ensuring the "freedoms" are preserved for all subsequent users.
- Contrast with Proprietary: Directly opposes the traditional proprietary licensing model prevalent for most IBM mainframe software, where source code is typically withheld, and distribution/modification is restricted.
- "Viral" Nature: Often described as "viral" because the license "infects" derivative works, meaning if you link proprietary code with copyleft-licensed code, your proprietary code might be required to be released under the copyleft license.
- Common Examples: The GNU General Public License (GPL) is the most well-known and widely used copyleft license, frequently applied to tools and utilities ported to or developed for z/OS.
- Source Code Availability: Guarantees that the source code for the software and any derivatives must be made available to recipients.

Use Cases

- Open Source Tools on z/OS: Using open-source utilities like Git for z/OS, Python for z/OS, Perl for z/OS, or GCC, which are often distributed under copyleft licenses (e.g., GPL), for development, scripting, or system administration tasks.
- Custom Application Development: Developing new applications on z/OS that incorporate or link with copyleft-licensed open-source libraries or frameworks.
- Porting Open Source Solutions: Porting existing open-source applications from other platforms to z/OS, which inherently brings their original copyleft licensing terms to the mainframe environment.
- Educational and Research Projects: Utilizing copyleft software in academic or internal research projects on z/OS where the intent is to share modifications openly.

Related Concepts

Copyleft stands in direct contrast to proprietary software licensing, which is the dominant model for IBM's z/OS operating system, CICS, DB2, IMS, and most commercial Independent Software Vendor (ISV) products on the mainframe. It is a subset of open source software (OSS) licensing, differentiating itself from more permissive licenses (like MIT or Apache) that allow proprietary derivatives. Understanding copyleft is crucial for managing intellectual property (IP) and software supply chain risk when integrating non-IBM components into a mainframe ecosystem.

Best Practices:

License Due Diligence: Thoroughly review the license terms of any open-source software, especially those with copyleft clauses, before integrating them into proprietary mainframe applications or systems.
Legal Consultation: Engage legal counsel to assess the implications of using copyleft-licensed components, particularly regarding the "viral" nature and potential impact on proprietary codebases.
Isolate Copyleft Components: When possible, design system architectures to isolate copyleft-licensed components (e.g., via clear API boundaries or separate processes) to minimize the risk of license propagation to proprietary code.
Maintain Compliance Records: Keep detailed records of all open-source components used on z/OS, their respective licenses, and documentation of compliance efforts, including source code availability if required.
Educate Teams: Ensure development and operations teams working with z/OS are aware of different open-source licenses, especially copyleft, and their implications for development and distribution.