Open source on z/OS – Don’t let breaking changes break you

Aug 20, 2025

Chief Technology Officer, Phoenix Software International

Ed began his software development career by writing applications for government and research organizations in Washington, D.C. After moving to Los Angeles in 1982, he transitioned to the banking industry and eventually joined Phoenix Software International in 1987. He became Manager of Research & Development in the mid-1990s and was named Chief Technology Officer in 2009. Ed manages the SHARE Core Platform focus area and is recognized throughout the mainframe community as a subject matter expert and strong advocate for the IBM Z platform.

Running open source on z/OS allows it to better integrate with off-platform solutions. It also provides user interfaces familiar to engineering and computer science students, who, we hope, will become the next generation of z/OS programmers and sysadmins. Of course, no technology is ever a complete superset of another, and each has its drawbacks. This article discusses breaking changes that can break your system.

Enterprise environments today are heterogeneous, and IBM is working hard to transform the z/OS experience into one that is more consistent with Linux, the popular open-source operating system.

The approach so far has been to:

  1. Modify the z/OS infrastructure in ways that enable and encourage the use of popular open source tooling on z/OS.
  2. Sponsor numerous open source projects both on and off the platform.
  3. Provide IBM-vetted locations for clients to obtain open source code compatible with z/OS.

What are breaking changes?

As the name suggests, a breaking change is any change that can break a client’s application. Usually, breaking changes involve modifying or deleting existing parts of an API.

Db2 Workload Performance on Fire

To be clear, no software is perfect, and no design can foresee every possible future requirement. Any software that’s being regularly enhanced on any platform might be forced to occasionally implement a breaking change.

That said, I have observed significant differences in the quantity of breaking changes when comparing open source to enterprise software. My enterprise software experiences stretch back more than four decades. My open source experience is roughly half a dozen years…

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