IBM Semeru Runtime Certified Edition for z/OS 25: Supplementary documentation

Content

The supplementary documentation is updated only if there are notable changes, such as special advisories, in a particular release. This document was last updated during 25.0.4.0 release.

The documentation to support this version is available in IBM Documentation. For links to downloads, fixes, and a table of OpenJDK versions on which this release is based, see IBM Semeru Runtime Certified Edition for z/OS refreshes.

Supplementary information is available for the following code refreshes:

• 25.0.4.0
• First release

25.0.4.0 (September 2026)

Health Center might trigger unexpected global GC with compaction

Starting with IBM Semeru Runtime Certified Edition for z/OS release 25.0.4.0 (OpenJ9 v 0.60), enabling the Health Center agent might cause a stop-the-world (STW) global garbage collection (GC) with compaction every 30 seconds. The GC is reported in the verbose GC log with the reason "rasdump".

This scenario occurs because Health Center collects thread information every 30 seconds by using ThreadMXBean.getThreadInfo() with lockedSynchronizers=true. In OpenJ9 v0.6.0 and later, this operation might require the JVM to rebuild its internal Ownable Synchronizer list by walking the heap, which triggers a stop-the-world compacting GC before the heap walk can proceed.

Workaround

Until a fix is available in a future Health Center release, disable Health Center thread data collection by specifying -Dcom.ibm.diagnostics.healthcenter.data.threads=off. This setting prevents the thread data collection that triggers the unexpected GC.

First release 25.0.1.0 (April 2026)

Garbled terminal output with System.out and System.err

Applications that write UTF-8 encoded bytes using System.out.write() or System.err.write() might experience garbled terminal output on z/OS. This issue affects applications including Jenkins agents on z/OS, Log4j, and Gradle. This known issue will be addressed in a subsequent update. For more information, see APAR IJ57789 and Usage guidelines for System.out and System.err on z/OS.