Is Jira v4.2.1-b588#588 compatible with Unix 15.3 verison?
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There's no way to answer that, I think you're not giving us enough information.
As the Linux kernel is only up to version 5.9, I think you might be looking at a specific distribution version. Also, Linux is not Unix, and you mention both in your question.
That said, we can partially answer this. Jira 4 runs on a narrow range of Java versions and that abstracts it away from the operating system. Your question should change to "does the Java Jira needs run on this operating system?"
To go any further, you need to look at what OS you're running.
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