On Debian, kernel.core_pattern may be handled by an external command instead of writing a plain core file directly to disk. Some OpenJDK test setups require a plain file-based pattern; otherwise those tests may be skipped entirely.

First, check the current core pattern:

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sysctl kernel.core_pattern

For those test runs, set a simple pattern:

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sudo sysctl -w kernel.core_pattern=core

When done, reload system defaults:

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sudo sysctl --system

This approach provides predictable test-time core files while still returning to Debian’s default configuration.