NOTE: With release 4.13_b.8, release 4.14 beta and release 4.5, the behavior is exactly opposite. That is, the default is to drop the core. In order to spin, the "STX9" variable must be set.
All releases after 4.14 beta and after 4.51, the default is to spin until attached to or killed. If the environment variable Debug_Enable_Core is set, the core file is generated. This means in release 4.14 and above, and in release 4.1x and release 4.52 and above, the environment variable Debug_Enable_Core's presence or lack thereof, determines whether the server will drop core or not; inherently making the debugging process more straightforward.
NOTE: The variable STX9 is no longer used after releases 4.13 and 4.51.
The summary table below shows this best historically.
Summary Table