There have been odd reports of difficult-to-reproduce bugs of the JVM crashing (mainly on linux so far) with Java 5.

Normally this will manifest if you are compiling rules over and over (may take quite a long time to manifest).

But it may show up in the error log for the JVM as something like:

Current CompileTask: opto:877  !   org.drools.lang.RuleParser.rule()Lorg/drools/lang/descr/RuleDescr; (2152 bytes)

A quick solution to this is to set the compiler to janino via the system property

-Ddrools.compiler=JANINO

We think this may be a bug in either JDT core or the JVM

this implies that it is the JVM, so the problem may go away in a future release of the JVM for linux. If you compile and cache rules, its unlikely that you would see this problem.