FULL PRODUCT VERSION :
(CentOS)
java version "1.6.0_12"
xJava(TM) SE Runtime Environment (build 1.6.0_12-b04)
Java HotSpot(TM) Client VM (build 11.2-b01, mixed mode, sharing)

(Ubuntu)
java version "1.6.0_03"
Java(TM) SE Runtime Environment (build 1.6.0_06-b05)
Java HotSpot(TM) Client VM (build 1.60.0_03-b05, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Linux 2.6.18-92.1.22.el5 (CentOS 5.2)
Linux 2.6.22-16-generic (Ubuntu 7.10)


A DESCRIPTION OF THE PROBLEM :
When a shutdown hook contains System.exit() the jvm will hang and not close properly.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the attached source code and run as:
java Hook.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I was expecting the JVM to exit.
ACTUAL -
The JVM hangs.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class Hook {
public static void main(String[] args) {
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
public void run() {
System.exit(0);
}
}));
System.out.println("Hook registered");
}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Don't call system.exit from inside a shutdown hook.