Attempting to use the Java preferences API from a servlet, receiving:

java.util.prefs.FileSystemPreferences$2 run
WARNING: Couldn't create user preferences directory. User preferences are unusable.

I've created the following under both JAVA_HOME and CATALINA_HOME:

.systemPrefs/.system.lock
.systemPrefs/.systemRootModFile

and restarted Tomcat, but to no avail. Any enlightenment appreciated.

Try using the same API from a standalone Java program on z/OS. Does it work there without running under Tomcat?

Turns out that the home directory / user.home spec was invalid. Thanks.