OK, I feel like a complete newbie posting this, but this has baffeled
me completely. I tried to execute the following:

java -cp a.jar -jar b.jar

Of course b.jar requires a.jar to run and both jars are in the same
directory. It worked on windows but not on Debian. I've checked a
million times that a.jar could be found by Debian (tried absolute
paths, relative paths, exported classpath env. variables, path env.
variables etc etc).

What could explain the difference between Windows and Debian? Are jars
treated differently on both platforms? Is it something in the manifest?