How do I get rid of Java child processes when my Java app exits/crashes?

As you said, addShutdownHook is the way to go.

BUT:

• There's no real guarantee that your shutdown hooks are executed if the program terminates. Someone could kill the Java process and in that case your shutdown hook will not be executed. (as said in this SO question)

• some of the standard libraries have their own hooks which may run before yours.

• beware of deadlocks.

Another possibility would be to wrap your java program in a service.

I worked it out myself already. I add a shutdown hook, as follows:

final String[] cmd = {"<childProcessName>"};
final Process process = Runtime.getRuntime().exec(cmd);
Runnable runnable = new Runnable() {
    public void run() {
        process.destroy();
    }
};
Runtime.getRuntime().addShutdownHook(new Thread(runnable));