Java ProcessBuilder: Deadlocks, Zombies, and the 64KB Wall

Originally published in Level Up Coding on Medium. You can read the original version here. Recently at IBM Software Labs, I worked on a task that forced me to understand something many Java developers rarely think about — how Java interacts with the operating system. Most of our daily work happens safely inside the JVM. Memory management, threads, and file handling — the JVM abstracts these away nicely. But sometimes you need to step outside. You want to run a shell script, invoke a system binary, or trigger a native tool that no Java library wraps. This is where ProcessBuilder comes in. ProcessBuilder is the modern Java API for executing native OS commands from Java code. But the moment you call pb.start(), you leave the JVM's safe world. What follows is deadlocks, zombie processes, file descriptor leakage, and race conditions — OS-level problems the JVM cannot protect you from. ProcessBuilder: The Basics Before we go any deeper, let me show you what ProcessBuilder actually looks like