zombie processes

Sometimes you cannot kill some processes via the regular command kill -9 PID When you list them with ps -aux you will see the entry defunct Those defunct processes are apparently still hanging around mostly because their parent application is waiting for them to receive something. These processes are already dead, that's why they are called "zombies". In order to kill them, you have to kill the parent application first. You can figure out what the parent's PID is by issuing pstree PID