What are these zombie processes that show up in ps or top?
Zombies are dead processes. You cannot kill the dead. All processes eventually die, and when they do they become zombies. They consume almost no resources, which is to be expected because they are dead! The reason for zombies is so the zombie's parent (process) can retrieve the zombie's exit status and resource usage statistics. The parent signals the operating system that it no longer needs the zombie by using one of the wait() system calls.
When a process dies, its child processes all become children of process number 1, which is the init process. Init is ``always'' waiting for children to die, so that they don't remain as zombies.
If you have zombie processes it means those zombies have not been waited for by their parent
