A process can exist in one of many states:

• A process can exist in one of many states:

• Runnable
• on run queue, in effect one of currently executing processes
• Sleeping
• waiting for event to occur to wake up and react/start up
• Stopped
• not currently executing, waiting to be killed or restarted
• Uninterruptable sleep
• cannot be woken until specific expected event
• Defunct (zombie) process
• just before a process dies, it notifies its parent and waits for an acknowledgment If it never receives it, its PID is not freed up but all other resources are freed. Zombies can usually be cleared by rebooting/restarting the system.