Process management command

init: Process number is 1

Classification of processes：
     the processes associated with the terminal
     Terminal independent process

1.process state：

     D： Non interrupted sleep
     R： Run or ready
     S： Interrupted sleep
     T： Stop it
     Z:  Zombie state

     <:  High priority process
     N： Low priority process
     +： Processes in the foreground process group
     l ...