process

backgrounds:

PPID : parent PID

echo $$  (show current shell PID)

init process PID=1, it is started by kernel

command: ps

1. ps　　(show process relevant to current shell)

example: 

hanying@feelcool-PC:~$ ps
PID TTY TIME CMD
4618 pts/1 00:00:00 bash
5411 pts/1 00:00:00 ps

PID: process id

TTY: id of the terminal which start this process

TIME: the time this process use CPU time (accumulate)

2. 

process

原文：http://www.cnblogs.com/hanying/p/4189895.html