注意：一下均是非实时进程的优先级的设置
nice(1): 以指定优先级运行程序
nice [OPTION] [COMMAND [ARG]...]
nice –n 1 ls
renice(8): 调整运行进程的优先级
renice priority [[-p] pid ...] [[-g] pgrp ...] [[-u] user ...]
renice +1 987 -u daemon root -p 32
API：
nice(2): 改变进程优先级
int nice(int inc);
getpriority(2): 获取优先级
int getpriority(int which, int who);
setpriority(2): 设置优先级
int setpriority(int which, int who, int prio);