nice
nice功能说明：设置优先权。
语 法：nice [-n <优先等级>][--help][--version][执行指令]
补充说明：nice指令可以改变程序执行的优先权等级。
参 数：
-n<优先等级>或-<优先等级>或--adjustment=<优先等级> 设置欲执行的指令的优先权等级。等级的范围从-20－19，其中-20最高，19最低，只有系统管理者可以设置负数的等级。
--help 在线帮助。
--version 显示版本信息。
nice
nice [option] [command [arguments] ]
Execute a command (with its arguments) with lower priority (i.e., be "nice" to other users). With no command, nice prints the current scheduling priority (niceness). If nice is a child process, it prints the parent process's scheduling priority. Niceness has a range of -20 (highest priority) to 19 (lowest priority).
Options
Print a help message and then exit.
Run command with niceness incremented by adjustment (1-19); default is 10. A privileged user can raise priority by specifying a negative adjustment (e.g., -5).
Print version information and then exit.