nice-调整进程的优先级

# nice
## 使用帮助
```shell
root@pi:~# nice --help
Usage: nice [OPTION] [COMMAND [ARG]...]
Run COMMAND with an adjusted niceness, which affects process scheduling.
With no COMMAND, print the current niceness.  Niceness values range from
-20 (most favorable to the process) to 19 (least favorable to the process).

Mandatory arguments to long options are mandatory for short options too.
  -n, --adjustment=N   add integer N to the niceness (default 10)
      --help     display this help and exit
      --version  output version information and exit

NOTE: your shell may have its own version of nice, which usually supersedes
the version described here.  Please refer to your shell's documentation
for details about the options it supports.

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Full documentation at: <https://www.gnu.org/software/coreutils/nice>
or available locally via: info '(coreutils) nice invocation'
```

## 示例
- 默认优先级为10，最高优先级为-20，最低为19，数字越小优先级越高，`优先级越高获取的CPU运行时间就越多`

```
nice -n -20 echo "I'm the most favorable process on CPU"
```

## 查看
- top
默认为0
![](/media/202108/2021-08-13_153804.png)

- nice -n -20 top -c 
设置为-20
![](/media/202108/2021-08-13_153859.png)