RK3399 ubuntu更换国内源

RK3399 的ubuntu-arm源和 X86源不一样，故做个记录。

1.备份源

sudo cp /etc/apt/sources.list /etc/apt/sources.list.tmp

2.添加国内源到系统文件中

sudo vim /etc/apt/sources.list

加入如下源并保存：

 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic multiverse
 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-updates multiverse
 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-backports main restricted universe multiverse
 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-security main restricted
 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-security universe
 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-security multiverse

3.更新源

sudo apt-get update
sudo apt-get upgrade