RK3399 的ubuntu-arm源和 X86源不一樣，故做個記錄。
1.備份源
sudo cp /etc/apt/sources.list /etc/apt/sources.list.tmp
2.添加國內源到系統文件中
sudo vim /etc/apt/sources.list
加入如下源並保存：
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