百度了很久，网上全是抄抄抄，特别是 CSDN ,要么卡，要么404，根本用不了。
将下面的源替换到 /etc/apt/source/list 即可

 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic universe
 deb http://mirrors.ustc.edu.cn/ubuntu-ports/ bionic-updates universe
 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