备份系统默认的源。
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
打开sources.list文件。
vim /etc/apt/sources.list
删除原有内容，dd
然后将里面的内容替换为以下内容并保存关闭。
阿里源：
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
清华源：
# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释 deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted universe multiverse # deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-security main restricted universe multiverse # 预发布软件源，不建议启用 # deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse
中科大源：
deb http://mirrors.ustc.edu.cn/ubuntu/ xenial main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-security main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-security main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse