注意：不同版本（16.04,18.04,20.04）的源是不一样的
更新源步骤
首先安装vim
Ctrl+Alt+T，打开terminal终端
输入如下命令
sudo apt-get install vim
以网易源举例如下
16.04的网易源
deb http://mirrors.163.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ xenial-backports main restricted universe multiverse
下面两种源未进行核对，不建议使用，否则安装软件时会报各种各样的错误
如unstable，，软件包级别大于……且……正在被安装
deb http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ wily-backports main restricted universe multiverse
