新手上路 Ubuntu 更新源无法使用命令update

关于Ubuntu 在虚拟机中出现各种 sudo apt update 问题，只是更新源是国外网站而已，无法访问，找过很多帖子，大多解决不了问题，于是写下此帖以避雷之。

1，打开终端 ctrl + alt + t

2，vi /etc/apt/sources.list

deb http://mirrors.aliyun.com/ubuntu/ trusty main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-security main multiverse restricted universe
deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main multiverse restricted universe
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main multiverse restricted universe

3，清空Ubuntu上原sources.list 上所有文字，粘贴保存退出

4，打开终端 输入 sudo apt update