Failed to fetch http://mirrors.cloud.aliyuncs.com/

服务器版本：阿里云 ubuntu 16.04

问题：
阿里云安装软件时，提示

W: Failed to fetch http://mirrors.cloud.aliyuncs.com/ubuntu/dists/xenial/InRelea                                                 se  Could not resolve 'mirrors.cloud.aliyuncs.com'
W: Failed to fetch http://mirrors.cloud.aliyuncs.com/ubuntu/dists/xenial-updates                                                 /InRelease  Could not resolve 'mirrors.cloud.aliyuncs.com'
W: Failed to fetch http://mirrors.cloud.aliyuncs.com/ubuntu/dists/xenial-securit                                                 y/InRelease  Could not resolve 'mirrors.cloud.aliyuncs.com'
W: Some index files failed to download. They have been ignored, or old ones used                                                  instead.

先给出正确的解决方案，再告诉大家，我怎么分析的

 cd /etc/apt/sources.list.d
 cp sources-aliyun-0.list sources-aliyun-0.list.bak   # 保留原版本以防改错

将 sources-aliyun-0.list 内的内容替换成以下内容

deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
##测试版源
deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
# 源码
deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted universe multiverse
##测试版源
deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted universe multiverse
# Canonical 合作伙伴和附加
deb http://archive.canonical.com/ubuntu/ xenial partner

修改完毕执行

apt-get update  # 更新源

到此，问题解决。

回顾解决过程
1、从百度和goole尚搜索，大多指向的是dns解析问题。
比如让我修改 dns 配置文件

vim /etc/resolvconf/resolv.conf.d/base

增加 2个dns解析

nameserver 8.8.8.8
nameserver 8.8.4.4

修改完毕后，执行命令

resolvconf -u

添加了dns 其实还是不行，原因就是，错误提示的网址根本没法访问。

知道了问题出在哪里，那我们就可以根据问题来解决
2、百度搜索 阿里云更换 apt-get 源。
搜索后，就出现了，文章开头的解决方案啦！