1，换源文件   /etc/apt/sources.list
        

  deb http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe multiv    erse                                                                        
  deb http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted univer    se multiverse
  deb http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted univers    e multiverse
 deb http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted univer    se multiverse
  deb http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted unive    rse multiverse
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial main restricted universe mu    ltiverse
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-security main restricted un    iverse multiverse
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-updates main restricted uni    verse multiverse
   deb-src http://mirrors.aliyun.com/ubuntu/ xenial-proposed main restricted un    iverse multiverse
  deb-src http://mirrors.aliyun.com/ubuntu/ xenial-backports main restricted u    niverse multiverse

2，解决 apt-get update 失败

问题 ： 报的是 网址出错一类的（明明PC浏览器可以正常访问网址）

解决：两个方向

        （1）命令行 ping 百度，ping不通的话。网卡IP问题

                     vim /etc/network/interfaces

                      修改点 ：  auto ens33
                                        #iface ens33 inet static
                                        iface ens33 inet dhcp  （打开自动获取IP，再次尝试）

        （2） 有些可能是 DNS问题，自行百度