问题现象

ubuntu apt-get update 失败

问题现象如：

W: Failed to fetch http://mirrors.aliyun.com/debian/dists/wheezy/InRelease Temporary failure resolving ‘mirrors.aliyun.com’
W: Failed to fetch http://mirrors.aliyun.com/debian/dists/wheezy-updates/InRelease Temporary failure resolving ‘mirrors.aliyun.com’
W: Failed to fetch http://mirrors.aliyun.com/debian-security/dists/wheezy/updates/InRelease Temporary failure resolving ‘mirrors.aliyun.com’
W: Some index files failed to download. They have been ignored, or old ones used instead.

以及： 各种东西下载失败 ping www.baidu.com ping不通等等

解决方法1（临时办法）

vim /etc/resolv.conf # 追加 
nameserver 8.8.8.8
nameserver 8.8.4.4
nameserver 198.153.192.1
nameserver 198.153.194.1
nameserver 208.67.222.222
nameserver 208.67.220.220# 然后重启网络   其实不重启也行
sudo /etc/init.d/networking restart
# 注意重启后就重置然后失效了 需要重新添加

解决方法2

大部分上不去网都是DNS的问题

修改dns

# 取消DNS行注释，并增加DNS配置如：114.114.114.114，修改后重启下计算机
vim /etc/systemd/resolved.conf

修改如下：