问题：

虚拟机安装 ubuntu 后，更新源无效，以及无法联网安装软件； 
错误提示： 
Err http://security.ubuntu.com/ubuntu/ trusty-security/universe putty-tools amd64 0.63-4ubuntu0.1 
Could not resolve 'security.ubuntu.com' 
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/universe/p/putty/putty_0.63-4ubuntu0.1_amd64.deb Could not resolve 'security.ubuntu.com'
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

apt-get install putty-tools 
Reading package lists… Done 
Building dependency tree 
Reading state information… Done 
Suggested packages: 
putty-doc 
The following NEW packages will be installed: 
putty-tools 
0 upgraded, 1 newly installed, 0 to remove and 11 not upgraded. 
Need to get 298 kB of archives. 
After this operation, 1,522 kB of additional disk space will be used. 
WARNING: The following packages cannot be authenticated! 
putty-tools 
Install these packages without verification? [y/N] Y 
Err http://us.archive.ubuntu.com/ubuntu/ trusty-updates/universe putty-tools amd64 0.63-4ubuntu0.1 
Could not resolve ‘us.archive.ubuntu.com’ 
Err http://security.ubuntu.com/ubuntu/ trusty-security/universe putty-tools amd64 0.63-4ubuntu0.1 
Could not resolve ‘security.ubuntu.com’ 
E: Failed to fetch http://security.ubuntu.com/ubuntu/pool/universe/p/putty/putty-tools_0.63-4ubuntu0.1_amd64.deb Could not resolve ‘security.ubuntu.com’ 
E: Unable to fetch some archives, maybe run apt-get update or try with –fix-missing?

解决方法：

修改DNS，编辑如下文件：

# edit /etc/resolv.conf

nameserver 8.8.8.8

nameserver 8.8.4.4

搞定！！！

http://blog.csdn.net/tmt123421/article/details/52912224