NPM无法工作！ “错误：ECONNREFUSED，无法联系DNS服务器”

当我输入“npm install express”时，会显示这些提示。

soasme@ubuntu:~/Desktop/nodeex$ npm install express
npm ERR! Error: ECONNREFUSED, Could not contact DNS servers
npm ERR!     at IOWatcher.callback (dns.js:74:15)
npm ERR! Report this *entire* log at:
npm ERR!     <;
npm ERR! or email it to:
npm ERR!     <[email protected]>
npm ERR! 
npm ERR! System Linux 2.6.38-8-generic
npm ERR! command "node" "/usr/local/bin/npm" "install" "express"
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /home/soasme/Desktop/nodeex/npm-debug.log
npm not ok

有没有什么可以帮到它？我对“DNS服务器”感到困惑。这是否意味着我无法解析更新的网址？日志文件写在下面：

info it worked if it ends with ok
verbose cli [ 'node', '/usr/local/bin/npm', 'install', 'express' ]
info using [email protected]
info using [email protected]
verbose config file /home/soasme/.npmrc
verbose config file /usr/local/etc/npmrc
verbose into /home/soasme/Desktop/nodeex [ 'express' ]
verbose cache add [ 'express', null ]
info addNamed [ 'express', '' ]
verbose addNamed [ null, '' ]
verbose GET express
verbose raw, before any munging express
verbose url resolving [ '/', './express' ]
verbose url resolved 
verbose url parsed { protocol: 'http:',
verbose url parsed   slashes: true,
verbose url parsed   host: 'registry.npmjs',
verbose url parsed   hostname: 'registry.npmjs',
verbose url parsed   href: '',
verbose url parsed   pathname: '/express' }
ERR! Error: ECONNREFUSED, Could not contact DNS servers
ERR!     at IOWatcher.callback (dns.js:74:15)
ERR! Report this *entire* log at:
ERR!     <;
ERR! or email it to:
ERR!     <[email protected]>
ERR! 
ERR! System Linux 2.6.38-8-generic
ERR! command "node" "/usr/local/bin/npm" "install" "express"
verbose exit [ 11, true ]

默认使用代理http://127.0.0.1.8087

所以执行：

npm config set proxy null