npm安装forever 报错：npm ERR! network 'proxy' config is set properly. See: 'npm help config'

 # 安装：
npm install forever -g

报错，错误信息如下，

npm WARN optional dep failed, continuing [email protected]
npm ERR! Linux 3.10.0-229.el7.x86_64
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "forever"
npm ERR! node v4.2.2
npm ERR! npm  v2.14.7
npm ERR! code ECONNRESET
npm ERR! errno ECONNRESET
npm ERR! syscall read

npm ERR! network read ECONNRESET
npm ERR! network This is most likely not a problem with npm itself
npm ERR! network and is related to network connectivity.
npm ERR! network In most cases you are behind a proxy or have bad network settings.
npm ERR! network 
npm ERR! network If you are behind a proxy, please make sure that the
npm ERR! network 'proxy' config is set properly.  See: 'npm help config'
npm ERR! Linux 3.10.0-229.el7.x86_64
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" &#