原因：自带源在国内无法连接。

源路径：/etc/apt/sources.list

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1、用命令打开源配置文件

　　sudo vim /etc/apt/sources.list

2、将内容替换如下

　　deb http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
　　deb http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
　　deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
　　deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
　　deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
　　deb-src http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
　　deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
　　deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
　　deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
　　deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse

3、更新列表

　　sudo apt-get update

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