mirrors.yun-idc.com,这个源可比ubuntu自带的源快多了,我的source.list文件内容如下：
deb http://mirrors.yun-idc.com/ubuntu/ trusty main universe restricted multiverse
deb-src http://mirrors.yun-idc.com/ubuntu/ trusty main universe restricted multiverse
deb http://mirrors.yun-idc.com/ubuntu/ trusty-security universe main multiverse restricted
deb-src http://mirrors.yun-idc.com/ubuntu/ trusty-security universe main multiverse restricted
deb http://mirrors.yun-idc.com/ubuntu/ trusty-updates universe main multiverse restricted
deb http://mirrors.yun-idc.com/ubuntu/ trusty-proposed universe main multiverse restricted
deb-src http://mirrors.yun-idc.com/ubuntu/ trusty-proposed universe main multiverse restricted
deb http://mirrors.yun-idc.com/ubuntu/ trusty-backports universe main multiverse restricted
deb-src http://mirrors.yun-idc.com/ubuntu/ trusty-backports universe main multiverse restricted
deb-src http://mirrors.yun-idc.com/ubuntu/ trusty-updates universe main multiverse restricted