在树莓派上装了Ubuntu 14.04，自带的源在http://ports.ubuntuo.org/ 速度奇慢无比，但由于armhf的源实在稀少，国内反正是没找到。只找到两个国外的，希望能稍微提升点速度吧。
方法：
在/etc/apt/source.list.d/中添加文件trusty_source.list，内容：
deb http://mirrors.mit.edu/ubuntu-ports/ trusty main restricted universe multiverse
deb http://mirrors.mit.edu/ubuntu-ports/ trusty-updates main restricted universe multiverse
deb http://mirrors.mit.edu/ubuntu-ports/ trusty-security main restricted universe multiverse
deb http://mirrors.mit.edu/ubuntu-ports/ trusty-backports main restricted universe multiverse
deb http://mirror.csclub.uwaterloo.ca/ubuntu-ports/ trusty main restricted universe multiverse
deb http://mirror.csclub.uwaterloo.ca/ubuntu-ports/ trusty-updates main restricted universe multiverse
deb http://mirror.csclub.uwaterloo.ca/ubuntu-ports/ trusty-security main restricted universe multiverse
deb http://mirror.csclub.uwaterloo.ca/ubuntu-ports/ trusty-backports main restricted universe multiverse
然后执行：
sudo apt-get update