重装raspberry pi系统，将apt-get的源换成阿里云的。执行报错如下：

W: Duplicate sources.list entry http://mirrors.aliyun.com/raspbian/raspbian/ jessie/main armhf Packages (/var/lib/apt/lists/mirrors.aliyun.com_raspbian_raspbian_dists_jessie_main_binary-armhf_Packages)
W: Duplicate sources.list entry http://mirrors.aliyun.com/raspbian/raspbian/ jessie/non-free armhf Packages (/var/lib/apt/lists/mirrors.aliyun.com_raspbian_raspbian_dists_jessie_non-free_binary-armhf_Packages)
W: Duplicate sources.list entry http://mirrors.aliyun.com/raspbian/raspbian/ jessie/contrib armhf Packages (/var/lib/apt/lists/mirrors.aliyun.com_raspbian_raspbian_dists_jessie_contrib_binary-armhf_Packages)
W: You may want to run apt-get update to correct these problems

解决
直接删除/etc/apt/sources.list.d/下面的文件，再次更新。