在使用树莓派的时候,我是用了阿里云开源镜像站的树莓派源

deb http://mirrors.aliyun.com/raspbian/raspbian/ wheezy main non-free contrib  
deb-src http://mirrors.aliyun.com/raspbian/raspbian/ wheezy main non-free contrib  

出现了以下提醒

WARNING: The following packages cannot be authenticated!  
Install these packages without verification [y/N]?  

在运行

apt-get install debian-archive-keyring  
apt-get update  

无效的时候,使用

sudo apt-get upgrade -allow-unauthenticated  

成功upgrade