apt-get更新问题：Failed to Fetch : http://

解决方案：

cd /var/lib/apt/lists/partial
rm *

sshd允许Root登录

cd /etc/ssh
vim sshd_config
PermitRootLogin yes
service ssh restart

中国国内源更换

https://lug.ustc.edu.cn/repogen/

# testing 源
deb http://mirrors.ustc.edu.cn/debian testing main contrib non-free
deb-src http://mirrors.ustc.edu.cn/debian testing main contrib non-free
deb http://mirrors.ustc.edu.cn/debian testing-proposed-updates main contrib non-free
deb-src http://mirrors.ustc.edu.cn/debian testing-proposed-updates main contrib non-free
deb http://mirrors.ustc.edu.cn/debian testing-updates main contrib non-free
deb-src http://mirrors.ustc.edu.cn/debian testing-updates main contrib non-free