Debian更新时出现W: There is no public key available for the following key IDs的解决方法
刚重装debian系统，更新时出现：
W: There is no public key available for the following key IDs:
9D6D8F6BC857C906
W: There is no public key available for the following key IDs:
7638D0442B90D010
解决方法如下：
apt-get install debian-keyring debian-archive-keyring
apt-key update
