错误代码：
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
2.解决方法：
#apt-get install debian-keyring debian-archive-keyring #apt-key update
3.验证：
#apt-get update
原文：http://my.oschina.net/jk409/blog/472780