apt-get update : pulic key error

apt-get update  出现 这种错误

Reading package lists... Done

W: There is no public key available for the following key IDs:

7638D0442B90D010

W: There is no public key available for the following key IDs:

7638D0442B90D010

W: There is no public key available for the following key IDs:

9D6D8F6BC857C906

  google bing之后， 得到解答：

  

?

1 2	apt-get install debian-keyring debian-archive-keyring apt-get update

  整个世界，清静了 :-Dapt-get update  出现 这种错误

Reading package lists... Done

W: There is no public key available for the following key IDs:

7638D0442B90D010

W: There is no public key available for the following key IDs:

7638D0442B90D010

W: There is no public key available for the following key IDs:

9D6D8F6BC857C906

  google bing之后， 得到解答：

  

?

1 2	apt-get install debian-keyring debian-archive-keyring apt-get update

  整个世界，清静了 :-Dapt-get update  出现 这种错误

Reading package lists... Done

W: There is no public key available for the following key IDs:

7638D0442B90D010

W: There is no public key available for the following key IDs:

7638D0442B90D010

W: There is no public key available for the following key IDs:

9D6D8F6BC857C906

  google bing之后， 得到解答：

  

?

1 2	apt-get install debian-keyring debian-archive-keyring apt-get update

  整个世界，清静了 :-D