ubuntu public key

一种方法如下：

Try this as root:
# gpg --recv-keys 4D270D06F42584E6
# gpg --export 4D270D06F42584E6 | apt-key add -
That should download the key from a public keyserver and then the second command adds it to apt. You may need to specify a keyserver if the default doesn't work. There are several public ones available.
另一种方法似乎更为简单：

# apt-get install debian-keyring debian-archive-keyring
# apt-key update
尝试了第二种方法，成功解决了public key的问题。