The following signature cannot be verified because there is no public key: no_pubkey

From: http://blog.sina.com.cn/s/blog_613126600100r4uv.html

I don't know which software was installed. An error was reported during Ubuntu update. No. I found one from the Internet.
Install untrusted software packages

First, execute the update.

Sudo apt-Get update

There is a sense of error.

Reading the package list... complete W: GPG error: http://ppa.launchpad.net natty release: unable to verify the following signature because there is no public key: no_pubkey f1773af13b1510fd W: GPG error: http://ppa.launchpad.net natty release: unable to verify the following signature because there is no public key: no_pubkey 38b43cc308516fbe

The Public Key is missing. It seems that you need to download the public key. Download the public key from the PGP Public Key Server
There are many servers. I found them in subkeys.pgp.net. Wwwkeys.pgp.net is frequently used. If subkeys cannot be found, switch to wwwkeys.

GPG -- keyserver subkeys.pgp.net -- Recv 3b1510fd

Note that the red part is the last 8 bits of no_pubkey f1773af13b1510fd in the previous article.

Import key

GPG -- export -- armor 3b1510fd | sudo apt-key add-

Complete