[Ubuntu] W: GPG error: http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available:

The link above provides detailed explanation with screenshots. It also has some other simple methods that could be tried before doing this manually. Since it is not accessible from some regions let me describe the method that worked for me.

1. Go to the OpenPGP Public Key Server. There you can enter your key into the Search String field, leaving everything else as is, then click "Search!".
   When searching for a key, always prepend 0x to it! This means that, for example, you have to search for 0x6AF0E1940624A220 instead of 6AF0E1940624A220.
2. Click on the link provided in the pub section. This should take you to page containing the key. The page's heading should be similar to Public Key Server -- Get "0x6AF0E1940624A220"
3. Copy everything from underneath the title (starting from -----BEGIN PGP PUBLIC KEY BLOCK-----) and save it in a file (e.g. key1).

4. Once you have the file, run the following command

   sudo apt-key add key1
   

You will get an "OK" response.

And you are done. Repeat the procedure of other keys that might be missing.

 

 

에러메시지에 보면 마지막 PUBLIC KEY 하고 뒤에 키값이 나온다....

OpenPGP Public Key Server 링크 클릭 후 그 키 값 앞에 0x 를 붙여서 검색..

그리고 나온 링크를 클릭하면 key 값이 나오는데 그걸 복사해서 저장한다.

그리고 sudo apt-key add 키파일명 을 해주고 apt-get update 를 다시 실행.