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

I get the following error when i do sudo apt-get update

W: GPG error: http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6AF0E940624A220

I tried following ways after reading various questions here and also by googling.

I tried

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6AF0E1940624A220

It did not help. I also tried

sudo gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys

thinking port 11371(default) may be blocked due to firewall.

I also tried to reset everything as follows

sudo rm /var/lib/apt/lists/* -vf
sudo apt-get update && sudo apt-get upgrade

still i get the same error or get update. Any other possible solution I can try?

The second approach mentioned in this link worked for me. Manually download the key and add it. Hope that helps others too.

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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 : Youtube.

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.