I came across this error while doing sudo apt-get update
W: GPG error: http://ppa.launchpad.net karmic Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 5A9BF3BB4E5E19B8
W: GPG error: http://ppa.launchpad.net karmic Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 9ABD05E22847688C
This made me do some hunting on the web. I tried quite a few solutions out of which the following worked.
Run the following command in terminal:
gpg --keyserver subkeys.pgp.net --recv 5A9BF3BB4E5E19B8
gpg --export --armor 5A9BF3BB4E5E19B8 | sudo apt-key add –
Replace 5A9BF3BB4E5E19B8 with your own key. This solved the error. I repeated the procedure for second key and I stopped getting error messages.
On the first command, sometimes the server maybe down. In that case you can try the following servers.
To use these servers just replace subkeys.pgp.net with any of the server above. For eg;
gpg --keyserver http://keys.gnupg.net --recv 5A9BF3BB4E5E19B8