Ubutun no public key signature can not verify the problem!

W:GPG Signature validation Error: Http://ppa.launchpad.net karmic Release: Because there is no public key, the following signatures cannot be verified: No_pubkey fa9c98d5dda4db69 Solution
When the above error prompts, just put the last eight bits of the copy down, and in [terminal] Enter the following command and add the eight-digit number to enter!
sudo apt-key adv--recv-keys--keyserver keyserver. Ubuntu.com dda4db69
Such problems can be resolved as such

Ubutun no public key signature can not verify the problem!