Ubuntu GPG error: http://ppa.launchpad.net

If you come across this error after running aptitude update

W: GPG error: http://ppa.launchpad.net intrepid Release: The following signatures couldn't be verified because the public key is not available:
NO_PUBKEY 7D2C7A23BF810CD5
W: You may want to run apt-get update to correct these problems




due to a missing GPG key do the following to correct the problem

gpg --keyserver subkeys.pgp.net --recv 7D2C7A23BF810CD5




Replace the key number “7D2C7A23BF810CD5″ with the one included in your error message

gpg --export --armor 7D2C7A23BF810CD5 | sudo apt-key add -

After that, the key will be added to a list and the error will not reappear.

轉自：http://gentoo-blog.de/ubuntu/ubuntu-gpg-error-httpppalaunchpadnet-intrepid-release/