W: GPG error: http://ppa.launchpad.net/webupd8team/java/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248 EEA14886 code example
Example: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6494C6D6997C215E