I am attempting to update my Ubuntu/Debian system and I am getting an error:
GPG error: http://deb.opera.com stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E585066A30C18A2B
Try following approach, is from there
NO_PUBKEY E585066A30C18A2Bis the key for the Opera web browser. To correct the error, run the following code.
wget -O - http://deb.opera.com/archive.key | apt-key add