eu faço isso e funciona para mim:
wget -nv https://download.opensuse.org/repositories/home:selmf/xUbuntu_16.04/Release.key -O Release.key
sudo apt-key add - < Release.key
sudo apt-get update
source: link
W: GPG error: http://download.opensuse.org/repositories/home:/strycore/xUbuntu_16.04 ./ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 2F7F0DA5FD5B64B9
W: The repository 'http://download.opensuse.org/repositories/home:/strycore/xUbuntu_16.04 ./ Release' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
Estou tentando me livrar da mensagem de erro acima, aparentemente relacionada ao release key e ao URL opensuse.
Qual seria a solução adequada?