公開鍵が利用できないため、次の署名を検証できませんでした：NO_PUBKEY

Following Signatures Couldnt Be Verified Because Public Key Is Not Available

W: GPG error: http://mirrors.ustc.edu.cn/kubernetes/apt kubernetes-xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6A030B21BA07F4FB E: The repository 'http://mirrors.ustc.edu.cn/kubernetes/apt kubernetes-xenial InRelease' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6A030B21BA07F4FB