W: The repository 'cdrom://Ubuntu 16.04.1 LTS _Xenial Xerus_ - Release AMD64 (20160719) xenial Release' does not have a Release file.
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.
E: Failed to fetch cdrom://Ubuntu 16.04.1 LTS _Xenial Xerus_ - Release AMD64 (20160719)/dists/xenial/main/binary-AMD64/Packages Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
E: Some index files failed to download. They have been ignored, or old ones used instead.
[設定]-[ソフトウェアと更新]に移動します。 [Ubuntu Software]タブで、最初の4つのチェックボックスをオンにし、[Download from]ドロップダウンで正しい値または[Main server]を選択します