W:The repository 'cdrom://Ubuntu 16.04.1 LTS _Xenial Xerus_ - Release amd64 (20160719) xenial Release' does not have a Release file., W

ata from such a repository can't be authenticated and is therefore potentially dangerous to use., W:See apt-secure(8) manpage for repository creation and user configuration details., W:The repository '
xenial Release' does not have a Release file., W

ata from such a repository can't be authenticated and is therefore potentially dangerous to use., W: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:Failed to fetch
404 Not Found, E:Some index files failed to download. They have been ignored, or old ones used instead.