i try to update something and when i change the download server, it says my software is out-of-date and i press reload after it the download is interupted and saying this:
Check your internet connection:
W:The repository 'cdrom://Ubuntu 16.04.1 LTS Xenial Xerus - Release amd64 (20160719) xenial Release' does not have a Release file.,
W:Data 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:Some index files failed to download. They have been ignored, or old ones used instead.
sorry for my bad english. thanks.