How to resolve this problem? "Failed to download repository information"

Question

i try to update something and when i change the download server, it says my software is out-of-date and i press reload after it the download is interupted and saying this: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.

Answer 1

Your configuration seems to include the CD you installed from, which is no longer mounted, and is useless for updates.

Either ignore the error (after all, They have been ignored, or old ones used instead. or find the line(s) in /etc/apt/sources.list and /etc/apt/sources.list.d/* that mention "deb cdrom://Ubuntu 16.04.1 LTS ..." and comment (with a # in the first column) or delete these lines.