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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.
Adon Naaman
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2 Answers2

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Go to Settings - Software and Updates. On "Ubuntu Softare" tab, check the first four checkboxes and then in "Download from" dropdown select sane values or "Main server"

Barafu Albino
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  • Thanks man but I have the same error when try to reload 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. – Adon Naaman Sep 26 '16 at 06:07
  • 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. – Adon Naaman Sep 26 '16 at 06:07
  • @Adon Naaman You can and should remove the CD-ROM from software sources. Please check the other answer and consider accepting it. –  Sep 26 '16 at 06:12
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Remove the CD-ROM from the software sources.

Open System Settings > Software Properties and go to the tab "Other Software" (as pictured).

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Select the CD-ROM and press Remove. Type your password when prompted. Close and accept the prompt to refresh.

  • Thanks I did it but I have this error now W: The repository 'http://ppa.launchpad.net/simonschneegans/testing/ubuntu 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 http://ppa.launchpad.net/simonschneegans/testing/ubuntu/dists/xenial/main/source/Sources 403 Forbidden E: Some index files failed to download. They have been ignored, or old ones used instead. – Adon Naaman Sep 26 '16 at 06:41
  • That's a different and unrelated error albeit of the same nature: Messed up software sources. Please accept this answer and ask a new question describing that error and posting also the full error messages of sudo apt update. –  Sep 26 '16 at 06:48