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Failed to download repository information due to missing CDROM

W:Failed to fetch cdrom://Ubuntu 12.04 LTS Precise Pangolin - Release i386 
(20120423)/dists/precise/main/binary-i386/Packages 
Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
W:Failed to fetch cdrom://Ubuntu 12.04 LTS Precise Pangolin - Release i386 
(20120423)/dists/precise/restricted/binary-i386/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.

The above information is a crash info. It happens when I manually update Ubuntu. I have marked all checkboxes in settings that weren't marked by default.

What is the reason for this problem?

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marked as duplicate by jokerdino, LnxSlck, Anwar Shah, Jorge Castro, hexafraction Sep 21 '12 at 19:27

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1 Answer 1

up vote 2 down vote accepted

If you've checked the CD-ROM in the sources and do not have the CD in the drive, the error message correctly tells that it was unable to fetch packages from it.

It is usually unnecessary to check them after a working installation, so you can safely uncheck them.

(Alternatively you can insert the installation media into the drive and check if the error message goes away.)

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