I would like to erase the following message:
HOW to do so?

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
, W:Failed to fetch http://ppa.launchpad.net/yannubuntu/...-i386/Packages 404 Not Found
, E:Some index files failed to download. They have been ignored, or old ones used instead.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
, W:Failed to fetch http://ppa.launchpad.net/yannubuntu/...-i386/Packages 404 Not Found
, E:Some index files failed to download. They have been ignored, or old ones used instead.

If you really mean "erase the following message" then closing down the application in which the message appeared should get rid of it. If you mean fix the error that occurred then that is another story. Please clarify what you want to do. It seem like your are trying to add new packages from a CD when you should be downloading them from a repository. If this is what you want then post the content of your /etc/apt/sources.list file.
jdk

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you should be able to disable the cdrom repo and the ppa in the ubuntu sources app. once the sources are removed, reload your sources and the errors should be gone.

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If that doesn't work, try apt-get clean as root in a terminal (assuming Ubuntu still has apt). From the man page:

I had a similar issue recently and apt-get clean fixed it.

1 members found this post helpful.

I have been busy moving to a retirement apartment; and that has been done. I plan to get out the notebook containing Ubuntu OS and will try Frank Bell's approach initially. Hope that will work!

I appreciate the suggestions by dolphin oracle and jdkaye. Thanks to all.

In reply to Frank Bell's suggestion, I tried:

william2@william2-laptop:~$ apt-get clean
E: Could not open lock file /var/cache/apt/archives/lock - open (13: Permission denied)
E: Unable to lock the download directory

Any suggestions appreciated. Thanks.

Your prompt shows you are running the command as an ordinary user and that won't work. Preface it with sudo and enter your user password when prompted:

Actually, I ran the command as yancek suggested initially. I have rerun the command, entered the password, and received the same response as indicated above. I have also tried repeating the command several times; always the same response. Suggestions appreciated.

1. Did you use your own password (not root's) when using sudo?
2. Are you on the sudoers list?
3. If you don't know 2 then post the output of this command which must be executed as root:
You should see your username in this file or else you can't use sudo until the file is edited.
4. If you can't use sudo then give this command from a terminal:
and give the root password.
Now you can give the command
and it should work.
jdk

Hi jdk,

I attempted to follow your suggestions, however, I am beginning to suspect that the password I used is no longer recognized as such (or I do not know how to know how to execute as root).
When I entered cat /etc/sudoers, the response was: cat: /etc/sudoers: Permission denied
When I entered su, followed by entry of my password, the response was Authentication failure.

What next?

If you have a live disc version of linux you can chroot to the ubuntu install and use passwd to set/reset the password. Check to see if the caps lock key is on as passwords are case sensitive in linux. On laptops you can sometimes push the Fn key and set the keyboard into a mode where the numberpad characters are typed instead of the qwerty ones. So that could be a few things that prevent your password from working as expected.

It sounds like you might have had a failure mid-install / update. You can recover from it, but not always simple to do.

$ sudo nano /etc/apt/sources.list

And add a # in front of the cdrom lines to comment them out. If you had a power outage during an upgrade you could have corrupted your apt files.

$ sudo dpkg --clear-avail
$ sudo dselect update

Please remember that your password as a user is different with root's password.

Enter:

then enter your password as a normal user.

Enter

then enter root's password

Here are easy instructions (with screenshots) to reset a forgotten password in Ubuntu:

http://www.psychocats.net/ubuntu/resetpassword

In the event that "sudo" has stopped working:

http://www.psychocats.net/ubuntu/fixsudo

Important note: There is no "root user" in Ubuntu and "su" won't work. Some of the users above have given you excellent advice for non-Ubuntu distros, but please don't try this well-intentioned advice in Ubuntu! Make sure any tutorials you follow come from Ubuntu-specific sources.

Ohh. Didn't know that. Thanks for pointing that out.