[Ubuntu] Error while running "sudo apt-get update" or "sudo apt-get install" on live cd Ubuntu

source: http://askubuntu.com/questions/140940/why-do-i-receive-the-duplicate-sources-error-message-during-an-ubuntu-12-04-li

Question:

When I boot the Ubuntu 12.04 desktop Live CD and run the command sudo apt-get update, the final messages are the warning messages below.

Reading package lists... Done
W: Duplicate sources.list entry cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Release amd64 (20120425)/ precise/main i386 Packages (/var/lib/apt/lists/Ubuntu%2012.04%20LTS%20%5fPrecise%20Pangolin%5f%20-%20Release%20amd64%20(20120425)_dists_precise_main_binary-i386_Packages)
W: Duplicate sources.list entry cdrom://Ubuntu 12.04 LTS _Precise Pangolin_ - Release amd64 (20120425)/ precise/restricted i386 Packages (/var/lib/apt/lists/Ubuntu%2012.04%20LTS%20%5fPrecise%20Pangolin%5f%20-%20Release%20amd64%20(20120425)_dists_precise_restricted_binary-i386_Packages)
W: You may want to run apt-get update to correct these problems

However, there do not appear to be any duplicate sources in /etc/apt/sources.list

# /etc/apt/sources.list

deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release amd64 (20120425)]/ dists/precise/main/binary-i386/
deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release amd64 (20120425)]/ dists/precise/restricted/binary-i386/
deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release amd64 (20120425)]/ precise main restricted
deb http://archive.ubuntu.com/ubuntu/ precise main restricted
deb http://security.ubuntu.com/ubuntu/ precise-security main restricted
deb http://archive.ubuntu.com/ubuntu/ precise-updates main restricted

Answer:

1. Remove or rename /etc/apt/sources.list.

2. Run "gksudo software-properties-gtk" to configure a new sources.list file.
(Check proper select boxes through each tabs, including 'change server' for your region.
 


3. Now, run "sudo apt-get update" to apply new sources.list to the system.

4. You are ready to go. For example, run "sudo apt-get install vlc"