Tengo este error:
W: Failed to fetch cdrom://Ubuntu 12.04.3 LTS _Precise Pangolin_ - Release amd64 (20130820.1)/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 bzip2:/var/lib/apt/lists/partial/jo.archive.ubuntu.com_ubuntu_dists_precise-updates_main_binary-amd64_Packages Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.