/etc/apt/sources.listへのリポジトリの追加エラー
Ubuntu 14.04で http://mirror.its.dal.ca/cran/bin/linux/ubuntu/README に従いました
Installation and compilation of R or some of its packages may require Ubuntu packages from the "backports" repositories. In particular, this is the case for Tcl/Tk 8.5 on Hardy. Therefore, it is suggested to activate the backports repositories with an entry like
deb http://<my.favorite.ubuntu.mirror>/ raring-backports main restricted universe
in your /etc/apt/sources.list file. See https://launchpad.net/ubuntu/+archivemirrors for the list of Ubuntu mirrors.
https://launchpad.net/ubuntu/+archivemirrors で、「UC BerkeleyのOpen Computing Facility」を選択し、リンクをコピーしました（ http：//mirrors.ocf。 berkeley.edu/ubuntu/ ）の「http」を追加し、/etc/apt/sources.listに追加します。
deb http://mirrors.ocf.berkeley.edu/ubuntu/ raring-backports main restricted universe
Sudo apt-get updateを実行すると、次のエラーが発生します。
Err http://mirrors.ocf.berkeley.edu raring-backports/main AMD64 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/restricted AMD64 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/universe AMD64 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/main i386 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/restricted i386 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/universe i386 Packages
404 Not Found
Ign http://mirrors.ocf.berkeley.edu raring-backports/main Translation-en_US
Ign http://mirrors.ocf.berkeley.edu raring-backports/main Translation-en
Ign http://mirrors.ocf.berkeley.edu raring-backports/restricted Translation-en_US
Ign http://mirrors.ocf.berkeley.edu raring-backports/restricted Translation-en
Ign http://mirrors.ocf.berkeley.edu raring-backports/universe Translation-en_US
Ign http://mirrors.ocf.berkeley.edu raring-backports/universe Translation-en
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/main/binary-AMD64/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/restricted/binary-AMD64/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/universe/binary-AMD64/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/main/binary-i386/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/restricted/binary-i386/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/universe/binary-i386/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
出力全体は、この投稿の最後にあります。なぜ問題が発生し、どのように解決するのだろうか？ありがとう！
$ Sudo apt-get update
Ign http://us.archive.ubuntu.com trusty InRelease
Ign http://security.ubuntu.com trusty-security InRelease
Ign http://us.archive.ubuntu.com trusty-updates InRelease
Hit http://security.ubuntu.com trusty-security Release.gpg
Ign http://dl.google.com stable InRelease
Ign http://us.archive.ubuntu.com trusty-backports InRelease
Hit http://security.ubuntu.com trusty-security Release
Hit http://us.archive.ubuntu.com trusty Release.gpg
Hit http://us.archive.ubuntu.com trusty-updates Release.gpg
Hit http://security.ubuntu.com trusty-security/main Sources
Hit http://us.archive.ubuntu.com trusty-backports Release.gpg
Hit http://security.ubuntu.com trusty-security/restricted Sources
Hit http://us.archive.ubuntu.com trusty Release
Hit http://security.ubuntu.com trusty-security/universe Sources
Hit http://us.archive.ubuntu.com trusty-updates Release
Hit http://us.archive.ubuntu.com trusty-backports Release
Hit http://security.ubuntu.com trusty-security/multiverse Sources
Ign http://archive.canonical.com trusty InRelease
Hit http://us.archive.ubuntu.com trusty/main Sources
Hit http://security.ubuntu.com trusty-security/main AMD64 Packages
Hit http://us.archive.ubuntu.com trusty/restricted Sources
Ign http://extras.ubuntu.com trusty InRelease
Hit http://security.ubuntu.com trusty-security/restricted AMD64 Packages
Hit http://us.archive.ubuntu.com trusty/universe Sources
Hit http://security.ubuntu.com trusty-security/universe AMD64 Packages
Hit http://us.archive.ubuntu.com trusty/multiverse Sources
Ign http://stat.ethz.ch trusty/ InRelease
Hit http://security.ubuntu.com trusty-security/multiverse AMD64 Packages
Hit http://us.archive.ubuntu.com trusty/main AMD64 Packages
Hit http://security.ubuntu.com trusty-security/main i386 Packages
Hit http://us.archive.ubuntu.com trusty/restricted AMD64 Packages
Hit http://security.ubuntu.com trusty-security/restricted i386 Packages
Ign http://archive.canonical.com trusty InRelease
Hit http://us.archive.ubuntu.com trusty/universe AMD64 Packages
Hit http://security.ubuntu.com trusty-security/universe i386 Packages
Hit http://extras.ubuntu.com trusty Release.gpg
Hit http://us.archive.ubuntu.com trusty/multiverse AMD64 Packages
Hit http://security.ubuntu.com trusty-security/multiverse i386 Packages
Hit http://us.archive.ubuntu.com trusty/main i386 Packages
Hit http://security.ubuntu.com trusty-security/main Translation-en
Ign http://mirrors.ocf.berkeley.edu raring-backports InRelease
Hit http://us.archive.ubuntu.com trusty/restricted i386 Packages
Hit http://security.ubuntu.com trusty-security/multiverse Translation-en
Ign http://dl.google.com stable InRelease
Hit http://security.ubuntu.com trusty-security/restricted Translation-en
Hit http://archive.canonical.com trusty Release.gpg
Hit http://stat.ethz.ch trusty/ Release.gpg
Hit http://extras.ubuntu.com trusty Release
Hit http://us.archive.ubuntu.com trusty/universe i386 Packages
Ign http://mirrors.ocf.berkeley.edu raring-backports Release.gpg
Hit http://us.archive.ubuntu.com trusty/multiverse i386 Packages
Hit http://dl.google.com stable Release.gpg
Hit http://security.ubuntu.com trusty-security/universe Translation-en
Hit http://archive.canonical.com trusty Release.gpg
Hit http://us.archive.ubuntu.com trusty/main Translation-en
Hit http://dl.google.com stable Release.gpg
Hit http://stat.ethz.ch trusty/ Release
Hit http://us.archive.ubuntu.com trusty/multiverse Translation-en
Hit http://extras.ubuntu.com trusty/main Sources
Hit http://dl.google.com stable Release
Ign http://mirrors.ocf.berkeley.edu raring-backports Release
Hit http://us.archive.ubuntu.com trusty/restricted Translation-en
Hit http://archive.canonical.com trusty Release
Hit http://dl.google.com stable Release
Hit http://us.archive.ubuntu.com trusty/universe Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/main Sources
Hit http://us.archive.ubuntu.com trusty-updates/restricted Sources
Hit http://dl.google.com stable/main AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/universe Sources
Hit http://extras.ubuntu.com trusty/main AMD64 Packages
Hit http://stat.ethz.ch trusty/ Packages
Hit http://us.archive.ubuntu.com trusty-updates/multiverse Sources
Hit http://archive.canonical.com trusty Release
Hit http://us.archive.ubuntu.com trusty-updates/main AMD64 Packages
Hit http://dl.google.com stable/main i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/restricted AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/universe AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/multiverse AMD64 Packages
Hit http://extras.ubuntu.com trusty/main i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/main i386 Packages
Hit http://archive.canonical.com trusty/partner Sources
Hit http://dl.google.com stable/main AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/restricted i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/universe i386 Packages
Hit http://dl.google.com stable/main i386 Packages
Hit http://us.archive.ubuntu.com trusty-updates/multiverse i386 Packages
Hit http://archive.canonical.com trusty/partner AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-updates/main Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/multiverse Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/universe Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/main Sources
Ign https://private-ppa.launchpad.net precise InRelease
Hit http://us.archive.ubuntu.com trusty-backports/restricted Sources
Hit http://archive.canonical.com trusty/partner i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/universe Sources
Hit http://us.archive.ubuntu.com trusty-backports/multiverse Sources
Hit http://us.archive.ubuntu.com trusty-backports/main AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/restricted AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/universe AMD64 Packages
Hit https://private-ppa.launchpad.net precise Release.gpg
Hit http://us.archive.ubuntu.com trusty-backports/multiverse AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/main i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/restricted i386 Packages
Hit http://archive.canonical.com trusty/partner Sources
Hit https://private-ppa.launchpad.net precise Release
Hit http://us.archive.ubuntu.com trusty-backports/universe i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/multiverse i386 Packages
Hit http://us.archive.ubuntu.com trusty-backports/main Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/multiverse Translation-en
Hit http://archive.canonical.com trusty/partner AMD64 Packages
Hit http://us.archive.ubuntu.com trusty-backports/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/universe Translation-en
Hit https://private-ppa.launchpad.net precise/main AMD64 Packages
Hit http://archive.canonical.com trusty/partner i386 Packages
Hit https://private-ppa.launchpad.net precise/main i386 Packages
Ign http://us.archive.ubuntu.com trusty/main Translation-en_US
Ign http://us.archive.ubuntu.com trusty/multiverse Translation-en_US
Ign http://us.archive.ubuntu.com trusty/restricted Translation-en_US
Ign http://us.archive.ubuntu.com trusty/universe Translation-en_US
Ign http://dl.google.com stable/main Translation-en_US
Ign http://extras.ubuntu.com trusty/main Translation-en_US
Ign http://dl.google.com stable/main Translation-en
Ign http://dl.google.com stable/main Translation-en_US
Ign http://dl.google.com stable/main Translation-en
Ign http://archive.canonical.com trusty/partner Translation-en
Ign http://extras.ubuntu.com trusty/main Translation-en
Ign http://stat.ethz.ch trusty/ Translation-en_US
Ign http://archive.canonical.com trusty/partner Translation-en
Ign http://stat.ethz.ch trusty/ Translation-en
Ign https://private-ppa.launchpad.net precise/main Translation-en_US
Ign https://private-ppa.launchpad.net precise/main Translation-en
Err http://mirrors.ocf.berkeley.edu raring-backports/main AMD64 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/restricted AMD64 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/universe AMD64 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/main i386 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/restricted i386 Packages
404 Not Found
Err http://mirrors.ocf.berkeley.edu raring-backports/universe i386 Packages
404 Not Found
Ign http://mirrors.ocf.berkeley.edu raring-backports/main Translation-en_US
Ign http://mirrors.ocf.berkeley.edu raring-backports/main Translation-en
Ign http://mirrors.ocf.berkeley.edu raring-backports/restricted Translation-en_US
Ign http://mirrors.ocf.berkeley.edu raring-backports/restricted Translation-en
Ign http://mirrors.ocf.berkeley.edu raring-backports/universe Translation-en_US
Ign http://mirrors.ocf.berkeley.edu raring-backports/universe Translation-en
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/main/binary-AMD64/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/restricted/binary-AMD64/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/universe/binary-AMD64/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/main/binary-i386/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/restricted/binary-i386/Packages 404 Not Found
W: Failed to fetch http://mirrors.ocf.berkeley.edu/ubuntu/dists/raring-backports/universe/binary-i386/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
Ubuntu 13.04 "Raring Ringtail"のサポートは2014-01-27で終了したため、ほとんどのミラーはraring-backportsもう。
Ubuntu 14.04を使用しており、すでにtrusty-backportsアクティブ化されたパッケージソースを使用する理由はありません。削除するだけです。
READMEは古くなっているようです（バックポートを用意する必要はありません）。CRANミラー（たとえば、ウィーンのCRANマスター）に次の行を追加します。
deb http://cran.at.r-project.org/bin/linux/ubuntu trusty/
あるいは、次の構文を使用して追加できる buntu R PPA を使用できます。
Sudo add-apt-repository ppa:marutter/rrutter
この行を削除します。
deb http://mirrors.ocf.berkeley.edu/ubuntu/ raring-backports main restricted universe
this listを使用してミラーを選択します。
Florian Dieschがすでに答えているように：
Ubuntu 13.04 "Raring Ringtail"のサポートは2014-01-27で終了したため、ほとんどのミラーはraring-backportsを提供しなくなりました。