最近在ubuntu 12.10上执行sudo apt-get update 命令后出现了如下错误：
Ign http://extras.ubuntu.com natty/main TranslationIndex Err http://extras.ubuntu.com natty/main Sources 404 Not Found Err http://extras.ubuntu.com natty/main i386 Packages 404 Not Found Ign http://extras.ubuntu.com natty/main Translation-en_US Err http://security.ubuntu.com natty-security/universe Sources 404 Not Found [IP: 91.189.92.200 80] Err http://security.ubuntu.com natty-security/multiverse Sources 404 Not Found [IP: 91.189.92.200 80] Ign http://extras.ubuntu.com natty/main Translation-en Err http://security.ubuntu.com natty-security/universe i386 Packages 404 Not Found [IP: 91.189.92.200 80] Err http://security.ubuntu.com natty-security/multiverse i386 Packages 404 Not Found [IP: 91.189.92.200 80] Err http://security.ubuntu.com natty-security/main Sources 404 Not Found [IP: 91.189.92.200 80] Err http://security.ubuntu.com natty-security/restricted Sources 404 Not Found [IP: 91.189.92.200 80] Err http://security.ubuntu.com natty-security/main i386 Packages 404 Not Found [IP: 91.189.92.200 80] Err http://security.ubuntu.com natty-security/restricted i386 Packages 404 Not Found [IP: 91.189.92.200 80] Ign http://security.ubuntu.com natty-security/main Translation-en_US Ign http://security.ubuntu.com natty-security/main Translation-en Ign http://security.ubuntu.com natty-security/multiverse Translation-en_US Ign http://security.ubuntu.com natty-security/multiverse Translation-en Ign http://security.ubuntu.com natty-security/restricted Translation-en_US Ign http://security.ubuntu.com natty-security/restricted Translation-en Ign http://security.ubuntu.com natty-security/universe Translation-en_US Ign http://security.ubuntu.com natty-security/universe Translation-en W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/main/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/restricted/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/universe/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/multiverse/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/main/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/restricted/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/universe/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty/multiverse/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/main/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/restricted/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/universe/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/multiverse/source/Sources 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/main/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/restricted/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/universe/binary-i386/Packages 404 Not Found W: Failed to fetch http://cn.archive.ubuntu.com/ubuntu/dists/natty-updates/multiverse/binary-i386/Packages 404 Not Found W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/universe/source/Sources 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/multiverse/source/Sources 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/universe/binary-i386/Packages 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/multiverse/binary-i386/Packages 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/main/source/Sources 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/restricted/source/Sources 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/main/binary-i386/Packages 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/natty-security/restricted/binary-i386/Packages 404 Not Found [IP: 91.189.92.200 80] W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/natty/main/source/Sources 404 Not Found W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/natty/main/binary-i386/Packages 404 Not Found E: Some index files failed to download. They have been ignored, or old ones used instead. chaihuasong@chaihuasong:~$ sudo apt-get install git Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package git
发现很多源找不到，需要重新寻找更新源，最后把/etc/apt/sources.list文件中的内容直接替换成:
# deb cdrom:[Ubuntu 15.04 _Vivid Vervet_ - Release i386 (20150422)]/ vivid main restricted # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to # newer versions of the distribution. deb http://us.archive.ubuntu.com/ubuntu/ vivid main restricted deb-src http://us.archive.ubuntu.com/ubuntu/ vivid main restricted ## Major bug fix updates produced after the final release of the ## distribution. ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team. Also, please note that software in universe WILL NOT receive any ## review or updates from the Ubuntu security team. deb http://us.archive.ubuntu.com/ubuntu/ vivid universe deb-src http://us.archive.ubuntu.com/ubuntu/ vivid universe ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team, and may not be under a free licence. Please satisfy yourself as to ## your rights to use the software. Also, please note that software in ## multiverse WILL NOT receive any review or updates from the Ubuntu ## security team. deb http://us.archive.ubuntu.com/ubuntu/ vivid multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ vivid multiverse ## N.B. software from this repository may not have been tested as ## extensively as that contained in the main release, although it includes ## newer versions of some applications which may provide useful features. ## Also, please note that software in backports WILL NOT receive any review ## or updates from the Ubuntu security team. deb http://us.archive.ubuntu.com/ubuntu/ vivid-backports main restricted universe multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ vivid-backports main restricted universe multiverse deb http://security.ubuntu.com/ubuntu vivid-security main restricted deb-src http://security.ubuntu.com/ubuntu vivid-security main restricted deb http://security.ubuntu.com/ubuntu vivid-security universe deb-src http://security.ubuntu.com/ubuntu vivid-security universe deb http://security.ubuntu.com/ubuntu vivid-security multiverse deb-src http://security.ubuntu.com/ubuntu vivid-security multiverse ## Uncomment the following two lines to add software from Canonical's ## 'partner' repository. ## This software is not part of Ubuntu, but is offered by Canonical and the ## respective vendors as a service to Ubuntu users. # deb http://archive.canonical.com/ubuntu vivid partner # deb-src http://archive.canonical.com/ubuntu vivid partner