sources.list作用的总结

Ubuntu中软件更新的源服务器地址存储再/etc/apt/soures.list中。文件中的内容如下：
deb http://archive.ubuntu.com/ubuntu/ trusty main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
上面是ubuntu官方的软件源。具体含义如下，

每一行的开头是deb和deb-src，表示直接通过.deb文件或者源文件的方式来进行安装;
第二字段，即deb和deb-src字段后是一段URL，这是软件源的地址
第三字段，即URL后的字段，是再URL路径中的dists目录下对应的文件夹，如图所示

第四～七字段都是第三字段对应的目录下的子目录

但是由于ubuntu的官方软件源下载速度慢而且有些第三方软件的安装包过于陈旧，已不能满足用户的需求。因此需要添加第三方软件更新源。本文以163的软件源为例讲述更新软件源的方法。

更新sources.list

在网上能够很方便的查到163的ubuntu的软件源的方法，sudo gedit /etc/apt/source.list，再打开的文件中添加如下内容：
deb http://mirrors.163.com/ubuntu/ raring main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ raring-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ raring-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ raring-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ raring-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ raring main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ raring-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ raring-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ raring-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ raring-backports main restricted universe multiverse
保存退出后运行命令：sudo apt-get update。
但是，这样修改后会在更新软件时会出现404 not found的错误，这是由于对于ubuntu各个版本的软件位置是不一样的，因此，需要根据ubuntu的版本号来选择对应的软件源路径。

选择对应版本的软件源

ubuntu各版本的名称如下

由于我的ubuntu版本是14.04所以需要将上面的内容修改为：
deb http://tel.mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://tel.mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://tel.mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://tel.mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://tel.mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://tel.mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://tel.mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://tel.mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://tel.mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://tel.mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
然后再次保存，sudo apt-get update

总结

保存sources.list，sudo cp /etc/apt/sources.list
/etc/apt/sources.list-backup;

打开sources.list，sudo gedit /etc/apt/sources.list;

将需要更新的软件源复制到文档中;

根据ubuntu的版本将每行的第三个字段换成对应版本的名称;

保存文档，并退出;

刷新软件源，sudo apt-get update

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参考资料：
[1]http://www.cnblogs.com/jiangz/p/4076811.html?utm_source=tuicool&utm_medium=referral
[2]http://www.cnblogs.com/tsingke/p/3832765.html
[3]http://baike.baidu.com/link?url=35tSbrwOYsEaxPsGPV3PeM16UibDD8ot1lUar0cOKvsJCc1rd7NgVMxZzDPet17QQq2rrOPhzW4Ceccsi8RVua