安装VIM出错和更新Ubuntu源

1. 安装vim时遇到如下问题：

$ sudo apt-get install vim
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 vim : Depends: vim-common (= 2:7.3.429-2ubuntu2) but 2:7.3.429-2ubuntu2.1 is to be installed
E: Unable to correct problems, you have held broken packages.

解决方法如下：

a.卸载vim-common, "$ sudo apt-get remove vim-common "

b. 再进行安装vim, "$ sudo apt-get install vim"

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2. 执行apt-get install xxx时，提示404错误，更新源地址失效，需要更新源，

解决方法如下：

a. 备份已有源

$ mv /etc/apt/sources.list /etc/apt/sources.list.bak

b. 重新建立新源文件

$ sudo vi /etc/apt/sources.list //复制下列新源
deb http://cn.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ precise-proposed main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ precise-updates main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ precise-proposed main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse

c. 执行更新

$ sudo apt-get update