ubuntu server 系統，更換阿裡雲源（用戶更新源）

Ubuntu安裝完畢後，默認使用的是官方的源，在國內訪問速度很慢，這裡介紹更換為阿裡雲的源方法。 步驟如下： 1.備份源配置文件 sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup 2.用編輯器打開源配置文件 sudo vim /etc/apt/sources.list 3.刪除文件內容，更換為以下內容（也可使用其他源）

deb http://mirrors.aliyun.com/ubuntu trusty main restricted
deb-src http://mirrors.aliyun.com/ubuntu trusty main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://mirrors.aliyun.com/ubuntu trusty-updates main restricted
deb-src http://mirrors.aliyun.com/ubuntu trusty-updates main restricted

## 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://mirrors.aliyun.com/ubuntu trusty universe
deb-src http://mirrors.aliyun.com/ubuntu trusty universe
deb http://mirrors.aliyun.com/ubuntu trusty-updates universe
deb-src http://mirrors.aliyun.com/ubuntu trusty-updates 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://mirrors.aliyun.com/ubuntu trusty multiverse
deb-src http://mirrors.aliyun.com/ubuntu trusty multiverse
deb http://mirrors.aliyun.com/ubuntu trusty-updates multiverse
deb-src http://mirrors.aliyun.com/ubuntu trusty-updates 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://mirrors.aliyun.com/ubuntu trusty-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu trusty-backports main restricted universe multiverse

deb http://security.ubuntu.com/ubuntu trusty-security main restricted
deb-src http://security.ubuntu.com/ubuntu trusty-security main restricted
deb http://security.ubuntu.com/ubuntu trusty-security universe
deb-src http://security.ubuntu.com/ubuntu trusty-security universe
deb http://security.ubuntu.com/ubuntu trusty-security multiverse
deb-src http://security.ubuntu.com/ubuntu trusty-security multiverse

4.執行以下命令，刷新 sudo apt-get clean sudo apt-get update