from:http://blog.csdn.net/minicto/article/details/62240020
ubuntu系统默认源更改为阿里源
ubuntu默认使用的国外的源，在更新的时候会很慢，可以使用国内的阿里的源，速度很快。
依次执行如下命令，
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak #备份
sudo vim /etc/apt/sources.list #修改
sudo apt-get update #更新列表阿里的源，如下，
deb http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ trusty-backports main restricted universe multiverse接着执行，如下，
apt-get update可以看到如下更新过程的详细内容，
Get:71 http://mirrors.aliyun.com trusty-backports/multiverse Translation-en [1,215 B]
Get:72 http://mirrors.aliyun.com trusty-backports/restricted Translation-en [28 B]
Get:73 http://mirrors.aliyun.com trusty-backports/universe Translation-en [36.8 kB]
Get:74 http://mirrors.aliyun.com trusty Release [58.5 kB]
Get:75 http://mirrors.aliyun.com trusty/main Sources [1,064 kB]
Get:76 http://mirrors.aliyun.com trusty/restricted Sources [5,433 B]
Get:77 http://mirrors.aliyun.com trusty/universe Sources [6,399 kB]
Get:78 http://mirrors.aliyun.com trusty/multiverse Sources [174 kB]
Get:79 http://mirrors.aliyun.com trusty/main amd64 Packages [1,350 kB]
Get:80 http://mirrors.aliyun.com trusty/restricted amd64 Packages [13.0 kB]
Get:81 http://mirrors.aliyun.com trusty/universe amd64 Packages [5,859 kB]
Get:82 http://mirrors.aliyun.com trusty/multiverse amd64 Packages [132 kB]
Get:83 http://mirrors.aliyun.com trusty/main i386 Packages [1,348 kB]
Get:84 http://mirrors.aliyun.com trusty/restricted i386 Packages [13.4 kB]
Get:85 http://mirrors.aliyun.com trusty/universe i386 Packages [5,866 kB]
Get:86 http://mirrors.aliyun.com trusty/multiverse i386 Packages [134 kB]
Get:87 http://mirrors.aliyun.com trusty/main Translation-en [762 kB]
Get:88 http://mirrors.aliyun.com trusty/multiverse Translation-en [102 kB]
Get:89 http://mirrors.aliyun.com trusty/restricted Translation-en [3,457 B]
Get:90 http://mirrors.aliyun.com trusty/universe Translation-en [4,089 kB]
Ign http://mirrors.aliyun.com trusty/main Translation-en_US
Ign http://mirrors.aliyun.com trusty/multiverse Translation-en_US
Ign http://mirrors.aliyun.com trusty/restricted Translation-en_US
Ign http://mirrors.aliyun.com trusty/universe Translation-en_US 说明已经使用阿里源在进行更新了。