ubuntu如果下载软件慢，原因可能是下载源是国外或资源不多，可改变下载源地址，可按如下方法更改
打开
/etc/apt/sources.list，添加以下国内软件源
deb
http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.sohu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.sohu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-backports main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-proposed main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-security main restricted universe multiverse
deb http://mirrors.oschina.net/ubuntu/ trusty-updates main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-proposed main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-security main restricted universe multiverse
deb-src http://mirrors.oschina.net/ubuntu/ trusty-updates main restricted universe multiverse
最后
sudo apt-get update使之生效
如果出现：W: 以下ID的密钥没有可用的公钥
3B4FE6ACC0B21F32
则执行以下命令即可解决
gpg --keyserver subkeys.pgp.net --recv C0B21F32
gpg --export --armor C0B21F32| sudo apt-key add -
其中数据为公钥的后8位
再次apt-get update试试