sudo apt-get update会报一堆错误，显示源有问题
首先备份源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
修改更新源
sudo gedit /etc/apt/sources.list
将下面代码写进去
deb http://mirrors.163.com/ubuntu/ vivid main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ vivid-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ vivid-backports main restricted universe multiverse
之后即可成功执行第一条命令