首先确定DNS没问题
ping www.baidu.com
sudo apt-get update 找不到相应的package
是因为x86平台上的镜像源和ARM平台上的镜像源是不能通用的，所以需要配置一下ARM平台下的镜像源
1、备份：
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2、修改：
清华源
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial-security main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial-updates main multiverse restricted universe
deb http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial-backports main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial-security main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial-updates main multiverse restricted universe
deb-src http://mirrors.tuna.tsinghua.edu.cn/ubuntu-ports/ xenial-backports main multiverse restricted universe
阿里源
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial main
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial main
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates main
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates main
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial universe
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial universe
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates universe
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-updates universe
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-security main
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-security main
deb http://mirrors.aliyun.com/ubuntu-ports/ xenial-security universe
deb-src http://mirrors.aliyun.com/ubuntu-ports/ xenial-security universe
3、更新
sudo apt-get update