安装完虚拟机机后登陆
    which ssh 先检查电脑是否安装了ssh，如没有需要安装。
    安装Ubuntu Linux install OpenSSH server
    apt update
    apt upgrade
    sudo -i（获取管理员所有权限）
    apt install openssh-server 安装打开ssh服务器
    ps -x | grep ssh 可以通过命令看看是不是启用了sshd
    如果没有启用可以在/etc/init.d里面找到启用.
    /etc/init.d/ssh start 开启
    /etc/init.d/ssh stop 关闭
    /etc/init.d/ssh restart 重启

    虚拟机设置为桥接模式，并选择 复制物理网络连接状态。
    重启reboot
    重新登录虚拟机
    查看虚拟机IP地址ifconfig
    用第三方ssh登陆软件登录

    更改更新源。使用国外源太慢了，修改为国内源会快很多。
    cp /etc/apt/sources.list /etc/apt/sources.list.bak 复制源文件备份，以防万一
    uname -a 查看系统版本
    Ubuntu 12.04 (LTS)代号为precise。
    Ubuntu 14.04 (LTS)代号为trusty。
    Ubuntu 15.04 代号为vivid。
    Ubuntu 15.10 代号为wily。
    Ubuntu 16.04 (LTS)代号为xenial。
    Ubuntu 18.04 (LTS)代号为bionic。
    nano /etc/apt/sources.list 修改更新源，将原来的更新源地址注释掉或者删除
    替换默认的http://archive.ubuntu.com/为mirrors.aliyun.com

    阿里云源：（Ubuntu 18.04 (LTS)代号为bionic）
    deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
    deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
    deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
    deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
    deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
    deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
    deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
    deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
    deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
    deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse

    网易源
    deb http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
    deb http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
    deb http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
    deb http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
    deb http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse
    deb-src http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
    deb-src http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
    deb-src http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
    deb-src http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
    deb-src http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse

    中科院源
    deb https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
    deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
    deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
    deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
    deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
    deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
    deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
    deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
    deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
    deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse