docker 官网：
https://docs.docker.com/install/linux/docker-ce/centos/#os-requirements
1 先卸载系统上已经存在docker,卸载旧版本的
yum remove docker \
docker-client \
docker-client-latest \
docker-common \
docker-latest \
docker-latest-logrotate \
docker-logrotate \
docker-selinux \
docker-engine-selinux \
docker-engine
2 安装docker:
yum install -y yum-utils \
device-mapper-persistent-data \
lvm2
sudo yum-config-manager \
--add-repo \
https://download.docker.com/linux/centos/docker-ce.repo
yum install docker-ce
3 启动docker server
sudo systemctl start docker
sudo docker version
4 Verify that docker is installed correctly by running the hello-world image.
sudo docker run hello-world
5 more Vagrantfile
config.vm.provision "shell" , inline: <<-SHELL
apt-get update
apt-get install -y apache2
SHELL
在机器启动以后，自动运行一些命令，比如自动安装一些软件
查看image 列表
sudo docker image ls
image 获取1
image 获取2 
sudo docker pull ubuntu:14.04
docke pull ubuntu 不加版本号，默认拉取最新版
如 docker pull bitnami/wordpress