docker 官網：
https://docs.docker.com/install/linux/docker-ce/centos/#os-requirements
1 先卸載系統上已經存在docker,卸載舊版本的
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 安裝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 啓動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
在機器啓動以後，自動運行一些命令，比如自動安裝一些軟件
查看image 列表
sudo docker image ls
image 獲取1
image 獲取2 
sudo docker pull ubuntu:14.04
docke pull ubuntu 不加版本號，默認拉取最新版
如 docker pull bitnami/wordpress