centos 安装流程：
1.删除原来旧版本docker
sudo yum remove docker docker-common docker-selinux docker-engine
2.使用yum安装先安装依赖包
sudo yum install -y yum-utils device-mapper-persistent-data lvm2
3.执行下面的命令添加 yum 软件源国内源
sudo yum-config-manager --add-repo https://mirrors.ustc.edu.cn/docker-ce/linux/centos/docker-ce.repo
官方源
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
4.更新 yum 软件源缓存，并安装 docker-ce
$ sudo yum makecache fast
$ sudo yum install docker-ce
5.启动 Docker CE
$ sudo systemctl enable docker
$ sudo systemctl start docker
6.建立 docker 用户组
6.1建立 docker 组：
$ sudo groupadd docker
6.2将当前用户加入 docker 组：
$ sudo usermod -aG docker $USER
7.测试 Docker 是否安装正确
sudo docker run hello-world
Hello from Docker! This message shows that your installation appears to be working correctly. To generate this message, Docker took the following steps: 1. The Docker client contacted the Docker daemon. 2. The Docker daemon pulled the "hello-world" image from the Docker Hub. (amd64) 3. The Docker daemon created a new container from that image which runs the executable that produces the output you are currently reading. 4. The Docker daemon streamed that output to the Docker client, which sent it to your terminal. To try something more ambitious, you can run an Ubuntu container with: $ docker run -it ubuntu bash Share images, automate workflows, and more with a free Docker ID: https://hub.docker.com/ For more examples and ideas, visit: https://docs.docker.com/get-started/
出现这个就是安装成功的标志
运行docker时，如果出现
Cannot connect to the Docker daemon at tcp://0.0.0.0:2375. Is the docker daemon running?
那就在命令前面加上sudo