注意，出于安全考虑，开始安装在普通用户下面安装，后面也会指导如何创建一个docker group不用sudo命令操作docker相关命令
官网安装教程https://docs.docker.com/engine/installation/linux/centos/
1、检查CentOS版本，Docker官网要求：Docker requires a 64-bit installation regardless of your CentOS version. Also, your kernel must be 3.10 at minimum, which CentOS 7 runs.
命令：uname -r
输出：3.10.0-229.el7.x86_64
2、安装或更新yum
命令：sudo yum update
3、将docker repository交予yum管理，便于下载更新
命令：
$ sudo tee /etc/yum.repos.d/docker.repo <<-'EOF' [dockerrepo] name=Docker Repository baseurl=https://yum.dockerproject.org/repo/main/centos/7/ enabled=1 gpgcheck=1 gpgkey=https://yum.dockerproject.org/gpg EOF
4、安装docker
命令：sudo yum install docker-engine
5、启动docker daemon
命令：sudo service docker start
6、测试是否安装成功
命令：sudo docker run hello-world
输出：
Unable to find image 'hello-world:latest' locally
latest: Pulling from hello-world
a8219747be10: Pull complete
91c95931e552: Already exists
hello-world:latest: The image you are pulling has been verified. Important: image verification is a tech preview feature and should not be relied on to provide security.
Digest: sha256:aa03e5d0d5553b4c3473e89c8619cf79df368babd1.7.1cf5daeb82aab55838d
Status: Downloaded newer image for hello-world:latest
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. (Assuming it was not already locally available.)
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
For more examples and ideas, visit: http://docs.docker.com/userguide/
7、为避免每次执行docker命令都加上sudo，创建docker用户组
命令：sudo groupadd docker
8、添加不需要使用sudo来执行docker命令的用户加入docker用户组（比如，系统中我有普通用户hjp，以后就用hjp用户执行docker命令）
命令：sudo usermod -aG docker hjp
9、退出当前用户，登入hjp用户，测试是否设置成功
命令：docker run hello-world
输出：
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.
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 Hub account:
https://hub.docker.com
For more examples and ideas, visit:
https://docs.docker.com/engine/userguide/
10、设置登入系统后，启动docker
命令：sudo chkconfig docker on