在CentOS 7上安装Docker环境

官网文档：https://docs.docker.com/engine/installation/linux/centos/ ，本文大部分是照搬官方文档写的，如果你英文还不错，那么就直接移步官方文档吧，如果你英文实在是不行，那就勉强看一下本人这生涩的翻译~

以下操作均在root用户下完成

1.配置yum软件库

为保证安装的成功，首先使用yum update更新Yum包，表示我的好多yum包都需要更新，1500+的包，如果你像我一样好久没有更新过，那就耐心等候吧。

然后在yum软件库中新增docker的配置：

#  tee /etc/yum.repos.d/docker.repo <<-'EOF'
[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7/
enabled=
gpgcheck=
gpgkey=https://yum.dockerproject.org/gpg
EOF

2.安装Docker

有了yum软件库的配置之后，安装也变得异常的简单，只需要以下一句即可：

# yum install docker-engine

3.启动Docker

一切就绪之后，使用start命令来启动Docker守护进程：

# service docker start

4.输出hello-world

程序员貌似跟hello-world有仇，有事儿没事就打印人家一下，玩docker咱们当前也不例外，先来个hello-world吧，这里的基本原理是利用人家已经写好的hello-world镜像，下载到本地，然后把他运行起来~

使用以下命令：

# docker run hello-world

然后控制端会输出类似于如下的信息，就证明我们的docker环境安装成功了~

在这里，我第一次失败了~显示：

Unable to find image 'hello-world:latest' locally
docker: Error response from daemon: Get https://registry-1.docker.io/v2/library/hello-world/manifests/latest: Get https://auth.docker.io/token?scope=repository%3Alibrary%2Fhello-world%3Apull&service=registry.docker.io: net/http: TLS handshake timeout.
See 'docker run --help'.

然后我又来了一次就好了，应该是墙的原因吧，看着是网络访问失败了~

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
c04b14da8d14: Pull complete
Digest: sha256:0256e8a36e2070f7bf2d0b0763dbabdd67798512411de4cdcf9431a1feb60fd9
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:
 . The Docker client contacted the Docker daemon.
 . The Docker daemon pulled the "hello-world" image from the Docker Hub.
 . The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 . 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/