四、CentOS Docker 安装

Docker 可以运行在 CentOS 上，但对 CentOS 系统版本和内核版本有一定的要求

1. CentOS 的版本必须在 6.5+ ，且必须是 64 位，然后必须是发行版本
2. 如果是 Docker CE ，则要求系统版本是 7.0+
3. 如果是 CentOS 7 ，则要求系统内核版本为 3.10 以上
4. 如果是 CentOS 6.5 或更高的版本的 CentOS 上，则要求系统内核版本为 2.6.32-431 或者更高版本

查看 CentOS 系统内核版本

如果你不确定自己的 CentOS 的内核版本是多少，可以使用 uname -r 命令查看一下

[root@localhost ~]# uname -r
3.10.0-327.el7.x86_64

CentOS 安装 Docker

目前最快速的安装 Docker 的方式是使用官方给出的脚本 https://get.docker.com/

只需要在终端里输入以下命令即可开始安装

[root@localhost ~]# curl -fsSL get.docker.com -o get-docker.sh
[root@localhost ~]# sudo sh get-docker.sh
...
...

If you would like to use Docker as a non-root user, you should now consider
adding your user to the "docker" group with something like:

  sudo usermod -aG docker your-user

Remember to log out and back in for this to take effect!

WARNING: Adding a user to the "docker" group grants the ability to run
         containers which can be used to obtain root privileges on the
         docker host.
         Refer to https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface
         for more information.

如果你使用的是 root 用户，可以先轻松下再回来，如果你使用的是普通用户，那么需要 sudo sh get-docker.sh，然后输入登录密码

稍等片刻，Docker 就会安装完毕，是不是很省事，因为我们连一张图都没发

可以安装完成后最后那几段提示

If you would like to use Docker as a non-root user, you should now consider
    adding your user to the "docker" group with something like:

    sudo usermod -aG docker your-user

   Remember that you will have to log out and back in for this to take effect!

意思是说，如果以非 root 用户可以运行 docker 时，需要执行 sudo usermod -aG docker cmsblogs 命令然后重新登陆，否则会有如下报错

[yufei@localhost ~]docker fun hello-world
docker: Cannot connect to the Docker daemon. Is the docker daemon running on this host ?
...

启动 Docker 服务

如果是 Centos 7 以上版本，则使用下面的命令启动 Docker 服务

systemctl start docker

如果是较低的版本，则使用下面的命令启动 Docker 服务

service docker start

Docker Hello World

我们可以使用 docker run hello-world 命令来检查下是否安装成功

[root@localhost ~]# docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
9bb5a5d4561a: Pull complete 
Digest: sha256:f5233545e43561214ca4891fd1157e1c3c563316ed8e237750d59bde73361e77
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.
    (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/engine/userguide/

如果运行没有错误，那么安装成功