镜像（image）：An image is a filesystem and parameters to use at runtime. It doesn’t have state and never changes
容器（container): A container is a running instance of an image.
简言之，容器是镜像的实例。
运行命令的时候，执行如下步骤：
1 检查是否有名叫 hello-world 软件镜像（image）
2 如果没有，则从 docker hub 上下载
3 加载该镜像（image)到 容器（container）中，并运行
创建自己的镜像 image
首先运行 docker run docker/whalesay cowsay boo-boo
下载运行 docker hub 上的 whalesay 镜像。
- 创建一个 Dockerfile 文件
添加如下命令到文件中：
FROM docker/whalesay:latest （告诉docker当前的image是依靠于哪个image生成的）
RUN apt-get -y update && apt-get install -y fortunes（whalesay 镜像是基于ubuntu的，使用apt-get install来安装packages. 这两个命令更新了packages包，并安装了fortune 程序）
CMD /usr/games/fortune -a | cowsay（告诉镜像image在环境设置好以后的最后一个命令，该命令运行了furtune -a,并将输出发给额cowsay命令）
到这里，一个基本的Dockerfile就创建好了
- 根据 Dockerfile 来 Build 镜像
使用 docker build 命令来来创建镜像
-t 参数，给创建的镜像命名（give a tag）
. 不要忘记这个命令（就是一个英文句号），告诉 docker build 查找当前目录里的 dockerfile 文件。
$ docker build -t docker-whale .Sending build context to Docker daemon 2.048 kB ...snip...Removing intermediate container cb53c9d09f3bSuccessfully built c2c3152907b5Docker检查确认所有build所需都齐了,输出如下消息：
Sending build context to Docker daemon 2.048 kBDocker 检查
whalesayimage 是否存在，不存在则从Docker Hub上pull下来。Step 1 : FROM docker/whalesay:latest ---> 6b362a9f73eb在每一步结束，都会有一个ID被打印出来。这个ID是每一步创建出的 Layer 的ID。 Dockerfile 中每一行命令都和 image 中的一个 Layer 相关。你自己的ID会显示的不一样。
Docker 创建一个临时容器 container 来运行
whalesay镜像image。在这个临时容器中，Docker 运行 Dockerfile中的下一条命令, 即RUN命令。这会安装fortune。这里会有很多输出，就和在 Ubuntu 中创建出来的消息一样。Step 2 : RUN apt-get -y update && apt-get install -y fortunes ---> Running in 05d4eda04526 Ign http://archive.ubuntu.com trusty InRelease Get:1 http://archive.ubuntu.com trusty-updates InRelease [65.9 kB] Get:2 http://archive.ubuntu.com trusty-security InRelease [65.9 kB] Hit http://archive.ubuntu.com trusty Release.gpg Hit http://archive.ubuntu.com trusty Release Get:3 http://archive.ubuntu.com trusty-updates/main Sources [480 kB] Get:4 http://archive.ubuntu.com trusty-updates/restricted Sources [5921 B] Get:5 http://archive.ubuntu.com trusty-updates/universe Sources [214 kB] Get:6 http://archive.ubuntu.com trusty-updates/main amd64 Packages [1160 kB] Get:7 http://archive.ubuntu.com trusty-updates/restricted amd64 Packages [20.4 kB] Get:8 http://archive.ubuntu.com trusty-updates/universe amd64 Packages [505 kB] Get:9 http://archive.ubuntu.com trusty-security/main Sources [157 kB] Get:10 http://archive.ubuntu.com trusty-security/restricted Sources [4621 B] Get:11 http://archive.ubuntu.com trusty-security/universe Sources [54.5 kB] Get:12 http://archive.ubuntu.com trusty-security/main amd64 Packages [700 kB] Get:13 http://archive.ubuntu.com trusty-security/restricted amd64 Packages [17.0 kB] Get:14 http://archive.ubuntu.com trusty-security/universe amd64 Packages [191 kB] Hit http://archive.ubuntu.com trusty/main Sources Hit http://archive.ubuntu.com trusty/restricted Sources Hit http://archive.ubuntu.com trusty/universe Sources Hit http://archive.ubuntu.com trusty/main amd64 Packages Hit http://archive.ubuntu.com trusty/restricted amd64 Packages Hit http://archive.ubuntu.com trusty/universe amd64 Packages Fetched 3640 kB in 11s (329 kB/s) Reading package lists... Reading package lists... Building dependency tree... Reading state information... The following extra packages will be installed: fortune-mod fortunes-min librecode0 Suggested packages: x11-utils bsdmainutils The following NEW packages will be installed: fortune-mod fortunes fortunes-min librecode0 0 upgraded, 4 newly installed, 0 to remove and 92 not upgraded. Need to get 1961 kB of archives. After this operation, 4817 kB of additional disk space will be used. Get:1 http://archive.ubuntu.com/ubuntu/ trusty/main librecode0 amd64 3.6-21 [771 kB] Get:2 http://archive.ubuntu.com/ubuntu/ trusty/universe fortune-mod amd64 1:1.99.1-7 [39.5 kB] Get:3 http://archive.ubuntu.com/ubuntu/ trusty/universe fortunes-min all 1:1.99.1-7 [61.8 kB] Get:4 http://archive.ubuntu.com/ubuntu/ trusty/universe fortunes all 1:1.99.1-7 [1089 kB] debconf: unable to initialize frontend: Dialog debconf: (TERM is not set, so the dialog frontend is not usable.) debconf: falling back to frontend: Readline debconf: unable to initialize frontend: Readline debconf: (This frontend requires a controlling tty.) debconf: falling back to frontend: Teletype dpkg-preconfigure: unable to re-open stdin: Fetched 1961 kB in 19s (101 kB/s) Selecting previously unselected package librecode0:amd64. (Reading database ... 13116 files and directories currently installed.) Preparing to unpack .../librecode0_3.6-21_amd64.deb ... Unpacking librecode0:amd64 (3.6-21) ... Selecting previously unselected package fortune-mod. Preparing to unpack .../fortune-mod_1%3a1.99.1-7_amd64.deb ... Unpacking fortune-mod (1:1.99.1-7) ... Selecting previously unselected package fortunes-min. Preparing to unpack .../fortunes-min_1%3a1.99.1-7_all.deb ... Unpacking fortunes-min (1:1.99.1-7) ... Selecting previously unselected package fortunes. Preparing to unpack .../fortunes_1%3a1.99.1-7_all.deb ... Unpacking fortunes (1:1.99.1-7) ... Setting up librecode0:amd64 (3.6-21) ... Setting up fortune-mod (1:1.99.1-7) ... Setting up fortunes-min (1:1.99.1-7) ... Setting up fortunes (1:1.99.1-7) ... Processing triggers for libc-bin (2.19-0ubuntu6.6) ... ---> dfaf993d4a2e Removing intermediate container 05d4eda04526RUN结束，有一个 layer 会被创建，并且之前创建的临时容器 container 也被去除了。一个新的临时容器 container 被创建出来，Docker 为CMD命令添加一个 Layer，然后在移除该容器 congtainer
Step 3 : CMD /usr/games/fortune -a | cowsay ---> Running in a8e6faa88df3 ---> 7d9495d03763 Removing intermediate container a8e6faa88df3 Successfully built 7d9495d03763
到这里，我们就创建了一个自己的镜像 image，名叫 docker-whale.
接下来直接运行 docker run docker-whale