在介绍中，我们发现Docker images是container的基本容器。在之前的章节，我们已经使用已经存在的Docker images了，例如Ubuntu image和training/webapp image。
Docker stores下载在Docker 主机上下载images。如果image 不存在本地，则将从Docker Hub上下载。
我们将在本节学到一些Docker images：
- 与本地Docker host上images工作，及管理它们。
- 创建一个基础images。
- 上传images到Docker Hub Registry。
列举主机上的images
我们从列举本地主机上的images开始学习。我们可以像这样使用docker images：
$ sudo docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
training/webapp latest fc77f57ad303 3 weeks ago 280.5 MB
ubuntu 13.10 5e019ab7bf6d 4 weeks ago 180 MB
ubuntu saucy 5e019ab7bf6d 4 weeks ago 180 MB
ubuntu 12.04 74fe38d11401 4 weeks ago 209.6 MB
ubuntu precise 74fe38d11401 4 weeks ago 209.6 MB
ubuntu 12.10 a7cf8ae4e998 4 weeks ago 171.3 MB
ubuntu quantal a7cf8ae4e998 4 weeks ago 171.3 MB
ubuntu 14.04 99ec81b80c55 4 weeks ago 266 MB
ubuntu latest 99ec81b80c55 4 weeks ago 266 MB
ubuntu trusty 99ec81b80c55 4 weeks ago 266 MB
ubuntu 13.04 316b678ddf48 4 weeks ago 169.4 MB
ubuntu raring 316b678ddf48 4 weeks ago 169.4 MB
ubuntu 10.04 3db9c44f4520 4 weeks ago 183 MB
ubuntu lucid 3db9c44f4520 4 weeks ago 183 MB我们将看到之前使用的images。当我们使用image启动容器的时候，每一个都已经从Docker Hub上下载了。
我们从列表中看三个重要的信息：
- 他们来源的repository，例如：ubuntu。
- 每一个image的tags，例如14.04。
- 每个image的ID。
ubuntu:14.04$ sudo docker run -t -i ubuntu:14.04 /bin/bash$ sudo docker run -t -i ubuntu:12.04 /bin/bash注意：建议指定image的tag，这样可以准确的知道我们使用的image类型。
获得一个新的image
怎样获得新的images呢？如果Docker主机上不存在，则Docker会自动下载image。这将潜在的增加一些时间来启动container。如果我们想要预加载一个image，可以使用docker pull命令下载它。我们可以下载centos image。
$ sudo docker pull centos
Pulling repository centos
b7de3133ff98: Pulling dependent layers
5cc9e91966f7: Pulling fs layer
511136ea3c5a: Download complete
ef52fb1fe610: Download complete
. . .
Status: Downloaded newer image for centos我们看到image的每一个层都已经下载，现在我们从这个image的运行container，我们将不用等待去下载这个image。
$ sudo docker run -t -i centos /bin/bash
bash-4.1#Docker的一个特性是，许多人创建了用于不同目的的Docker images。许多已经上传到了Docker Hub。我们可以在Docker Hub网站上搜索这些image。
我们也可以在命令行中使用命令docker search搜索image。我们团队需要一个image，Ruby和Sinatra已经被安装在WEB应用开发环境。我们可以使用docker search搜索合适image，搜索出那些包含sinatra的image。
$ sudo docker search sinatra
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
training/sinatra Sinatra training image 0 [OK]
marceldegraaf/sinatra Sinatra test app 0
mattwarren/docker-sinatra-demo 0 [OK]
luisbebop/docker-sinatra-hello-world 0 [OK]
bmorearty/handson-sinatra handson-ruby + Sinatra for Hands on with D... 0
subwiz/sinatra 0
bmorearty/sinatra 0
. . .我们会回顾了可用的image，我们决定使用training/sinatra image。到目前为止，我们使用了两种类型的image repositories，images像Ubuntu这样的，称为base或者root images。这些base images有Docker Inc提供、构建、验证和支出。这些可以被单个名字标识。
我们也可以看用户images，例如我们选择的training/sinatra。一个用户image属于Docker community成员，由他们构建和维护。你可以标识这些用户image，他们前缀使用创建者的名字，这里是training。
推送image
我们标识一个合适image，training/sinatra，我们现在可以使用docker pull命令下载。
$ sudo docker pull training/sinatra$ sudo docker run -t -i training/sinatra /bin/bash
root@a8cb6ce02d85:/#团队发现training/sinatra image 相当有用，但是他们想在上面做出一些改变。这里有两种方法来更新和创建images。
1. 我们更新由image创建来的container，然后提交结果到一个image。
2. 我们使用Dockerfile来特定的指令创建image。
更新和提交image
在更新一个image之前，我们先用想用更新的image创建一个container。
$ sudo docker run -t -i training/sinatra /bin/bash
root@0b2616b0e5a8:/#在运行的container内部，我们添加json gem。
root@0b2616b0e5a8:/# gem install json现在我们有一个container的变化需要去做。我们可以提交container的副本作为image，使用docker commit命令。
$ sudo docker commit -m "Added json gem" -a "Kate Smith" \
0b2616b0e5a8 ouruser/sinatra:v2
4f177bd27a9ff0f6dc2a830403925b5360bfe0b93d476f7fc3231110e7f71b1c我们使用了docker commit指令。我们指定两个flag：-m 和 -a 。-m 允许我们指定提交的信息，更像是向版本控制系统提交。-a允许我们指定这个更新的作者。
我们也可以指定这个新的image创建来的container，0b2616b0e5a8（我们记录的container ID）和我们为这个image指定了目标。
ouruser/sinatra:v2我们可以看到我们新的ourser/sinatra image，使用docker images命令。
$ sudo docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
training/sinatra latest 5bc342fa0b91 10 hours ago 446.7 MB
ouruser/sinatra v2 3c59e02ddd1a 10 hours ago 446.7 MB
ouruser/sinatra latest 5db5f8471261 10 hours ago 446.7 MB$ sudo docker run -t -i ouruser/sinatra:v2 /bin/bash
root@78e82f680994:/#使用docker commit指令是一个相当简单的扩展image的方法，但是它有一点麻烦，在团队之中分享images的开发进度不是很方便。替代方法，我们使用一个新的命令docker build，从草稿中构建新的image。
为了实现这个，我们创建了一个dockerfile，它包含了一系列指令告诉Dicker如何构建image。
首先创建一个目录和Dockerfile。
$ mkdir sinatra
$ cd sinatra
$ touch Dockerfile每一指令创建了一个新的image层。让我们看一个简单的例子，为我们开发团队构建一个自己的sinatra image。
# This is a comment
FROM ubuntu:14.04
MAINTAINER Kate Smith <ksmith@example.com>
RUN apt-get update && apt-get install -y ruby ruby-dev
RUN gem install sinatraINSTRUCTION statement第一个指令From告诉Docker我们的image的来源，在这个例子中我们将新的image构建在一个Ubuntu 14.04 image上。
下一步我们使用MAINTAINER指令来指定谁来维护我们的新image。
最后，我们指定了两个RUN指令。一个RUN指令执行一个命令在image中，例如安装包。这个我们更新了APT缓存，安装Ruby和RubyGems 和安装了Sinatra gem。
注意：a lot more instructions available to us in a Dockerfile
现在我们那Dockerfile和使用docker build命令来创建一个image。
$ sudo docker build -t ouruser/sinatra:v2 .
Sending build context to Docker daemon 2.048 kB
Sending build context to Docker daemon
Step 0 : FROM ubuntu:14.04
---> e54ca5efa2e9
Step 1 : MAINTAINER Kate Smith <ksmith@example.com>
---> Using cache
---> 851baf55332b
Step 2 : RUN apt-get update && apt-get install -y ruby ruby-dev
---> Running in 3a2558904e9b
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---> c55c31703134
Removing intermediate container 3a2558904e9b
Step 3 : RUN gem install sinatra
---> Running in 6b81cb6313e5
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Successfully installed rack-1.5.2
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Successfully installed sinatra-1.4.5
4 gems installed
Installing ri documentation for rack-1.5.2...
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---> 97feabe5d2ed
Removing intermediate container 6b81cb6313e5
Successfully built 97feabe5d2ed我们指定了我们的docker build命令，使用了-t 去表示我们新的image属于用户ouruser，这个repository名字sinatra，给了一个tag：v2。
我们也可以指定我们Dockerfile的路径，使用. 标识Docker在当前路径。
注意：也可以为Dockerfile指定一个路径。
现在我们每一个Dockerfile中的指令都被一步一步的执行。我们可以看到每一步创建一个新的container，在container中运行指令，然后提交变化，类似之前看到的docker commit工作流。当所有的指令执行之后，我们留下了97feabe5d2ed image（被标记为ouruser/sinatra:v2）和所有的中间容器将被完全清楚。
注意：一个image在不包括storage driver的情况下，不能操作127层。这个限制有利于优化image的大小。
我们可以从新image中运行container。
$ sudo docker run -t -i ouruser/sinatra:v2 /bin/bash
root@8196968dac35:/#注意：这只是一个简单的image创建指南。我们跳过了很大一群可以使用的指令。我们将在后面的章节或者dockerfile索引中看到详细的描述和每个指令的例子。Best Practices guide有利于写出清晰、可读、可维护的Dockerfile。
在image上设置tag
我们可以在你提交或者构建见后，添加tag在存在的image上。我们可以使用dicker tag命令。我们添加一个新的tag到我们的ouruser/sinatra image。
$ sudo docker tag 5db5f8471261 ouruser/sinatra:devel我们使用docker image命令查看新的tag。
$ sudo docker images ouruser/sinatra
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
ouruser/sinatra latest 5db5f8471261 11 hours ago 446.7 MB
ouruser/sinatra devel 5db5f8471261 11 hours ago 446.7 MB
ouruser/sinatra v2 5db5f8471261 11 hours ago 446.7 MB一旦我们构建或者创建了一个新的image，我们可以使用docker push命令将它推送到Docker Hub上。这让你将它分享给其他人，也可以推送到私有的repository。
$ sudo docker push ouruser/sinatra
The push refers to a repository [ouruser/sinatra] (len: 1)
Sending image list
Pushing repository ouruser/sinatra (3 tags)
. . .使用docker rmi命令移除Docker 主机上的image，这个类似于移除container。
删除不在需要的training/sinatra image。
$ sudo docker rmi training/sinatra
Untagged: training/sinatra:latest
Deleted: 5bc342fa0b91cabf65246837015197eecfa24b2213ed6a51a8974ae250fedd8d
Deleted: ed0fffdcdae5eb2c3a55549857a8be7fc8bc4241fb19ad714364cbfd7a56b22f
Deleted: 5c58979d73ae448df5af1d8142436d81116187a7633082650549c52c3a2418f0