【Docker】从零开始：8.Docker命令:Commit提交命令

【Docker】从零开始：8.Docker命令:Commit命令

基本概念
- 镜像
- 镜像分层
- - 什么是镜像分层
  - [为什么 Docker 镜像要采用这种分层结构](#为什么 Docker 镜像要采用这种分层结构)
本章要点
[commit 命令](#commit 命令)
- 命令格式
- [docker commit 操作参数](#docker commit 操作参数)
- 实例演示
- 总结

了解commit命令之前我们先了解下涉及的相关知识

为什么这里又说镜像，因为之前了解的只是个大概，现在涉及镜像的原理

基本概念

镜像

是一种轻量级、可执行的独立软件包，它包含运行某个软件所需的所有内容，我们把应用程序和配置依赖打包好形成一个可交付的运行环境(包括代码、运行时需要的库、环境变量和配置文件等)，这个打包好的运行环境就是image镜像文件。
只有通过这个镜像文件才能生成Docker容器实例(类似Java中new出来一个对象)。

镜像分层

什么是镜像分层

"镜像是有分层的"
- 如图所示：
镜像的使用的文件技术是UnionFS
- UnionFS（联合文件系统）
  - UnionFS（联合文件系统）：Union文件系统（UnionFS）是一种分层、轻量级并且高性能的文件系统，它支持对文件系统的修改作为一次提交来一层层的叠加，同时可以将不同目录挂载到同一个虚拟文件系统下(unite several directories into a single virtual filesystem)。Union 文件系统是 Docker 镜像的基础。镜像可以通过分层来进行继承，基于基础镜像（没有父镜像），可以制作各种具体的应用镜像。
  - 特性：一次同时加载多个文件系统，但从外面看起来，只能看到一个文件系统，联合加载会把各层文件系统叠加起来，这样最终的文件系统会包含所有底层的文件和目录
Docker镜像加载原理：
- Docker的镜像实际上由一层一层的文件系统组成，这种层级的文件系统UnionFS。
- Bootfs(boot file system)主要包含bootloader和kernel, bootloader主要是引导加载kernel, Linux刚启动时会加载bootfs文件系统，在Docker镜像的最底层是引导文件系统bootfs。这一层与我们典型的Linux/Unix系统是一样的，包含boot加载器和内核。当boot加载完成之后整个内核就都在内存中了，此时内存的使用权已由bootfs转交给内核，此时系统也会卸载Bootfs。
- rootfs (root file system) ，在bootfs之上。包含的就是典型 Linux 系统中的 /dev, /proc, /bin, /etc 等标准目录和文件。rootfs就是各种不同的操作系统发行版，比如Ubuntu，Centos等等。

对于一个精简的OS，rootfs可以很小，只需要包括最基本的命令、工具和程序库就可以了，因为底层直接用Host的kernel，自己只需要提供 rootfs 就行了。由此可见对于不同的linux发行版, bootfs基本是一致的, rootfs会有差别, 因此不同的发行版可以公用bootfs。

为什么 Docker 镜像要采用这种分层结构

比如说有多个镜像都从相同的 base 镜像构建而来，那么 Docker Host 只需在磁盘上保存一份 base 镜像；
同时内存中也只需加载一份 base 镜像，就可以为所有容器服务了。而且镜像的每一层都可以被共享。

本章要点

Docker镜像层都是只读的，容器层是可写的。
当容器启动时，一个新的可写层被加载到镜像的顶部。这一层通常被称作"容器层"，"容器层"之下的都叫"镜像层"。
所有对容器的改动 - 无论添加、删除、还是修改文件都只会发生在容器层中。只有容器层是可写的，容器层下面的所有镜像层都是只读的。

commit 命令

docker commit 命令用于根据 Docker容器的更改创建一个新的 Dokcer镜像。该命令后面的 CONTAINER 可以是容器Id，或者是容器名。

命令格式

bash 复制代码

docker commit -m="[提交的描述信息]" -a="[作者]" [容器ID] [新的镜像名称]:[新的镜像标签]

docker commit 操作参数

参数	描述
-a, --author string	作者。
-c, --change list	应用 dockerfile 指令来创建图像。
-m, --message	string
-p, --pause	提交期间暂停容器（默认为true）。

实例演示

1.下载一个新的ubuntu镜像

bash 复制代码

[root@docker ~]# docker search ubuntu
NAME                             DESCRIPTION                                      STARS     OFFICIAL   AUTOMATED
ubuntu                           Ubuntu is a Debian-based Linux operating sys...   16622     [OK]       
websphere-liberty                WebSphere Liberty multi-architecture images ...   297       [OK]       
open-liberty                     Open Liberty multi-architecture images based...   62        [OK]       
neurodebian                      NeuroDebian provides neuroscience research s...   105       [OK]       
ubuntu-debootstrap               DEPRECATED; use "ubuntu" instead                 52        [OK]       
ubuntu-upstart                   DEPRECATED, as is Upstart (find other proces...   115       [OK]       
ubuntu/nginx                     Nginx, a high-performance reverse proxy & we...   102                  
ubuntu/squid                     Squid is a caching proxy for the Web. Long-t...   70                   
ubuntu/cortex                    Cortex provides storage for Prometheus. Long...   4                    
ubuntu/apache2                   Apache, a secure & extensible open-source HT...   65                   
ubuntu/prometheus                Prometheus is a systems and service monitori...   51                   
ubuntu/kafka                     Apache Kafka, a distributed event streaming ...   37                   
ubuntu/bind9                     BIND 9 is a very flexible, full-featured DNS...   64                   
ubuntu/mysql                     MySQL open source fast, stable, multi-thread...   54                   
ubuntu/zookeeper                 ZooKeeper maintains configuration informatio...   12                   
ubuntu/postgres                  PostgreSQL is an open source object-relation...   31                   
ubuntu/redis                     Redis, an open source key-value store. Long-...   21                   
ubuntu/jre                       Distroless Java runtime based on Ubuntu. Lon...   9                    
ubuntu/grafana                   Grafana, a feature rich metrics dashboard & ...   9                    
ubuntu/dotnet-aspnet             Chiselled Ubuntu runtime image for ASP.NET a...   13                   
ubuntu/memcached                 Memcached, in-memory keyvalue store for smal...   5                    
ubuntu/dotnet-deps               Chiselled Ubuntu for self-contained .NET & A...   11                   
ubuntu/prometheus-alertmanager   Alertmanager handles client alerts from Prom...   9                    
ubuntu/dotnet-runtime            Chiselled Ubuntu runtime image for .NET apps...   13                   
ubuntu/cassandra                 Cassandra, an open source NoSQL distributed ...   2                    
[root@docker ~]# docker pull ubuntu
Using default tag: latest
latest: Pulling from library/ubuntu
7b1a6ab2e44d: Pull complete 
Digest: sha256:626ffe58f6e7566e00254b638eb7e0f3b11d4da9675088f4781a50ae288f3322
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest
[root@docker ~]#

2.运行容器

bash 复制代码

[root@docker ~]# docker run -it ba6acccedd29 /bin/bash
root@792de8cbe835:/#

3.查看并安装vim

bash 复制代码

[root@docker ~]# docker run -it ba6acccedd29 /bin/bash
root@ce128f008eea:/# vim aaa.txt 
oot@ce128f008eea:/# apt-get update
Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Get:2 http://archive.ubuntu.com/ubuntu focal InRelease [265 kB]
Get:3 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages [3221 kB]
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Get:6 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages [1275 kB]
Get:7 http://archive.ubuntu.com/ubuntu focal/multiverse amd64 Packages [177 kB] 
Get:8 http://archive.ubuntu.com/ubuntu focal/restricted amd64 Packages [33.4 kB]
Get:9 http://security.ubuntu.com/ubuntu focal-security/universe amd64 Packages [1129 kB]
Get:10 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages [11.3 MB]            
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Reading package lists... Done
root@ce128f008eea:/# apt-get install -y vim
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  alsa-topology-conf alsa-ucm-conf file libasound2 libasound2-data libcanberra0 libexpat1 libgpm2 libltdl7 libmagic-mgc libmagic1 libmpdec2 libogg0 libpython3.8 libpython3.8-minimal libpython3.8-stdlib libreadline8 libsqlite3-0 libssl1.1 libtdb1 libvorbis0a libvorbisfile3 mime-support readline-common sound-theme-freedesktop
  vim-common vim-runtime xxd xz-utils
Suggested packages:
  libasound2-plugins alsa-utils libcanberra-gtk0 libcanberra-pulse gpm readline-doc ctags vim-doc vim-scripts
The following NEW packages will be installed:
  alsa-topology-conf alsa-ucm-conf file libasound2 libasound2-data libcanberra0 libexpat1 libgpm2 libltdl7 libmagic-mgc libmagic1 libmpdec2 libogg0 libpython3.8 libpython3.8-minimal libpython3.8-stdlib libreadline8 libsqlite3-0 libssl1.1 libtdb1 libvorbis0a libvorbisfile3 mime-support readline-common sound-theme-freedesktop vim
  vim-common vim-runtime xxd xz-utils
0 upgraded, 30 newly installed, 0 to remove and 51 not upgraded.
Need to get 15.0 MB of archives.
After this operation, 70.6 MB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal/main amd64 libmagic-mgc amd64 1:5.38-4 [218 kB]
Get:2 http://archive.ubuntu.com/ubuntu focal/main amd64 libmagic1 amd64 1:5.38-4 [75.9 kB]
Get:3 http://archive.ubuntu.com/ubuntu focal/main amd64 file amd64 1:5.38-4 [23.3 kB]
Get:4 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libexpat1 amd64 2.2.9-1ubuntu0.6 [74.6 kB]
Get:5 http://archive.ubuntu.com/ubuntu focal/main amd64 libmpdec2 amd64 2.4.2-3 [81.1 kB]
Get:6 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libssl1.1 amd64 1.1.1f-1ubuntu2.20 [1321 kB]
Get:7 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libpython3.8-minimal amd64 3.8.10-0ubuntu1~20.04.8 [717 kB]
Get:8 http://archive.ubuntu.com/ubuntu focal/main amd64 mime-support all 3.64ubuntu1 [30.6 kB]
Get:9 http://archive.ubuntu.com/ubuntu focal/main amd64 readline-common all 8.0-4 [53.5 kB]
Get:10 http://archive.ubuntu.com/ubuntu focal/main amd64 libreadline8 amd64 8.0-4 [131 kB]
Get:11 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libsqlite3-0 amd64 3.31.1-4ubuntu0.5 [549 kB]
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Get:13 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 xxd amd64 2:8.1.2269-1ubuntu5.20 [52.6 kB]
Get:14 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 vim-common all 2:8.1.2269-1ubuntu5.20 [87.6 kB]
Get:15 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 xz-utils amd64 5.2.4-1ubuntu1.1 [82.6 kB]
Get:16 http://archive.ubuntu.com/ubuntu focal/main amd64 alsa-topology-conf all 1.2.2-1 [7364 B]
Get:17 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 alsa-ucm-conf all 1.2.2-1ubuntu0.13 [27.0 kB]
Get:18 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libasound2-data all 1.2.2-2.1ubuntu2.5 [20.1 kB]
Get:19 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libasound2 amd64 1.2.2-2.1ubuntu2.5 [335 kB]
Get:20 http://archive.ubuntu.com/ubuntu focal/main amd64 libltdl7 amd64 2.4.6-14 [38.5 kB]
Get:21 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libtdb1 amd64 1.4.5-0ubuntu0.20.04.1 [44.2 kB]
Get:22 http://archive.ubuntu.com/ubuntu focal/main amd64 libogg0 amd64 1.3.4-0ubuntu1 [24.0 kB]
Get:23 http://archive.ubuntu.com/ubuntu focal/main amd64 libvorbis0a amd64 1.3.6-2ubuntu1 [87.0 kB]
Get:24 http://archive.ubuntu.com/ubuntu focal/main amd64 libvorbisfile3 amd64 1.3.6-2ubuntu1 [16.1 kB]
Get:25 http://archive.ubuntu.com/ubuntu focal/main amd64 sound-theme-freedesktop all 0.8-2ubuntu1 [384 kB]
Get:26 http://archive.ubuntu.com/ubuntu focal/main amd64 libcanberra0 amd64 0.30-7ubuntu1 [38.1 kB]
Get:27 http://archive.ubuntu.com/ubuntu focal/main amd64 libgpm2 amd64 1.20.7-5 [15.1 kB]
Get:28 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libpython3.8 amd64 3.8.10-0ubuntu1~20.04.8 [1625 kB]
Get:29 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 vim-runtime all 2:8.1.2269-1ubuntu5.20 [5878 kB]
Get:30 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 vim amd64 2:8.1.2269-1ubuntu5.20 [1242 kB]
Fetched 15.0 MB in 5s (2983 kB/s)
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update-alternatives: warning: skip creation of /usr/share/man/man1/lzma.1.gz because associated file /usr/share/man/man1/xz.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/unlzma.1.gz because associated file /usr/share/man/man1/unxz.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzcat.1.gz because associated file /usr/share/man/man1/xzcat.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzmore.1.gz because associated file /usr/share/man/man1/xzmore.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzless.1.gz because associated file /usr/share/man/man1/xzless.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzdiff.1.gz because associated file /usr/share/man/man1/xzdiff.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzcmp.1.gz because associated file /usr/share/man/man1/xzcmp.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzgrep.1.gz because associated file /usr/share/man/man1/xzgrep.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzegrep.1.gz because associated file /usr/share/man/man1/xzegrep.1.gz (of link group lzma) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/lzfgrep.1.gz because associated file /usr/share/man/man1/xzfgrep.1.gz (of link group lzma) doesn't exist
Setting up libvorbis0a:amd64 (1.3.6-2ubuntu1) ...
Setting up libltdl7:amd64 (2.4.6-14) ...
Setting up alsa-topology-conf (1.2.2-1) ...
Setting up sound-theme-freedesktop (0.8-2ubuntu1) ...
Setting up libasound2:amd64 (1.2.2-2.1ubuntu2.5) ...
Setting up libmpdec2:amd64 (2.4.2-3) ...
Setting up vim-runtime (2:8.1.2269-1ubuntu5.20) ...
Setting up readline-common (8.0-4) ...
Setting up libpython3.8-minimal:amd64 (3.8.10-0ubuntu1~20.04.8) ...
Setting up libreadline8:amd64 (8.0-4) ...
Setting up libvorbisfile3:amd64 (1.3.6-2ubuntu1) ...
Setting up libpython3.8-stdlib:amd64 (3.8.10-0ubuntu1~20.04.8) ...
Setting up libcanberra0:amd64 (0.30-7ubuntu1) ...
Setting up libpython3.8:amd64 (3.8.10-0ubuntu1~20.04.8) ...
Setting up vim (2:8.1.2269-1ubuntu5.20) ...
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vim (vim) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vimdiff (vimdiff) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/rvim (rvim) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/rview (rview) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vi (vi) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/vi.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/vi.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/vi.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/vi.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/vi.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/vi.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/vi.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/vi.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/view (view) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/view.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/view.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/view.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/view.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/view.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/view.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/view.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/view.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/ex (ex) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/ex.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/ex.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/ex.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/ex.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/ex.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/ex.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/ex.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/ex.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/editor (editor) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/editor.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/editor.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/editor.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/editor.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/editor.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/editor.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/editor.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/editor.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group editor) doesn't exist
Processing triggers for libc-bin (2.31-0ubuntu9.2) ...
root@ce128f008eea:/#

4.退出容器

bash 复制代码

root@ce128f008eea:/# exit
exit
[root@docker ~]#

5提交自己的镜像

bash 复制代码

[root@docker ~]# docker ps -a
CONTAINER ID   IMAGE           COMMAND                   CREATED              STATUS                            PORTS     NAMES
dd90b084d152   ubuntu:latest   "/bin/bash"               About a minute ago   Up About a minute                           ubuntu_vim
ccb457c15659   mysql:5.6       "docker-entrypoint.s..."   49 minutes ago       Exited (1) 49 minutes ago                   relaxed_bartik
f919fcfcb7b0   hello-world     "/hello"                  19 hours ago         Exited (0) 19 hours ago                     fervent_benz
a4016a83fc04   hello-world     "/hello"                  23 hours ago         Exited (0) 23 hours ago                     hopeful_bardeen
f30bd054e899   9c7a54a9a43c    "/hello"                  40 hours ago         Exited (0) 40 hours ago                     mystifying_shockley
[root@docker ~]# docker commit -m="installed vim" -a="circle" dd90b084d152 cirlce/ubuntu:1.0
sha256:4eac314fbf24dffd018c0682a47044f4108f5fef02d8af5d6a79e91c8bfa0765
[root@docker ~]#

对比

bash 复制代码

[root@docker ~]# docker images
REPOSITORY      TAG       IMAGE ID       CREATED         SIZE
'cirlce/ubuntu'   1.0       4eac314fbf24   2 minutes ago   72.8MB
mysql           5.6       dd3b2a5dcb48   23 months ago   303MB
'ubuntu'          latest    ba6acccedd29   2 years ago     72.8MB
hello-world     latest    feb5d9fea6a5   2 years ago     13.3kB
[root@docker ~]#

总结

Docker中的镜像分层，支持通过扩展现有镜像，创建新的镜像。类似Java继承于一个Base基础类，自己再按需扩展。
新镜像是从 base 镜像一层一层叠加生成的。每安装一个软件，就在现有镜像的基础上增加一层