【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
- 本章要点
- commit 命令
- 命令格式
- docker commit 操作参数
- 实例演示
- 1.下载一个新的ubuntu镜像
- 2.运行容器
- 3.查看并安装vim
- 4.退出容器
- 5提交自己的镜像
- 对比
- 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：
- 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
- UnionFS（联合文件系统）
- 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
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
[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
[root@docker ~]# docker run -it ba6acccedd29 /bin/bash
root@792de8cbe835:/#
3.查看并安装vim
[root@docker ~]# docker run -it ba6acccedd29 /bin/bash
root@ce128f008eea:/# vim aaa.txt
oot@ce128f008eea:/# apt-get update
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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-freedesktopvim-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 vimvim-common vim-runtime xxd xz-utils
0 upgraded, 30 newly installed, 0 to remove and 51 not upgraded.
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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
root@ce128f008eea:/# exit
exit
[root@docker ~]#
5提交自己的镜像
[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
[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
