【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vim4.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: 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

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, --messagestring-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

Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]

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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.

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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

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