docker学习3-镜像的基本使用

前言

Docker的三大核心概念:镜像、容器、仓库。初学者对镜像和容器往往分不清楚，学过面向对象的应该知道类和实例，这跟面向对象里面的概念很相似

我们可以把镜像看作类，把容器看作类实例化后的对象。

docker	面向对象
镜像	类
容器	实例

查看镜像列表

使用docker images查看本地已经下载的镜像

• REPOSITORY：表示镜像的仓库源
• TAG：镜像的标签，区分不同版本
• IMAGE ID：镜像ID，16进制组成，唯一标识
• CREATED：镜像创建时间
• SIZE：镜像大小

[root@yoyo ~]# docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
centos/python-36-centos7   latest              b8d15efaa8ec        2 months ago        651MB
ubuntu                     15.10               9b9cb95443b5        2 years ago         137MB
training/webapp            latest              6fae60ef3446        4 years ago         349MB
[root@yoyo ~]#

我们本地下载的镜像文件是从仓库下载过来的，每个镜像在仓库源都有个名称，也就是 REPOSITORY，同一个镜像源可以有不同的版本，同标签(TAG)区分

下载镜像

直接使用 docker pull centos 默认是下载的最新的latest版本

docker pull centos

[root@yoyo ~]# docker pull centos
Using default tag: latest
latest: Pulling from library/centos
8ba884070f61: Already exists
Digest: sha256:b5e66c4651870a1ad435cd75922fe2cb943c9e973a9673822d1414824a1d0475
Status: Downloaded newer image for centos:latest
[root@yoyo ~]# docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
centos/python-36-centos7   latest              b8d15efaa8ec        2 months ago        651MB
centos                     latest              9f38484d220f        3 months ago        202MB
ubuntu                     15.10               9b9cb95443b5        2 years ago         137MB
training/webapp            latest              6fae60ef3446        4 years ago         349MB
[root@yoyo ~]#

搜索镜像

docker search搜索相关的镜像文件

[root@yoyo ~]# docker search centos
NAME                               DESCRIPTION                                     STARS               OFFICIAL            AUTOMATED
centos                             The official build of CentOS.                   5424                [OK]
ansible/centos7-ansible            Ansible on Centos7                              121                                     [OK]
jdeathe/centos-ssh                 CentOS-6 6.10 x86_64 / CentOS-7 7.6.1810 x86…   110                                     [OK]
consol/centos-xfce-vnc             Centos container with "headless" VNC session…   91                                      [OK]
imagine10255/centos6-lnmp-php56    centos6-lnmp-php56                              57                                      [OK]
centos/mysql-57-centos7            MySQL 5.7 SQL database server                   54
tutum/centos                       Simple CentOS docker image with SSH access      44
centos/postgresql-96-centos7       PostgreSQL is an advanced Object-Relational …   37
kinogmt/centos-ssh                 CentOS with SSH                                 27                                      [OK]

如果我想下载一个centos7.5的镜像版本，该如何找到呢？

查找TAG版本

如果要找到指定的TAG版本，需打开docker官网https://hub.docker.com/search/?type=image，搜索框输入：centos搜索。

点击详情，找到TAGS，就可以看到不同的标签版本了

接下来指定TAG名称下载，后面加个冒号:标签名称

docker pull centos:centos7.5.1804

[root@yoyo ~]# docker pull centos:centos7.5.1804
centos7.5.1804: Pulling from library/centos
5ad559c5ae16: Pull complete
Digest: sha256:7a45e4a1efbaafc1d9aa89925b6fdb33288a96d35ea0581412316e2f0ad3720a
Status: Downloaded newer image for centos:centos7.5.1804
[root@yoyo ~]# docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
centos/python-36-centos7   latest              b8d15efaa8ec        2 months ago        651MB
centos                     centos7.5.1804      cf49811e3cdb        3 months ago        200MB
centos                     latest              9f38484d220f        3 months ago        202MB
ubuntu                     15.10               9b9cb95443b5        2 years ago         137MB
training/webapp            latest              6fae60ef3446        4 years ago         349MB
[root@yoyo ~]#

更新镜像

上面下载的TAG名称是centos7.5.1804，这个太长了不太好记，可以改成一个自己喜欢的TAG名称，比如7.5

更新镜像需先启动容器

docker run -d centos:centos7.5.1804

[root@yoyo ~]# docker run -d centos:centos7.5.1804
64cc20e825e3cb70bdbb5c22dac72b061fba77895e794ae7a06d57d2ddfb8a96
[root@yoyo ~]# docker ps -a
CONTAINER ID        IMAGE                      COMMAND                  CREATED             STATUS                      PORTS               NAMES
64cc20e825e3        centos:centos7.5.1804      "/bin/bash"              38 seconds ago      Exited (0) 35 seconds ago                       recursing_ardinghelli
fefdcbb9c662        centos/python-36-centos7   "container-entrypoin…"   24 hours ago        Exited (0) 24 hours ago                         quirky_cray
9df329b5effd        centos/python-36-centos7   "container-entrypoin…"   24 hours ago        Exited (0) 24 hours ago                         nifty_roentgen

启动之后，查看到容器id号64cc20e825e3，根据容器id，去修改

• -m:提交的描述信息
• -a:指定镜像作者
• e218edb10161：容器ID
• runoob/ubuntu:v2:指定要创建的目标镜像名

docker commit -m="update tag name" -a="yoyo" 64cc20e825e3 centos:7.5

[root@yoyo ~]# docker commit -m="update tag name" -a="yoyo" 64cc20e825e3  centos:7.5
sha256:254d4dfe9df7765ccf511bd8e7ff1f5de96b0b5a0af2542ee4cd30c8ac0575b3
[root@yoyo ~]# docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED              SIZE
centos                     7.5                 254d4dfe9df7        8 seconds ago        200MB
centos                     latest              b9af5ce31055        35 seconds ago       200MB
centos/python-36-centos7   latest              b8d15efaa8ec        2 months ago         651MB
ubuntu                     15.10               9b9cb95443b5        2 years ago          137MB
training/webapp            latest              6fae60ef3446        4 years ago          349MB
[root@yoyo ~]#

设置镜像TAG

如果只是修改镜像TAG名称，可以用docker tag给镜像取个新的tag名称, 这里的id是镜像的id

docker tag 254d4dfe9df7 centos:v7.5

[root@yoyo ~]# docker tag 254d4dfe9df7 centos:v7.5
[root@yoyo ~]# docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
centos                     7.5                 254d4dfe9df7        9 minutes ago       200MB
centos                     v7.5                254d4dfe9df7        9 minutes ago       200MB
centos                     latest              b9af5ce31055        9 minutes ago       200MB
centos/python-36-centos7   latest              b8d15efaa8ec        2 months ago        651MB
ubuntu                     15.10               9b9cb95443b5        2 years ago         137MB
training/webapp            latest              6fae60ef3446        4 years ago         349MB
[root@yoyo ~]#

这时候会多了一个v7.5的标签

删除镜像

上面多了个7.5的TAG，并且IMAGE ID是重复的，可以使用docker rmi 删掉它,可以加-f参数强制删除

• -f :强制删除；
• --no-prune :不移除该镜像的过程镜像，默认移除；

[root@yoyo ~]# docker rmi centos:7.5
Untagged: centos:7.5
[root@yoyo ~]# docker images
REPOSITORY                 TAG                 IMAGE ID            CREATED             SIZE
centos                     v7.5                254d4dfe9df7        12 minutes ago      200MB
centos                     latest              b9af5ce31055        12 minutes ago      200MB
centos/7.5                 latest              62a395cab78e        13 minutes ago      200MB
centos/python-36-centos7   latest              b8d15efaa8ec        2 months ago        651MB
centos                     centos7.5.1804      cf49811e3cdb        3 months ago        200MB
centos                     <none>              9f38484d220f        3 months ago        202MB
ubuntu                     15.10               9b9cb95443b5        2 years ago         137MB
training/webapp            latest              6fae60ef3446        4 years ago         349MB
[root@yoyo ~]#

想在别人的基础上重新做一个镜像，需要创建一个 Dockerfile 文件，后面讲 Docker 如何构建我们的镜像。

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