1. 镜像是什么？
- 一个分层存储的文件
- 一个软件的环境
- 一个镜像可以创建N个容器
- 一种标准化的交付
- 一个不包含Linux内核而又精简的Linux操作系统
镜像不是一个单一的文件，而是有多层组成。我们可以通过docker history <ID/NAME>查看镜像中各层内容及大小，每层对应着Dockerfile中的一条指令。Docker镜像默认存储在/var/lib/docker/<storage-driver>中。
2. 镜像从哪里来？
Docker Hub是由Docker公司负责维护的公共注册中心，包含大量的容器镜像，Docker工具默认从这个公共镜像库下载镜像。地址：https://hub.docker.com/explore
配置镜像加速器：https://www.daocloud.io/mirror
curl -sSL https://get.daocloud.io/daotools/set_mirror.sh | sh -s http://f1361db2.m.daocloud.io
[root@localhost ~]# curl -sSL https://get.daocloud.io/daotools/set_mirror.sh | sh -s http://f1361db2.m.daocloud.io ---配置后下载镜像会加快
docker version >= 1.12
{"registry-mirrors": ["http://f1361db2.m.daocloud.io"]}
Success.
You need to restart docker to take effect: sudo systemctl restart docker
[root@localhost ~]# systemctl restart docker
[root@localhost ~]# docker pull nginx ---下载个nginx镜像测试下
3. 镜像与容器的联系
image.png
如图，容器其实是在镜像的最上面加了一层读写层，在运行容器里文件改动时，会先从镜像里要写的文件复制到容器自己的文件系统中（读写层）。
如果容器删除了，最上面的读写层也就删除了，改动也就丢失了。所以无论多少个容器共享一个镜像，所做的写操作都是从镜像的文件系统中复制过来操作的，并不会修改镜像的源文件，这种方式提高磁盘利用率。
若想持久化这些改动，可以通过docker commit将容器保存成一个新镜像。
4. 管理镜像常用命令
image.png
[root@localhost ~]# docker image ls ---列出镜像信息
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx latest f09fe80eb0e7 13 days ago 109MB
hello-world latest fce289e99eb9 7 weeks ago 1.84kB
[root@localhost ~]# docker pull nginx:1.14 ---下载nginx1.14镜像
1.14: Pulling from library/nginx
6ae821421a7d: Already exists
7edc8c3fac48: Pull complete
a19c4a4a77fe: Pull complete
Digest: sha256:a82bee663ef9d49720e7b79952e122871405bd2a2b3112be8c44ff6e96dd3aa3
Status: Downloaded newer image for nginx:1.14
[root@localhost ~]# docker image rm nginx:1.14 ---删除nginx1.14镜像，可以看出把所有分层的目录一并删除
Untagged: nginx:1.14
Untagged: nginx@sha256:a82bee663ef9d49720e7b79952e122871405bd2a2b3112be8c44ff6e96dd3aa3
Deleted: sha256:1293e2b0a1af4854799d5f4a335c59f475cb68ef34e35f8e901d77971eb47315
Deleted: sha256:7016890e9376cbb07ba5ac82aa99da0183ecc886bd3307f7b0bdb08cb6d862f6
Deleted: sha256:7860b3787f080232f56aedd7d431277c2cae522773a7a04c38b158db4b7756d5
[root@localhost ~]# docker image inspect nginx ---查看nginx镜像的详细信息
[
{
"Id": "sha256:f09fe80eb0e75e97b04b9dfb065ac3fda37a8fac0161f42fca1e6fe4d0977c80",
"RepoTags": [
"nginx:latest"
],
"RepoDigests": [
"nginx@sha256:dd2d0ac3fff2f007d99e033b64854be0941e19a2ad51f174d9240dda20d9f534"
],
"Parent": "",
"Comment": "",
"Created": "2019-02-06T08:11:09.870777091Z",
"Container": "97f09173241402d70db198f1851fe29c5b8838a1557a6d9d13611dac10cfb4cc",
"ContainerConfig": {
"Hostname": "97f091732414",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"80/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
"NGINX_VERSION=1.15.8-1~stretch",
"NJS_VERSION=1.15.8.0.2.7-1~stretch"
],
"Cmd": [
"/bin/sh",
"-c",
"#(nop) ",
"CMD [\"nginx\" \"-g\" \"daemon off;\"]"
],
"ArgsEscaped": true,
"Image": "sha256:ef23a318d592d7839af9a0fb77d6282096c1be351ee92598440abd727fa65ab9",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {
"maintainer": "NGINX Docker Maintainers <docker-maint@nginx.com>"
},
"StopSignal": "SIGTERM"
},
"DockerVersion": "18.06.1-ce",
"Author": "",
"Config": {
"Hostname": "",
"Domainname": "",
"User": "",
"AttachStdin": false,
"AttachStdout": false,
"AttachStderr": false,
"ExposedPorts": {
"80/tcp": {}
},
"Tty": false,
"OpenStdin": false,
"StdinOnce": false,
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
"NGINX_VERSION=1.15.8-1~stretch",
"NJS_VERSION=1.15.8.0.2.7-1~stretch"
],
"Cmd": [
"nginx",
"-g",
"daemon off;"
],
"ArgsEscaped": true,
"Image": "sha256:ef23a318d592d7839af9a0fb77d6282096c1be351ee92598440abd727fa65ab9",
"Volumes": null,
"WorkingDir": "",
"Entrypoint": null,
"OnBuild": null,
"Labels": {
"maintainer": "NGINX Docker Maintainers <docker-maint@nginx.com>"
},
"StopSignal": "SIGTERM"
},
"Architecture": "amd64",
"Os": "linux",
"Size": 109202600,
"VirtualSize": 109202600,
"GraphDriver": {
"Data": {
"LowerDir": "/var/lib/docker/overlay2/63a2167ed0245134b23888d1ec25c4c7da7dbb5c56b36bd594375149fb450416/diff:/var/lib/docker/overlay2/7d229741b9a8b4afad7e94caa5acdc6e97c8e268d835bdfab199cd9350c12396/diff",
"MergedDir": "/var/lib/docker/overlay2/e5683ad895e15d8ab0dd2df6b552e8c39590df62ec41e9cd45ff3f7b6e4a96d0/merged",
"UpperDir": "/var/lib/docker/overlay2/e5683ad895e15d8ab0dd2df6b552e8c39590df62ec41e9cd45ff3f7b6e4a96d0/diff",
"WorkDir": "/var/lib/docker/overlay2/e5683ad895e15d8ab0dd2df6b552e8c39590df62ec41e9cd45ff3f7b6e4a96d0/work"
},
"Name": "overlay2"
},
"RootFS": {
"Type": "layers",
"Layers": [
"sha256:0a07e81f5da36e4cd6c89d9bc3af643345e56bb2ed74cc8772e42ec0d393aee3",
"sha256:92c15149e23b2b6b3bb21992622b4af6074d8c7cc6682ec2712c08ff1ca0fc9f",
"sha256:6b5e2ed60418ce61aa042febfd08b691826552742b0c777de9901de6548bf40a"
]
},
"Metadata": {
"LastTagTime": "0001-01-01T00:00:00Z"
}
}
]
[root@localhost ~]# docker image prune ---移除未使用的镜像，由于本测试环境没有未使用的镜像，所以释放0B空间
WARNING! This will remove all dangling images.
Are you sure you want to continue? [y/N] y
Total reclaimed space: 0B
[root@localhost ~]# docker image tag nginx nginx:v1 ---给镜像打标记
[root@localhost ~]# docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx latest f09fe80eb0e7 13 days ago 109MB
nginx v1 f09fe80eb0e7 13 days ago 109MB ---标记成功
hello-world latest fce289e99eb9 7 weeks ago 1.84kB
[root@localhost ~]# docker image save nginx > nginx.tar ---把nginx镜像保存为名为nginx.tar的归档文件
[root@localhost ~]# du -sh nginx.tar
108M nginx.tar
[root@localhost ~]# docker image rm nginx ---删除原来的nginx镜像
Untagged: nginx:latest
[root@localhost ~]# docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx v1 f09fe80eb0e7 13 days ago 109MB
hello-world latest fce289e99eb9 7 weeks ago 1.84kB
[root@localhost ~]# docker image load < nginx.tar ---导入nginx.tar中的镜像
Loaded image: nginx:latest
Loaded image: nginx:v1
[root@localhost ~]# docker images ---导入成功
REPOSITORY TAG IMAGE ID CREATED SIZE
nginx latest f09fe80eb0e7 13 days ago 109MB
nginx v1 f09fe80eb0e7 13 days ago 109MB
hello-world latest fce289e99eb9 7 weeks ago 1.84kB
[root@localhost ~]# docker history nginx ---查看nginx镜像的历史记录
IMAGE CREATED CREATED BY SIZE COMMENT
5a3221f0137b 31 hours ago /bin/sh -c #(nop) CMD ["nginx" "-g" "daemon… 0B
<missing> 31 hours ago /bin/sh -c #(nop) STOPSIGNAL SIGTERM 0B
<missing> 31 hours ago /bin/sh -c #(nop) EXPOSE 80 0B
<missing> 31 hours ago /bin/sh -c ln -sf /dev/stdout /var/log/nginx… 22B
<missing> 31 hours ago /bin/sh -c set -x && addgroup --system -… 56.8MB
<missing> 31 hours ago /bin/sh -c #(nop) ENV PKG_RELEASE=1~buster 0B
<missing> 31 hours ago /bin/sh -c #(nop) ENV NJS_VERSION=0.3.5 0B
<missing> 31 hours ago /bin/sh -c #(nop) ENV NGINX_VERSION=1.17.3 0B
<missing> 2 days ago /bin/sh -c #(nop) LABEL maintainer=NGINX Do… 0B
<missing> 3 days ago /bin/sh -c #(nop) CMD ["bash"] 0B
<missing> 3 days ago /bin/sh -c #(nop) ADD file:330bfb91168adb4a9… 69.2MB
