Docker image常用命令
1 简介
docker image命令用于管理镜像，常见使用方式如下。
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❯ docker image --help
Usage: docker image COMMAND
Manage images
Commands:
build Build an image from a Dockerfile
history Show the history of an image
import Import the contents from a tarball to create a filesystem image
inspect Display detailed information on one or more images
load Load an image from a tar archive or STDIN
ls List images
prune Remove unused images
pull Pull an image or a repository from a registry
push Push an image or a repository to a registry
rm Remove one or more images
save Save one or more images to a tar archive (streamed to STDOUT by default)
tag Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE
2 image inspect
示例使用的say镜像的Dockerfile如下：
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FROM scratch
WORKDIR /
COPY ./say /
CMD ["/say"]
这里，着重梳理一下inspect。inspect用于查看镜像的详细信息。
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❯ docker image inspect say
[
{
"Id": "sha256:aa5bb1e797b5648a5c61618c0b6171a25189a2d6e18ec37b9466743a35945ab9",
"RepoTags": [
"say:latest"
],
"RepoDigests": [],
"Parent": "sha256:378b8f2564caa9bf6903179a94ae392776f77c2652dec3327889b34bfc742272",
"Comment": "",
"Created": "2021-11-05T05:02:17.489994051Z",
"Container": "5acca3b69c9336715e078374b8cc00625325d1e93c0045be064d446ca1514e7e",
"ContainerConfig": {
... ...
"Cmd": [
"/bin/sh",
"-c",
"#(nop) ",
"CMD [\"/say\"]"
],
"Image": "sha256:378b8f2564caa9bf6903179a94ae392776f77c2652dec3327889b34bfc742272",
"Volumes": null,
"WorkingDir": "/",
... ...
},
"DockerVersion": "20.10.9",
"Author": "",
"Config": {
... ...
"Cmd": [
"/say"
],
"Image": "sha256:378b8f2564caa9bf6903179a94ae392776f77c2652dec3327889b34bfc742272",
... ...
},
... ...
"GraphDriver": {
"Data": {
"MergedDir": "/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c/merged",
"UpperDir": "/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c/diff",
"WorkDir": "/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c/work"
},
"Name": "overlay2"
},
... ...
}
]
这里，关注Parent、GraphDriver。
Parent指的是该镜像的基础镜像，docker的镜像是一层一层叠加而来的，没执行Dockerfile中的一条指令就会产生一个层镜像，可以使用docker image history查看镜像的叠加关系。
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❯ docker image history say
IMAGE CREATED CREATED BY SIZE COMMENT
aa5bb1e797b5 2 hours ago /bin/sh -c #(nop) CMD ["/say"] 0B
378b8f2564ca 2 hours ago /bin/sh -c #(nop) COPY file:0ca1aaab19fa1703… 923kB
81ec91d2bac1 2 hours ago /bin/sh -c #(nop) WORKDIR / 0B
inspect信息中的Parent: sha256:378b8f2564ca ... ...，同第二层镜像（378b8f2564ca 2 hours ago /bin/sh -c #(nop) COPY file:0ca1aaab19fa1703… 即COPY操作）对应。
GraphDriver.Data指向目录/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29... ...，该目录是镜像的overlay2存储目录。
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/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c
├── committed
├── diff
│ └── say
└── link
第二层镜像378b8f2564ca的overlay2存储目录同样指向目录/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29... ...，这是因为第三层镜像是执行CMD得到的，没有更改镜像上的任何文件。
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docker image inspect 378b8 | grep 'overlay2'
"MergedDir": "/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c/merged",
"UpperDir": "/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c/diff",
"WorkDir": "/var/lib/docker/overlay2/de4b43fcc2e259b223c2e5a29c5883711aa15ca0b127e8df2482bfc00ed4e84c/work"
"Name": "overlay2"
而第一层镜像81ec91d2bac1的Parent和GraphDriver.Data均为空，这是应为say镜像是FROM scratch，scratch是空镜像。
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docker image inspect 81ec91d2bac1
... ...
"Parent": "",
... ...
"GraphDriver": {
"Data": null,
"Name": "overlay2"
},
... ...