Demonstration
$ docker save hello-world -o /tmp/hello-world.tar
Error response from daemon: No such image: hello-world
$ docker pull hello-world
…
$ docker save hello-world
cowardly refusing to save to a terminal. Use the -o flag or redirect
$ docker save hello-world -o /tmp/hello-world.tar
$ tar tf /tmp/hello-world.tar
d2c94e258dcb3c5ac2798d32e1249e42ef01cba4841c2234249495f87264ac5a.json
df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/
df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/VERSION
df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/json
df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/layer.tar
manifest.json
repositories
Create directory /tmp/hello-world-image-content and extract tar content into this directory:
$ mkdir /tmp/hello-world-image-content
$ tar xf /tmp/hello-world.tar -C /tmp/hello-world-image-content
Files in directory
$ ls /tmp/hello-world-image-content/
d2c94e258dcb3c5ac2798d32e1249e42ef01cba4841c2234249495f87264ac5a.json df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c manifest.json repositories
manifest.json lists filesystem layers and the name of the json file that has the Container properties.
jq makes the content of this JSON file more human readable:
$ jq . /tmp/hello-world-image-content/manifest.json
[
{
"Config": "d2c94e258dcb3c5ac2798d32e1249e42ef01cba4841c2234249495f87264ac5a.json",
"RepoTags": [
"hello-world:latest"
],
"Layers": [
"df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/layer.tar"
]
}
]
$ jq . /tmp/hello-world-image-content/d2c94e258dcb3c5ac2798d32e1249e42ef01cba4841c2234249495f87264ac5a.json
{
"architecture": "amd64",
"config": {
"Env": [
"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
],
"Cmd": [
"/hello"
],
"WorkingDir": "/",
"ArgsEscaped": true,
"OnBuild": null
},
"created": "2023-05-02T16:49:27Z",
"history": [
{
"created": "2023-05-02T16:49:27Z",
"created_by": "COPY hello / # buildkit",
"comment": "buildkit.dockerfile.v0"
},
{
"created": "2023-05-02T16:49:27Z",
"created_by": "CMD [\"/hello\"]",
"comment": "buildkit.dockerfile.v0",
"empty_layer": true
}
],
"os": "linux",
"rootfs": {
"type": "layers",
"diff_ids": [
"sha256:ac28800ec8bb38d5c35b49d45a6ac4777544941199075dff8c4eb63e093aa81e"
]
}
}
$ cat /tmp/hello-world-image-content/df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/VERSION ; echo
1.0
$ jq . /tmp/hello-world-image-content/df1c22f7c9ab11ff627ce477eae827d0eb29e637b95bffe1c5fd3f414ace672c/json
…