docker镜像的默认命令

Question

我如何才能知道容器使用基础镜像运行的默认命令，而不是实际从镜像创建新的容器？

是不是我在这里遗漏了什么概念？我正在写一个使用基本图像的dockerfile，但是我不知道在CMD部分中放什么。

Answer 1

你总是可以在终端上执行docker image inspect <image>，在那里你会得到一堆信息。

我运行docker image inspect busybox (一些随机图像)，得到以下结果

[
    {
        
        "Parent": "",
        "Comment": "",
        "Created": "2021-05-04T00:19:49.531663542Z",
        "Container": "22c781af50cbbf2c31a3fb57c21d4dcfb266d6691441657088db6750d4068d22",
        "ContainerConfig": {
            "Hostname": "22c781af50cb",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
            ],
            "Cmd": [
                "/bin/sh",
                "-c",
                "#(nop) ",
                "CMD [\"sh\"]"
            ],
            
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": {}
        },
        "DockerVersion": "19.03.12",
        "Author": "",
        "Config": {
            "Hostname": "",
            "Domainname": "",
            "User": "",
            "AttachStdin": false,
            "AttachStdout": false,
            "AttachStderr": false,
            "Tty": false,
            "OpenStdin": false,
            "StdinOnce": false,
            "Env": [
                "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
            ],
            "Cmd": [
                "sh"
            ],
            
            "Volumes": null,
            "WorkingDir": "",
            "Entrypoint": null,
            "OnBuild": null,
            "Labels": null
        },
        "Architecture": "amd64",
        "Os": "linux",
        "Size": 1235829,
        "VirtualSize": 1235829,
        "GraphDriver": {
            "Data": {
      },
            "Name": "overlay2"
        },
        "RootFS": {
            "Type": "layers",
        },
        "Metadata": {
            "LastTagTime": "0001-01-01T00:00:00Z"
        }
    }
]

在这里您可以看到CMD字段

Answer 2

docker image inspect

将为您提供更多详细信息。

例如：

$ docker pull nginx
$ docker image inspect nginx:latest
...
"0":
  "Config": {
    ...
    "Cmd": [
      "nginx",
       "-g",
       "daemon off;"
    ],
    ...
}

因此，对于Nginx来说，它是[nginx, -g, daemon off;]

或者，如果安装了jq，则显示ubuntu:20.04的输出

$ docker pull ubuntu:20.04
$ docker image inspect ubuntu:20.04 | jq '.[0].Config.Cmd'
[
  "/bin/bash"
]