[Docker] How to see the contents of Volumes. Start a container with root privileges.

How to check the folders and files in the Docker volume.

Confirmation method

1. Check the volume point (absolute path) with docker volume inspect.
2. Start a container with root privileges from the image.
3. Use the ls command in the terminal inside the container

Checking the mount point of volume

#Display volume list
docker volume ls

#Check mount point
docker volume inspect [Volume name]

Start a container with root privileges and check the contents of the volume

#Start container with root authority
$ docker run -it --privileged --pid=host [Image name] nsenter -t 1 -m -u -n -i sh

#Show the contents of the volume
/ # ls [Absolute path of mountpoint]

#End interactive mode
/ # exit

With the above operation, the contents of volume can be confirmed.

Check the image

$ docker images
REPOSITORY                                      TAG                 IMAGE ID            CREATED             SIZE
tomcat                                          latest              35064a4fcc93        2 weeks ago         648MB
django_web                                      latest              7f0eff7ebc94        2 weeks ago         937MB
debian                                          latest              1510e8501783        5 weeks ago         114MB
python                                          3                   dfc47c6cee13        6 weeks ago         886MB
postgres                                        latest              817f2d3d51ec        7 weeks ago         314MB
vuecli                                          3                   4040959eab16        2 months ago        338MB

Display volume list

$ docker volume ls
DRIVER              VOLUME NAME
local               0adf7a2b08b8e09f74ffb7799716e48263f012612dc2047da1d7137a75f12b5d
local               vuecli3_vue-cli-node-volume

Check mount point

$ docker volume inspect vuecli3_vue-cli-node-volume
[
    {
        "CreatedAt": "2020-09-08T05:35:36Z",
        "Driver": "local",
        "Labels": {
            "com.docker.compose.project": "vuecli3",
            "com.docker.compose.version": "1.26.2",
            "com.docker.compose.volume": "vue-cli-node-volume"
        },
        "Mountpoint": "/var/lib/docker/volumes/vuecli3_vue-cli-node-volume/_data",
        "Name": "vuecli3_vue-cli-node-volume",
        "Options": null,
        "Scope": "local"
    }
]

Enter docker interactive mode

$ docker run -it --privileged --pid=host [Image name] nsenter -t 1 -m -u -n -i sh

docker interactive mode

/ # ls
EFI         boot        dev         home        lib         mnt         proc        run         srv         tmp         var
bin         containers  etc         init        media       opt         root        sbin        sys         usr

Check volume

/ # ls /var/lib/docker/volumes/micres_micres-node_modules2/_data
@babel                                       mime-db
@csstools                                    mime-types
@mdi                                         mimic-response
@nicolo-ribaudo                              mini-css-extract-plugin
@npmcli                                      minimalistic-assert
@rails                                       minimalistic-crypto-utils

Details of starting a container with root privileges

What is the most important command to start a container with root privileges?

Command $ docker run -it --privileged --pid = host [image name] nsenter -t 1 -m -u -n -i sh`

・ -It -t pseudo terminal (--tty) -i Standard output always ON (--interactive)

・ --Privileged Privileged mode. Launch a special container with root privileges on the host.

・ --Pid = host --pit = Specify the PID namespace for the container. Use the host-side PID namespace inside the host container.

・ Nsenter A command line tool for entering namespaces created with Docker. A combination of acronyms for "ENTER into Name Spaces".

・ -M "--Mount" Enter the mount name space. If no namespace is specified, the process specified by PID will be used.

・ ｀ ｀ Enter the "-uts" UTS namespace. If no namespace is specified, the process specified by PID will be used.

uts stands for Unix Time Sharing.

・ ｀ ｀ Enter the "--net" network namespace. If no namespace is specified, the process specified by PID will be used.

・ -I Enter the "--ipc" IPC namespace. If no namespace is specified, the process specified by PID will be used.

In short, it seems that various namespaces will be launched by processing PID = 1.

List of Linux nsenter options