[docker] How can I add a volume to an existing Docker container?

I have a Docker container that I've created simply by installing Docker on Ubuntu and doing:

sudo docker run -i -t ubuntu /bin/bash

I immediately started installing Java and some other tools, spent some time with it, and stopped the container by

exit

Then I wanted to add a volume and realised that this is not as straightforward as I thought it would be. If I use sudo docker -v /somedir run ... then I end up with a fresh new container, so I'd have to install Java and do what I've already done before just to arrive at a container with a mounted volume.

All the documentation about mounting a folder from the host seems to imply that mounting a volume is something that can be done when creating a container. So the only option I have to avoid reconfiguring a new container from scratch is to commit the existing container to a repository and use that as the basis of a new one whilst mounting the volume.

Is this indeed the only way to add a volume to an existing container?

I've successfully mount /home/<user-name> folder of my host to the /mnt folder of the existing (not running) container. You can do it in the following way:

1. Open configuration file corresponding to the stopped container, which can be found at /var/lib/docker/containers/99d...1fb/config.v2.json (may be config.json for older versions of docker).

2. Find MountPoints section, which was empty in my case: "MountPoints":{}. Next replace the contents with something like this (you can copy proper contents from another container with proper settings):

"MountPoints":{"/mnt":{"Source":"/home/<user-name>","Destination":"/mnt","RW":true,"Name":"","Driver":"","Type":"bind","Propagation":"rprivate","Spec":{"Type":"bind","Source":"/home/<user-name>","Target":"/mnt"},"SkipMountpointCreation":false}}

or the same (formatted):

  "MountPoints": {
    "/mnt": {
      "Source": "/home/<user-name>",
      "Destination": "/mnt",
      "RW": true,
      "Name": "",
      "Driver": "",
      "Type": "bind",
      "Propagation": "rprivate",
      "Spec": {
        "Type": "bind",
        "Source": "/home/<user-name>",
        "Target": "/mnt"
      },
      "SkipMountpointCreation": false
    }
  }

3. Restart the docker service: service docker restart

This works for me with Ubuntu 18.04.1 and Docker 18.09.0

Jérôme Petazzoni has a pretty interesting blog post on how to Attach a volume to a container while it is running. This isn't something that's built into Docker out of the box, but possible to accomplish.

As he also points out

This will not work on filesystems which are not based on block devices.

It will only work if /proc/mounts correctly lists the block device node (which, as we saw above, is not necessarily true).

Also, I only tested this on my local environment; I didn’t even try on a cloud instance or anything like that

YMMV

A note for using Docker Windows containers after I had to look for this problem for a long time!

Condiditions:

• Windows 10
• Docker Desktop (latest version)
• using Docker Windows Container for image microsoft/mssql-server-windows-developer

Problem:

• I wanted to mount a host dictionary into my windows container.

Solution as partially discripted here:

• create docker container

docker run -d -p 1433:1433 -e sa_password=<STRONG_PASSWORD> -e ACCEPT_EULA=Y microsoft/mssql-server-windows-developer

• go to command shell in container

docker exec -it <CONTAINERID> cmd.exe

• create DIR

mkdir DirForMount

• stop container

docker container stop <CONTAINERID>

• commit container

docker commit <CONTAINERID> <NEWIMAGENAME>

• delete old container

docker container rm <CONTAINERID>

• create new container with new image and volume mounting

docker run -d -p 1433:1433 -e sa_password=<STRONG_PASSWORD> -e ACCEPT_EULA=Y -v C:\DirToMount:C:\DirForMount <NEWIMAGENAME>

After this i solved this problem on docker windows containers.

The best way is to copy all the files and folders inside a directory on your local file system by: docker cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH

SRC_PATH is on container DEST_PATH is on localhost

Then do docker-compose down attach a volume to the same DEST_PATH and run Docker containers by using docker-compose up -d

Add volume by following in docker-compose.yml

volumes:
 - DEST_PATH:SRC_PATH

We don't have any way to add volume in running container, but to achieve this objective you may use the below commands:

Copy files/folders between a container and the local filesystem:

docker cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH

docker cp [OPTIONS] SRC_PATH CONTAINER:DEST_PATH

For reference see:

https://docs.docker.com/engine/reference/commandline/cp/

Unfortunately the switch option to mount a volume is only found in the run command.

docker run --help

-v, --volume list Bind mount a volume (default [])

There is a way you can work around this though so you won't have to reinstall the applications you've already set up on your container.

1. Export your container docker container export -o ./myimage.docker mycontainer
2. Import as an image docker import ./myimage.docker myimage
3. Then docker run -i -t -v /somedir --name mycontainer myimage /bin/bash