Demo Docker Volume

In this tutorial, you’ll learn how to create, inspect, mount, and remove Docker volumes. Volumes are the preferred mechanism for persisting container data, ensuring it lives beyond the lifecycle of individual containers.

1. List and Create a Volume

Before you begin, list existing volumes (you should see none):

$ docker volume ls
DRIVER    VOLUME NAME

Create a new volume called testvol:

$ docker volume create testvol
testvol

$ docker volume ls
DRIVER    VOLUME NAME
local     testvol

2. Mounting a Volume with -v

You can mount testvol into a container at /yogesh using the shorthand -v flag:

$ docker run -itd --name test -v testvol:/yogesh centos:7

Verify the mount inside the container:

$ docker exec -it test df -h | grep /yogesh
/dev/mapper/centos-root  50G  1.2G   49G   3% /yogesh

3. Inspect Volume Details

On the host, inspect testvol to discover its data directory:

$ docker volume inspect testvol
[
  {
    "CreatedAt": "2020-05-04T17:34:47Z",
    "Driver": "local",
    "Mountpoint": "/var/lib/docker/volumes/testvol/_data",
    "Name": "testvol",
    "Scope": "local"
  }
]

Create sample files inside the volume:

$ docker exec test bash -c "touch /yogesh/abc /yogesh/def"

4. Removing Containers vs. Volumes

Stopping or removing the container does not delete the attached volume:

$ docker stop test
$ docker rm test

$ docker volume ls
DRIVER    VOLUME NAME
local     testvol

To remove the volume and reclaim space:

$ docker volume rm testvol
testvol

5. Mounting a Volume with --mount

For clearer syntax and advanced options, use --mount:

$ docker volume create testvol
testvol

$ docker run -itd --name test \
    --mount source=testvol,destination=/yogesh \
    centos:7

Check that your files persist:

$ docker exec -it test ls /yogesh
abc  def

Comparing -v vs --mount

6. Handling Volume-in-Use Errors

If you try to remove a volume that’s still attached, you’ll see an error:

$ docker volume rm testvol
Error response from daemon: remove testvol: volume is in use - [container_id]

Stop and remove the container, then retry:

$ docker stop test
$ docker rm test
$ docker volume rm testvol
testvol

You can also remove all unused volumes in one command:

$ docker volume prune
WARNING! This will remove all local volumes not used by at least one container.
Are you sure you want to continue? [y/N] y
Total reclaimed space: 0B

7. Read-Write vs Read-Only Mounts

By default, mounts are read-write (rw). Here’s how to confirm:

$ docker volume create data_vol1
data_vol1

$ docker run -itd --name volume_rw \
    --mount source=data_vol1,destination=/yogesh \
    centos:7

$ docker inspect volume_rw --format '{{json .Mounts}}'
[{"Destination":"/yogesh","Mode":"rw", ...}]

To mount that same volume as read-only (ro):

$ docker run -itd --name volume_ro \
    --mount source=data_vol1,destination=/yogesh,readonly=true \
    centos:7

$ docker inspect volume_ro --format '{{json .Mounts}}'
[{"Destination":"/yogesh","Mode":"ro", ...}]

Clean up:

$ docker stop volume_rw volume_ro
$ docker rm volume_rw volume_ro
$ docker volume prune -f

8. Bind Mounts

Bind mounts let you map any host directory directly into a container:

$ mkdir /data

$ docker run -itd --name bindtest \
    --mount type=bind,source=/data,destination=/yogesh \
    centos:7

Inside bindtest, the path /yogesh is backed by /data on the host. Note that bind mounts do not show up in docker volume ls.

Links and References

• Docker Volumes
• Bind Mounts
• Docker Run Reference