Docker mount volume to running container
Introduction Show
Docker volumes are widely used and useful tools for ensuring data persistence while working in containers. They are a better alternative than compiling additional writable layers, which increase Docker image size. In this tutorial, learn how to use Docker Volumes with practical examples. What are Docker Volumes?Docker volumes are file systems mounted on Docker containers to preserve data generated by the running container. The volumes are stored on the host, independent of the container life cycle. This allows users to back up data and share file systems between containers easily. Getting Started With Docker VolumesThere are different ways to mount a Docker volume while launching a container. Users can decide between the This article shows examples of both flags in use. How to Create a Docker VolumeTo create a Docker Volume use the command:
Docker automatically creates a directory for the volume on the host under the /var/lib/docker/volume/ path. You can now mount this volume on a container, ensuring data persistence and data sharing among multiple containers. For example, to create a volume under the name data, you would run the command:
List Docker VolumesTo verify you have successfully created a Docker volume, prompt Docker to list all available volumes with:
The output displays a list of volumes, specifying their location (DRIVER) and their VOLUME NAME. In the image below, you can see the volume data created in the previous section. Inspecting Docker VolumesTo see more information about a Docker volume, use the
It lists details of a volume, including its location on the host file (Mountpoint). Everything stored within the data volume can also be found in the directory listed under the mountpoint path. Mounting a Data VolumeTo mount a data volume to a container add the To run a container and mount a data volume to it, follow the basic syntax:
Replace For example, to launch an Ubuntu container and mount the data volume to it, run:
The command instructs Docker to run a
container in interactive mode ( Then, check to verify the volume was successfully mounted by listing the content of the container:
Find the Docker volume under the name defined while launching the container. In this example, it is data. Copying Files Between Containers From a Shared VolumeLet’s see how Docker volumes allow you to share files between containers. To do so, we use the volume and container created in the previous section. This included running the commands:
1. Once you have switched to the container command prompt, move to the data volume directory:
2. Create an empty sample file using the touch command:
3. Now, exit the container:
4. Then, launch a new container example2 with the same data volume:
5. List the content of the container. You should find the data directory, as in example1:
6. Move to the data directory and list the content of it:
The output should list the sample1.txt file you created in the previous container (example1). Mounting a Host Directory as a Data volumeYou can also mount an existing directory from the host machine to a container. This type of volume is called Host Volumes. You can mount host volumes by using the Everything within the host directory is then available in the container. What’s more, all the data generated inside the container and placed in the data volume is safely stored on the host directory. The basic syntax for mounting a host directory is:
The The following example outlines how this is done. 1. First, create a sample directory on the host under the name tmp and move into it:
2. Once inside the directory, create a test file to see whether it will be available from the container:
2. Then, use the
This launches the container in interactive mode and mounts a volume under the name data1. 3. List the content of the container and verify there is a data1 directory:
4. Open the mounted directory and list the content. The output should display the file you created on the host:
Volume Permission and OwnershipVolume permissions van be changed by configuring the ownership within the Dockerfile. Use the Alternatively, you can change the ownership of the directory used as the host volume. For instructions on how to use the To delete a Docker volume, you need to specify its name. The basic syntax for removing a Docker volume in the command line is:
Docker removes volumes only if they are not in use at the moment. If there is a container with the
specified volume, it responds with an error. To proceed, stop and remove the container and then rerun the Note: If you don’t know the name of the volume, use the How to Delete All Volumes at OnceTo delete all unused Docker volumes with a single command:
The output warns you it will remove all local volumes not used by at least one container. Press y to continue. Conclusion After reading this article, you should have a better understanding of how Docker volumes work, as well as how to mount volumes to containers. Can we create volume in existing container?You can commit your existing container (that is create a new image from container's changes) and then run it with your new mounts. If it's all OK, stop your old container, and use this new one.
Can a docker volume be mounted to multiple containers?Yes you can add same location as a volume to many docker containers. Additionally you can use --volumes-from to mount your log directory in one container not actually running any application and then use the volumes from this container in your other containers without having to repeat the paths everywhere.
Which docker command is used to attach to a running container?Use docker attach to attach your terminal's standard input, output, and error (or any combination of the three) to a running container using the container's ID or name. This allows you to view its ongoing output or to control it interactively, as though the commands were running directly in your terminal.
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