Volumes and Bind Mounts

When you run a Docker container, it gets its own isolated filesystem. Any files created or changed inside that container exist only for the lifetime of the container unless you explicitly persist them. This is important to understand when running stateful services like databases. Example: MySQL stores its data under /var/lib/mysql inside the container. If you create databases and then remove the container, all of that data disappears:

# run an example MySQL container (the official image requires a root password env var)
docker run --name mysql-sample -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mysql:latest
docker stop mysql-sample
docker rm mysql-sample

Because the container’s filesystem is ephemeral, deleting the container removes /var/lib/mysql and any databases created inside it. To persist data beyond the container lifecycle, mount storage from the Docker host into the container. Bind mount the host directory /opt/datadir into the container’s /var/lib/mysql using the short -v syntax:

# bind-mount host directory /opt/datadir into container's /var/lib/mysql
docker run --name mysql-persist -v /opt/datadir:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mysql:latest

With this bind mount, MySQL writes its files into /opt/datadir on the host. Removing the container (docker rm) does not remove data stored in /opt/datadir.

Bind mounts map a host directory (or file) into a container. The host path must be absolute when using --mount and is created automatically with -v if it does not exist.

A quick comparison: -v (or --volume) vs --mount

-v / --volume (short form) accepts a single colon-separated string (for example, /host/path:/container/path) and is concise.
--mount is more explicit and recommended for clarity, especially for complex mounts; it accepts key-value pairs and requires you to set type, source, and target.

Use the table below to compare these two forms and see sample usage:

Feature	`-v` / `--volume`	`--mount`
Syntax style	Single colon-separated string	Key-value pairs
Example	`-v /opt/datadir:/var/lib/mysql`	`--mount type=bind,source=/opt/datadir,target=/var/lib/mysql`
Host directory creation	`-v` will create the host directory if it doesn’t exist	With `--mount type=bind` you should create the host directory beforehand
Clarity for advanced options	Less explicit	More explicit, easier to read for complex setups
When to prefer	Quick, simple mounts	Production, complex mounts, or when readability matters

Equivalent --mount example to the earlier -v bind mount:

docker run --name mysql-persist \
  --mount type=bind,source=/opt/datadir,target=/var/lib/mysql \
  -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mysql:latest

Best practices and operational notes

Always use absolute host paths with --mount type=bind.
Create host directories ahead of time when using --mount to avoid surprises.
Check file ownership and permissions: files created by the container may be owned by different UIDs/GIDs on the host. You may need to adjust permissions or use consistent UID/GID mappings.
For SELinux-enabled hosts, you might need :z or :Z mount options with -v to allow container access (e.g., -v /opt/datadir:/var/lib/mysql:Z).
For production deployments, prefer Docker named volumes, managed storage solutions, or networked storage backends and implement a regular backup strategy.

Persisting data with bind mounts exposes host files to the container. Misconfigured mounts can lead to data loss or security issues. Always back up important data and verify mount ownership/permissions before trusting a mount for production workloads.

Summary

Containers are ephemeral by default; files inside a removed container are removed with it.
Bind mounts let you map a host directory into a container so data persists independently of the container lifecycle.
-v is concise and convenient; --mount is more explicit and recommended for clarity and production use.
Consider file permissions, SELinux contexts, and backup strategies when persisting data.

Links and references

Introduction

Docker Commands

Docker Images

Docker Compose

Docker Engine, Storage

Docker Networking

Docker Registry

Docker on Mac & Windows

Container Orchestration - Docker Swarm & Kubernetes

Conclusion

Docker Run Commands

Volumes and Bind Mounts

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