unregistry

Unregistry is a lightweight container image registry that stores and serves images directly from your Docker daemon’s storage.

The included docker pussh command (extra ‘s’ for SSH) lets you push images straight to remote Docker servers over SSH. It transfers only the missing layers, making it fast and efficient.

https://github.com/user-attachments/assets/9d704b87-8e0d-4c8a-9544-17d4c63bd050

The problem

You’ve built a Docker image locally. Now you need it on your server. Your options suck:

• Docker Hub / GitHub Container Registry - Your code is now public, or you’re paying for private repos
• Self-hosted registry - Another service to maintain, secure, and pay for storage
• Save/Load - docker save | ssh <remote server> docker load transfers the entire image, even if 90% already exists on the server
• Rebuild remotely - Wastes time and server resources. Plus now you’re debugging why the build fails in production

You just want to move an image from A to B. Why is this so hard?

The solution

docker pussh myapp:latest user@server

That’s it. Your image is on the remote server. No registry setup, no subscription, no intermediate storage, no exposed ports. Just a direct transfer of the missing layers over SSH.

Here’s what happens under the hood:

1. Establishes SSH tunnel to the remote server
2. Starts a temporary unregistry container on the server
3. Forwards a random localhost port to the unregistry port over the tunnel
4. docker push to unregistry through the forwarded port, transferring only the layers that don’t already exist remotely. The transferred image is instantly available on the remote Docker daemon
5. Stops the unregistry container and closes the SSH tunnel

It’s like rsync for Docker images — simple and efficient.

[!NOTE] Unregistry was created for Uncloud, a lightweight tool for deploying containers across multiple Docker hosts. We needed something simpler than a full registry but more efficient than save/load.

Requirements

On local machine

• Docker CLI with plugin support (Docker 19.03+)
• OpenSSH client

On remote server

• Docker is installed and running
• SSH user has permissions to run docker commands (user is root or non-root user is in docker group — see Manage Docker as a non-root user for details)
• If sudo is required, ensure the user can run sudo docker without a password prompt
• Your server has internet access to ghcr.io to pull the unregistry image ghcr.io/psviderski/unregistry:latest on first docker pussh use.
  • If your server requires a proxy to access the internet, configure Docker to use it by following the Daemon proxy configuration guide.
  • For air-gapped environments or where the access to ghcr.io is restricted, you can preload the image manually:

    # Get the needed unregistry image version from the plugin version output
    docker pussh --version
    # Will return:
    #   ...
    #   unregistry image: ghcr.io/psviderski/unregistry:X.Y.Z
    
    # On a machine with internet access
    docker pull ghcr.io/psviderski/unregistry:X.Y.Z
    docker save ghcr.io/psviderski/unregistry:X.Y.Z | ssh user@server docker load
    

• Unregistry container requires access to the containerd socket at /run/containerd/containerd.sock, so the container runs as root to have the necessary permissions

Installation

macOS/Linux via Homebrew

brew install psviderski/tap/docker-pussh

After installation, to use docker-pussh as a Docker CLI plugin (docker pussh command) you need to create a symlink:

mkdir -p ~/.docker/cli-plugins
ln -sf $(brew --prefix)/bin/docker-pussh ~/.docker/cli-plugins/docker-pussh

macOS/Linux via direct download

Download the current version:

mkdir -p ~/.docker/cli-plugins

# Download the script to the docker plugins directory
curl -sSL https://raw.githubusercontent.com/psviderski/unregistry/v0.4.3/docker-pussh \
  -o ~/.docker/cli-plugins/docker-pussh

# Make it executable
chmod +x ~/.docker/cli-plugins/docker-pussh

If you want to download and use the latest version from the main branch:

curl -sSL https://raw.githubusercontent.com/psviderski/unregistry/main/docker-pussh \
  -o ~/.docker/cli-plugins/docker-pussh
chmod +x ~/.docker/cli-plugins/docker-pussh

Debian

Via unofficial repository packages created and maintained at unregistry-debian by @dariogriffo

You can install unregistry the debian way by running:

sudo install -d -m 0755 /etc/apt/keyrings
curl -fsSL https://deb.griffo.io/EA0F721D231FDD3A0A17B9AC7808B4DD62C41256.asc | sudo gpg --dearmor --yes -o /etc/apt/keyrings/deb.griffo.io.gpg
echo "deb [signed-by=/etc/apt/keyrings/deb.griffo.io.gpg] https://deb.griffo.io/apt $(lsb_release -sc 2>/dev/null) main" | sudo tee /etc/apt/sources.list.d/deb.griffo.io.list
sudo apt update
sudo apt install -y unregistry docker-pussh

or in the releases page of the repository here

Windows

Windows is not currently supported, but you can try using WSL 2 with the above Linux instructions.

Verify installation

docker pussh --help

⚠️ Containerd image store configuration

Unregistry stores images directly in containerd’s image store, which is the underlying container runtime used by Docker. However, by default, Docker maintains its own separate storage layer and doesn’t directly use images from containerd.

When you enable containerd image store in Docker, it allows Docker to directly use the same images that unregistry stores in containerd, eliminating duplication.

With containerd image store enabled (recommended)

• Images pushed through unregistry are immediately available to Docker
• No additional storage space is used (images are stored once in containerd)
• Faster pussh operations without the additional pull step from unregistry to the classic Docker image store

Without containerd image store (default Docker behaviour)

• After pushing, pussh runs an additional docker pull on the remote host to pull the image from unregistry to make it available to Docker
• Images are stored twice: once in containerd (by unregistry) and once in the classic Docker image store
• These unmanaged images in containerd can fill up disk space over time. To manage them manually, use:

  sudo ctr -n moby images ls
  sudo ctr -n moby images rm <image>
  

How to enable containerd image store

Please refer to the official Docker documentation: Enable containerd image store on Docker Engine.

[!WARNING] Switching to containerd image store causes you to temporarily lose images and containers created using the classic storage driver. Those resources still exist on your filesystem, and you can retrieve them by turning off the containerd image store feature.

Usage

Push an image to a remote server. Please make sure the SSH user has permissions to run docker commands (user is root or non-root user is in docker group). If sudo is required, ensure the user can run sudo docker without a password prompt.

docker pussh myapp:latest [email protected]

With SSH key authentication if the private key is not added to your SSH agent:

docker pussh myapp:latest [email protected] -i ~/.ssh/id_rsa

Using a custom SSH port:

docker pussh myapp:latest user@server:2222

Using a custom SSH config file:

docker pussh myapp:latest prod-server -F ~/.ssh/config.prod

Push a specific platform for a multi-platform image. The local Docker has to use containerd image store to support multi-platform images.

docker pussh myapp:latest user@server --platform linux/amd64

Use a specific unregistry image version on the remote host:

UNREGISTRY_IMAGE=ghcr.io/psviderski/unregistry:A.B.C docker pussh myapp:latest [email protected]

Use cases

Deploy to production servers

Build locally and push directly to your production servers. No middleman.

docker build --platform linux/amd64 -t myapp:1.2.3 .
docker pussh myapp:1.2.3 deploy@prod-server
ssh deploy@prod-server docker run -d myapp:1.2.3

CI/CD pipelines

Skip the registry complexity in your pipelines. Build and push directly to deployment targets.

- name: Build and deploy
  run: |
    docker build -t myapp:${{ github.sha }} .
    docker pussh myapp:${{ github.sha }} deploy@staging-server

Homelab and air-gapped environments

Distribute images in isolated networks that can’t access public registries over the internet.

Advanced usage

Running unregistry standalone

Sometimes you want a local registry without the overhead. Unregistry works great for this:

# Run unregistry locally and expose it on port 5000
docker run -d -p 5000:5000 --name unregistry \
  -v /run/containerd/containerd.sock:/run/containerd/containerd.sock \
  ghcr.io/psviderski/unregistry

# Use it like any registry
docker tag myapp:latest localhost:5000/myapp:latest
docker push localhost:5000/myapp:latest

Custom SSH options

Need custom SSH settings? Use the standard SSH config file, or pass a specific config with -F:

# ~/.ssh/config
Host prod-server
    HostName server.example.com
    User deploy
    Port 2222
    IdentityFile ~/.ssh/deploy_key

# Now just use
docker pussh myapp:latest prod-server

# Or use an alternate config file
docker pussh myapp:latest prod-server -F ~/.ssh/config.prod

Third-party projects

• https://github.com/SonOfBytes/unregistry-action - GitHub Action to push Docker images to remote servers using docker-pussh plugin for Docker CLI
• https://github.com/RezaKargar/setup-unregistry - GitHub Action to install docker-pussh plugin for Docker CLI
• https://github.com/iloveitaly/docker-image-cleanup - Python tool to manage Docker images in self-hosted registries by automatically removing outdated images while preserving recent and actively used ones

Contributing

Found a bug or have a feature idea? We’d love your help!

• 🐛 Found a bug? Open an issue

• 💡 Have questions, ideas, or need help?
  • Start a discussion or join an existing one in the Discussions.
  • Join the Uncloud Discord community where we discuss features, roadmap, implementation details, and help each other out.

Inspiration & acknowledgements

• Spegel - P2P container image registry that inspired me to implement a registry that uses containerd image store as a backend.
• Docker Distribution - the bulletproof Docker registry implementation that unregistry is based on.