linuxserver/sealskin repository overview

The LinuxServer.io⁠ team brings you another container release featuring:

• regular and timely application updates
• easy user mappings (PGID, PUID)
• custom base image with s6 overlay
• weekly base OS updates with common layers across the entire LinuxServer.io ecosystem to minimise space usage, down time and bandwidth
• regular security updates

Find us at:

• Blog⁠ - all the things you can do with our containers including How-To guides, opinions and much more!
• Discord⁠ - realtime support / chat with the community and the team.
• Discussions⁠ - post on our community forum.
• GitHub⁠ - view the source for all of our repositories.
• Open Collective⁠ - please consider helping us by either donating or contributing to our budget

⁠linuxserver/sealskin⁠

Sealskin⁠ is a self-hosted browser isolation and remote application streaming platform. It runs desktop applications in isolated containers on a server you control and streams them to any browser or phone. Clients include a browser extension, mobile apps, and a web app served by the server itself. Each turns links, files, downloads, and text selections into something you open remotely instead of locally, so nothing from the web runs on the device in front of you.

⁠Supported Architectures

We utilise the docker manifest for multi-platform awareness. More information is available from docker here⁠ and our announcement here⁠.

Simply pulling lscr.io/linuxserver/sealskin:latest should retrieve the correct image for your arch, but you can also pull specific arch images via tags.

The architectures supported by this image are:

⁠Application Setup

This image hosts the server component of the SealSkin platform: the API, the Caddy proxy, and the web app it serves. The full documentation lives at selkies-project.github.io/sealskin⁠.

⁠Clients

⁠First run

On the first start with an empty /config the container generates a self-signed certificate for the proxy and the server's RSA key, then the server finds no administrator and writes two credentials for the built-in admin account:

• /config/root_key is an application key for the web app. Open https://<server>:8443/ and paste it in to sign in.
• /config/admin.json is the key file for the browser extension and mobile apps. If HOST_URL was set it can be imported as is, otherwise edit it and replace the string HOST_URL with your server's IP or hostname.

Once signed in you can install applications from the App Store, create users and groups, and make application keys for other devices from the dashboard.

On the web the root key is the only sign-in the server handles itself. Everyone else signs in through an identity provider (OpenID Connect or SAML) or a reverse proxy that signs users in, whose groups make administrators and carry limits. See Signing in⁠ before inviting a second person. Extension and mobile users can also be given key files from the Users panel.

⁠Scripted installation

Included in this repository is a helper script to spin up SealSkin with a trusted certificate using Duck DNS. Before using this script please navigate to https://www.duckdns.org/⁠, log in, make a sub domain, and get your token.

mkdir sealskin
cd sealskin
bash <(curl -sSL https://raw.githubusercontent.com/linuxserver/docker-sealskin/refs/heads/master/install.sh)

This will set up pathing, ownership, the compose file, and a trusted wildcard SSL certificate for Duck DNS.

You can also renew your wildcard SSL certificate by running the same script again in the same directory.

cd sealskin
bash <(curl -sSL https://raw.githubusercontent.com/linuxserver/docker-sealskin/refs/heads/master/install.sh)

⁠Basic Requirements

• The container must be named sealskin. The server inspects its own container to learn the host paths behind /config and /storage, the externally mapped ports, and the Docker network. The name is also the server's identity in its own records, so a container recreated under another name is another node. If you cannot keep the name, set hostname: sealskin or SEALSKIN_NODE_NAME.
• The Docker socket is required. Every session is a container the server starts through it. If launches fail with a permission error, make the socket group writable on the host with sudo chmod g+rw /var/run/docker.sock.
• PUID and PGID own everything. The server, its files and every session container run as that user, so /config and /storage on the host must be writable by it.
• Ports. 8443 carries the web app, the API and the streamed sessions. 8000 is only needed for the Chrome self-signed fallback. 8444 is the peer listener, only publish it to join several servers into a cluster⁠.

The server can be exposed directly to the internet, its own Caddy instance terminates TLS and authenticates every request to a session. It can also run behind a reverse proxy⁠ by setting SEALSKIN_PUBLIC_URL and SEALSKIN_TRUSTED_PROXIES, plus SEALSKIN_HTTP_PORT for a proxy that terminates TLS, with guides for SWAG, Traefik, Nginx Proxy Manager and Caddy. Every environment variable the server reads is listed in the Settings Reference⁠. The same image also runs on Kubernetes⁠ from the upstream manifest, with sessions as pods.

⁠NVIDIA Support

NVIDIA support requires the proprietary driver 580 or newer (no MIT/GPL kernel modules) with the nvidia-drm.modeset=1 kernel parameter set, and the NVIDIA Container Toolkit v1.20.1 or higher registered with Docker. The toolkit's refresh service creates the modeset device at boot so headless hosts need nothing more.

⁠Key & Certificate Management

The server requires several cryptographic keys to function. You can either let the container perform an automatic setup on its first run or provide your own for more control.

⁠Automatic First-Run Setup (Recommended)

On the first launch with an empty /config volume:

1. An init process generates the mandatory server key (ssl/server_key.pem) and a self-signed SSL certificate for the proxy (ssl/proxy_key.pem, ssl/proxy_cert.pem).
2. The server detects that no administrator exists, creates the default user admin, and writes /config/admin.json and /config/root_key as described above.

⁠Manual Pre-Configuration (Advanced)

Place the files in the /config volume before the first launch.

• To use a custom Admin Key:

  1. Generate your own RSA keypair.
  2. Create a file containing only your public key PEM data at /path/to/config/.config/sealskin/keys/admins/admin.
  3. The server will detect this file and write no admin.json. You use your private key to log in from the extension, and admin signs in to the web app with the root key alone.

• To use a custom SSL Certificate:

  • Place your certificate and private key at /path/to/config/ssl/proxy_cert.pem and /path/to/config/ssl/proxy_key.pem. This overrides the self-signed certificate and can be replaced later with a restart.

• To use a custom Server E2EE Key:

  • Place your RSA private key at /path/to/config/ssl/server_key.pem. This is the core key for the API's end-to-end encryption and validates the server when a client is configured with its public key.
    • Generation Command: openssl genpkey -algorithm RSA -out /path/to/config/ssl/server_key.pem -pkeyopt rsa_keygen_bits:4096
    • Extraction Command (public key for clients): openssl rsa -in server_key.pem -pubout

⁠Upgrading from 0.3

Nothing on disk needs changing, existing users, groups, installed apps, templates and sessions load as before and key files keep working. On the first start after the upgrade the server writes /config/root_key for the web app, sign in with it then copy and delete the file. Keep the container name sealskin or set SEALSKIN_NODE_NAME so the server keeps its identity. Collaboration rooms need application images with a Selkies release after 2.0.0, and NVIDIA hosts need the Container Toolkit v1.20.1 or higher.

⁠Usage

To help you get started creating a container from this image you can either use docker-compose or the docker cli.

⁠docker-compose (recommended, click here for more info⁠)

---
services:
  sealskin:
    image: lscr.io/linuxserver/sealskin:latest
    container_name: sealskin
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=Etc/UTC
      - "HOST_URL=IP or subdomain.domain.com" #optional
    volumes:
      - /path/to/sealskin/config:/config
      - /path/to/sealskin/storage:/storage
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - 8443:8443
      - 8000:8000 #optional
      - 8444:8444 #optional
    restart: unless-stopped

⁠docker cli (click here for more info⁠)

docker run -d \
  --name=sealskin \
  -e PUID=1000 \
  -e PGID=1000 \
  -e TZ=Etc/UTC \
  -e HOST_URL="IP or subdomain.domain.com" `#optional` \
  -p 8443:8443 \
  -p 8000:8000 `#optional` \
  -p 8444:8444 `#optional` \
  -v /path/to/sealskin/config:/config \
  -v /path/to/sealskin/storage:/storage \
  -v /var/run/docker.sock:/var/run/docker.sock \
  --restart unless-stopped \
  lscr.io/linuxserver/sealskin:latest

⁠Parameters

Containers are configured using parameters passed at runtime (such as those above). These parameters are separated by a colon and indicate <external>:<internal> respectively. For example, -p 8080:80 would expose port 80 from inside the container to be accessible from the host's IP on port 8080 outside the container.

⁠Environment variables from files (Docker secrets)

You can set any environment variable from a file by using a special prepend FILE__.

As an example:

-e FILE__MYVAR=/run/secrets/mysecretvariable

Will set the environment variable MYVAR based on the contents of the /run/secrets/mysecretvariable file.

⁠Umask for running applications

For all of our images we provide the ability to override the default umask settings for services started within the containers using the optional -e UMASK=022 setting. Keep in mind umask is not chmod it subtracts from permissions based on it's value it does not add. Please read up here⁠ before asking for support.

⁠User / Group Identifiers

When using volumes (-v flags), permissions issues can arise between the host OS and the container, we avoid this issue by allowing you to specify the user PUID and group PGID.

Ensure any volume directories on the host are owned by the same user you specify and any permissions issues will vanish like magic.

In this instance PUID=1000 and PGID=1000, to find yours use id your_user as below:

id your_user

Example output:

uid=1000(your_user) gid=1000(your_user) groups=1000(your_user)

⁠Docker Mods

We publish various Docker Mods⁠ to enable additional functionality within the containers. The list of Mods available for this image (if any) as well as universal mods that can be applied to any one of our images can be accessed via the dynamic badges above.

⁠Support Info

• Shell access whilst the container is running:

  docker exec -it sealskin /bin/bash
  

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• To monitor the logs of the container in realtime:

  docker logs -f sealskin
  

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• Container version number:

  docker inspect -f '{{ index .Config.Labels "build_version" }}' sealskin
  

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• Image version number:

  docker inspect -f '{{ index .Config.Labels "build_version" }}' lscr.io/linuxserver/sealskin:latest
  

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⁠Updating Info

Most of our images are static, versioned, and require an image update and container recreation to update the app inside. With some exceptions (noted in the relevant readme.md), we do not recommend or support updating apps inside the container. Please consult the Application Setup⁠ section above to see if it is recommended for the image.

Below are the instructions for updating containers:

⁠Via Docker Compose

• Update images:

  • All images:

    docker-compose pull
    

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  • Single image:

    docker-compose pull sealskin
    

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• Update containers:

  • All containers:

    docker-compose up -d
    

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  • Single container:

    docker-compose up -d sealskin
    

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• You can also remove the old dangling images:

  docker image prune
  

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⁠Via Docker Run

• Update the image:

  docker pull lscr.io/linuxserver/sealskin:latest
  

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• Stop the running container:

  docker stop sealskin
  

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• Delete the container:

  docker rm sealskin
  

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• Recreate a new container with the same docker run parameters as instructed above (if mapped correctly to a host folder, your /config folder and settings will be preserved)

• You can also remove the old dangling images:

  docker image prune
  

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⁠Image Update Notifications - Diun (Docker Image Update Notifier)

⁠Building locally

If you want to make local modifications to these images for development purposes or just to customize the logic:

git clone https://github.com/linuxserver/docker-sealskin.git
cd docker-sealskin
docker build \
  --no-cache \
  --pull \
  -t lscr.io/linuxserver/sealskin:latest .

The ARM variants can be built on x86_64 hardware and vice versa using lscr.io/linuxserver/qemu-static

docker run --rm --privileged lscr.io/linuxserver/qemu-static --reset

Once registered you can define the dockerfile to use with -f Dockerfile.aarch64.

⁠Versions

• 20.10.26: - Update docs and installer for the 0.4.0 release: web app and root key sign in, reverse proxy support, cluster peer port.
• 05.09.26: - Install Sealskin from the upstream Python wheel, rebase to Alpine 3.24.
• 11.02.26: - Rebase to Alpine 3.23.
• 19.01.26: - Fix init race condition.
• 17.01.26: - Update docs to remove network and port requirement, add link to Firefox add on.
• 08.01.26: - Improve permission fixing.
• 31.10.25: - Initial Release.