FTB Skies 2: Aero – Docker server for Unraid

Docker image and Unraid template for a dedicated server running the FTB Skies 2: Aero modpack (Minecraft 1.21.1, NeoForge 21.1.250, Java 21).

The image is on Docker Hub as jonaxio/ftb-skies-2-aero. It contains Java 21 and the official FTB server installer. On the first start the modpack (about 1.3 GB) is installed into /data; after that the server starts right away.

Install on Unraid

1. Get the template: In the Apps tab (Community Apps), search for FTB-Skies-2-Aero and click Install. If the app is not listed (yet), add the template in the Unraid terminal (>_ icon, top right) instead, then go to Docker → Add Container and pick FTB-Skies-2-Aero under Template:

   curl -fsSL --create-dirs -o /boot/config/plugins/dockerMan/templates-user/my-FTB-Skies-2-Aero.xml https://raw.githubusercontent.com/JonaxScript/ftb-skies-2-aero-docker/main/templates/ftb-skies-2-aero.xml
   

2. Set EULA to true, adjust OPS, MOTD and the RAM in JVM_OPTS → Apply. Unraid downloads the image from Docker Hub and starts the container.

3. Watch the start: In the Docker tab, click the container icon → Logs. The first install takes a few minutes, the first server start including world generation a few more. The server is ready when it logs Done (...)! For help, type "help".

4. Connect: In the FTB App (same pack version, currently 1.13.0), add the server <unraid-ip>:25565.

Without a template

You can also create the container by hand: Docker → Add Container, then

• Name: FTB-Skies-2-Aero, Repository: jonaxio/ftb-skies-2-aero:latest
• Extra Parameters (advanced view): --stop-timeout=120
• via Add another Path, Port, Variable, Label or Device:
  • Port: container port 25565, protocol TCP
  • Path: container path /data, host path /mnt/user/appdata/ftb-skies-2-aero
  • Variable EULA with the value true, plus any other variables you want to change

Image updates

When a new image is published, the Docker tab shows update ready for the container; click it and confirm with apply update. The world and all server files are kept in the appdata folder, and your settings stay in the template. Modpack updates are separate, see Modpack updates.

Other Docker hosts

docker run -d --name ftb-skies-2-aero -p 25565:25565 -v ftb-data:/data \
  -e EULA=true --stop-timeout 120 jonaxio/ftb-skies-2-aero:latest

Variables

Path: /data → /mnt/user/appdata/ftb-skies-2-aero (world, configs, mods, logs). In Unraid, LEVEL, the path, PUID/PGID and FTB_VERSION_ID are under Show more settings.

Modpack updates

Updates are not automatic; the version is pinned via FTB_VERSION_ID. To update:

1. Find the new version ID: the FTB versions page lists it for every version, e.g. "1.13.0 Release ID 100527".
2. Stop the container and back up the appdata folder, at least the world folder (e.g. with the Appdata Backup plugin from Community Apps).
3. In Unraid, edit the container → Show more settings → change FTB_VERSION_ID → Apply.
4. All players update the pack to the same version in the FTB App.

On start, the container detects the new ID (/data/.ftb-installed-version) and runs the FTB installer as an update. No new image is needed for this. Tested with an update from 1.10.0 to 1.13.0:

Rolling back: Restore the backup and set FTB_VERSION_ID back to the old ID. Only resetting the ID also works (the installer then downgrades), but the world has already been loaded by the newer version.

To repair a broken installation, delete .ftb-installed-version and restart the container.

Building the image yourself

Local testing: Set EULA to "true" in docker-compose.yml, then run docker compose up --build. The server data is stored in the Docker volume ftb-data.

Own build on Unraid: Build with docker build -t ftb-skies-2-aero:latest . and set Repository in the container settings to ftb-skies-2-aero:latest. The update column then shows "not available", which is expected for local images.

Publishing to Docker Hub (maintainers):

docker buildx build --platform linux/amd64 --provenance=false --sbom=false \
  --output type=image,name=docker.io/jonaxio/ftb-skies-2-aero:latest,push=true,oci-mediatypes=false .

This pushes a plain single-platform Docker manifest without attestations, the same format a classic docker push creates.

Notes

• -Xmx must fit into the free RAM of your server; Java needs roughly 1–2 GB on top of -Xmx.
• The template sets --stop-timeout=120 so the server has enough time to save the world when it stops (otherwise Docker kills containers after 10 seconds).
• server.properties is created from the modpack's defaults on the first start (including allow-flight=true, which matters for airships). After that, only motd, level-name and server-port are set on every start; you can change everything else directly in the file.
• run.sh and user_jvm_args.txt from the FTB installer are not executed (run.sh is only read to find the installed NeoForge version). Memory and Java options come from JVM_OPTS only.
• Server console: add -it to Extra Parameters to send commands via docker attach FTB-Skies-2-Aero (detach with Ctrl+P, Ctrl+Q). Alternatively, run commands in-game as an op.
• x86-64 only (the Unraid default).

License

The files in this repository are licensed under the MIT License. The modpack, Minecraft and the FTB server installer are downloaded at runtime and are subject to their own licenses and the Minecraft EULA. This project is not affiliated with Feed The Beast or Mojang.