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Startup: Java version and variables

Which Java version runs and which settings apply at start-up.

3 min read · in the Panel

Startup shows how the server is started. We set the command itself; you can change the Docker image and the Variables.

Java version (Minecraft)

  1. Minecraft 1.20.5 and newer needs Java 21, 26.1 and newer Java 25. Older versions run on Java 17; 1.16 and older often only on Java 8 or 11.
  2. Pick the matching Java version under Docker image and restart the server.
  3. When you switch versions in the Panel under Versions, we set the matching Java automatically.

If the console shows UnsupportedClassVersionError or requires Java on start, the Java version is almost always wrong.

Variables

Variables are start-up settings, for example MINECRAFT VERSION, SERVER JAR FILE or, for other games, name, password and world size. Click into the field and change the value. It's saved immediately and takes effect after the next restart.

For Minecraft, switch software and version under Versions instead: there we adjust everything together and back up first.

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