Everything about your world lives in universe/: the worlds themselves and the players' save data. If you had to keep a single folder, it would be this one.
Inside universe/
universe/worlds/All the playable worlds, one folder each.
universe/worlds/<world>/config.jsonThat world's own settings: seed, PvP, fall damage, NPCs and more.
Don't edit world files while running
The server is constantly saving chunks and player data. Copy, move or replace world files only with the server stopped.
Downloading it
Stop the server, then download universe/ over SFTP or from the file manager. That's a complete copy of your world.
About this guide: An original guide from the EnduranceNodes team, written for the servers we host. If a step no longer matches what you see, tell us and we will update it.
