Update a Minecraft Java Server to 26.3 Without Losing the World

Copy first, then the jar

Tell players and stop the process. Wait until it finishes writing. The general copy method is the Minecraft backup guide. For this patch the archive needs at least:

• the world folder named by level-name in server.properties, including region, playerdata and level.dat;
• server.properties, whitelist.json, ops.json, banned-players.json and banned-ips.json;
• the plugins or mods folder, if you use one.

Open the archive. A copy of region alone drops inventories.

Paper, Fabric, Forge or NeoForge do not update by dropping the vanilla server.jar on top. Wait for a build that says 26.3. The software choice is in Paper or Spigot and mods or plugins. Run the vanilla jar, or that compatible build, against a copy of the world before you touch the group's server.

What 26.3 changes for the operator

The article says the white-list property now defaults to true. It does not say an existing server.properties that already contains white-list=false is rewritten. A new file, or a file missing the key, will start with the whitelist on. After the first boot, read the line. If regular players cannot join, add them from the console with whitelist add and the account name, then check whitelist.json.

Log lines that panels used to watch have been removed. Mojang points at the Minecraft Server Management Protocol instead. In 26.3, version 3.1.0 adds notifications for a full world upgrade at startup: minecraft:notification/world/upgrade_started, upgrade_progress, upgrade_finished and upgrade_failed.

The protocol itself is from snapshot 25w35a, not from 26.3. In that article it is off by default: management-server-enabled=false, management-server-host=localhost, management-server-port=25585. 26.3 does not restate those defaults. If you turn it on, leave it on localhost unless you have a reason not to. It is an admin API, not a game port. Methods are listed by rpc.discover on the running server. Do not treat a snapshot example as a complete method list for 26.3.

Boot the copy, then the real server

Replace the vanilla jar with the one shipped for 26.3. Keep the world folder and the old server.properties if you want your settings. Start the copy. Read the console until it is ready, or the upgrade notifications if the protocol is enabled. On upgrade_failed, stop. Do not keep restarting. Restore the archive.

Join with an account that is supposed to be allowed. Check a known spot, a chest and the inventory. Restart. If the whitelist blocks everyone, that is the new default or an empty whitelist.json, not a port. The connection guide is the next page when the process itself is answering.

Java offers: Minecraft Java comparison.

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