How to enable hardcore mode on a Minecraft server

Hardcore mode locks the difficulty to Hard and changes what happens after a player dies. The setup method depends on whether the world has already been generated.

Hardcore mode can make player deaths permanent. Back up the entire world before changing this setting.

Enable hardcore mode for a new world

You must enable hardcore mode before the world is generated:

Stop your Minecraft server.
Open server.properties in the file manager.
Find hardcore= and change it to:

hardcore=true

Make sure the server will generate a new world. Change level-name to an unused name, or back up and remove the existing world folder.
Save the file and start the server.

The newly generated world will use hardcore mode.

Change hardcore mode on an existing world

Changing hardcore in server.properties does not update a world that has already been generated. Edit the world's level.dat file instead:

Stop the server.
Create and download a full backup of the world.
Download level.dat from the active world folder.
Open the file in an NBT editor.
Find the hardcore property inside the Data compound.
Set its byte value to 1 to enable hardcore mode or 0 to disable it.
Save the file and upload it to the world folder, replacing the existing level.dat.
Start the server and verify the world settings.

Do not edit or replace level.dat while the server is running. The server may overwrite your change or corrupt the world data.

Frequently asked questions

Does hardcore mode delete the world?

No. A dedicated server does not automatically delete the world when a player dies. What a dead player can do next depends on the Minecraft version and server software.

Why did changing server.properties not work?

The world already has its hardcore setting stored in level.dat. Use an NBT editor to change the hardcore property for that existing world.