2core

2Core

Run a second Fabric server as a separate JVM process — one mod, two roles.

What is this?

2Core lets you run two Minecraft servers on the same machine from a single mod. The primary server launches and manages the secondary server as an external JVM process. Both servers use the same mod JAR — the role (primary or secondary) is determined automatically at startup.

No plugins, no proxies, no extra software required.

Features

• One mod, two servers — install once, the mod handles both roles automatically
• Cross-server chat sync — chat messages, join/leave notifications, and death messages are relayed between servers in real time
• Player list — /listother shows online players on the other server (available to all players)
• Full process management — start, stop, restart the secondary server with simple commands
• Console relay — optionally mirror the secondary server's console output to the primary
• Auto-start — optionally start the secondary server automatically when the primary starts
• Configurable messages — customize join/leave/chat/death message formats independently for each server with color code support (&6, &a, etc.)
• Safe IPC — servers communicate over a localhost-only TCP socket, no external exposure

Requirements

Server-side only. No client installation needed.

Setup

1. Install the mod on your primary server (along with Fabric API and Fabric Language Kotlin)
2. Start the primary server — the mod creates a 2core/ folder and a 2core/2core.properties config file
3. Place your secondary server files inside 2core/ (or configure copy_mode to copy them automatically)
4. Run /2core start to launch the secondary server

The mod copies itself into 2core/mods/ automatically — no need to install it separately on the secondary.

Commands

Available on both servers (all players)

Admin commands — primary server only (/2core ...)

Configuration

Config file: 2core/2core.properties

Placeholders: %player%, %message%. Color codes: &0–&9, &a–&f, &l, &o, &r, etc.

How it works

When the primary server starts, it launches the secondary server as a child JVM process with -Dtwocore.role=secondary. Both JVMs run the same mod JAR — the secondary detects its role via the system property and skips all process management logic. Inter-server communication (chat sync, player list queries) happens over a localhost TCP socket managed by the mod.