Forge Crashes / Fabric Mods – Install Mods on Minecraft Server

This guide shows you step by step how to install mods on your Minecraft server. We cover the two most common modloaders: Forge and Fabric. Mods add new blocks, creatures, dimensions and game mechanics to your server.

Note: Detailed subpages on individual modpacks and performance optimization can be found in the left navigation.

Important difference: Forge vs. Fabric

Mods are not cross-compatible. A Forge mod won't run on Fabric and vice versa. Choose the modloader based on the mods you want to use.

Requirements

• A running Minecraft server (Vanilla)
• SSH or FTP access to the server
• Java 17 or newer (for Minecraft 1.18+)
• Sufficient RAM – at least 4-6 GB with mods, 8 GB recommended
• A backup of your world (in case something goes wrong)

Method A: Install Forge

Step 1: Download Forge Installer

1. Visit the official Forge website: files.minecraftforge.net
2. Select the Minecraft version your server uses
3. Download the Installer (not the "Universal" JAR)

Step 2: Install Forge Server

# In your server directory
cd /path/to/your/minecraft-server

# Run Forge installer (Java 17+ required)
java -jar forge-*-installer.jar --installServer

The installer creates the following files:

• forge-xxx-universal.jar – The new server JAR
• mods/ – The mod folder (created automatically)
• libraries/ – Required libraries

Step 3: Adjust startup script

Replace your old startup script. Instead of java -jar server.jar use:

java -Xmx8G -Xms4G -jar forge-xxx-universal.jar nogui

Adjust -Xmx8G to your available RAM. Never start below 4 GB with mods.

Step 4: Install mods

1. Download mods from trusted sources:
   • CurseForge – Largest mod platform
   • Modrinth – Open-source alternative
2. Download the .jar files of the mods
3. Upload them to the mods/ folder on your server
4. Restart the server – the mods are loaded automatically

Method B: Install Fabric

Step 1: Download Fabric Installer

1. Visit the official Fabric website: fabricmc.net/use/server
2. Select the Minecraft version
3. Download the Server JAR

Step 2: Start Fabric Server

# In your server directory
cd /path/to/your/minecraft-server

# Rename Fabric server JAR
mv fabric-server-launch.jar server.jar

# Start server
java -Xmx8G -Xms4G -jar server.jar nogui

Fabric automatically creates the mods/ folder on first start.

Step 3: Install Fabric API (important!)

Almost all Fabric mods require the Fabric API as a foundation:

1. Download the Fabric API from CurseForge or Modrinth
2. Upload the JAR file to the mods/ folder
3. The Fabric API must always be first in the folder

Step 4: Install additional mods

1. Download more Fabric mods from CurseForge or Modrinth
2. Upload the JAR files to the mods/ folder
3. Restart the server

Essential mods every server should have

Performance mods (Fabric)

• Lithium: Massively optimizes server performance – 40-50% less CPU load
• Phosphor / Starlight: Optimizes light calculation – faster chunk loading
• FerriteCore: Reduces RAM usage

Performance mods (Forge)

• Rubidium: Forge port of Sodium – better performance
• Radium Reforged: Forge port of Lithium
• Canary: Optimizes many server systems

Keep mods in sync between client and server

Players joining your server must have exactly the same mods installed. Exceptions:

• Server-side mods (like Lithium) only need to be installed on the server
• Client-side mods (like Sodium) only need to be installed by the player
• Mods that add new blocks/items must be installed on both sides

Common problems and solutions

Server won't start after mod installation:

• Check the server logs: logs/latest.log
• Missing dependencies? Many mods require other mods as a foundation
• Wrong modloader version? A Forge mod won't run on Fabric
• Wrong Minecraft version? A 1.19 mod won't run on 1.20

Players cannot join ("Mod rejections"):

• Player has different mods or different mod versions than the server
• Solution: Distribute the same mods with the same versions to all players

Server lags after mod installation:

• Too many or too resource-intensive mods
• Install performance mods like Lithium or Starlight
• Increase RAM – with many mods, 8-12 GB is often necessary

Detailed guides on individual modpacks and performance optimization can be found in the articles in the left navigation.