Server setup

How to Install a Forge Server

Vanilla won't run mods. A Forge server does the heavy lifting: you run the installer with --installServer, accept the EULA, drop your mods into /mods, and watch the console report Loading N mods before it prints Done. Here is the exact sequence, with the two errors everyone hits.

forge-1.20.1, server console
~/forge $ java -jar forge-installer.jar --installServer
Extracting main jar:
  Downloading library net.minecraftforge:fmlcore
  Downloading library net.minecraftforge:javafmllanguage
Successfully installed server into this directory
~/forge $ java -Xmx4G -jar forge-server.jar nogui
[main/ERROR]: Failed to load eula.txt, you need to agree to the EULA
~/forge $ sed -i 's/eula=false/eula=true/' eula.txt
[Server thread/INFO]: Loading 6 mods:
  - minecraft 1.20.1   - forge 47.2.0
  - jei 15.2.0.27       - create 0.5.1
[Server thread/INFO]: Preparing level "world"
[Server thread/INFO]: Done (18.402s)! For help, type "help"
~/forge $ 

The install in one pass

Work in a fresh, empty directory. Run java -jar forge-1.20.1-47.2.0-installer.jar --installServer and wait for Successfully installed server into this directory. Start it once with java -Xmx4G -jar <server-jar> nogui so it generates eula.txt, flip eula=false to eula=true, then start again. On modern versions (1.17+) launch through run.sh and set memory in user_jvm_args.txt. Add server-side mods to /mods, restart, and confirm the Loading N mods list matches your client.

Quick answers

Why does the server stop on the first launch?

Forge cannot run until you agree to Mojang's EULA. The first boot generates eula.txt with eula=false. Change it to eula=true and start again. This is normal, not an error.

What does --installServer actually do?

It runs the installer in headless mode: it downloads Forge's libraries, the vanilla server jar, and writes the run scripts (run.sh / run.bat) plus a user_jvm_args.txt. It does not start the server.

Why won't my mods load?

Every mod must match the Minecraft AND Forge version, and must be a server-compatible build. Client-only mods (shaders, minimaps) crash a dedicated server. Check the latest.log line that names the failing mod.

How much RAM should I give a Forge server?

Start at -Xmx4G for a small modpack and 6-8G for heavy packs like All the Mods. Never set -Xmx above your machine's physical RAM, and leave headroom for the OS.

Modern Forge (1.17+) uses run.sh instead of a single jar?

Yes. From 1.17 onward Forge boots through run.sh / run.bat which reads user_jvm_args.txt. Put your memory flags there (-Xmx6G) rather than editing the command each time.

My client can't join the modded server.

The client must run the identical Forge version and the same set of mods that have a client side. Mismatched mod lists are rejected at the handshake. Match the modpack exactly on both ends.