How to Set Up a Forge Server

Before you start

• Use the exact Minecraft and Forge version your modpack or mods require. Forge builds are tied to one Minecraft version.
• Install the matching Java: Java 8 for 1.16.5 and older, Java 17 for 1.18–1.20.4 (e.g. 1.20.1), Java 21 for 1.20.5–1.21.11. The installer itself runs on the same Java.
• Download the official installer for your version from the Forge download page — MCJarHub links the installer on Forge's own maven, with its published SHA-256.

Minecraft 1.17 and newer (e.g. 1.20.1)

1. Put the installer into an empty folder and run:

   java -jar forge-1.20.1-47.4.28-installer.jar --installServer

   It downloads the Minecraft server and all libraries into the folder (libraries/) and creates run.sh, run.bat and user_jvm_args.txt. The scripts start Java with @user_jvm_args.txt plus Forge's own argument file, which is why there is no single jar to run.
2. Set the memory in user_jvm_args.txt — uncomment or add a line such as:

   -Xms6G
   -Xmx6G

3. Start the server with ./run.sh (Linux/macOS; chmod +x run.sh first) or run.bat (Windows). To run without the console window, pass nogui to the script: ./run.sh nogui (the generated scripts forward extra arguments to the server).
4. Accept the EULA: set eula=true in eula.txt and start again.
5. Put mods into mods/ and restart. You can delete the installer jar and installer.log.

Minecraft 1.16.5 and older (e.g. 1.12.2)

1. Run the installer the same way: java -jar forge-<version>-installer.jar --installServer.
2. It creates a Forge server jar (named like forge-1.12.2-14.23.5.2859.jar; the oldest versions use a …-universal.jar) plus the vanilla server jar and libraries. There are no run scripts.
3. Start the Forge jar directly, e.g. java -Xms6G -Xmx6G -jar forge-1.12.2-14.23.5.2859.jar nogui, then accept the EULA and restart.

Old versions such as 1.7.10–1.16.5 are affected by Log4Shell; apply the mitigation shown on their version pages (for example Forge 1.12.2).

Common problems

• "Unsupported class file major version" or UnsupportedClassVersionError: wrong Java for this Minecraft version — fix.
• Server closes right after "Loading mods": read logs/latest.log and the crash report in crash-reports/; it usually names a missing dependency or a client-only mod.
• Players can't join: they need the same mods and versions; check port problems if nobody can connect.
• Out of memory: modpacks need more RAM than vanilla — see how much RAM.

For Minecraft 1.20.2 and newer, many mods target NeoForge instead. Comparison: Fabric vs Forge vs NeoForge.