How to Host an ATM 9 Server

What Is All The Mods 9?

All The Mods 9 (ATM9) is the predecessor to ATM10 and still one of the most popular kitchen-sink modpacks available. Built on Forge for Minecraft 1.20.1, it packs 300+ mods covering tech, magic, exploration, and building. Key mods include Mekanism, Create, Ars Nouveau, Applied Energistics 2, Botania, and Immersive Engineering. ATM9 is a proven, stable pack with months of community testing and bug fixes, making it a reliable choice for server admins who want the kitchen-sink experience without bleeding-edge instability.

Compared to ATM10, ATM9 uses standard Forge rather than NeoForge, which means broader compatibility with server-side utilities and a larger pool of documented solutions for common issues. If you want to host an ATM 9 server, you get a mature pack with fewer surprises.

Server Requirements

Forge and Java Version

ATM9 runs on Forge for Minecraft 1.20.1 and requires Java 17. The server pack from CurseForge pins the exact Forge version. Do not use a different build unless the pack maintainers recommend it. Java 21 works on some setups but is not officially required, so stick with Java 17 for stability.

RAM Allocation

Player Count	Minimum RAM	Recommended RAM
1–5 players	8 GB	10 GB
6–12 players	10 GB	12 GB
12–20 players	12 GB	14 GB

ATM9 is memory-hungry. Over 300 mods register thousands of blocks, items, and recipes that stay resident in memory. The base footprint before any player joins is roughly 4 to 5 GB. Use the RAM calculator to estimate your needs when you host an ATM 9 server.

Downloading and Installing

Download the ATM9 server pack from CurseForge. Extract, run the startup script, accept the EULA, and restart:

chmod +x startserver.sh
./startserver.sh

First boot takes 4 to 7 minutes as Forge loads every mod. Watch the console for errors. As long as lines keep scrolling, the server is working.

Config Tweaks

Pre-Generate Your World

ATM9's custom worldgen mods (Terralith, YUNG's structures, Biomes O' Plenty) make chunk generation slow. Pre-generate a play area before opening the server:

/chunky radius 3000
/chunky start

Let it run for a few hours. The resulting terrain loads instantly during gameplay.

Disable Unused Mods

If your community focuses on tech and nobody touches magic, removing Ars Nouveau, Occultism, or similar mods frees memory and reduces tick overhead. Check CurseForge for dependency chains before removing anything.

Common Issues

Forge Version Mismatch

Using a Forge build other than what the pack specifies causes immediate crashes. The error log will mention missing dependencies or unsupported mod versions. Always extract the server pack fresh and let the startup script handle Forge installation.

Worldgen Lag on Exploration

When multiple players explore new terrain, the server struggles to generate chunks fast enough. This is the main reason to pre-generate. Set a world border matching your pre-generated area to prevent players from venturing into ungenerated territory.

Performance Tuning

Set view-distance=8 and simulation-distance=6. With 300+ mods adding block entities to every chunk, reducing the simulation radius noticeably improves TPS.

JVM flags for Java 17:

java -Xms8G -Xmx10G -XX:+UseG1GC -XX:MaxGCPauseMillis=130
-XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=40
-XX:G1MaxNewSizePercent=50 -XX:G1HeapRegionSize=16M
-XX:G1ReservePercent=15 -XX:InitiatingHeapOccupancyPercent=20
-XX:+AlwaysPreTouch -jar forge-server.jar nogui

For complete flag documentation, visit our JVM flags guide. Compare with the ATM10 guide if you are deciding between the two, or check the Enigmatica 9 guide for a similarly sized but more curated alternative.

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