How to Fix an All the Mods 9 Server That Keeps Crashing
All the Mods 9 is the ATM Team's Forge 1.20.1 kitchen-sink flagship — the direct predecessor to ATM10, with over 13 million downloads and a mod list spanning tech, magic, exploration, and automation. Its age and popularity mean most of its crash causes are well understood by now; the four below cover the overwhelming majority of reports.
See the All the Mods 9 pack page for the full RAM and setup breakdown before you chase anything else.
1. Server won't boot: check the Java version first
Forge on Minecraft 1.20.1 requires Java 17. A server migrated from an older pack or set up with a host that defaults to Java 8 or Java 11 will typically fail before the world even loads — and the error output often looks unrelated to Java at all, which sends people chasing the wrong fix.
- Confirm the server is launching under Java 17, not an older runtime
- A boot-time crash with no players online points here before anything else
2. Tick-cost spikes during endgame content
ATM9's endgame — crafting the ATM Star or fighting the Gregstar boss — concentrates a lot of dense machine networks and simultaneous entity/particle activity in a short window. That's a real, predictable load spike specific to this stage of the pack, not a sign of a broken install.
If TPS is healthy right up until the fight starts and only dips during it, that's expected. If TPS was already sagging well before the fight, the fight is just exposing a problem that already existed.
3. Automation sprawl adding tick load over time
ATM9 rewards deep, long-running automation setups — large item/fluid pipe networks, automated farms, and multi-block machine chains. Each of these adds a small amount of per-tick overhead, and a world that's been running for weeks with sprawling automation can be noticeably heavier than a fresh one, even with the same player count.
4. RAM under the pack's realistic floor
The real floor for ATM9 is 10 GB. Below that, you'll typically see cascading lag and longer garbage-collection pauses building over a session rather than one clean crash — and that degradation is exactly what makes the endgame tick spikes in section 2 far more likely to tip the server into a watchdog kill.
FAQ
Why does my ATM9 server fail to boot at all?+
Check the Java version before anything else. ATM9 runs on Forge for Minecraft 1.20.1, which requires Java 17 — a server that was set up or migrated with Java 8 or Java 11 will typically fail during startup, often with errors that don't obviously point at Java.
Why does my server crash specifically during the ATM Star or Gregstar fight?+
That's a tick-cost spike, not a bug. ATM9's endgame content — crafting the ATM Star or fighting the Gregstar boss — involves dense machine networks and a lot of simultaneous entity/particle activity. If your server's TPS was already marginal before the fight, the extra load is enough to trip a watchdog timeout.
How much RAM does ATM9 actually need?+
The real floor is 10 GB. With 400+ mods and the depth of automation ATM9 encourages over a long-running world, going lower tends to show up as rising lag and GC pauses well before an outright crash — and makes endgame content like the ATM Star fight much more likely to push the server over.
Host ATM9 on hardware sized for its real floor
ATM9 needs a real 10 GB floor to absorb endgame tick spikes without tipping into a watchdog kill, and taking a backup before any risky change keeps a bad edit from costing a long-running automation setup.
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