How to Fix a Parasites 100 Days Server That Keeps Crashing
Parasites 100 Days is OkRobert's post-nuclear hardcore survival pack built around parasitic creature swarms overrunning the world — the same pack from the 100 Days YouTube series. It runs on Forge 1.12.2, and most of the crashes and freezes people report trace back to a small set of well-known 1.12.2-era issues rather than anything exotic. This guide walks through them in the order worth checking.
See the Parasites 100 Days pack page for the full RAM and setup breakdown before you chase anything else.
1. Swarm AI tick-cost spikes during fights
A large simultaneous swarm of infected mobs — all pathing toward and attacking players or each other at once — is a classic tick-cost spike pattern on this pack. Forge 1.12.2's server tick loop is single-threaded, so dozens of mobs recalculating pathing every tick can eat the available tick budget fast, and once the server starts missing ticks badly enough, the watchdog can kill the process entirely.
- If crashes cluster around big swarm encounters specifically, this is the most likely cause
- Reducing mob caps or fighting swarms in open terrain (less pathing complexity) can reduce the spike before you touch anything else
2. Running the wrong Java version
Forge 1.12.2 requires Java 8 specifically — newer Java runtimes are a well-documented source of silent startup failures and odd runtime crashes on packs from this era. If the server is on Java 11, 17, or 21, that's worth ruling out before anything else, since it can produce crash symptoms that look unrelated to Java at all.
3. Simple Voice Chat vs. Forge's bundled Mixin version
This pack has a documented hard incompatibility: Simple Voice Chat requires Mixin 0.8, but Forge 1.12.2 ships with Mixin 0.7.11 built in. Running both on the dedicated server crashes it outright. The fix is to remove Simple Voice Chat from the server-side mods folder — client-side voice mods generally don't need the server copy to function for connecting players.
4. Corrupted chunk data from ungraceful shutdowns mid-fight
If the server is forcibly killed or restarted while a swarm fight is actively generating heavy chunk activity, region files can end up partially written. On 1.12.2-era packs this shows up later as a crash when a player walks back into that chunk, not at the time of the original shutdown — which makes it easy to misdiagnose as a new, unrelated bug. A clean stop (not a kill) and a recent backup are the practical mitigation here.
5. RAM under the pack's realistic floor
5 GB is the real floor for this pack. Under-provisioning rarely produces an instant, clean crash — what you'll actually see is garbage collection pauses getting longer and more frequent during swarm fights, tick times climbing, and then eventually a watchdog timeout that looks like a generic crash in the log unless you were watching TPS at the time.
FAQ
Why does my Parasites 100 Days server lag or crash specifically during big fights?+
Large parasite swarms running pathing and attack AI at the same time is the most common tick-cost spike on this pack. Each infected mob recalculating paths toward players or other mobs every tick adds up fast on 1.12.2's single-threaded tick loop, so a swarm fight can push server TPS down hard enough to trigger a watchdog crash even on hardware that runs fine the rest of the time.
I added Simple Voice Chat and now the server won't start — why?+
This is a known hard incompatibility on this pack. Simple Voice Chat needs Mixin 0.8, but Forge 1.12.2 ships with Mixin 0.7.11 bundled in, and the dedicated server crashes on startup when the two collide. The fix is to remove Simple Voice Chat (and any mod depending on the same newer Mixin version) from the server-side mods folder — it doesn't need to run server-side to work for players anyway.
How much RAM does a Parasites 100 Days server actually need?+
5 GB is the real floor for this pack, not a generic 1.12.2 modpack guess. Below that you won't usually see an instant crash — you'll see garbage collection pauses stacking up during swarm events until the server misses enough ticks to hit a watchdog timeout, which looks identical to a normal crash in the logs unless you're watching TPS at the time.
Host Parasites 100 Days on hardware sized for its real floor
Give the server its real 5 GB floor instead of a generic guess, and take a backup before removing or swapping any mod like Simple Voice Chat so a bad change is a quick rollback instead of a lost world.
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