# Server — Properties, JVM, Operations

Three server tiers are provided as drop-in presets in `presets/<tier>/server/`
(see `presets/README.md`). The **Medium** tier is the recommended default.

| Tier | Host RAM | view-distance | simulation-distance | max-players |
|------|----------|---------------|---------------------|-------------|
| Low | 8-16 GB | 5 | 4 | 8 |
| **Medium** | 16-32 GB | 8 | 6 | 8 |
| High | 32 GB+ | 12 | 10 | 16 |

Apply a tier (after `packwiz install`):

```bash
cp presets/medium/server/server.properties server_pack/server.properties
# then use the matching jvm-flags.txt when launching
```

`server_pack/eula.txt` → `eula=true` (after review).

## Recommended JVM Flags (server, Medium)

```bash
java -Xms4G -Xmx8G \
  -XX:+UseG1GC \
  -XX:+ParallelRefProcEnabled \
  -XX:MaxGCPauseMillis=200 \
  -XX:+UnlockExperimentalVMOptions \
  -XX:+DisableExplicitGC \
  -XX:+AlwaysPreTouch \
  -XX:G1NewSizePercent=30 \
  -XX:G1MaxNewSizePercent=40 \
  -XX:G1HeapRegionSize=8M \
  -XX:G1ReservePercent=20 \
  -XX:G1HeapWastePercent=5 \
  -XX:G1MixedGCCountTarget=4 \
  -XX:InitiatingHeapOccupancyPercent=15 \
  -XX:G1MixedGCLiveThresholdPercent=90 \
  -XX:G1RSetUpdatingPauseTimePercent=5 \
  -Dlog4j2.formatMsgNoLookups=true \
  -jar neoforge-21.1.248-server.jar nogui
```

Notes:
- G1 tuning keeps large-tech-server TPS stable under chunk gen (Krypton
  Reno + BadOptimizations help server-side).
- `-Xms4G` avoids early GC churn. Cap at 8G for Medium; this pack is
  RAM-hungry from AE2/Mekanism tick load but Medium does not need 16G.
- See `presets/low/server/jvm-flags.txt` (2-4G) and
  `presets/high/server/jvm-flags.txt` (8-16G) for the other tiers.

## Server start order

1. `packwiz install --dir server_pack` (first time / after changes)
2. Accept EULA.
3. Launch with the JVM flags above.

## Common failures

| Symptom | Fix |
|---------|-----|
| "Mismatched mods" on client join | Run `packwiz refresh` both packs, redeploy. |
| Sinytra connector errors | Update Sinytra Connector + Forgified Fabric API together. |
| Iris black screen | Disable flywheel compat first, then test without shaders. |
| Crash on world gen (Deeper and Darker) | Ensure CF 659011 + its lithostitched data load; update both. |
| TPS lag from many AE2 cells | Check FTB chunk claims; lower `simulation-distance`. |
| Immersive Portals won't load | Must be the Fabric jar added via `url add --force` (Modrinth blocks loader mismatch). |

## Backups

- World: copy `server_pack/world/` (or use FTB Chunks backups).
- Configs: `server_pack/config/` mirrors client defaults; keep both in sync
  when changing KubeJS scripts or FTB settings.