---
name: minecraft-modpack-server
description: "Host modded Minecraft servers (CurseForge, Modrinth)."
tags: [minecraft, gaming, server, neoforge, forge, modpack]
platforms: [linux, macos]
---

# Minecraft Modpack Server Setup

## When to use
- User wants to set up a modded Minecraft server from a server pack zip
- User needs help with NeoForge/Forge server configuration
- User asks about Minecraft server performance tuning or backups

## Gather User Preferences First
Before starting setup, ask the user for:
- **Server name / MOTD** — what should it say in the server list?
- **Seed** — specific seed or random?
- **Difficulty** — peaceful / easy / normal / hard?
- **Gamemode** — survival / creative / adventure?
- **Online mode** — true (Mojang auth, legit accounts) or false (LAN/cracked friendly)?
- **Player count** — how many players expected? (affects RAM & view distance tuning)
- **RAM allocation** — or let agent decide based on mod count & available RAM?
- **View distance / simulation distance** — or let agent pick based on player count & hardware?
- **PvP** — on or off?
- **Whitelist** — open server or whitelist only?
- **Backups** — want automated backups? How often?

Use sensible defaults if the user doesn't care, but always ask before generating the config.

## Steps

### 1. Download & Inspect the Pack
```bash
mkdir -p ~/minecraft-server
cd ~/minecraft-server
wget -O serverpack.zip "<URL>"
unzip -o serverpack.zip -d server
ls server/
```
Look for: `startserver.sh`, installer jar (neoforge/forge), `user_jvm_args.txt`, `mods/` folder.
Check the script to determine: mod loader type, version, and required Java version.

### 2. Install Java
- Minecraft 1.21+ → Java 21: `sudo apt install openjdk-21-jre-headless`
- Minecraft 1.18-1.20 → Java 17: `sudo apt install openjdk-17-jre-headless`
- Minecraft 1.16 and below → Java 8: `sudo apt install openjdk-8-jre-headless`
- Verify: `java -version`

### 3. Install the Mod Loader
Most server packs include an install script. Use the INSTALL_ONLY env var to install without launching:
```bash
cd ~/minecraft-server/server
ATM10_INSTALL_ONLY=true bash startserver.sh
# Or for generic Forge packs:
# java -jar forge-*-installer.jar --installServer
```
This downloads libraries, patches the server jar, etc.

### 4. Accept EULA
```bash
echo "eula=true" > ~/minecraft-server/server/eula.txt
```

### 5. Configure server.properties
Key settings for modded/LAN:
```properties
motd=\u00a7b\u00a7lServer Name \u00a7r\u00a78| \u00a7aModpack Name
server-port=25565
online-mode=true          # false for LAN without Mojang auth
enforce-secure-profile=true  # match online-mode
difficulty=hard            # most modpacks balance around hard
allow-flight=true          # REQUIRED for modded (flying mounts/items)
spawn-protection=0         # let everyone build at spawn
max-tick-time=180000       # modded needs longer tick timeout
enable-command-block=true
```

Performance settings (scale to hardware):
```properties
# 2 players, beefy machine:
view-distance=16
simulation-distance=10

# 4-6 players, moderate machine:
view-distance=10
simulation-distance=6

# 8+ players or weaker hardware:
view-distance=8
simulation-distance=4
```

### 6. Tune JVM Args (user_jvm_args.txt)
Scale RAM to player count and mod count. Rule of thumb for modded:
- 100-200 mods: 6-12GB
- 200-350+ mods: 12-24GB
- Leave at least 8GB free for the OS/other tasks

```
-Xms12G
-Xmx24G
-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
-XX:SurvivorRatio=32
-XX:+PerfDisableSharedMem
-XX:MaxTenuringThreshold=1
```

### 7. Open Firewall
```bash
sudo ufw allow 25565/tcp comment "Minecraft Server"
```
Check with: `sudo ufw status | grep 25565`

### 8. Create Launch Script
```bash
cat > ~/start-minecraft.sh << 'EOF'
#!/bin/bash
cd ~/minecraft-server/server
java @user_jvm_args.txt @libraries/net/neoforged/neoforge/<VERSION>/unix_args.txt nogui
EOF
chmod +x ~/start-minecraft.sh
```
Note: For Forge (not NeoForge), the args file path differs. Check `startserver.sh` for the exact path.

### 9. Set Up Automated Backups
Create backup script:
```bash
cat > ~/minecraft-server/backup.sh << 'SCRIPT'
#!/bin/bash
SERVER_DIR="$HOME/minecraft-server/server"
BACKUP_DIR="$HOME/minecraft-server/backups"
WORLD_DIR="$SERVER_DIR/world"
MAX_BACKUPS=24
mkdir -p "$BACKUP_DIR"
[ ! -d "$WORLD_DIR" ] && echo "[BACKUP] No world folder" && exit 0
TIMESTAMP=$(date +%Y-%m-%d_%H-%M-%S)
BACKUP_FILE="$BACKUP_DIR/world_${TIMESTAMP}.tar.gz"
echo "[BACKUP] Starting at $(date)"
tar -czf "$BACKUP_FILE" -C "$SERVER_DIR" world
SIZE=$(du -h "$BACKUP_FILE" | cut -f1)
echo "[BACKUP] Saved: $BACKUP_FILE ($SIZE)"
BACKUP_COUNT=$(ls -1t "$BACKUP_DIR"/world_*.tar.gz 2>/dev/null | wc -l)
if [ "$BACKUP_COUNT" -gt "$MAX_BACKUPS" ]; then
    REMOVE=$((BACKUP_COUNT - MAX_BACKUPS))
    ls -1t "$BACKUP_DIR"/world_*.tar.gz | tail -n "$REMOVE" | xargs rm -f
    echo "[BACKUP] Pruned $REMOVE old backup(s)"
fi
echo "[BACKUP] Done at $(date)"
SCRIPT
chmod +x ~/minecraft-server/backup.sh
```

Add hourly cron:
```bash
(crontab -l 2>/dev/null | grep -v "minecraft/backup.sh"; echo "0 * * * * $HOME/minecraft-server/backup.sh >> $HOME/minecraft-server/backups/backup.log 2>&1") | crontab -
```

## Pitfalls
- ALWAYS set `allow-flight=true` for modded — mods with jetpacks/flight will kick players otherwise
- `max-tick-time=180000` or higher — modded servers often have long ticks during worldgen
- First startup is SLOW (several minutes for big packs) — don't panic
- "Can't keep up!" warnings on first launch are normal, settles after initial chunk gen
- If online-mode=false, set enforce-secure-profile=false too or clients get rejected
- The pack's startserver.sh often has an auto-restart loop — make a clean launch script without it
- Delete the world/ folder to regenerate with a new seed
- Some packs have env vars to control behavior (e.g., ATM10 uses ATM10_JAVA, ATM10_RESTART, ATM10_INSTALL_ONLY)

## Verification
- `pgrep -fa neoforge` or `pgrep -fa minecraft` to check if running
- Check logs: `tail -f ~/minecraft-server/server/logs/latest.log`
- Look for "Done (Xs)!" in the log = server is ready
- Test connection: player adds server IP in Multiplayer


---
Source attribution: CUexter
Original project: https://github.com/CUexter/hermes-agent/blob/e1eba6f8ccd272ff9c213afbd6c0397bf828be72/skills/gaming/minecraft-modpack-server/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Dave AI.

## Upstream license notice

MIT License

Copyright (c) 2025 Nous Research

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Dave AI resource metadata

Creator / publisher: CUexter
Original project: https://github.com/CUexter/hermes-agent/blob/e1eba6f8ccd272ff9c213afbd6c0397bf828be72/skills/gaming/minecraft-modpack-server/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Sales, Customer Support
Roles: Customer Success Manager, Game Developer, Support Agent
Specialties: Backend
Tools: Neoforge
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 858f64c0e67efb296f832e63fdd3aedd16e954a2da474619eeaafef3cafec821