Minecraft Modpack Server

Minecraft Modpack Server Setup

When to Use

Use this skill when the user wants to:

• Set up a modded Minecraft server from a server pack zip (CurseForge, Modrinth)
• Configure NeoForge or Forge server settings
• Tune Minecraft server performance (JVM args, view distance, simulation distance)
• Set up automated world backups for a Minecraft server
• Troubleshoot a modded server that won't start or kicks players

Trigger keywords: minecraft server, modpack server, neoforge, forge, server.properties, user_jvm_args, server pack, modded minecraft, ATM, all the mods, enigmatica, create above and beyond.

Prerequisites

• A Linux or macOS host with sufficient RAM (minimum 16 GB for 100+ mod packs; 32 GB+ for 200+ mod packs)
• Sudo access for package installation and firewall configuration
• A server pack zip URL or local file (from CurseForge or Modrinth)
• The user's preferences gathered before generating configs (see step 1)

Procedure

1. Gather User Preferences

Before generating any configuration, ask the user for the following. Use sensible defaults only if the user explicitly says they don't care:

2. Download and Inspect the Pack

mkdir -p ~/minecraft-server
cd ~/minecraft-server
wget -O serverpack.zip "<URL>"
unzip -o serverpack.zip -d server
ls server/

Look for these files in the extracted directory:

• startserver.sh — the pack's launch script (read it to determine mod loader type, version, and required Java version)
• Installer jar (e.g., neoforge-*-installer.jar or forge-*-installer.jar)
• user_jvm_args.txt — JVM argument template
• mods/ folder — contains all mod jars

Check the start script to determine the mod loader type, version, and required Java version:

cat ~/minecraft-server/server/startserver.sh

3. Install Java

Match the Java version to the Minecraft version:

Verify the installation:

java -version

4. Install the Mod Loader

Most server packs include an install script. Use the INSTALL_ONLY environment variable to install libraries without launching the server:

cd ~/minecraft-server/server
ATM10_INSTALL_ONLY=true bash startserver.sh

For generic Forge packs without an install script:

java -jar forge-*-installer.jar --installServer

This downloads libraries, patches the server jar, and generates the args files needed for launch.

Some packs use pack-specific env vars to control behavior. For example, ATM10 uses:

• ATM10_JAVA — path to Java executable
• ATM10_RESTART — enable/disable auto-restart loop
• ATM10_INSTALL_ONLY — install only, don't launch

Check the pack's startserver.sh for pack-specific variables.

5. Accept the EULA

echo "eula=true" > ~/minecraft-server/server/eula.txt

6. Configure server.properties

Key settings for modded servers:

motd=\u00a7b\u00a7lServer Name \u00a7r\u00a78| \u00a7aModpack Name
server-port=25565
online-mode=true
enforce-secure-profile=true
difficulty=hard
allow-flight=true
spawn-protection=0
max-tick-time=180000
enable-command-block=true

HARD RULES for modded server.properties:

• allow-flight=true is REQUIRED — mods with jetpacks, flight rings, or flying mounts will kick players without it
• max-tick-time=180000 or higher — modded servers often have long ticks during worldgen; the default 60000 will crash the server
• If online-mode=false, you MUST also set enforce-secure-profile=false or clients get rejected
• spawn-protection=0 lets all players build at spawn (most modpacks expect this)

Performance settings — scale to hardware and player count:

# 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

7. Tune JVM Args (user_jvm_args.txt)

Scale RAM to player count and mod count. Rule of thumb for modded:

Write the JVM args file:

cat > ~/minecraft-server/server/user_jvm_args.txt << 'EOF'
-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
EOF

Adjust -Xms and -Xmx based on the RAM table above. Always leave at least 8 GB free for the OS and other tasks.

8. Open Firewall

sudo ufw allow 25565/tcp comment "Minecraft Server"

Verify:

sudo ufw status | grep 25565

9. Create a Clean Launch Script

The pack's startserver.sh often has an auto-restart loop. Create a clean launch script without it:

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

For Forge (not NeoForge), the args file path differs. Check startserver.sh for the exact path — it is typically @libraries/net/minecraftforge/forge/<VERSION>/unix_args.txt.

10. Set Up Automated Backups

Create the backup script:

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 job:

(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 -

11. First Launch

~/start-minecraft.sh

First startup is SLOW — several minutes for big packs. Do not panic. "Can't keep up!" warnings on first launch are normal and settle after initial chunk generation completes.

Pitfalls

1. allow-flight=true is mandatory for modded — mods with jetpacks, flight rings, or flying mounts will kick players without it. Never set this to false on a modded server.

2. max-tick-time must be 180000 or higher — modded servers often have long ticks during worldgen. The vanilla default of 60000 will crash the server on first load with large modpacks.

3. First startup is very slow — several minutes for big packs. Do not kill the process thinking it's hung. Wait for "Done!" in the log.

4. "Can't keep up!" warnings are normal on first launch — these settle after initial chunk generation completes.

5. online-mode=false requires enforce-secure-profile=false — if you set one without the other, clients get rejected with cryptic errors.

6. The pack's startserver.sh often has an auto-restart loop — always create a clean launch script (step 9) without the restart loop for production use.

7. Delete the world/ folder to regenerate with a new seed — changing level-seed in server.properties only affects new chunks, not existing worlds.

8. Pack-specific env vars — some packs have env vars that control behavior (e.g., ATM10 uses ATM10_JAVA, ATM10_RESTART, ATM10_INSTALL_ONLY). Always read startserver.sh to find these.

9. Forge vs NeoForge args paths differ — NeoForge uses @libraries/net/neoforged/neoforge/<VERSION>/unix_args.txt; Forge uses @libraries/net/minecraftforge/forge/<VERSION>/unix_args.txt. Check startserver.sh for the exact path.

10. Never allocate more RAM than physically available minus 8 GB — the OS and other processes need headroom. Oversubscribing RAM causes swap thrashing and worse performance than under-allocating.

Verification

1. Check if the server process is running:

   pgrep -fa neoforge
   # or
   pgrep -fa minecraft
   

2. Monitor server logs in real time:

   tail -f ~/minecraft-server/server/logs/latest.log
   

3. Confirm server is ready — look for this line in the log:

   Done (Xs)! For help, type "help"
   

   This means the server is accepting connections.

4. Test player connection — add the server IP in Minecraft Multiplayer and verify it appears in the server list with the correct MOTD.

5. Verify firewall is open:

   sudo ufw status | grep 25565
   

   Expected output:

   25565/tcp                  ALLOW       Anywhere                   # Minecraft Server
   

6. Verify backups are working:

   ls -lh ~/minecraft-server/backups/
   

   Should show world_YYYY-MM-DD_HH-MM-SS.tar.gz files.

7. Verify cron is scheduled:

   crontab -l | grep backup
   

   Expected output:

   0 * * * * /home/<user>/minecraft-server/backup.sh >> /home/<user>/minecraft-server/backups/backup.log 2>&1