Minecraft Server Not Working? 15 Common Problems & Fixes (2026)

Nothing is more frustrating than gathering your friends for a Minecraft session only to discover your server won’t work. Whether you’re getting “Connection Refused” errors, experiencing severe lag, or watching your server crash repeatedly, we’ve compiled the 15 most common Minecraft server problems and their solutions.

This troubleshooting guide covers both self-hosted servers and managed hosting scenarios, with step-by-step instructions to get you back online fast.

Table of Contents

1. “Connection Refused” or “Can’t Reach Server”
2. “Connection Timed Out” Error
3. Server Not Appearing in Server List
4. “Outdated Server” or Version Mismatch
5. “Failed to Verify Username” / Authentication Issues
6. Whitelist Blocking Players
7. Server Lag and Low TPS
8. Server Crashes on Startup
9. Java Version Errors
10. Out of Memory / RAM Issues
11. Plugin/Mod Conflicts
12. World Corruption Issues
13. “Internal Exception: java.io.IOException”
14. Operator (OP) Commands Not Working
15. Server Stuck on “Stopping Server”

1. “Connection Refused” or “Can’t Reach Server”

Symptoms:

• “Connection refused: no further information”
• “Can’t reach server”
• Players cannot connect at all

Problem: The server isn’t accepting connections on the expected port, usually due to the server not running, incorrect IP/port, or firewall blocking.

Solutions:

Step 1: Verify the Server Is Running Check your server console or control panel to confirm the server is actually started. Look for messages like:

[Server] Done (X.XXXs)! For help, type "help"

Step 2: Confirm Port and IP Address

• Default Minecraft port: 25565
• If using a custom port, players must include it: yourserver.com:25566
• Verify your public IP (check whatsmyip.com) matches what you’re sharing

Step 3: Check Port Forwarding (Self-Hosted) Access your router’s admin panel (usually 192.168.1.1 or 192.168.0.1):

1. Find “Port Forwarding” or “Virtual Servers”
2. Create a rule for port 25565 (TCP)
3. Point it to your server’s local IP address
4. Save and restart your router

Step 4: Disable Firewall Temporarily Test with firewall disabled:

# Windows
netsh advfirewall set allprofiles state off

# Linux
sudo ufw disable

If this works, add a firewall exception for port 25565 rather than leaving the firewall off.

Managed Hosting Solution: With a managed host like Mamba Host, port forwarding and firewall rules are handled automatically. If you’re still having issues, check your control panel to ensure the server is running and note the correct IP and port.

2. “Connection Timed Out” Error

Symptoms:

• “io.netty.channel.ConnectTimeoutException: connection timed out”
• Long loading time followed by disconnect
• Works locally but not for remote players

Problem: Network packets aren’t reaching the server, typically due to incorrect IP, ISP blocking, or server overload.

Solutions:

Step 1: Verify External vs. Internal IP If you’re hosting at home:

• Local connections use: localhost or 127.0.0.1
• Remote players need your public IP (find at whatsmyip.com)
• Never share your internal IP (192.168.x.x) with remote players

Step 2: Check ISP Restrictions Some ISPs block gaming ports or don’t allow incoming connections. Contact your ISP or try:

• Using a VPN with port forwarding capability
• Switching to a different port (configure in server.properties)
• Using a managed hosting provider

Step 3: Reduce Server Load If the server is overloaded, connections may time out:

• Check CPU and RAM usage
• Reduce view distance in server.properties
• Limit entity counts with plugins

Step 4: Test with Direct IP Avoid DNS issues by testing with the direct IP address instead of a domain name.

3. Server Not Appearing in Server List

Symptoms:

• Server doesn’t show in the multiplayer list
• Refresh shows no results
• Can connect with direct IP but not from list

Problem: Query protocol issues or server-list-ping configuration problems.

Solutions:

Step 1: Enable Query in server.properties

enable-query=true
query.port=25565

Step 2: Check server.properties Settings Ensure these are correctly configured:

server-ip=
server-port=25565
enable-status=true

Leave server-ip blank to bind to all interfaces.

Step 3: Forward Query Port If using a custom query port, forward it separately (UDP protocol).

Step 4: Use Direct Connect As a workaround, add the server manually using “Direct Connect” with the full IP:port.

4. “Outdated Server” or Version Mismatch

Symptoms:

• “Outdated server! I’m still on X.X.X”
• “Outdated client! Please use X.X.X”
• Version number mismatch errors

Problem: The client and server Minecraft versions don’t match.

Solutions:

Step 1: Check Server Version Look at your server startup log:

[Server] Starting minecraft server version 1.21.2

Step 2: Match Client Version In the Minecraft launcher:

1. Go to “Installations”
2. Create or edit a profile
3. Select the matching version
4. Launch with that profile

Step 3: Update the Server Download the latest server jar from minecraft.net:

1. Stop your server
2. Replace the server jar file
3. Start the server
4. Accept new EULA if prompted

Step 4: Use ViaVersion Plugin (Optional) For Paper/Spigot servers, the ViaVersion plugin allows players on newer versions to join older servers.

5. “Failed to Verify Username” / Authentication Issues

Symptoms:

• “Failed to verify username!”
• “Invalid session (Try restarting your game)”
• Cannot authenticate with Mojang/Microsoft servers

Problem: Session authentication failure or online-mode misconfiguration.

Solutions:

Step 1: Restart Minecraft Completely Close Minecraft entirely and reopen. This refreshes your authentication token.

Step 2: Re-login to Your Account

1. Log out of the Minecraft launcher
2. Log back in
3. Launch the game fresh

Step 3: Check online-mode Setting In server.properties:

online-mode=true

• true = Authentication required (recommended for security)
• false = No authentication (allows cracked clients, not recommended)

Step 4: Wait for Mojang Services Check status.mojang.com for service outages. Authentication issues often resolve within minutes.

Step 5: Flush DNS Cache

# Windows
ipconfig /flushdns

# macOS
sudo dscacheutil -flushcache

# Linux
sudo systemd-resolve --flush-caches

6. Whitelist Blocking Players

Symptoms:

• “You are not whitelisted on this server!”
• New players can’t join
• Whitelist commands seem to have no effect

Problem: Whitelist is enabled but players aren’t added, or whitelist.json is corrupted.

Solutions:

Step 1: Check Whitelist Status In-game or console:

/whitelist list

Step 2: Add Players Correctly

/whitelist add PlayerUsername

Use the exact username (case-sensitive for some servers).

Step 3: Reload the Whitelist

/whitelist reload

Step 4: Verify whitelist.json Check the file for proper formatting:

[
  {
    "uuid": "player-uuid-here",
    "name": "PlayerName"
  }
]

Step 5: Disable Whitelist (If Needed)

/whitelist off

Or in server.properties:

white-list=false

7. Server Lag and Low TPS

Symptoms:

• Block breaking delay
• Mob movement stuttering
• TPS (ticks per second) below 20
• “Can’t keep up!” warnings in console

Problem: Server is overloaded due to hardware limitations, inefficient plugins, or world issues.

Solutions:

Step 1: Check TPS Use Spark or similar:

/spark tps

Healthy TPS = 20. Below 15 is noticeable lag.

Step 2: Reduce View Distance In server.properties:

view-distance=8
simulation-distance=6

Lower values = less CPU/RAM usage.

Step 3: Limit Entities Use plugins like ClearLagg or configure spawn limits:

spawn-limits.monsters=50
spawn-limits.animals=10

Step 4: Upgrade Hardware Minimum recommended specs:

• Vanilla 1-10 players: 2GB RAM, 1 CPU core
• Modded 10-20 players: 4-6GB RAM, 2 CPU cores
• Large modpacks 20+: 8GB+ RAM, 4 CPU cores, NVMe storage

Step 5: Pre-generate World Chunks Use Chunky plugin to pre-generate a 5000-block radius, eliminating chunk generation lag during play.

Step 6: Optimize Server Software Switch from vanilla to Paper or Purpur for better performance with identical gameplay.

8. Server Crashes on Startup

Symptoms:

• Server starts then immediately stops
• Error messages in console before crash
• “Failed to start” messages

Problem: Configuration errors, corrupted files, or incompatible software.

Solutions:

Step 1: Read the Error Log Check logs/latest.log for the specific error. Common causes include:

• Missing EULA agreement
• Port already in use
• Corrupted world files

Step 2: Accept the EULA Edit eula.txt:

eula=true

Step 3: Check for Port Conflicts If another process uses port 25565:

# Windows
netstat -aon | findstr :25565

# Linux
lsof -i :25565

Either stop the conflicting process or change your server port.

Step 4: Remove Problematic Plugins/Mods If crashing after adding new plugins:

1. Remove all new additions
2. Start the server
3. Add them back one by one to identify the culprit

Step 5: Reset Corrupted Files Try deleting and letting the server regenerate:

• server.properties (will regenerate defaults)
• bukkit.yml / spigot.yml / paper.yml (for Paper servers)

9. Java Version Errors

Symptoms:

• “Unsupported class file major version”
• “java.lang.UnsupportedClassVersionError”
• “This version of Minecraft requires Java XX”

Problem: Wrong Java version installed for your Minecraft version.

Solutions:

Java Version Requirements:

Step 1: Check Current Java Version

java -version

Step 2: Install Correct Java Version Download from Adoptium:

• Temurin 21 for Minecraft 1.20.5+
• Temurin 17 for Minecraft 1.18-1.20.4

Step 3: Update Server Startup Script Specify the correct Java path:

# Windows
"C:\Program Files\Eclipse Adoptium\jdk-21\bin\java.exe" -jar server.jar

# Linux
/usr/lib/jvm/java-21-openjdk/bin/java -jar server.jar

10. Out of Memory / RAM Issues

Symptoms:

• “java.lang.OutOfMemoryError”
• Server freezes then crashes
• “GC overhead limit exceeded”

Problem: Insufficient RAM allocated or memory leak from plugins/mods.

Solutions:

Step 1: Increase RAM Allocation Modify your startup flags:

java -Xmx4G -Xms4G -jar server.jar

• -Xmx4G = Maximum 4GB RAM
• -Xms4G = Starting 4GB RAM

Step 2: Use Aikar’s Flags Optimized garbage collection flags for Minecraft:

java -Xms4G -Xmx4G -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 -jar server.jar

Step 3: Identify Memory-Hungry Plugins Use Spark profiler:

/spark heapsummary

Remove or replace plugins using excessive memory.

Step 4: Upgrade Your Plan If consistently running out of RAM, upgrade to a higher tier. RAM requirements:

• Vanilla: 2-3GB
• Small modpacks: 4-6GB
• Large modpacks: 8-12GB
• Networks with multiple worlds: 12GB+

11. Plugin/Mod Conflicts

Symptoms:

• Specific features not working
• Random crashes after installing new plugins
• Error spam in console mentioning plugin names

Problem: Incompatible plugins or mods interfering with each other.

Solutions:

Step 1: Identify the Conflict

1. Remove all plugins/mods
2. Add them back in groups of 3-4
3. Test after each batch
4. Narrow down the problematic combination

Step 2: Check Version Compatibility Ensure plugins match your server software and Minecraft version:

• Spigot plugins for Spigot/Paper
• Fabric mods for Fabric
• Forge mods for Forge (NeoForge for newer versions)

Step 3: Read Plugin Documentation Many plugins have known incompatibilities listed on their pages (SpigotMC, Modrinth, CurseForge).

Step 4: Check for Updates Outdated plugins often cause issues with newer Minecraft versions. Update all plugins to their latest versions.

Step 5: Ask for Support Check the plugin’s Discord or GitHub issues for similar problems and solutions.

12. World Corruption Issues

Symptoms:

• Missing chunks (holes in the world)
• Players losing inventory
• “Region file corrupted” errors
• Server refuses to load world

Problem: World data files became corrupted due to crashes, improper shutdowns, or storage issues.

Solutions:

Step 1: Restore from Backup The safest solution. Replace corrupted region files with backup versions from your world/region/ folder.

Step 2: Use Region Fixer Tools Download and run Minecraft Region Fixer:

python region-fixer.py --delete-corrupted world/

Step 3: Delete Corrupted Chunks Using NBTExplorer or MCA Selector, identify and delete corrupted chunks. They’ll regenerate when players visit.

Step 4: Prevent Future Corruption

• Always use /stop command (never force-kill the server)
• Enable automatic backups
• Use NVMe storage (faster writes = safer saves)
• Configure autosave intervals appropriately

13. “Internal Exception: java.io.IOException”

Symptoms:

• “Internal Exception: java.io.IOException: An existing connection was forcibly closed”
• Random disconnects mid-gameplay
• Usually affects specific players, not all

Problem: Network instability, ISP issues, or server-side packet handling errors.

Solutions:

Step 1: Check Network Stability

• Run a ping test to the server IP
• Check for packet loss using ping -t serverip
• Look for inconsistent response times

Step 2: Adjust network-compression-threshold In server.properties:

network-compression-threshold=256

Try increasing to 512 or disabling with -1 for testing.

Step 3: Update Network Drivers For players experiencing this:

• Update network adapter drivers
• Disable VPN/proxy services
• Try a different network connection

Step 4: Check for Specific Triggers If disconnects happen during specific actions (opening chests, using certain items), a corrupted item or chunk may be the cause.

14. Operator (OP) Commands Not Working

Symptoms:

• “/op playername” doesn’t work
• Commands return “You don’t have permission”
• Ops.json appears correct but permissions fail

Problem: Permission plugin conflicts, incorrect permission levels, or ops.json issues.

Solutions:

Step 1: Check OP Level In ops.json, ensure level is 4 (highest):

[
  {
    "uuid": "player-uuid",
    "name": "PlayerName",
    "level": 4,
    "bypassesPlayerLimit": true
  }
]

Step 2: Use Console to OP Run from the server console (not in-game):

op PlayerName

Step 3: Check Permission Plugin Settings If using LuckPerms, PermissionsEx, or similar:

• OPs may still be restricted by group permissions
• Add players to admin group or grant wildcard permission

Step 4: Verify ops.json Syntax Validate JSON syntax at jsonlint.com. Missing commas or brackets break the file.

15. Server Stuck on “Stopping Server”

Symptoms:

• Server hangs on “Stopping server…”
• /stop doesn’t complete
• Must force-kill the process

Problem: Plugin preventing clean shutdown, world save hanging, or deadlock.

Solutions:

Step 1: Wait Longer Large worlds can take 2-5 minutes to save. Wait at least 5 minutes before force-stopping.

Step 2: Check for Problematic Plugins Some plugins hook into shutdown events poorly. Test by removing all plugins and stopping.

Step 3: Force Stop (Last Resort)

# Windows
taskkill /F /IM java.exe

# Linux
kill -9 $(pgrep -f "server.jar")

Step 4: Enable Save-on-Stop Ensure world saves complete before shutdown:

/save-all
/stop

Step 5: Consider Upgrading Storage Slow HDDs cause long save times. NVMe SSDs can reduce world save time by 80%+.

When to Use Managed Hosting

If you’re spending more time troubleshooting than playing, managed hosting eliminates most headaches:

Benefits of managed hosting like Mamba Host:

• Pre-configured servers that just work
• Automatic Java version management
• No port forwarding required
• DDoS protection included
• 24/7 support for technical issues
• One-click mod/plugin installation
• Automatic backups

Starting at $2.99/month, managed hosting saves hours of troubleshooting time and provides:

• Instant server deployment
• Enterprise-grade NVMe storage
• Sub-30ms latency for North American players
• 99.9% uptime SLA

Quick Reference: Error → Solution Table

Summary

Most Minecraft server issues fall into these categories:

1. Connection problems - Port forwarding, firewall, IP configuration
2. Version mismatches - Minecraft and Java version compatibility
3. Performance issues - RAM, CPU, storage optimization
4. Configuration errors - server.properties and plugin settings
5. Corruption - World files and improper shutdowns

When troubleshooting, always:

• Check server logs first (logs/latest.log)
• Test one change at a time
• Keep backups before making changes
• Consider managed hosting to eliminate infrastructure issues

Still stuck? Join the Mamba Host Discord community for help from experienced server admins and our support team.

Need reliable Minecraft hosting? Skip the troubleshooting with Mamba Host’s managed Minecraft servers. Instant setup, automatic updates, and expert support when you need it.

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