Minecraft Server Not Starting? Causes and Fixes

A Minecraft server not starting almost always writes the reason in its log. Open logs/latest.log (or crash-reports/ if it crashed), find the first error, and match it: an unaccepted EULA, the wrong Java version, a port already in use, too little memory, a broken mod or plugin, or a world from a newer Minecraft version. Each one has a short fix, listed below.

Whether the window closes as soon as you open it or the console never reaches Done, the cause is in the same two places. Here is where to look and what each real error means.

Where to look first: latest.log and crash reports

The PaperMC troubleshooting guide puts it simply: for startup problems, always check latest.log in your logs folder. If the server crashed, the crash report is saved in the crash-reports folder instead. Both live in the server folder, next to server.properties.

1. Read from the bottom up. Scroll up to the first line with ERROR, Exception or Caused by. That first error is the cause; the rest is usually fallout.
2. The window closes instantly? On Windows, a start.bat window closes as soon as the server stops, so you never see the error. Add a line with pause at the end of the file, or start the server from a terminal opened in the folder, and the message stays on screen.
3. No log at all? Then Java never launched the server. Look at the terminal: Error: Unable to access jarfile server.jar means the name in your start command does not match the .jar in the folder.

Minecraft server not starting: error, cause and fix

Search the log for the text in the first column.

The EULA is not accepted

This is the classic first-run stop. The Minecraft Wiki’s server setup tutorial explains that eula.txt is created the first time you run the server, and that until you change eula=false to eula=true, the server shuts down immediately when you try to start it. Open the file, change that one line, save it and start the server again.

Wrong Java version: UnsupportedClassVersionError

If the log shows something like the example in the PaperMC docs, java.lang.UnsupportedClassVersionError: org/bukkit/craftbukkit/Main has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0, your Java is older than the server needs. The two numbers tell you what you have and what you need:

In that example the server was built for Java 21 (65) and ran on Java 17 (61). These are the minimums from the Minecraft Wiki:

Check what you have with java -version. If you have several Java versions installed, the java in your start command may not be the one you think; use the full path to the right one. This error shows up most often right after an update, which is why checking Java is a step in how to update a Minecraft server.

FAILED TO BIND TO PORT

The server could not take its network port (25565 by default, set by server-port in server.properties). The Minecraft Wiki and the PaperMC docs list two causes:

• Something already uses the port. Usually another copy of the server that is still running: a second window, or a Java process left behind after a crash. Close it (on Windows, end the java.exe or javaw.exe process in Task Manager) or change server-port.
• server-ip has an address that is not on this machine. People often paste their public IP there. The wiki notes that if server-ip is empty, the server listens on all available addresses, which is what you want. Leave it blank.

On a hosted server the port is assigned to you. Keep the port the panel shows and leave server-ip empty. If the server starts but friends get a timeout, that is a different problem, covered in Minecraft server connection timed out.

Out of memory: OutOfMemoryError and -Xmx

-Xmx sets the most memory Java may use; -Xms only sets what it starts with. Oracle’s documentation describes java.lang.OutOfMemoryError: Java heap space as an object that could not be allocated in the heap, often just a heap that is too small for the application. For Minecraft, that usually means a big world or modpack needs more than -Xmx allows.

The opposite mistake also stops servers. An -Xmx higher than the machine’s real RAM does not create memory; when the server grows past what exists, the system can stop the process, sometimes with no Java error in the log. Leave room for the operating system on a home PC, and on a hosted plan keep within the plan’s RAM. Sizes for each kind of server are in how much RAM a Minecraft server needs.

Broken mods or plugins

If the crash report or log names a mod or plugin, start there. The common cases:

• Client-only mods on the server. Shaders, minimaps and HUD mods belong on players’ PCs. Fabric mods can declare this with "environment": "client" in their fabric.mod.json, but not every mod does. Keep only server-side and both-side mods in mods/, and if a crash report names a client mod, remove it.
• Missing dependency. The Fabric spec says an unmet required dependency causes a hard failure, and NeoForge’s docs say a required dependency that is missing prevents the mod from loading. The log names what is missing.
• Wrong loader or version. A Fabric mod will not load on Forge, and a mod built for another Minecraft version often fails.
• Outdated plugin on Paper. After an update, an old plugin is the usual suspect. If Paper reports Circular plugin loading detected!, two plugins depend on each other; the PaperMC docs mention the -Dpaper.useLegacyPluginLoading=true flag only as a last resort.

When the log does not point at one file, search by halves, as the PaperMC guide suggests. Rename plugins to plugins-disabled (or move half of mods/ out) and start. If it starts, the problem is in the half you removed. Put back half of that group and repeat until one file is left. With 40 mods that takes about six starts. Clean installs are covered in how to install mods on a Minecraft server.

The world or level.dat is the problem

• World from a newer version. Paper prints Server attempted to load chunk saved with newer version of minecraft! followed by two data version numbers. Someone opened the world in a newer Minecraft, or you switched the server to an older version. Run the version the world was saved in or newer. Do not force a newer world onto an older server.
• Damaged level.dat. The Minecraft Wiki explains that each time a world loads, the current level.dat is copied to level.dat_old. If level.dat is damaged after a power cut or a crash, stop the server, keep a copy of both files, and rename level.dat_old to level.dat.

Also check level-name in server.properties. It must match the world folder name exactly, or the server creates a new, empty world and it looks like your world is gone.

Fixing a server that won’t start on TheGameHosting

The causes are the same, but you fix them from the browser, even on your phone:

• Console shows the log live as the server starts, so you see the error the moment it appears.
• File Manager (or full sFTP) lets you edit eula.txt and server.properties, read logs/latest.log and move mods or plugins out to test by halves.
• Version Changer switches between 28+ platforms (Paper, Purpur, Fabric, Forge, NeoForge and more) and versions, so you can match the version your world was saved in. You can also upload your own JAR.
• Backups create and restore copies of the server, so a bad update or a damaged world is a restore, not a lost world.
• Support 24/7 by chat, email and tickets if the log still makes no sense.

There is no port to forward and no PC to keep on: see Minecraft server hosting.

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