---
title: "Minecraft Server Won't Start: Errors and Fixes (Java, EULA)"
description: "Fix a Minecraft server that will not start: Java version errors, EULA, port in use, jar not found, out of memory, plugin crashes and corrupt worlds."
url: "https://www.zcraftstudios.com/blog/minecraft-server-wont-start-errors-fixes"
updated: "2026-10-29T08:05:38.407341+00:00"
source: "ZCraft Studios"
---

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# Minecraft Server Won't Start: Errors and Fixes (Java, EULA)

ZCraft StudiosOct 29, 2026

Fix a Minecraft server that will not start: Java version errors, EULA, port in use, jar not found, out of memory, plugin crashes and corrupt worlds.

## In this guide

- [Find the real error first](#find-the-real-error-first)
- [Common start-up errors](#common-start-up-errors)
- [Step-by-step fixes](#step-by-step-fixes)
- [After a version update](#after-a-version-update)
- [Prevent start-up problems](#prevent-start-up-problems)
- [Frequently asked questions](#frequently-asked-questions)
- [Related reading](#related-reading)

## Minecraft Server Won't Start: Errors and Fixes (Java, EULA)

**Quick answer:** read the **last error in the console or `logs/latest.log`**. Most start-up failures are one of these: the wrong Java version, the EULA not accepted, the port already in use, a wrong jar name, not enough memory, or a broken plugin. Match your message to the table below.

## Find the real error first

1. Run the server from a terminal so the window does not close. A start script with `pause` on Windows keeps it open.
2. Open `logs/latest.log` and scroll to the first error, not the last line.
3. If there is a crash report, open the newest file in `crash-reports/`. See [Read Minecraft Crash Reports](https://www.zcraftstudios.com/blog/minecraft-server-crash-report-guide).

## Common start-up errors

| Message                                            | Cause                              | Fix                                                                                     |
| -------------------------------------------------- | ---------------------------------- | --------------------------------------------------------------------------------------- |
| UnsupportedClassVersionError                       | Java is too old                    | Install the required Java version. Class version 65 means Java 21, and 69 means Java 25 |
| "You need to agree to the EULA"                    | EULA not accepted                  | Set eula=true in eula.txt after reading it                                              |
| Unable to access jarfile                           | Wrong file name or folder          | Run the command from the server folder, and match the jar name                          |
| Could not find or load main class                  | Corrupt or incomplete jar          | Download the server jar again                                                           |
| Failed to bind to port or "Address already in use" | Another program uses the port      | Stop the other process, or change server-port                                           |
| Invalid maximum heap size                          | Bad memory flag                    | Use \-Xmx4G form. See [RAM and Java Errors](https://www.zcraftstudios.com/blog/minecraft-java-heap-ram-errors)       |
| Could not reserve enough space for object heap     | Asking for more RAM than available | Lower \-Xmx                                                                             |
| OutOfMemoryError: Java heap space                  | Heap too small                     | Raise \-Xmx, remove heavy plugins or mods                                               |
| "Server thread/WARN Can't keep up"                 | Overloaded                         | See [Can't Keep Up Warning](https://www.zcraftstudios.com/blog/minecraft-server-cant-keep-up-warning-fix)            |
| Watchdog "A single server tick took 60.00 seconds" | A tick froze                       | Read the thread dump. Often a plugin or corrupt chunk                                   |
| "Could not load plugin"                            | Plugin problem                     | See [Plugin Not Loading?](https://www.zcraftstudios.com/blog/minecraft-plugin-not-loading-fix)                       |
| "Failed to load chunk" or a region error           | Corrupt world data                 | See [Chunk Corruption Recovery](https://www.zcraftstudios.com/blog/minecraft-server-chunk-corruption-recovery)       |

## Step-by-step fixes

### 1\. Match Java to Minecraft

| Minecraft version | Java    |
| ----------------- | ------- |
| 1.20 to 1.21.11   | Java 21 |
| 26.1 and newer    | Java 25 |

Check with `java -version`. On a hosting panel, change the Java or Docker image. See [How to Start a Minecraft Server](https://www.zcraftstudios.com/blog/start-minecraft-server) and [Update a Minecraft Server to 26.1+](https://www.zcraftstudios.com/blog/minecraft-26-1-server-update-guide).

### 2\. Accept the EULA

After the first run, open `eula.txt` and set `eula=true`. Start again.

### 3\. Fix the jar name and folder

Run `ls` or `dir` in the folder and confirm the jar name matches your command exactly, for example `java -jar paper.jar --nogui`.

### 4\. Free the port

Find what uses port 25565 and stop it. On Linux, check with `ss -ltnp`. On Windows, use `netstat -ano`. Or change `server-port`. See [Port 25565 Not Working](https://www.zcraftstudios.com/blog/minecraft-server-port-25565-not-working).

### 5\. Set memory correctly

Keep `-Xmx` below the memory your machine or panel allows. See [How Much RAM Does a Minecraft Server Need?](https://www.zcraftstudios.com/blog/how-much-ram-does-a-minecraft-server-need).

### 6\. Isolate plugins and mods

1. Move all plugins out of the `plugins` folder.
2. Start the server. If it works, add plugins back in small groups.
3. Check each plugin's supported version and dependencies. See [Find Plugin Conflicts](https://www.zcraftstudios.com/blog/minecraft-server-plugin-conflict-debugging).

### 7\. Check the world

If the crash happens when loading a world, restore a backup of the world folder. Do not delete the only copy. See [Backup Strategy](https://www.zcraftstudios.com/blog/minecraft-server-backup-strategy).

## After a version update

If it stopped starting after an update:

- Check the Java version and the plugin versions.
- Check whether the update changed world storage. See [Update a Minecraft Server to 26.1+](https://www.zcraftstudios.com/blog/minecraft-26-1-server-update-guide).
- Roll back to the pre-update backup if needed.

## Prevent start-up problems

1. Test updates on a staging copy. See [Staging Environment Guide](https://www.zcraftstudios.com/blog/minecraft-server-staging-environment-guide).
2. Keep backups and a written update checklist. See [Update Plugins Safely](https://www.zcraftstudios.com/blog/minecraft-server-plugin-update-checklist).
3. Use automatic restarts. See [Automatic Restarts and Crash Recovery](https://www.zcraftstudios.com/blog/minecraft-server-auto-restart-crash-recovery).

## Frequently asked questions

**Why does my Minecraft server close immediately?** Usually the EULA, the wrong Java version or a wrong jar path. Run it from a terminal to see the message.

**Why does my server crash on start?** Read the first error in `latest.log`. Plugins, memory and corrupt worlds are common causes.

**How do I fix "UnsupportedClassVersionError"?** Install the Java version your Minecraft version requires.

**What if the console says "Failed to bind to port"?** Another process uses the port, so stop it or change the port.

**Where are Minecraft server logs?** In the `logs` folder, with the current log in `latest.log`.

## Related reading

- [How to Make a Minecraft Server Public](https://www.zcraftstudios.com/blog/make-minecraft-server-public-port-forwarding)
- [server.properties Explained](https://www.zcraftstudios.com/blog/minecraft-server-properties-explained)
- [Minecraft Server Mistakes](https://www.zcraftstudios.com/blog/minecraft-server-mistakes)

## Continue reading

- [Minecraft Whitelist Not Working? Fixes for Access Errors](https://www.zcraftstudios.com/blog/minecraft-server-whitelist-not-working)
- [How to Start a Minecraft Server: Step-by-Step (Java, 2026)](https://www.zcraftstudios.com/blog/start-minecraft-server)
- [Update a Minecraft Server to 26.1+: Java 25, Paper, Plugins](https://www.zcraftstudios.com/blog/minecraft-26-1-server-update-guide)
- [ZGC for Minecraft Servers: Flags, Java Versions, G1 Choice](https://www.zcraftstudios.com/blog/zgc-minecraft-server-flags-guide)

[ Previous guide How Much RAM Does a Minecraft Server Need? (2026 Guide)](https://www.zcraftstudios.com/blog/how-much-ram-does-a-minecraft-server-need)[ Next guide How to Make a Minecraft Server Public: Port Forwarding Guide](https://www.zcraftstudios.com/blog/make-minecraft-server-public-port-forwarding)

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