[Bug]: Minecraft Java v1.20.5 not starting

[amazingSquid551]

User story

Server is not booting due to Java Runtime error

Game

Minecraft Java

Linux distro

Ubuntu 22.04

Command

command: start, command: debug

Further information

net/minecraft/bundler/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

Relevant log output

linuxgsm@ca8e7fd0ae77:/app$ ./mcserver debug

Minecraft Debuging
=================================
Distro:          Ubuntu 22.04.4 LTS
Architecture:    x86_64
Kernel:          6.2.16-3-pve
Hostname:        ca8e7fd0ae77
tmux:            3.2a
Avg Load:        0.04, 0.07, 0.06
Free Memory:     13GB
Free Disk:       27G
Game Server IP: 0.0.0.0:25565
Internet IP:    0.0.0.0:25565
Start parameters:
java -Xmx1024M -jar ./minecraft_server.jar nogui

Use debug for identifying server issues only!
Press CTRL+c to drop out of debug mode.
Warning! If mcserver is already running it will be stopped.
Continue? [Y/n] Y
[ INFO ] Debuging mcserver: Stopping any running servers
[ INFO ] Stopping mcserver: LinuxGSM is already stopped
[  OK  ] Debuging mcserver: Starting debug
Error: LinkageError occurred while loading main class net.minecraft.bundler.Main
        java.lang.UnsupportedClassVersionError: net/minecraft/bundler/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
[ ERROR ] Debuging mcserver: Server has stopped: exit code: 0
[ ERROR ] Debuging mcserver: Press ENTER to exit debug mode

Steps to reproduce

No response

[MicLieg]

This is happening because as of the letest Minecraft patch Java 21 is required.

I've already requestesd to update the java version used by LinuxGSM: #4562

In the meantime, run sudo apt install openjdk-21-jdk to install Java 21 (JDK).

[B1Z0N]

I got the same, but managed to fix it separately by doing the same as @MicLieg suggested. Also, I think this here is identical for both versions of Ubuntu. Probably this duplicate should be removed.

https://linuxgsm.com/servers/mcserver/