OS: Kubuntu 18.04.1 LTS

Forge: forge-1.12.2-14.23.5.2775-universal (fresh install)

Command: java -Xmx2G -jar forge-1.12.2-14.23.5.2775-universal.jar nogui

Output: 

user@hostname:~/test$ java -Xmx2G -jar forge-1.12.2-14.23.5.2775-universal.jar nogui
A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:564)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
Caused by: java.lang.ClassCastException: java.base/jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to java.base/java.net.URLClassLoader
        at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
        at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
        ... 6 more
user@hostname:~/test$

I started my server this morning after an OS upgrade last night only to be greeted with this, it worked fine the day before.

The vanilla server still works fine, it's the forge one that's having issues.

6 minutes ago, diesieben07 said:

You must use Java 8.

I'm using jre-8u191-linux, I was using jre-8u181-linux until I discovered this issue.

5 minutes ago, diesieben07 said:

The crash indicates you are in fact using Java 9 or above.

That's interesting I got from java.com and it said "Java 8 Update 191" how to fix?

 

(Edit: I just checked it's running Openjdk 10.0.2 O_o)

Edited November 18, 20186 yr by Kitsune_Ultima

11 minutes ago, diesieben07 said:

I am not sure why you would install things outside of the package manager on linux.

To install Java 8 on Ubuntu you use apt-get install openjdk-8-jre (or openjdk-8-jdk if you want the full JDK).

Make sure your JAVA_HOME environment variable is set properly.

Fixed! Thanks!

(Still, don't know why it auto-installed OpenJDK 10.0.2)

how do i check if its running through java 8? im having the same issue and when i open my java config is says java 8 but im still getting this error