I went through the install steps and the cam seemed to install fine. Unfortunately when I try to run the server, I get the following stack trace:

 

me@homestor:/minecraft2$ sudo java -jar forge-1.12.2-14.23.2.2615-universal.jar
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:62)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:31)
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

 

I'm running java 1.9 (to soon?)

java version "9.0.4"
Java(TM) SE Runtime Environment (build 9.0.4+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)

 

And it's running on Ubuntu Server 16.04. I've been running 1.11.2 fine up until now. Did I miss something?

 

I've attached the log file as well.

 

Thanks!

forge-1.12.2-14.23.2.2615-installer.jar.log

Well, I answered my own problem. Java 1.9 is too soon. I switch back to java 8 and it fired right up. Sorry to bother everyone here...