I have just recently created and used a 1.12.2 forge server (downloaded from the forgeinstaller.jar) running the well known modpack, RLCraft. The server runs perfectly fine once started up, but laggy game performance is persistent once in the server. As an attempt to correct this, I tried following guides online (Guides were Mac related) on how to allocate more RAM to a Forge Minecraft server but it never seemed to work and nothing ever started up. The forge version I am using is of the latest (forge-1.12.2-14.23.5.2847-installer) and so is my Java as well (Java 8 u231).
What I have done here is typed the letters "c" and "d" "SPACE" and dropped the server folder (with all the server files) into Terminal and pressed "Enter/Return". Afterwards I copied and pasted the following: "java -Xmx4096M -Xms4096M -jar forge_server.jar" (The point of me doing this was to allocate 4GB of RAM to the forge server ("forge_server.jar" is the name of my forge server file)). I then pressed "Enter/Return" and got these error logs:
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:567)
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: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
... 6 more
It would be very much appreciated if this issue were to be resolved. Thank you.