Ordinarily I run the -universal.jar file to host a server on my machine for mod testing purposes. I then run modded Minecraft and connect to my machine's server instance.

However, any forge version after 2397 no longer runs for this purpose.

The changelog for 2398 reads: "Update JOpt version on the dedicated server to match client."

 

To clarify: MultiMC does run Forge seemingly without issue for these versions—it's the universal that no longer runs. I have updated to the newest JRE: 8u144

By "won't run" I mean that double-clicking the universal.jar won't cause the window that "runs" the server to open, like as seen with the attached image. The server window depicted was run from forge-1.12-14.21.1.2397-universal.jar.

 

There is no log to post since as the 2398-universal.jar won't open, no log file is created.
 

I don't know command line flags so I don't know how to output the "4 more." Anyway, there's that "jopt" term again.

I think I've got it to work now, but I'll answer your question here for the benefit of anyone who needs it.

 

I thought I had done the following:

1. Make server folder
2. Run minecraft_server.1.12.jar in folder, which generates eula.txt
3. Set EULA flag within text to "true"
4. Run forge-1.12-14.21.1.2443-universal.jar

It's possible in the past that I copied successful client instances to those server folders so that they had all the libraries, but in this case running forge-1.12-14.21.1.2443-installer.jar between steps 3 and 4, and "installing server" to the folder, fetched the libraries I needed.

Thanks.

Right, perfect. I had thought that was necessary to get some of the library files. I had it in my head that you needed to run a vanilla game of version X at least one time before running a Forge game of version X, and that that applied to servers.