m.e

That file does not exist. There is only logs/latest.log (for that see https://gist.github.com/martinellison/c08e1e51648e7a6c2709.js, but it doesn't shine any light on the issue). There are also earlier versions of the server log.

When launching the Minecraft client, I get the ConcurrentModificationException error, and then the Mods button does not appear. 20:20:35 FATAL]: Fatal error launching game. Report this to http://bugs.mojang.com please! java.util.ConcurrentModificationException I used forge-1.8.9-11.15.0.1707-installer.jar to install Forge and minecraft_server.1.8.9.jar and the latest Minecraft.jar download. Java is: openjdk version "1.8.0_65" OpenJDK Runtime Environment (build 1.8.0_65-b17) OpenJDK 64-Bit Server VM (build 25.65-b01, mixed mode)