If you're trying to install Minecraft Forge Universal, or some other Forge based mod packs you may run into the following error when running your server:
[Server] INFO You will need to add them to your server before FML and Forge will run successfully.java.lang.ClassNotFoundException: net.minecraft.launchwrapper.Launch[Server] INFO We appear to be missing one or more essential library files.
This can be fixed by manually downloading the FML Library files and uploading them to the /libraries directory on your server. We've packed the neccessary files into a .zip archive so it's easier to do. Just download the archive linked below, then connect using FTP and upload them to the directory listed above and start your server.