This tutorial by user Virtualisation Works will help you get a Minecraft server set up with Java and Tmux on FreeBSD. Follow the link below for the full set of instructions.

A virtual world cannot be complete without a virtual reality environment like Minecraft.  In this article, I quickly go through the steps setting a Minecraft server with FreeBSD. Specifically, I will be installing a Spigot Minecraft Server.  I like it very much because it comes with lots of performance optimisations.  I assume you prepared your environment with my customisation script or something similar.  The whole process will take less than one hour if you have a good internet connection.

Step 1: Installing Java, Tmux, Bash, and Friends

As usual, installing packages in FreeBSD is easy.  It is simply “pkg install”.  Yet, Java and Bash requires special file systems at “/dev/fd” and “/proc”.  The file “/etc/fstab” is therefore appended and two more file systems are defined.  The file systems are mounted before we proceed on the next step.

Full tutorial: https://virtualisationworks.wordpress.com/2017/02/02/minecraft-with-java-and-tmux-on-freebsd/