Hacked together a set of scripts to run terraria servers using tmux. I don't recommend this. But it's cool since multiple people can use a console at once.

_terrariactl.sh

#!/bin/bash

# Place to put the server socket. Note that this should be owned by root
# but owned by, let's say, a group "terraria"
TMUX_ROOT=/var/tmux

# Root of terraria servers
TERRARIA_ROOT=/var/games/terraria

# Name of tmux socket to make
TMUX_SOCKET_NAME=terraria

# Config file to have tmux source. I wanted people in "terraria" group to be able to use the tmux session, 
# but not to enter commands and masquerade as me. This is actually my attempt to do that, but I don't think it's good.
# Fortunately, I trusted people on this machine, so it wasn't a problem.
# Just be careful if you are going to do this and maybe have the terraria server run as a terraria user as well.
# Actually don't use any of these files as they are given here. They're bad.
# Make your own, maybe these will help you if you are stuck.
TMUX_FILE_NAME=tmux.conf

# Name of tmux session inside the tmux socket
TMUX_SESSION_NAME=terraria

# Script to run if starting the server.
TERRARIA_SCRIPT=terraria.sh

# Get the socket path
TMUX_SOCKET_PATH="$TMUX_ROOT/$TMUX_SOCKET_NAME"

# Try to attach to the session with that name in that socket. If successful, source the given tmux config.
# If attaching was unsuccessful, start a new session with same configuration, run the terraria startup script,
# and source the tmux config.
tmux -S "$TMUX_SOCKET_PATH" attach-session -t "$TMUX_SESSION_NAME" \; source-file "$TERRARIA_ROOT/$TMUX_FILE_NAME" \
|| tmux -S "$TMUX_SOCKET_PATH" new-session -s "$TMUX_SESSION_NAME" "$TERRARIA_ROOT/$TERRARIA_SCRIPT" \; source-file "$TERRARIA_ROOT/$TMUX_FILE_NAME"

serverconfig.txt

world=/var/games/terraria/server/worlds/FC_Terraria_Server.wld
worldname=FC_Terraria_Server
autocreate=1
maxplayers=8
worldpath=/var/games/terraria/server/worlds
motd=Welcome to FrostCraft's Terraria server ~ frost.kapu.moe
password=*******

terraria.sh

#!/bin/sh
DEFAULT_SERVER_ROOT=/var/games/terraria/server

# Check if we have been given a SERVER ROOT
# If not, use the default.
if [ "0$SERVER_ROOT" = "0" ]; then
    SERVER_ROOT="$DEFAULT_SERVER_ROOT"
fi

# This binary can be obtained from Terraria's website.
# I had a few problems with the server config. I think it has to be in the same directory,
# and only an absolute path is allowed. Also, I think it has to have that name.
# I'm not sure now, since these comments are mostly post-mortem.
# Only the inane comments were actually written at the time I was using these files.
"$SERVER_ROOT/TerrariaServer.bin.x86_64" -config "$SERVER_ROOT/serverconfig.txt"

tmux.conf

set -g default-command nologin
unbind-key ":"