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SystemD

The two files below are the merger of other Minecraft SystemD service files I came across on the web and the screen-based method I originally used for running Minecraft instances.

Here's a breakdown of the processes that facilitate automatically loading the Minecraft server instance(s) when the system boots up:

  1. The systemd minecraft@ instance specific service launches screen. (ie: systemctl start minecraft@creative1)
  2. screen launches the script start-server-in-screen-systemd (as instructed by the SystemD service).
  3. start-server-in-screen-systemd launches "java fabric-server-launch.jar" (with a lot of other arguments for optimization)
  4. java loads fabric-server-launch.jar
  5. fabric-server-launch.jar takes care of loading your Minecraft server instance

I chose to use screen a bash script instead of launching java directly from systemd for these two reasons:

  1. screen allows you to directly interact with the Minecraft server console without needing an rcon application, and its the way I'm used to dealing with server instances.
  2. Using a bash script to launch the Minecraft server instance was easier to deal with per-instance customizations. You can facilitate the same thing directly from systemd, I just didn't want to take the time to learn how to do.
Setting up your environment

Below is an example of the files and folders that are needed for this setup.

# create minecraft systemd service and socket files
# copy contents of files from contents further down the page
vi /etc/systemd/system/minecraft@.service
vi /etc/systemd/system/minecraft@.socket

# example for server-instance creative1

# required files for server-instance creative1
# copy contents of file from contents further down the page
vi /opt/minecraft/server-instances/creative1/start-server-in-screen-systemd

# systemctl commands for server-instance creative1
systemctl enable minecraft@creative1.service
systemctl start minecraft@creative1.service
systemctl status minecraft@creative1.service
Prep commands
MCROOT=/opt/minecraft
mkdir -p $MCROOT/server-instances $MCROOT/tools

# change ownership if desired
chown -R minecraftuser:minecraftuser $MCROOT/server-instances

# git and make mcrcon
cd $MCROOT/tools
git clone https://github.com/Tiiffi/mcrcon.git
cd mcrcon
make
# only install it if you want, otherwise just run the binary from here
# sudo make install

# create server instance folders
MCINSTANCE1=$MCROOT/server-instances/creative1
mkdir -p $MCINSTANCE1
chown -R minecraftuser:minecraftuser $MCINSTANCE1
/etc/systemd/system/minecraft@.service
[Unit]
Description=Minecraft Server - %i
Wants=network-online.target
After=network-online.target
ConditionPathExists=/opt/minecraft/server-instances/%i

[Service]
WorkingDirectory=/opt/minecraft/server-instances/%i

User=minecraftuser
Group=minecraftuser

Sockets=minecraft@%i.socket
StandardInput=socket
StandardOutput=journal
StandardError=journal

PrivateUsers=true
ProtectSystem=full
ProtectHome=true
ProtectKernelTunables=true
ProtectKernelModules=true
ProtectControlGroups=true
NoNewPrivileges=true

WorkingDirectory=/opt/minecraft/server-instances/%i

Type=simple
ExecStart=screen -D -m -S minecraft-%i ./start-server-in-screen-systemd
ExecStop=/bin/sh -c "/bin/echo stop > /opt/minecraft/server-instances/%i/systemd.stdin"

Restart=on-failure
RestartSec=60s

[Install]
WantedBy=multi-user.target
/etc/systemd/system/minecraft@.socket
[Unit]
BindsTo=minecraft@%i.service

[Socket]
ListenFIFO=/opt/minecraft/server-instances/%i/systemd.stdin
Service=minecraft@%i.service
SocketUser=minecraftuser
SocketGroup=minecraftuser
RemoveOnStop=true
SocketMode=0600
/opt/minecraft/server-instances/%i/start-server-in-screen-systemd

The systemd service launches screen and tells it to run this file per instance, which actually runs SystemD Minecraft@ Service -> Screen -> start-server-in-screen-systemd -> Java -> Fabric -> Minecraft

#!/bin/bash

# Simple command to start fabric server with diffent RAM options
#java -Xms4096M -Xmx4096M -jar fabric-server-launch.jar nogui
#java -Xms6144M -Xmx6144M -jar fabric-server-launch.jar nogui

# 20211210
# Added the following line to fix a security bug announced today
# -Dlog4j2.formatMsgNoLookups=true

# Launching Minecraft with a specific java binary using Aikar's server flags
/usr/lib/jvm/java-17-oracle/bin/java -Xms8G -Xmx8G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=https://mcflags.emc.gs -Daikars.new.flags=true -jar fabric-server-launch.jar nogui

 

#end

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