Running as a Linux service

For a production network the master and the wrappers should start with the machine, restart on updates and keep their console reachable. This guide sets them up as systemd services that run inside tmux, so you can attach to the console at any time. It is the exact setup of our own test network.

1. A user for the cloud

Never run game servers as root:

sudo apt install tmux git curl
sudo useradd --create-home --shell /bin/bash cloud
sudo -iu cloud

2. Java 25

Download a JDK 25 for Linux x64 from adoptium.net and unpack it into the home folder:

mkdir -p ~/jdk-25
curl -L https://api.adoptium.net/v3/binary/latest/25/ga/linux/x64/jdk/hotspot/normal/eclipse | tar -xz --strip-components=1 -C ~/jdk-25
~/jdk-25/bin/java -version

The wrappers find runtimes in the home folder automatically, so groups can choose between this Java and any other one you install (e.g. Java 21 for old Minecraft versions).

3. Folders and start scripts

mkdir -p ~/master ~/wrapper
curl -L -o ~/master/launcher.jar https://repo.rexlcloud.de/downloads/de/rexlcloud/launcher/2.0.22/launcher-2.0.22.jar
cp ~/master/launcher.jar ~/wrapper/launcher.jar

~/master/start.sh:

#!/bin/sh
export PATH=/home/cloud/jdk-25/bin:$PATH
cd /home/cloud/master
exec java -Xms256M -Xmx1G -jar launcher.jar --master

~/wrapper/start.sh is the same with wrapper instead of master. Make both executable with chmod +x ~/master/start.sh ~/wrapper/start.sh.

Start each once by hand to set them up as described in the installation guide: register the wrapper with wrapper add, then stop both again (stop).

4. Detached servers

By default the servers are child processes of the wrapper and stop when it stops. With detached servers every server runs in its own tmux session and keeps running through wrapper restarts and updates. The wrapper attaches to them again when it comes back.

In ~/wrapper/config/wrapper.json:

"detachedServers": true

In this mode detach (and systemctl stop) leaves the servers running; only stop stops them. A server whose wrapper stays away for two minutes shuts itself down.

To look at a server’s console directly: tmux -L rexlcloud-2243 ls (the socket is named after the wrapper’s serverPort).

5. systemd units

Back as root, create /etc/systemd/system/rexlcloud-master.service:

[Unit]
Description=rexlCloud master (console: su - cloud -c "tmux -L master attach")
After=network-online.target
Wants=network-online.target

[Service]
Type=forking
User=cloud
WorkingDirectory=/home/cloud/master
ExecStart=/usr/bin/tmux -L master new-session -d -s master -x 200 -y 50 /home/cloud/master/start.sh
ExecStop=/bin/sh -c "tmux -L master send-keys -t master stop Enter; for i in $(seq 1 50); do tmux -L master has-session -t master 2>/dev/null || exit 0; sleep 1; done; tmux -L master kill-session -t master"
TimeoutStopSec=70

[Install]
WantedBy=multi-user.target

And /etc/systemd/system/rexlcloud-wrapper.service:

[Unit]
Description=rexlCloud wrapper (console: su - cloud -c "tmux -L wrapper attach")
After=network-online.target rexlcloud-master.service
Wants=network-online.target

[Service]
Type=forking
User=cloud
WorkingDirectory=/home/cloud/wrapper
ExecStart=/usr/bin/tmux -L wrapper new-session -d -s wrapper -x 200 -y 50 /home/cloud/wrapper/start.sh
ExecStop=/bin/sh -c "tmux -L wrapper send-keys -t wrapper detach Enter; for i in $(seq 1 50); do tmux -L wrapper has-session -t wrapper 2>/dev/null || exit 0; sleep 1; done; tmux -L wrapper kill-session -t wrapper"
TimeoutStopSec=70
# The servers run in their own tmux sessions (detachedServers) and must outlive the wrapper
KillMode=process

[Install]
WantedBy=multi-user.target

KillMode=process is important for detached servers. Without it systemd stops every process the service ever started when the wrapper stops, including the servers’ tmux sessions. Without detached servers, use stop instead of detach in ExecStop.

Enable and start both:

systemctl daemon-reload
systemctl enable --now rexlcloud-master rexlcloud-wrapper

Open a console with su - cloud -c "tmux -L master attach" and leave it again with Ctrl+B, D.

6. Updates

systemctl restart rexlcloud-master updates the master; the network keeps running, and the wrappers reconnect within seconds. systemctl restart rexlcloud-wrapper updates a wrapper; with detached servers its servers stay online.

7. Firewall

Port	Who needs it
25565 and up	Players (proxies)
1234	Wrappers on other machines (master)
4343	The web panel, if you use the RestModule
25700 and up	Only the proxies; block it for everyone else

With servers and proxies on the same machine, block the server ports from outside like this (also with ip6tables):

iptables -I INPUT -p tcp --dport 25700:25999 ! -i lo -j DROP

With wrappers on several machines, allow the proxy machines’ IPs instead of dropping everything.