MCSDNotifier

systemd integration for your Minecraft Server by making calls to sd_notify(3). Adds support for:

• Proper detection when the server is fully started

• Killing the server if startup takes longer than TimeoutStartSec=

• Killing the server if it hangs (no ticks finished) for longer than WatchdogSec=. This is more reliable than the watchdog integrated in Spigot, because it is implemented outside the server process

• Killing the server if stop takes longer than TimeoutStopSec=

• Displaying a status in systemctl status:

    $ systemctl status minecraft
    ● minecraft.service - Minecraft Server
    [...]
    Status: "Running Paper git-Paper-280 (MC: 1.20.2) with 0/20 players, 6 plugins, 3 worlds, TPS avg: 20.00 20.00 20.00"
    Memory: 1.3G
    CPU: 1min 1.049s
  

  This string can be overwritten by other plugins by registering a custom StatusProvider service

Requirements

• Java 9+
• Paper 1.15.2+ (or a fork)
• libsystemd (if you are running systemd you most likely have this already)
• (Only for Servers 1.16 and older) JNA
  • Only if the plugin tells you that JNA is missing when it starts, download a copy of the latest JNA 5.x jar and put it in the classpath of the Server. For technical reasons this dependency cannot be included in the plugin

Installation

Copy the MCSDNotifier-<VERSION>.jar file into your plugins/ directory. This plugin has no configuration and saves no data.

Add these lines to your Minecraft Server systemd service unit:

Type=notify
NotifyAccess=all
TimeoutStartSec=300
# Should be at least 5 seconds higher than Spigot's watchdog timeout
WatchdogSec=70
TimeoutStopSec=120

For a full example, see minecraft.service. Remember to adjust usernames, directories and so on.

The server console can be accessed by running sudo -u minecraft -- script -c "screen -x minecraft" /dev/null.

Spigot watchdog

Since the systemd watchdog will forcefully kill the server, it is recommended to leave the Spigot watchdog enabled to try and stop the server gracefully first. In spigot.yml configure:

settings:
  timeout-time: 60
  restart-on-crash: true
  restart-script: ./should-not-exist-lksdbgqp390t2q33t3w4uj

Make sure that WatchdogSec= is at least 5 seconds higher than spigot.yml timeout-time. Leave restart-on-crash enabled, but set restart-script to a filename that does not exist. This will make the server stop if Spigot watchdog detects a hang. The systemd service will then restart the server automatically; there is no need to fiddle around with shell scripts.

Building

Needs JDK 9+ installed. To build the plugin, run:

./mvnw

This command will download a copy of Maven and use it to build the plugin. Plugin jar file is placed in target/mcsdnotifier-<VERSION>.jar.

Backlog

• Replace libsystemd/JNA backend with direct socket communication

License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this program. If not, see https://www.gnu.org/licenses/.