Minecraft server daemon

Overview

minecraftd is a daemon that hosts a Java Virtual Machine to run a Minecraft server instance. Its notable features include:

• Support for being run as a systemd service, although nothing prevents it from being run as a SysV-style service.
• Exposes a D-Bus interface on the system bus to allow management of the server instance via any D-Bus client.

Why minecraftd?

Java applications typically do not lend themselves to being run as “normal” service processes, and Minecraft is no exception, with its control channel being standard input (or rcon). This has resulted in solutions such as using GNU Screen to manage the lifecycle of the process, and still allow “keyboard” input to be sent to the server console.

Additionally, because all Java applications are run using the java executable, process identification in tools such as top and ps become much harder when multiple Java processes are running simultaneously on a host.

minecraftd addresses both of these concerns. It overrides the process' standard input to a POSIX pipe, which the D-Bus interface writes to when its methods are called. This allows D-Bus clients in other processes to communicate with the Minecraft server console. And because minecraftd is an executable, it will show up in process listings as minecraftd, simplyifying identification of the process.

How does it work?

At the most basic level, minecraftd performs the same task as running java -jar minecraft_server.jar. It uses a combination of runtime dynamic linking and the Java Invocation API to create an instance of the JVM, and executes the Minecraft server code contained in the JAR using that JVM.

In addition to that, it registers a D-Bus interface on the system bus, granting D-Bus clients in the system the ability to communicate with the Minecraft server, e.g. sending it the stop command to shutdown the server.

Configuration

Configuration of minecraftd, and the JVM it hosts, is driven by the contents of the minecraftd.conf file. An example configuration enabling use of the concurrent mark-and-sweep garbage collector in the JVM is given below:

jvm: {
	arguments = [
		"-XX:+UseConcMarkSweepGC"
	];
};

The syntax of the configuration file is that of the libconfig library.

D-Bus Interface

minecraftd's D-Bus interface is registered on the system bus with the following values:

The Minecraftd1 interface consists of the following methods: