server.jar

server.jar
Author(s)	Mojang Studios;
Platform(s)	and other platforms that support running a JVM
Written in	Java
Latest version	Release: 26.2; Snapshot: 26.3 Snapshot 2;
Release date	June 8, 2009
Size	Only JAR: ≈ 54 MiB; With initial generated data: ≈ 114 MiB;
License	EULA
Source available	Partial
Links	Website ; Downloads 26.2; 26.3 Snapshot 2;

This feature is exclusive to Java Edition.

There is a related tutorial page for this topic!

See Tutorial:Setting up a Java Edition server.

server.jar is an executable JAR file containing the program and resources of the Java Edition server software. It is distributed by Mojang Studios and can be downloaded free of charge.

The server.jar file can be opened with a file archiving program that supports ZIP files. It contains the program and default resources shared with the client.jar, but excluding client-specific code, like rendering and audio output, GUI, models, and others; both are identical in gameplay. It is intended to host a dedicated environment for multiplayer, being able to launch a headless^[a] version of the game. The client.jar file also provides an internal server used for playing singleplayer worlds that can be opened into LAN.

The archive also contains a version.json file, which provides the game's version information, including the version ID (e.g., 26.2), data version, pack version, protocol version, and others.

Generated server directory

Upon running the server.jar, libraries from the contained META-INF directory are extracted into the working directory. This behavior can further be configured by a different main class available on the JAR file, see § Bundler options.

The following contents are generated by default when no option is specified:

"*" marks a file that is not generated until the EULA (in eula.txt) is accepted.

working directory: The working directory of the server software process.
- libraries: contains external libraries and JAR files required by the server software.
- versions/<version>/server-<version>.jar: a versioned JAR file that directly contains the game's code and resources (similar to client.jar without client-related files).
- logs: Contains logs.
  - YYYY-MM-DD-ordinal.log.gz: Rotated older log. There might be any number of these files depending on how many times the log was rotated. Same format as latest.log, but compressed with gzip.
  - latest.log: The most recent log. UTF-8 format with CRLF line endings on Windows or LF line endings on Linux and macOS.
- world*: World data directory. The name can be specified in server.properties by level-name option.
- banned-ips.json*: Specifies IP addresses that are banned from the server.
- banned-players.json*: Specifies players that are banned from the server.
- eula.txt: Contains information about the EULA applying to the server software, as well as specifying whether the user has accepted it.
- ops.json*: Specifies operator status of players.
- server-icon.png: Server icon in PNG file format with 64×64 pixels resolution, which appears for the client in their server list. Not generated automatically.
- server.jar: The server software JAR file, used to setup the working directory, and starting up the server. It must be placed in the same directory as the rest of the server files.
- server.properties: Preset configuration file used to configure most of the server's functionality.
- whitelist.json*: Specifies players that are whitelisted.

Files are generated on the first run if not present in the same directory as server.jar.

eula.txt

If an eula.txt file does not exist on startup, it is generated with default content and the program exits. The default content is as follows:

#By changing the setting below to TRUE you are indicating your agreement to our EULA (https://aka.ms/MinecraftEULA).
#[Generation time]
eula=false

Much like server.properties, it follows the .properties syntax. eula has to be set to true for the server to start.

Interface

The server software has both a command-line interface and a basic graphical user interface.

The command-line interface outputs logs to the standard output, and accepts newline delimited input from the standard input, which is executed by the server as commands (similar to being executed by command blocks, but with the highest privilege level). Running a command in the interface does not require / at the beginning of the line.

The GUI appears if the platform supports windowing and the --nogui or nogui option is not provided. It is written in Abstract Window Toolkit (AWT) and features three sections:

"Stats" which displays memory usage (graph and number percentage) and average tick time,
"Players" which displays a player list, and
"Log and chat" which displays logs and serves the same function as the command-line interface.

Command-line options

Option	Description
`--bonusChest`	Enable the bonus chest when generating a world for the first time.
`--demo`	Enable demo mode. Shows the players a demo pop-up, and players cannot break or place blocks after the 5 in-game days demo time has expired, even if they have purchased the game.
`--eraseCache`	Erase cached data like light levels and biome data, which must then be regenerated. Equivalent to the "Erase Cached Data" option of "Optimize World" in World Options on the client.
`--forceUpgrade`	Optimize the world by upgrading the level data to the latest format. Once the world is optimized, it is no longer compatible with older level formats. Equivalent to the "Optimize World" option in World Options on the client.
`--help`	Print available options without starting the server.
`--initSettings`	Initialize `server.properties` and `eula.txt` without starting the server. If either file is missing, it creates them with default values.
`--jfrProfile`	Initialize Java Flight Recorder profiler for the server. While the server is running, the profiler can be opened using an external tool or software, such as VisualVM. It enables monitoring of the server's CPU, memory, and threads usage. Additionally, it saves a `jfr` file on the `debug` folder of the `server.jar`, containing JVM and operating system events, and several Minecraft-related custom events. Further information on Commands/jfr § Usage.
`--nogui`	Disable the GUI when launching the server.
`nogui`	Legacy alias of `--nogui`.
`--pidFile <path>`	Create a text file at `path` containing the process identifier (PID) of the server process while it's running.
`--port <port>`	Specify the TCP port to use instead of the value in `server.properties`.
`--recreateRegionFiles`	Optimize the world similar to `--forceUpgrade`, but also rewrites all the chunks independently of whether they have been upgraded, creating fresh and defragmented region files.^[1] Using this option after changing `region-file-compression` in `server.properties` will recompress all region files in the new format.
`--safeMode`	Ensure the server only loads the vanilla data pack.
`--serverId <id>`	Specify the "Server Id" string used in the crash report details.
`--universe <path>`	Specify the path to the directory `level-name` in `server.properties` is relative to. If empty, it is relative to the working directory.
`--world <name>`	Specify the world name to use instead of the `level-name` value in `server.properties`.

Bundler options

The server.jar introduces an extra layer of code (called the "bundler") for extracting runtime libraries. This allows the main class to be specified at startup using system properties.

The following system properties can change the startup behavior:^[2]

bundlerMainClass: Specifies the main class to start. If not specified, the main class defined on META-INF/main-class file in the server.jar (usually net.minecraft.server.Main) is used instead. There are three available main classes:
- net.minecraft.server.Main: Used for launching the Minecraft server.
- net.minecraft.data.Main: Used as entry point for data generators^[vg].
- net.minecraft.gametest.Main: Used as an entry point for the GameTest framework, which provides its own command-line options.^[3]
- Unspecified: If no option is specified or an empty blank string ("") is entered, it results in Empty main class specified, exiting.

Before executing the main class, the JAR file automatically extracts libraries and versions folders, even for unspecified option.

bundlerRepoDir: Specifies the working directory for the resources extraction. If not specified, the current working directory is used instead.

System properties are specified like -D<property>, which property is the name defined above. They must be specified for the JVM program in the command-line, placed before -jar parameter (otherwise it will be specified for the server.jar file, which is invalid), e.g. java -DbundlerMainClass="net.minecraft.data.Main" -jar server.jar is a valid execution.

History

Java Edition Classic
server 1.2		The earliest archived version by the community (Omniarchive).
server 1.2		Server.properties options at this time include `port`, `server-name`, `max-players`, `motd`, `public`.
Java Edition Alpha
1.0.15		`server.jar` was released to the public for Survival multiplayer server.
Java Edition
1.0.0	Beta 1.9 Prerelease 4	Added `debug`, `enable-query`, `enable-rcon`, `query.port`, `rcon.password` and `rcon.port`.
1.0.0	Beta 1.9 Prerelease 4	This marked the first introduction of Query and Remote console (RCON) protocols.
1.0.1		`server.jar` was updated in a server-only release.
		Fixed `Invalid server key` error when logging in.
		Fixed `Null pointer exception` error when logging in.
1.3.1	12w18a	The server logic was separated from the client, making singleplayer effectively run an internal server.
	12w18a	Added command-line arguments: `--demo`, `--port`, `--singleplayer`, `--universe`, and `--world`. The legacy `nogui` argument remained functional.
	12w19a	Added the `--bonusChest` command-line argument.
	12w21a	Removed `server.jar` dependency in singleplayer.
1.16	20w20b	The dedicated server main class was changed from `net.minecraft.server.MinecraftServer` to `net.minecraft.server.Main`.
1.16	20w22a	Added the `--safeMode` command-line argument.
1.18	21w37a	Added the `--jfrProfile` command-line argument.
	21w39a	Changed the file structure of `server.jar`. Individual libraries are now bundled separately instead of being merged into a single archive.
		Server startup now unpacks libraries into a directory configured by the `bundlerRepoDir` property (defaults to the working directory).
		The main class can be changed using the `bundlerMainClass` property.
	1.18-pre3	Starting `server.jar` with an empty `bundlerMainClass` property now validates and extracts files, then exits.
1.20	23w06a	Added the `--pidFile` command-line argument.
1.20.2	23w31a	Removed the `--singleplayer` command-line argument.
1.20.5	24w04a	Added the `--recreateRegionFiles` command-line argument.
1.20.5	24w04a	Added the `region-file-compression` setting to server.properties.
1.21.4	24w45a	The data generator entry point (`net.minecraft.data.Main`) no longer generates the assets directory.
1.21.4	24w45a	The `--client` command-line option was removed for the data generator entry point.
1.21.5	25w03a	Added the `net.minecraft.gametest.Main` entry point for running automated game tests from `server.jar`.
1.21.5	25w03a	Added associated command-line arguments for the gametest entry point: `--help`, `--packs`, `--report`, `--tests`, `--universe`, and `--verify`.
1.21.9	25w35a	Added the Minecraft Server Management Protocol (MSMP).
	25w37a	MSMP clients must authenticate to access the API.
	25w37a	MSMP TLS is enabled by default.

Issues

Issues relating to "Server.jar", "Server jar", or "Java server" are maintained on the bug tracker. Issues should be reported and viewed there.

Notes

↑ On a headless environment without a graphical interface; if present, the server.jar will launch with a basic GUI by default, but can be disabled with --nogui option.

References

↑ "Minecraft Snapshot 24w04a" (§ Region file compression algorithm) by Java Team – Minecraft.net, January 24, 2024.
↑ "Minecraft Snapshot 21w39a" (§ Server bundling) by Adrian Östergård – Minecraft.net, September 29, 2021.
↑ "Minecraft Snapshot 25w03a" (§ Technical Changes) – Minecraft.net, January 15, 2025.