Environment variables

This page lists every MCRS_* environment variable that the server, the client and the test tools read, with its default. The list comes from grep -rn 'MCRS_' crates src on commit 51d45c26a. The server reads 11 of the variables. The client reads many more, and most of those are knobs for performance measurements.

WIP

The tables on this page are written by hand for now. They will be generated from ServerSettings and config.rs so that they cannot drift from the code. Some names here may change, because the client knobs move into plugin fields.¹ The old MCRS_OP_LOCAL variable no longer exists. The server now gives operator rights to a player who joins from the same machine, and ops.json names all other operators.

Server

The mcrs server binary reads the variables in the table below. When a variable is not set, the server uses the default. When a value does not parse, the server writes a warning to the log and also uses the default. The code is ServerSettings::read in crates/mcrs_minecraft_server_settings/src/server_settings.rs, which src/main.rs calls.

A variable that is on or off accepts on, 1, true or yes for on, and off, 0, false or no for off, in upper or lower case. Whitespace around a value is removed before it is read.

Variable	Default	What it does
MCRS_PORT	25565	Port to listen on. The server listens on all interfaces (0.0.0.0). Allowed: 1 to 65535.
MCRS_COMPUTE_THREADS	plugin default	Size of the compute thread pool. A positive number.
MCRS_WORLD_SEED	0	World seed, signed or unsigned 64-bit. A negative seed keeps its bits, like a Java long.
MCRS_WORLD_PRESET	normal	World preset, short (flat) or namespaced (minecraft:flat), lower-cased.
MCRS_DEFAULT_GAMEMODE	creative	Game mode of a new player: survival, creative, adventure or spectator.
MCRS_MOB_AI	on	Whether mobs think. Off removes the mob brain plugin.
MCRS_LAN_ANNOUNCE	on	Whether the server announces itself on the local network. A server that listens on loopback never announces.
MCRS_COMPRESSION_THRESHOLD	256	Packet size in bytes from which packets are compressed. A negative number turns compression off.
MCRS_ACCEPT_TRANSFERS	off	Whether the server accepts players that another server transfers.
MCRS_ENABLE_STATUS	on	Whether the server answers status requests (the server list ping).
MCRS_HIDE_ONLINE_PLAYERS	off	Whether the status leaves out the names of online players. The counts stay.

No authentication

The server has no online mode yet.² It listens on 0.0.0.0:25565, and anyone who connects can use any player name. Do not open the port to the internet.

The server also reads ops.json, whitelist and ban files from the working directory. Those are files, so this table does not list them.

Client

The client binary collects every MCRS_* variable of the process and removes the prefix. The code is in crates/mcrs_minecraft_client/src/native.rs. If a name appears twice, the first value counts. When a value is bad, the native client prints it to stderr and refuses to start. The browser build takes the same names from the query string in lower case, for example ?time=6000.

A client built with singleplayer has an integrated server, and that server also reads the server variables above, such as WORLD_SEED and WORLD_PRESET.

Variable	Default	What it does	File
MCRS_SERVER	none	host:port of a server to join. Without it, a singleplayer build hosts its own server.	native.rs
MCRS_USERNAME	Player	Player name.	config.rs
MCRS_VIEW	96	Render distance in columns, 2 to 96. Wins over the options file.	config.rs
MCRS_OPTIONS	none	Path to a JSON file with fov, fov_effect_scale, smooth_light, clouds, brightness, view_distance. Unknown fields are an error.	options.rs
MCRS_FULLSCREEN	off	Take over a whole display.	config.rs
MCRS_OPEN_TO_LAN	off	The integrated server listens on every interface and announces itself. There is no authentication, so anyone on the network can join under any name.	config.rs
MCRS_GUI_SCALE	0 (auto)	Fixed GUI scale.	config.rs
MCRS_HISTORY	none	File that keeps the command history.	config.rs
MCRS_VSYNC	off	Vertical sync. Off by default so frame times stay readable.	config.rs
MCRS_OCCLUSION	on	Depth pyramid occlusion test. 0 draws every group that passes the frustum and cave graph.	config.rs
MCRS_CAVE	on	Cave graph culling.	config.rs
MCRS_CHUNK_MAP, MCRS_LIGHT_LEVELS	off	Debug overlays.	config.rs
MCRS_ASYNC	half the cores, at least 4	Threads of the async compute pool (meshing, column decode, lighting).	config.rs
MCRS_MESH, MCRS_MESH_FLIGHT	2048, 2048 (web: 32, 128)	Sections the mesher admits per frame, and how many jobs may be in flight.	config.rs
MCRS_UPLOAD	4	Upload budget per frame, in MB.	config.rs
MCRS_ARENA	192,640,512 (web: 32,208,80)	Arena sizes in MB for quads, models and faces, as quads,models,faces.	config.rs
MCRS_JAR_WORKERS	crate default	Download workers in the online test of the client jar crate.	native.rs
MCRS_CERT	none	Certificate hash for a web client joining a server. Web build only.	config.rs

Measurement knobs

The variables in this section exist so that a performance reading can be repeated. Do not set them for normal play, because some of them change on purpose what is measured. Performance and PERF.md describe the method.

Variable	Default	What it does
MCRS_HOT	off	Keeps one CPU core spinning so the performance cores do not clock down. Engine time then reads two to three times shorter. It is not a setting for players.
MCRS_GPU_HOT	none	Burns that many GPU workgroups after the frame so the GPU stays at speed.
MCRS_STATS	none	Seconds between F3 lines written to the log with the overlay hidden.
MCRS_PROBE	auto	0 leaves GPU passes untimed, 1 times every frame.
MCRS_RESOLUTION	none	Opens a window of exactly <width>x<height>.
MCRS_LATENCY	none	Swapchain images the window may run ahead by.
MCRS_MONITOR	fastest display	primary opens the window on the primary display.
MCRS_CENSUS	none	Seconds between lines that count traced columns by stage.
MCRS_TRACY_PREVIEW	off	Streams frame images to Tracy. Costs a readback per frame.
MCRS_CHUNK_GUARD, MCRS_LIGHT_GUARD	off	1 crashes the client when the player stands in a column the client does not hold, warn only logs. MCRS_LIGHT_GUARD reads the same way for light.
MCRS_GPUTRACE	none	Path for a GPU trace capture.
MCRS_RASTER	none	Fraction from 0 to 1 for the raster pass.
MCRS_DRAWS	all	Comma list of draw numbers to keep.
MCRS_SKY	all	Comma list of sky passes to draw: disc,twilight,celestial,stars,clouds.
MCRS_FLY, MCRS_TURN	none	Scripted flight speed in blocks per tick, and seconds until one turn round.
MCRS_TIME	none	Pins every clock to a tick count.
MCRS_POS, MCRS_LOOK, MCRS_SCREEN, MCRS_CURSOR	none	Start position x,y,z, view yaw,pitch, a screen (inventory) and a cursor position, for scripted captures.
MCRS_CAPTURE	none	Write one screenshot to a .png path and exit.
MCRS_SCREENSHOT_DIR	none	Directory for screenshots.
MCRS_SCENE_DIR, MCRS_SCENE_RECORD	none	Windowless scene capture directory, and a record of the vanilla client to take entities from.

The client reads all of these in crates/mcrs_minecraft_client/src/config.rs, dev/knobs.rs and scene_capture.rs.

Tests, benchmarks and build

Variable	Used by	What it does
MCRS_BLESS	tests of mesh, entity model and entity animation	When it is set, a test rewrites a stale expected file. Without it the test fails and says so.
MCRS_CLIENT_JAR	entity render test	Path to the client jar.
MCRS_VANILLA_SERVER_JAR, MCRS_SCENE_CLIENT, MCRS_SCENE_ENTITIES	scene_frames test of the client	Server jar, another client binary, and where scene entities come from: summon, record or skip (the default).
MCRS_MOLANG_CORPUS, MCRS_GPU_FUZZ_PROGRAMS	Molang tests	Path to the corpus file, and the number of fuzz programs (default 10000).
MCRS_BENCH_WORLD, MCRS_BENCH_AREA	random_ticks_save bench	A saved world directory, and <dimension> <x> <z> <radius> to load only that area.
MCRS_BIN	mob-bench/run.sh	Path to the mcrs binary. The bench sets the server variables itself.
MCRS_VANILLA_SERVER	vanilla-server/run.sh	Address of a vanilla server that the script gives to the mcrs join test.
MCRS_DRAW_ONLY, MCRS_GPU_HOT, MCRS_SPLIT_DRAW	stress_field example of entity render	Draw only full_rigs or impostors, GPU hold workgroups (default 16384), and split the draw in two passes.
MCRS_COMMIT_HASH	build time of the network crate	Commit hash that the server reports. The crate reads it with option_env! when it is built, so the value at run time does not matter.

Footnotes

1. Works#278 The decision to configure the server only through its plugin. ↩

2. WIP#82 Tracks online mode: encryption and session authentication. ↩