How Launching Works

A detailed walkthrough of everything YggUtils does from startup to server launch.

When you run java -jar YggUtils.jar, several things happen in sequence before your Minecraft server starts.

Startup Sequence

Meta directory

YggUtils ensures a meta/ directory exists in the working directory. This is where authlibinjector.jar is stored.

Authlib-injector check

If meta/authlibinjector.jar is not present, YggUtils downloads it automatically from the official GitHub release. If the download fails, YggUtils exits with code 1 and prints an error.

Config validation

YggUtils reads YggUtils.yml and verifies:

The file exists
Both authserver and serverfile are non-empty strings
The file named in serverfile exists on disk

See Config Validation for full behaviour on each failure case.

Server launch

YggUtils starts the server via ProcessBuilder with the following effective command:

java -javaagent:meta/authlibinjector.jar=<authserver> -jar <serverfile> nogui

The nogui flag is always appended. stderr is merged into stdout so all output flows through a single stream.

Console forwarding

A background thread reads from your stdin and writes each line to the server process's stdin, forwarding your commands in real time.

Output piping

A second background thread reads the server's stdout line by line, prints each line to your console, and appends it to YggUtils-server.log.

The Restart Loop

After launching, YggUtils blocks waiting for the server process to exit. The exit code determines what happens next:

Exit Code	Meaning	Action
`0`	Clean shutdown (`/stop`)	YggUtils exits normally
Non-zero	Crash or unexpected exit	Wait 3 seconds, then relaunch

This loop continues until a clean shutdown occurs or YggUtils itself is terminated.

YggUtils does not pass any additional JVM flags to the server process. Flags such as heap size (-Xmx) or GC tuning options set on the YggUtils invocation itself do not carry through to the spawned server process.

If you need custom JVM flags for the server, configure them at the hosting level or wrap YggUtils in a startup script that launches the server directly with those flags in addition to the agent argument.