A Minecraft Java server starts with “java -Xms… -Xmx… -jar server.jar”. This tool builds the full command: fixed memory (-Xms = -Xmx), the G1GC flag set recommended by the PaperMC documentation (“Aikar's flags”) and the --nogui option.
How to use the tool
Enter the name of the jar you downloaded (paper.jar, purpur.jar, fabric-server-launch.jar, server.jar…).
Choose the RAM in GB, leaving 1 to 1.5 GB free for the system (e.g. 6 GB on an 8 GB machine).
Enable Aikar's flags (recommended for Paper and forks) and, if needed, the restart loop.
Download start.sh, put it in the server folder and make it executable: chmod +x start.sh.
Run ./start.sh. On first start, accept the EULA by setting eula=true in eula.txt.
Java version and Windows equivalent
According to the PaperMC documentation, current Paper requires at least Java 25; versions 1.20 to 1.21.11 use Java 21 and 1.17 to 1.19 use Java 17. Check PaperMC's “Getting started” page for your version. On Windows, put the same command on a single line in a start.bat file (followed by “pause”).
java -Xms6G -Xmx6G -jar paper.jar --nogui
pauseFrequently asked questions
- Why is -Xms equal to -Xmx?
- PaperMC recommends setting both values equal to avoid heap resizing, and leaving roughly 1 to 1.5 GB for the OS. Aikar's flags also include -XX:+AlwaysPreTouch, which commits the memory at startup.
- Do the flags apply to Vanilla or Fabric?
- They are JVM (G1GC) options, so they work with any Java server; only the “-jar” part changes (e.g. fabric-server-launch.jar). PaperMC documents them for Paper; for other servers, test and watch GC pauses.
