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.

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Start script generator (Aikar's flags)

Generate start.sh for Paper, Purpur, Fabric or Vanilla: RAM, Aikar's flags, --nogui, automatic restart and GC log.

Last updated: 10/9/2026

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Documentation

Server

Jar file

Exact name of the downloaded file, in the same folder as start.sh.

RAM (GB)

Leave 1 to 1.5 GB for the OS. -Xms and -Xmx get the same value.

Aikar's flags (G1GC)

Single flag set documented by PaperMC (docs.papermc.io/paper/aikars-flags).

No GUI (--nogui)

Script

Restart automatically after stop

GC log (logs/gc.log)

Java executable

Extra JVM arguments (one per line)

start.sh

Live preview — automatically saved in your browser.

#!/bin/bash
# Generated by games-tools.game-rank.com
cd "$(dirname "$0")"

java \
  -Xms6G \
  -Xmx6G \
  -XX:+UseG1GC \
  -XX:+ParallelRefProcEnabled \
  -XX:MaxGCPauseMillis=200 \
  -XX:+UnlockExperimentalVMOptions \
  -XX:+DisableExplicitGC \
  -XX:+AlwaysPreTouch \
  -XX:G1NewSizePercent=30 \
  -XX:G1MaxNewSizePercent=40 \
  -XX:G1HeapRegionSize=8M \
  -XX:G1ReservePercent=20 \
  -XX:G1HeapWastePercent=5 \
  -XX:G1MixedGCCountTarget=4 \
  -XX:InitiatingHeapOccupancyPercent=15 \
  -XX:G1MixedGCLiveThresholdPercent=90 \
  -XX:G1RSetUpdatingPauseTimePercent=5 \
  -XX:SurvivorRatio=32 \
  -XX:+PerfDisableSharedMem \
  -XX:MaxTenuringThreshold=1 \
  -Dusing.aikars.flags=https://mcflags.emc.gs \
  -Daikars.new.flags=true \
  -jar paper.jar --nogui

Server installation guideNo server yet? Install it locally or on a VPS / dedicated server, ports and firewall included.

How to use Start script generator (Aikar's flags)?

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.

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.

Read the full documentation →