Crash on Startup with v2.6.1 using Java 21, "Security Manager is deprecated"

[andrewlalis]

Your GTNH Discord Username

andrew

Your Pack Version

2.6.1

Your Server

SP

Java Version

Java 21

Type of Server

None

Your Actions

1. Downloaded the MultiMC pack at https://downloads.gtnewhorizons.com/Multi_mc_downloads/GT_New_Horizons_2.6.1_Java_17-21.zip
2. Imported to a new MMC instance.
3. Started up. Game crashed on startup and prompted me to add -Djava.system.class.loader=com.gtnewhorizons.retrofuturabootstrap.RfbSystemClassLoader jvm flag.
4. Added JVM flag and started again. Game crashes with the following error:

   Failed to start Minecraft:
   java.lang.UnsupportedOperationException: The Security Manager is deprecated and will be removed in a future release
   Exiting with -1

Crash Report

https://paste.ee/p/6hPvJ

Final Checklist

• [X] I have searched this issue tracker and there is nothing similar already. Posting on a closed issue saying the crash still exists will prompt us to investigate and reopen it once we confirm your report.
• [X] I can reproduce this crash consistently by following the exact steps I described above.
• [ ] I have asked other people and they confirm they also crash by following the exact steps I described above.

[wlhlm]

This is a drawback with MultiMC launching GTNH on java17+. Those java versions need additional arguments to be passed in, but that requires a manual step by the user on MultiMC. See point 5 in the MMC with Java 17-21 section in our Installation guide.

Alternatively, I recommand you try out PrismLauncher which doesn't need these additional setup steps.