Install GregTech: New Horizons Manually

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Install GregTech: New Horizons Manually

This guide explains how to manually install GregTech: New Horizons (GTNH) on an UltraServers Minecraft server using the official Java 17–25 server pack.

Warning: This process replaces the existing server installation. Create a server backup before deleting or replacing any files.

Prerequisites

Before continuing:

Confirm that your server has at least 6 GB of RAM.

Allocate additional RAM for multiple players and later stages of progression.

Confirm that you have sufficient storage for the modpack, world, and backups.

The official GTNH server guide recommends at least 20 GB of storage.

Install the same GTNH release version on every player's client.

The GTNH version must match between the server and every client.
The client and server do not need to use the same Java version.

Log in to the UltraServers panel.
Open the server on which you want to install GTNH.
Create a server backup.
Open the Console tab and click Stop.
Wait until the server shows as offline.

Note: The official GTNH server guide recommends Java 17 or newer. This guide uses Java 25 with the Java 17–25 server pack.

Copy the Server Pack URL

Open the official GTNH downloads page.
Locate the Server ZIPs section.
Find the latest stable release for Java 17–25.
1 Right-click the download link.
2 Click Copy link address.

Important: Select a file under Server ZIPs. Do not use a Prism, MultiMC, CurseForge, or client ZIP.

Clear the Server Files

Return to the UltraServers panel.
Open the 1 Files tab.
Confirm that the server backup completed successfully.
Use the 2 selection box to select all existing files and folders.
Click 3 Delete.
Review the listed files and click 4 Move to Trash.

Note: Files moved to Trash are automatically deleted after 24 hours. Select Permanently delete immediately only when you are certain that the files are no longer needed.

Warning: Do not continue until all existing installation files have been removed from the server's root directory.

Download the Server Pack

Remain on the Files tab.
Click the 1 Download from URL button.
Paste the official GTNH server-pack URL into the 2 File URL field.
Click 3 Download.
Wait until the complete ZIP file appears in /home/container/.

Note: The archive size changes between GTNH releases. Wait until the download finishes before extracting the file.

Extract the Server Pack

1 Open the action menu for the downloaded .zip file.
Click 2 Unarchive.
Wait until the extraction finishes.
Confirm that the server root contains folders such as:

config/
libraries/
mods/
serverutilities/

Confirm that the root also contains:

java9args.txt
A JAR whose filename ends in forgePatches.jar

Move the downloaded ZIP to Trash after successful extraction if you need to recover storage space.

Note: In GTNH 2.8.4, the required server JAR is named lwjgl3ify-forgePatches.jar. The filename may change in a future release.

Find the Server JAR

Locate the file whose name ends in 1 forgePatches.jar.
Copy or note its complete filename.

For GTNH 2.8.4, the filename is:

lwjgl3ify-forgePatches.jar

Important: The filename is case-sensitive. Copy it exactly, including the .jar extension.

Configure the Server JAR

Open the 2 Startup tab.
Locate Server JAR File under Variables.
Replace server.jar with the complete 3 forgePatches.jar filename.
Click outside the field and confirm that the value saves successfully.

Note: If the current pack contains lwjgl3ify-forgePatches.jar, enter that exact filename under Server JAR File.

Configure Java

Remain on the Startup tab.
Locate Docker Image.
Select 1 Java 25.
Click outside the selector and confirm that the value saves successfully.

Note: These instructions apply to the Java 17–25 server pack. If you intentionally downloaded the Java 8 pack, do not select Java 25.

Add the Startup Flag

Locate Startup Flags under Variables.
1 Check whether the following flag is already present:

-Djava.system.class.loader=com.gtnewhorizons.retrofuturabootstrap.RfbSystemClassLoader

If the flag is missing, add one space after the existing flags.
Append the class-loader flag.
Click outside the field and confirm that the value saves successfully.
Do not add a duplicate copy of the flag.

Warning: A space must separate the class-loader flag from the preceding flag. Missing spacing creates an invalid startup command and prevents the server from starting.

Start the Server

Open the Console tab.
Click Start.
Monitor the console while the server loads.
Allow several minutes for the first startup.
Do not repeatedly restart the server while libraries and world files are loading.
Wait until the console reports that startup has completed.
Confirm that the console identifies the expected GTNH version.
Connect using a client with the same GTNH release as the server.

Note: The first startup may take longer than later startups while the server loads libraries and generates files.

Troubleshooting

Server JAR Not Found

Confirm that the forgePatches.jar file is in /home/container/.
Confirm that Server JAR File exactly matches its filename.
Check the filename for incorrect capitalization, spaces, or spelling.
Confirm that the filename includes the .jar extension.

Server Crashes on Startup

Confirm that Docker Image is set to a Java version supported by the downloaded server pack.
Confirm that the class-loader flag appears once under Startup Flags.
Confirm that a space separates the class-loader flag from the preceding flag.
Confirm that the ZIP archive extracted completely.
Check the console for memory or missing-library errors.

Players Cannot Connect

Confirm that the server and every client use the same GTNH release.
Update or reinstall mismatched clients.
Confirm that the server completed startup before connecting.

Note: Players can use different supported Java versions, but every client must use the same GTNH release as the server.

Server Runs Out of Memory

Confirm that the server has at least 6 GB of RAM.
Allocate additional RAM for more players or advanced worlds.
Stop the server before changing its plan or memory allocation.

If you require further assistance, you can open a support ticket here.

Feedback and suggestions can be submitted here or further discussed on our Discord server.

Install GregTech: New Horizons Manually
Prerequisites
Copy the Server Pack URL
Clear the Server Files
Download the Server Pack
Extract the Server Pack
Find the Server JAR
Configure the Server JAR
Configure Java
Add the Startup Flag
Start the Server
Troubleshooting
Server JAR Not Found
Server Crashes on Startup
Players Cannot Connect
Server Runs Out of Memory