Forge Frequently Asked Questions

Knowledge Base Server Guides
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Forge Frequently Asked Questions

How do I run Forge using: start.sh/start.bat?

No need! AMP handles all that for you. Just select the version of Forge you’ll need, hit update, and start your server.

Where do I put custom start up arguments?

You can find this options under:

Configuration → Java and Memory → Additional java options

I installed a modpack using AMP’s FTB downloader, why did it start in Vanilla? or The update manager reported a successful update, but ./Minecraft/minecraft_server.jar is missing.

This is due to the FTB download API not providing AMP proper version information when downloading modpacks.

This can be resolved by:

  1. Looking at your FTB launcher and finding the version of Forge that the modpack runs on.

  2. Select that same version in AMP:

    • Select Forge under: Configuration → Server Settings → Server Type

    • Set the version under: Configuration → Server Settings → Forge Version

      (if you don’t see the version you’re looking for, scroll down)

    • Select [Autoselect] under: Configuration → Server Settings → Server JAR

  3. Press Download/Update

  4. Start the server

Note: You may need to delete the world folder if you want modded terrain generation within the spawn chunks. (if the server had fully loaded as Vanilla)

Problem Starting an FTB Old Source Pack?

There seem to be some S3 downloadable resources missing on FTB’s end, but no worry, you’ll have your server up after following these steps:

  1. Select the modpack in AMP

  2. Install the pack files

  3. Delete the file: minecraft_server.{version}.jar

  4. Set the proper version of Forge:

    • Select Forge under: Configuration → Server Settings → Server Type

    • Set the version under: Configuration → Server Settings → Forge Version

      (if you don’t see the version you’re looking for, scroll down)

    • Select [Autoselect] under: Configuration → Server Settings → Server JAR

  5. Press Download/Update

  6. Check your Java version

  7. Start the server

How do I import a modpack into AMP?

If applicable, run the pack’s install script on your computer to generate the server files.
Follow the guide here, then:

  1. Look at your CurseForge launcher, FTB launcher, etc and find the version of Forge that the modpack runs on.

  2. Select that same version in AMP:

    • Select Forge under: Configuration → Server Settings → Server Type

    • Set the version under: Configuration → Server Settings → Forge Version

      (if you don’t see the version you’re looking for, scroll down)

    • Select [Autoselect] under: Configuration → Server Settings → Server JAR

  3. Press Download/Update

  4. Start the server

I’m getting the error: Failed to verify username!

This can usually be solved by disabling Disallow Proxied Connections, found under Configuration → Server Settings → Disallow Proxied Connections, then restarting your server.

I’m getting the error: Can't keep up! Is the server overloaded? Running 2018ms or 40 ticks behind

This is most often caused by a lack of CPU resources due to Minecraft being a primarily single threaded game, alternatively this can be caused by limited Disk I/O, but that is far less common.

Forge in general can be taxing on the CPU, and the more recent the version of Minecraft, the more CPU it requires to run smoothly. This is clearly visible with 1.18+ with the increased chunk heights, so expect some problems when running large Forge 1.18+ packs.

There are ways to mitigate this, mainly by turning down the player’s render distance to around 8 and installing server side optimization mods:

I’m getting the error: … has been compiled by a more recent version of the Java Runtime … OR … cannot access class sun.security.util.ManifestEntryVerifier (in module java.base) because module java.base does not export sun.security.util to unnamed module …

This is caused by launching Forge with the improper version of the Java Runtime. Here’s a quick reference (under Configuration → Java and Memory → Java Version):

Forge 1.8 - 1.16.4 → Java 8

Forge 1.16.5 → Java 8 & Java 11

Forge 1.17 - 1.17.1 → Java 16 to Java 17

Forge 1.18 - 1.20.4 → Java 17

Forge 1.20.5 → Java 21

You can also double check the major version numbers here.

I don’t have X version of Java installed, how do I fix that?

You have three options to choose from:

  • Manually install Java

  • Install Java using this Linux command (as root):

    bash <(wget -qO- getamp.sh) installJava

  • Java 11 on Debian/Ubuntu: sudo apt install temurin-11-jdk

  • Java 16 on Debian/Ubuntu: sudo apt install openjdk-16-jdk

  • Run the server using docker

    Linux install command (as root): bash <(wget -qO- getamp.sh) installDocker

    Full guide: Configuring AMP to use Docker for instances

Why doesn’t my Forge server work with Bungeecord/Velocity?

Default Proxy Forge compatibility is choppy at best (thank the Forge devs for that one), so you’ll most likely need to use a fork of Forge that implements the compatibility or implements Bukkit on top of Forge. There’s some examples listed below.

Note: It gets more difficult 1.13+ due to some breaking changes that Forge implemented, and some software forks have created modified Proxies along side special Client mods that try and fix the issue. (Notably Magma created a fork of Velocity and Arclight created a fork of Waterfall (Bungeecord))

How do I install plugins on a Forge server?

Normally you wouldn’t, but it is possible with enough research and patience. There is a load of trial and error involved, and the possible loss of server data. Backups are a MUST. (There are older options you can use, but I’m not well versed in those, please feel free to leave some feedback)

There’s a few options to choose from:

  • SpongeForge:

    • Download

    • Type: Sponge + Forge

    • Versions: 1.8, 1.8.9, 1.9.4, 1.10, 1.10.2, 1.11, 1.11.2, 1.12, 1.12.1, 1.12.2, 1.16.5

    • Proxy Compatibility: at least up to 1.12.2

    • Note: Installed as a Mod, not compatible with Bukkit

  • Mohist:

    • Download

    • Type: Bukkit + Forge

    • Versions: 1.7.10, 1.12.2, 1.16.5, 1.19.3

    • Proxy Compatibility: at least up to 1.12.2

  • Magma:

    • Download

    • Type: Bukkit + Forge

    • Versions: 1.12.2, 1.16.5, 1.18.2, 1.19.3

    • Proxy Compatibility: up to 1.12.2, 1.13+ with their modifications

  • Arclight:

    • Download

    • Type: Bukkit + Forge

    • Versions: 1.12.2, 1.16.5, 1.18.2, 1.19.3

    • Proxy Compatibility: up to 1.12.2, 1.13+ with their modifications

CLI server options not working with Forge 1.18+

Due to Forge and their endless wisdom, they no longer use Jar files, this prevents AMP from using it’s usual method of adding CLI args, so here’s what you need to do:

  1. Open /libraries/net/minecraftforge/forge/{your-forge-version}/<os>_args.txt
  2. Add your CLI argument and save the file.
  3. Start your server

Could not find or load main class (with Forge 1.18+)

This is a bit of an uncommon issue, and a combination of a couple things. For starters, Forge 1.18+ makes use of a newer Java language feature called “modules”. When loading with an older Java version, you may end up with the error above. Now, onto the fixes:

  1. Go to Configuration → Java and Memory → Java Version
  2. Double check that you are running Java 17 or higher
  3. If you are, and the issue still shows, switch to a different installed Java version, then switch back to Java 17. Occasionally the setting will get stuck internally, and you need to do this to kick it over.

How to run NeoForge in AMP

In most situations, Forge/NeoForge 1.20.1 are interchangeable, so you can use old Forge 1.20.1, but you’d need to switch over to Forge on every connecting client, which isn’t always straightforward/possible. Here’s how to get things rolling:

  • Import the server files into AMP using the File Manager or AMP’s built-in SFTP
  • The following steps will be under: Configuration → Server Settings
    • Set Server Type to Custom
    • Set Server JAR to either the installer or the vanilla MC .jar in the server’s folder
      (This step is to trick the Custom config into running NeoForge)
    • Set Custom startup arguments to
      -Xmx{Memory}M @libraries/net/neoforged/forge/1.20.1-47.1.76/unix_args.txt
      (Substitute 1.20.1-47.1.76 for your NeoForge version)
  • Make sure Configuration → Java and Memory → Java Version is set to Java 17 or higher
  • Start the server and you should be ready to go

Error: Can’t connect to X11 window server using ‘:0’ as the value of the DISPLAY variable

Seems to happen at random, AMP may drop the nogui CLI flag. Easy fix though:

  1. Open libraries/net/minecraftforge/forge/{forge_version}/{OS}_args.txt
  2. Add nogui to the bottom of the list of args and save the file
  3. Start the server
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