Installing a Forge, Fabric, or CurseForge modpack

A modpack is a curated bundle of Minecraft mods designed to run together. This guide covers the two ways to get one running on ServerPrism — the one-click installer and a manual upload — plus the details that trip people up: Java version and matching your client.

The golden rule: server pack and client must match

A modpack has a server side and a client side, and they must be the same pack at the same version. If your friends join with a different version, or with the client-only pack, they'll get "mod mismatch" or connection errors. Always note the exact modpack name and version you're installing so everyone installs the same one locally.

Option 1: One-click installer (easiest)

Many popular modpacks can be installed straight from the panel:

1. Open your server and look for the Modpacks tab (or Software / Modpack Installer).
2. Search for the modpack by name.
3. Select the version you want and click Install.
4. Wait for it to download and set up — large packs take a few minutes.
5. Start the server from the Console tab.

The installer picks a sensible startup command and mod loader for you. If your pack is listed here, this is by far the easiest route.

Option 2: Manual server-pack upload

If your pack isn't in the installer, install it by hand:

1. Download the server pack (not the client pack) from the modpack's page — CurseForge and Modrinth both offer server files under the Files or Additional Files section.

2. Upload the zip to your server via SFTP (recommended for large packs) or the File Manager, then extract it in the root directory. See Uploading and managing files.

3. Some packs ship a start.sh / run.bat or a unix_args.txt — you generally don't run those directly; instead point your server's startup command at the modpack's launch file.

4. On the Startup tab, set the startup command. For modern Forge this is usually:

   @libraries/net/minecraftforge/forge/<version>/unix_args.txt
   

   and for NeoForge:

   @libraries/net/neoforged/neoforge/<version>/unix_args.txt
   

5. Start the server and watch the Console for the mod-loading progress.

Pick the right Java version

Modpacks are picky about Java. Set it on the Startup tab via the Docker image / Java version selector:

If the server crashes instantly on start with a message about an unsupported class version or "requires Java X", it's almost always the wrong Java version here.

Give it enough RAM

Modpacks are heavy. A small pack needs 4 GB; large kitchen-sink packs (200+ mods) want 6–8 GB or more. If the console shows OutOfMemoryError or the server dies during world-gen, you likely need a bigger plan — see How to Upgrade or Downgrade Your Plan.

Common issues

• Instant crash / "unsupported class version": wrong Java version — fix it on the Startup tab.
• OutOfMemoryError or crash during world-gen: not enough RAM — upgrade your plan.
• Friends get "mod mismatch" / can't join: their client isn't the exact same pack + version as the server.
• Server starts but has no mods: you uploaded the client pack, or the mods landed in the wrong folder — they must be in mods/.

Still stuck? Open a support ticket with the modpack name and version and we'll get it running for you — we can even install it on your server directly so you can see how it's set up.