How to host a Minecraft modpack server: files, loader, Java, RAM and setup

What does a modpack server need?

A modpack server is the dedicated-server side of a pack your players run in their launcher. It needs six things:

• The pack's server files: the pack without the mods that only work in the game client.
• The mod loader the pack was built for, at the loader version the pack names.
• The Java version that matches the pack's Minecraft version.
• Enough RAM for the pack and for the number of players online at once.
• An accepted Minecraft EULA, in a file called eula.txt.
• An open port, 25565 by default, so players can connect.

Your players join with the client version of the same pack, at the same pack version as the server.

Server pack or client pack: which one do I use?

A client pack is what players install in their launcher. It carries mods that only work in the game client, such as shaders, minimaps and HUD mods, and those mods crash a dedicated server. A server pack is the same pack with the client-only mods already removed.

Where the pack publishes server files, use them. If it does not, start from the client pack and remove the client-only mods yourself, which is the slow part of the job.

Which mod loader does my modpack use?

The pack's page names its loader and its Minecraft version. The server has to run that same loader, at the version the pack lists, because the pack's mods are built for it.

Do not guess the loader from a pack's name or its series. Packs in the same family can use different loaders, so read it off the pack page every time.

Which Java version does a modpack server need?

Java follows the pack's Minecraft version. Mojang's version manifest lists these:

For Minecraft 1.18 and newer, Mojang's release notes state the same requirement for the server. For 1.16.5 and older, the figure is what the launcher shipped clients with, which is a strong guide for the server but not a statement Mojang made about it. A loader or a pack can also need a specific Java release the table does not show, so check the pack's own notes.

Why do client-only mods crash a dedicated server?

Some of Minecraft's code, for rendering, screens and input, exists only in the game client. Forge and NeoForge strip client-only code out of the server at load time, and when a mod reaches for it anyway the loader stops the server with a message such as invalid dist DEDICATED_SERVER. On Fabric and Quilt, a mod can declare itself client-only in its own metadata.

The fix is to remove the client-only mod from the server's mods folder. Players keep it in their own client, where it still works in multiplayer. Expect more than one: a client pack can carry many, and they tend to surface a few at a time.

How much RAM does a modpack server need?

Memory depends on the pack and on how many players are online at once. As a rule of thumb, a vanilla or light server runs fine on 2 to 4 GB, most mid-size modpacks want 6 to 8 GB, and large packs with 200 or more mods need 10 GB or more. Check the pack's own recommended memory too: a pack that asks for 8 GB will not run well in 4.

Set Java's heap, the -Xmx flag, a little below the server's total memory. Java keeps classes, buffers and its own bookkeeping outside the heap, and a heap that fills the machine gets the process killed under load.

How do I set up a modpack server myself, step by step?

1. Pick the pack version, and note its Minecraft version and loader from the pack page.
2. Download the server files if the pack publishes them. If not, start from the client pack and remove its client-only mods.
3. Install the Java version that matches the Minecraft version.
4. Install the loader's server at the version the pack names. Forge and NeoForge ship an installer that can install a server; Fabric publishes a server launcher.
5. Copy the pack's mods and config folders into the server folder, if the server files did not include them.
6. Start the server once. It creates eula.txt and shuts down. Read Mojang's EULA, then change eula=false to eula=true.
7. Set the memory with the -Xmx flag in your start command, leaving room outside the heap.
8. Open the server's port, 25565 by default (server-port in server.properties), in your firewall and router.
9. Start the server and read the log from the top. Fix the first error before the rest.
10. Back up the world before every change of pack, mod or Minecraft version.

If the server stops on its first boot, the crash message names the problem. Our troubleshooting guides cover the common ones: client-only mods, missing dependencies, Fabric mod resolution, mixin failures and out-of-memory errors.

What does MineXHost automate when you install a pack?

On MineXHost you pick a pack from CurseForge, Modrinth or FTB and install it in one click. MineXEngine, the launcher we built and run inside every server, then handles most of the steps above:

Two limits, stated plainly. First, after a crash a customer server moves a mod aside without asking only in a few narrow cases: a mod whose mods.toml file is broken, a client-only mod that crashes the server, a mod MineXEngine has shown stops the server from starting, a second copy of a mod installed twice, and the old copy of a dependency it replaces with the version another mod needs. An empty mod file is removed; every other mod it moves goes to a separate folder and can be put back. Any other crashing mod is named in your console, and what to do with it is your call. Second, not every pack boots. Our QA Lab installs public CurseForge and Modrinth modpacks on test servers running MineXEngine and records whether each one starts and answers a server-list ping. That is a measured rate, not a promise about any particular modpack, and checkout marks packs with a known problem. The test servers may also automatically remove a mod that crashes the server in cases where a customer server only names it.