How to install a Minecraft modpack on your server

• Check the memory. Big packs need a lot. When you pick a pack the panel shows what the makers recommend next to what your server has. How much RAM a Minecraft server needs has the rule of thumb.
• Make a backup in the Backups tab if there is a world on the server you want to keep. A modpack usually comes with its own world settings, and modded worlds cannot be opened without the mods.
• Agree on the pack and version with your friends first. Everyone must use the same one.

Packs differ in what they are about and in how heavy they are. The kind of pack already tells you roughly what the server needs, before you look at a single mod:

When you click a pack in the Mods tab, the panel shows the memory its makers recommend next to what your server has. If the two are far apart, read how much RAM a Minecraft server needs before you install.

1. Open the Mods tab and go to CurseForge and FTB packs.
2. Search for the pack by name, for example All The Mods, Better MC or Cobblemon.
3. Pick the version you want. Choosing a version also sets the right loader and Minecraft version on your server.
4. Click Install this pack. The panel stops the server, downloads the pack's server files and installs them. Leave the page open; a big pack takes a few minutes.
5. When it says the pack is installed, start the server from the Console. The first start of a modpack is slow, often several minutes, while every mod sets itself up.

A pack only appears if its makers published a server version. Packs that are meant for singleplayer only do not show up, which saves you from installing something that cannot run on a server.

A pack can have dozens of versions, and not every one is a good choice for a server:

• Pick a release. CurseForge marks every file as Release, Beta or Alpha. Beta and alpha versions are tests and can break a world between updates.
• Pick the version your players can get. If friends already play the pack, use their version, or agree that everyone moves to the same new one.
• Look at the Minecraft version. Packs for older versions, such as 1.12.2 or 1.20.1, are often bigger and more finished, while packs for the newest version are still growing.

Some packs only offer their server files as a download on their own page, and a pack you put together yourself is in no list at all. You can still run it:

1. On the pack page, download the server files for the version you want. On CurseForge, open the Files tab of the pack, click the version and look for the server pack among its additional files.
2. Unpack the zip on your computer.
3. In Settings, under Server software, set the server type to the loader of the pack and the Minecraft version to the version of the pack, and save. Java follows the version you pick.
4. Stop the server, set an SFTP password in Files and copy the folders of the pack over SFTP: at least mods and config, plus defaultconfigs, kubejs or other folders if the pack has them.
5. Start the server and watch the Console until it says Done.

Leave the start scripts and installers that come with the pack on your computer. The panel starts the server itself, with the Java version and memory of your plan.

Unlike plugins, mods run on both sides. Every player needs the same pack at the same version in their own launcher.

1. Players install the CurseForge app, the FTB app, Prism Launcher or Modrinth, depending on where the pack lives.
2. They search the same pack and install exactly the same version as the server.
3. They start the game from that profile and join with the server address.

Join a modded Minecraft server is a page you can send to your players, with the errors they are most likely to see.

Launchers install the newest version of a pack unless you tell them otherwise, which is the most common reason a friend cannot join. Have each player check the version number against the one in the Mods tab:

A player who installed the wrong version can change it in the profile settings of most launchers, or remove the profile and install the right one. Nothing on the server is lost that way: the world lives on the server, not in the launcher.

You can also build your own set. In the Mods tab, search for a mod and install it: it lands in the mods folder, matched to your loader and Minecraft version. Restart to load it.

• Many mods need a library mod, such as Fabric API or Architectury. If the server stops at startup, the error names the missing one.
• Some mods are client only, such as minimaps or shader loaders. They do not belong on the server and can stop it from starting.
• Adding mods to a finished modpack is possible, but players must add the same ones.

A pack is made of mods, and almost every mod has settings. Where they live decides where you change them:

Open a file in Files, click Edit, save, and restart the server, because most mods only read their settings at startup. Write down every setting you change: a pack update can bring new copies of these files, and your changes are then easy to put back.

Many packs ship mods from FTB that are made for playing together, such as FTB Quests and FTB Chunks. A few things work differently than in singleplayer:

• Quests: progress in FTB Quests belongs to a team. Players who want to share progress form a team first; everyone else works through the quest book alone.
• Land claims: with FTB Chunks players claim chunks on the big map, so others cannot break or take anything there. It is the modded counterpart of a land claim plugin.
• Chunks kept loaded: the same mod can keep claimed chunks loaded while nobody is near, for farms and machines. Every loaded chunk costs the server time on every tick, so set a limit per player in its settings.
• Operators: give yourself op from the Console to use the admin parts of these mods, such as editing quests.

Pack updates can change world generation or remove items. Read the changelog, make a backup, install the new version in the Mods tab, and tell your players to update at the same moment. A player on the old version cannot join the new one.

1. Read the changelog of the new version. Look for a new Minecraft version and for mods that were removed, because their blocks and items disappear from the world.
2. Make a backup in the Backups tab.
3. Note the config files you changed yourself, as in the part on settings above.
4. Install the new version in the Mods tab, the same way as the first time.
5. Start the server and read the console. When the update moves to a new Minecraft version, the world is upgraded, and an upgraded world cannot go back without the backup.
6. Tell your players to update their launcher profile at the same moment, to the same version number.

If the update goes wrong, restore the backup: it holds the whole server folder, so the world and the old pack come back together. Restoring is covered step by step in back up and restore your server.

• A client only mod: the log names a mod and mentions a missing client class. Delete that mod from mods.
• Out of memory: the log shows OutOfMemoryError. The pack needs more RAM than the server has.
• Wrong Java: modern packs need a recent Java. Changing the Minecraft version in Settings sets the matching Java by itself; see which Java version your server needs.

Modded servers lag for other reasons than plugin servers. The usual suspects, from most to least common:

• New land being generated while players explore. Modded terrain is heavy to make, so pre-generate the area around spawn with the Chunky mod, as in pre-generate your world.
• Machines and farms in loaded chunks, especially when many chunks are kept loaded for them.
• Too many items or mobs in one place, such as a mob farm without a kill system or a farm whose items pile up on the ground.
• Too little memory, which shows as a memory graph close to the top and long pauses. Compare it with the memory the pack recommends.

The spark mod measures what takes the time on each tick and runs on Forge, NeoForge and Fabric. Reduce lag on your server explains how to read its report.

To move to another pack, make a backup and install the new pack from the Mods tab. The world is the hard part: a world from one pack rarely opens well in another, because the blocks and items of mods that are gone disappear. Most groups start a new world with the new pack.

Going back to plugins works the same way: pick Paper as the server type under Server software in Settings, and play on a new world, or on the world from before the pack restored from a backup. Change your Minecraft server seed shows how to make a fresh world.