Running a modded server for friends without the headaches

A modded server for a handful of friends works when three things are true: everyone runs exactly the same mods at exactly the same versions, the server has enough memory for the mods rather than for the player count, and nobody updates anything until the group has agreed and a backup exists. The practical way to get there is to pick one modpack or one shared mod list, distribute it as a launcher profile or pack file rather than a list of links, size the server at roughly twice what the vanilla game needs, and treat every update as a small migration. Most of the pain people associate with modded servers - crashes on join, "mod mismatch" kicks, worlds that will not load after an update - comes from skipping one of those.

This post is for the small private case: four to ten people, one world, no public listing. For the security side of running other people's code, read keeping a modded server clean; for Minecraft modpacks specifically, modded Minecraft without the crashes goes deeper.

How modding works in the games friends usually pick#

Every game handles mods differently, and the difference that matters most for a group is how each friend gets the mods onto their own machine.

The memory figures are starting points for a small group with a moderate mod list, not guarantees: a single heavy mod can double them, and the honest answer for any specific pack is to start it and watch the memory graph.

The games split into two groups. In Project Zomboid, DST, Factorio and Garry's Mod, the game itself downloads the server's mods for a joining player, so the server is the source of truth and friends barely have to think. In Minecraft, Valheim and RimWorld, each player installs mods themselves, so the group needs a way to make every install identical. Almost all "it works for me but not for him" problems happen in the second group.

A modpack, or your own list#

A published modpack - a Minecraft pack from CurseForge or Modrinth, a Valheim profile someone shares - has been tested together by its author. Versions are pinned, conflicts have been found, and a server pack is often provided. For a group that wants to play rather than tinker, this is the right choice. The trade is that you take the pack as it is, and removing mods from it later can break things the author never tested.

A custom list gives the group exactly what it wants and makes you the person responsible for testing it. It works well if one person enjoys that role. Keep it small: twenty mods that are understood beat two hundred that nobody can debug. Add mods one at a time and play a session between additions, so that when something breaks you know which change did it.

Either way, pick before the world is generated. Many content mods add ores, structures or biomes that only appear in chunks generated after the mod is installed, so adding a world-generation mod in week three means walking a long way to find any of it.

Getting everyone on identical mods#

For the self-install games, the rule is: never distribute a mod list as a set of links. Distribute something that installs the exact versions in one step.

• Minecraft. Share the modpack by name and version in the CurseForge app, the Modrinth app or Prism Launcher, or export your instance as a pack file (.mrpack for Modrinth, a CurseForge zip) and send that. Everyone imports the same file, and the versions match by construction.
• Valheim. In r2modman or the Thunderstore Mod Manager, use "Export profile as code" and paste the code to the group. Each friend uses "Import profile from code". The server needs the same server-relevant mods in its BepInEx/plugins folder; Valheim mods with BepInEx covers which mods must be on both sides.
• RimWorld. Share the mod list in load order, ideally exported from a mod manager, and have everyone subscribe to the same Workshop items. The multiplayer mod checks mods on join and will refuse a mismatch; RimWorld multiplayer server covers desyncs.

For the auto-download games, the work is on the server side. Project Zomboid needs each mod in both the WorkshopItems= and Mods= lines of the server's ini, and the format of those lines changed with build 42; Project Zomboid mods and the Workshop has the details. Don't Starve Together lists Workshop IDs in dedicated_server_mods_setup.lua and enables them per shard in modoverrides.lua. Garry's Mod uses a Workshop collection, covered in Garry's Mod Workshop and FastDL.

Client-only, server-only and both

Every mod belongs in one of three places, and putting it in the wrong one is the commonest cause of a crash on start.

• Client-only - shaders, minimaps, interface tweaks, sound mods. These must not be on a dedicated server. In Minecraft especially, a client-only mod on a server often crashes it at startup because it references rendering code a server does not have.
• Server-only - backup tools, admin utilities, performance mods that only touch the simulation. Friends do not need them.
• Both - anything that adds items, blocks, creatures, recipes or rules. Same mod, same version, everyone.

Mod pages usually say which. When a page does not, assume both and test.

Installing the mods on the server#

The order is the same for every game:

1. Start the server vanilla once, so it creates its folders, and stop it.
2. Upload the server-side mods. For a Minecraft modpack, use the pack's server files if the author provides them rather than copying your client folder, which includes client-only mods. A zip uploaded through a panel file manager can usually be unpacked in place, which is faster than uploading hundreds of small files.
3. Install or select the mod loader the pack expects, at the version it expects. A modpack built for one loader version may refuse to start on another.
4. Start the server and read the log until it either finishes loading or stops. The first start of a big pack can take minutes.
5. Have one friend join before everyone does.

server/  mods/              mod .jar files, server-relevant only  config/            mod settings, generated on first start  world/    serverconfig/    per-world settings on Forge and NeoForge  user_jvm_args.txt  memory flags on Forge and NeoForge  server.properties

Mods write their settings on first start. Change settings with the server stopped, and keep a copy of config/ alongside your backups, because a world restored without its matching mod configs can behave differently.

On RE:NODE mods go in through the file manager or SFTP, archives can be unpacked in place, and there is no list of approved mods to check against. The Minecraft line is set up for Paper; a Forge, NeoForge or Fabric modpack is a different server type, so ask in a ticket before you buy for one. For the other games, the mod route is the game's own, and SFTP and the file manager has the connection details.

Sizing for mods, not for players#

On a vanilla server, memory follows players and explored world. On a modded server, memory follows the mods. A Minecraft pack with 250 mods can sit at 5 GB with one player online, and adding a fourth friend barely moves it. Factorio, Valheim and DST are much lighter, but content mods still grow memory with every new thing they add to the world.

Two points apply everywhere. First, giving a Java server all of the plan's memory as heap leaves nothing for the rest of the process; leave a margin of around 1 GB or more. How much RAM does a Minecraft server need explains why. Second, CPU matters as much as memory for modded worlds: automation mods, machines and large farms load the main thread, and that is a single core no matter how many the plan has. CPU vs RAM for game servers is the way to tell which one you are short of.

On RE:NODE a server that reaches its memory limit is stopped and restarted clean instead of swapping, so a modded server that is too small shows up as restarts rather than slow decay - and anything not yet saved is lost at that moment. Moving up a tier changes the limits of the server you already have, so the world stays where it is.

Updates without breaking the world#

This is where modded servers die. A game patch breaks mods; a mod update changes a world format; someone updates their client and can no longer join.

• Switch off automatic updates for the game and for mods. Update deliberately, as a group.
• Back up before every update, the world and the mod folder together. A world restored without the mod versions it was saved with may not load.
• Update everyone at once. Pick an evening, update the server, update the shared profile or pack, and have everyone re-import before joining.
• Never remove a content mod from a live world without checking what it adds. Blocks, items and creatures from a removed mod are typically deleted from the world on load, including everything stored in chests or machines that belonged to it.
• Wait a week after a big game patch. Mod authors need time; the first day of a major patch is when everything is broken.

When an update breaks the server anyway, roll back to the backup and wait for the mods to catch up. What to do when a mod update breaks has the diagnosis steps.

Keeping it private#

A server for friends does not need to be findable, and being unlisted removes most moderation work.

• Turn on the whitelist, or a password where the game uses one. In Minecraft that is white-list=true and enforce-whitelist=true plus whitelist add for each friend; in Valheim a password plus, if you want, a permittedlist.txt.
• Leave public listing off: -public 0 on Valheim, no listing on community browsers.
• Share the address in a private group chat, not in public channels or screenshots.
• Give the one or two friends who help run it their own panel access with only the permissions they need instead of your account. Subusers and least privilege covers how.

Download mods only from the official platforms - CurseForge, Modrinth, Thunderstore, Nexus, the Steam Workshop, the game's own portal. Re-uploads on random sites are the common source of malware in modding, and a modded server runs every mod with the server's permissions.

When it breaks#

The server crashes on startup. Read the end of the log. The usual causes, in order: a client-only mod on the server, a missing dependency (a library mod that another mod needs), the wrong loader version, or not enough memory for the pack.

A friend is kicked on join with a mod mismatch. Their mod set differs from the server's. Have them re-import the shared profile or pack rather than fixing it mod by mod.

The world loads but things are missing. A content mod was removed or failed to load. Check the log for mods that errored during loading and restore from the backup taken before the change.

It runs but gets slower over days. Modded worlds accumulate entities, machines and loaded chunks. A scheduled restart helps, and so does finding the farm or machine that is costing the most; restart schedules that help covers when a restart is masking a real problem.

Everything was fine and now nobody can join. Someone's game or launcher auto-updated. Pin versions in the launcher and agree updates as a group.

FAQ#

How much RAM does a modded server for four friends need?

For a medium Minecraft modpack, about 6-8 GB. For Valheim or Project Zomboid with a moderate mod list, around 4-6 GB. Memory follows the mod list more than the player count, so start the server, watch the memory graph during a normal session, and size from that.

Do my friends need to install the mods too?

For mods that add content or change rules, yes, at the same version. In Project Zomboid, Don't Starve Together, Factorio and Garry's Mod the game downloads them on join; in Minecraft, Valheim and RimWorld each player installs them, ideally from a shared profile or pack file.

Can I add mods to a world we already started?

Usually yes for most mods, though world-generation content only appears in newly explored areas. Removing a content mod from an existing world is the dangerous direction, because its items and blocks are typically deleted. Back up first either way.

Should a modded server update automatically?

No. Automatic updates are the main reason modded servers break overnight. Update the game and mods deliberately, after a backup, with everyone updating their client the same evening.

Is it cheaper to host a modded server at home?

If you have a spare machine with enough memory and an internet connection you can forward ports on, it can be. The costs are electricity, the machine being on whenever anyone wants to play, and your home address being the server's address. Hosting at home vs renting runs the numbers.