Playing co-op

On this page

What co-op is here
What you need
Two players, step by step
Three or more players
Mods in co-op
Leaving
When something does not work

This page shows you how to play Elden Ring with friends, with mods, through the engine. You type a few commands in a terminal. Every command appears below, ready to copy.

What co-op is here
What you need
Connecting: LAN or VPN (ZeroTier, Tailscale; a separate page)
Two players, step by step
Three or more players
Mods in co-op
Leaving
When something does not work

What co-op is here

Two or more players share one world. The game's traffic travels directly between your machines, peer to peer. No FromSoftware server takes part, and Easy Anti-Cheat never runs. Before you start in the install guide has the safety rules; read them first.

Co-op is new. Sessions of up to three players have been tested.

What works

Players. Each player's character appears and moves in the others' games.
Enemies. Every player sees and fights the host's enemies, in the same places, and the enemies attack every player.
Fog-wall bosses. One boss appears on every screen, and every player sees it die. Confirmed on Margit.
Sites of grace. Host and joiners can rest.
Deaths. A player who dies respawns and stays in the session, and the others see them again. When the host dies, damaged enemies keep their damage and the time of day does not jump.
Spectating a boss fight. A player who dies in a fog-wall boss fight watches a survivor instead of respawning. Page Down switches between survivors. The dead respawn at the grace when the boss dies or everyone is down.

What does not work yet

World progress is not shared. The game records events such as a boss kill as flags, and the engine does not sync flags. A joiner's save does not record a boss the host's world killed.
Torrent. Riding does not work in a session: the rider is thrown off at once.
Giving up while spectating. A dead player waits for the fight to end.

What you need

Every player needs:

The engine installed. Follow the install guide. The commands below use ./ermod-engine, typed in the directory you unpacked it into, as the install guide does.
Game build 2.7.0.0 or 2.7.1.0. Co-op works on these builds only. To check yours:
```
./ermod-engine check-build
```
The same engine release. ./ermod-engine --version prints yours. Compare the first line with your friends'.
A character. The engine reads your Steam ID from your save, so play once through Steam if you never have.

These must match between players. The engine checks the game build (above) and game-changing mods (Mods in co-op). It does not yet check the rest, so a mismatch shows up as strange behaviour rather than a refusal:

Shadow of the Erdtree: every player has it installed, or nobody does.
A modded regulation.bin: every player loads the same file with --regulation, or nobody loads one. See deploy.md.

Your machines must reach each other on UDP port 7777: the same home network (LAN), or a VPN such as ZeroTier or Tailscale for friends elsewhere. network.md sets this up step by step, firewall included.

Each player needs a different Steam account. Two machines signed in to one account can still play together: give one of them --as and a Steam ID that nobody in the session uses, for example --as 76561198000000009. See Same Steam ID on two machines.

Two players, step by step

One player hosts; the other joins. The host goes first, every time.

1. Both players: swap IDs

Both of you run:

./ermod-engine coop id

It prints your Steam ID, your addresses, and the line a friend types to join you. For example (your numbers will differ):

Steam ID   76561198000000001   (from the folder the game keeps your own save in)
Address    192.168.1.10   (enp5s0)
           100.101.102.103   (tailscale0)
Port       7777 (UDP)

A friend joins you with:
  ermod-engine coop join 76561198000000001@192.168.1.10
  ermod-engine coop join 76561198000000001@100.101.102.103
(the address on the network you share with them)
Host first: run `ermod-engine coop host`, load into your world, then they join.

The host sends its friend the coop join line for the network they share: the home network's address, or the VPN's address. Each address shows its interface in brackets; network.md shows how to tell the VPN's apart (a VPN can hand out 192.168.… addresses too).

2. The host starts

./ermod-engine coop host

The game starts. At the title screen, press Continue (or load the character you want). Once your world loads, the command sets up the session. Wait for you are hosting. The terminal shows, abridged:

info: coop: your Steam ID is 76561198000000001 (from the folder the game keeps your own save in)
info: coop: [1/4] launch the game
info: coop: [2/4] wait for a loaded world: at the title screen, press Continue
info: coop: the game is at the title screen. Press Continue (or load the character you want to play); the co-op steps follow once you are in the world.
info: coop: the world is loaded
info: coop: [3/4] repoint the game's networking at UDP and fabricate the co-op lobby
info: coop: [4/4] host the session (the game's own CreateSession); joiners announce themselves when they join
info: coop: you are hosting. Your friends can join now, one at a time: ...
info: coop: this command ends when the game does.

The host does not type the friend's address. The host's game learns it when the friend joins.

3. The friend joins

Only after the host sees you are hosting, the friend types the line the host sent, with ./ in front:

./ermod-engine coop join 76561198000000001@192.168.1.10

Press Continue at the title screen as the host did. The terminal ends with, abridged:

info: coop: [4/4] announce this machine to its peers and join the host's session
info: coop: joined — the host answered and admitted you. Its world loads for you when the game's own join completes.
info: coop: this command ends when the game does.

joined appears only once the host has admitted you. It may also print the host knows you are here. The join waits until your game-changing mods match the host's. If your mods already match, the join starts by itself a moment later. If they differ, see Mods in co-op.

If the host has set coop_join_approval = "ask" in its engine.cfg, the host sees co-op: player … wants to join and chooses Allow or Refuse in the ermod menu. Your game does not start joining until the host allows you, so there is no hurry. If the host refuses, the terminal says the host (…) refused this machine. If nothing is decided within 15 minutes it says not joined and why: the host never answered, your mods still differ, or the host has not allowed you yet.

Leave the terminal open while you play.

4. Meet up

There is nothing to do: you arrive beside the host. Before your game starts, coop join asks the host where it stands, and loads your character right there, the way a summon arrives at the host. Your own respawn grace does not change, so if you die you get up at your grace, not at the host.

The host must be in its world when you join. If the host is on Torrent, coop join says so and waits up to 90 seconds for it to get off. If the host does not answer within a few seconds, you load where your own save stands and the log says why. Both players need an engine with this change (see the changelog).

Three or more players

The host still names nobody. Each joiner names the host and every player who joined before it, in any order after the host. Join one at a time.

# Friend 1 joins the host:
./ermod-engine coop join 76561198000000001@192.168.1.10

# Friend 2 joins the host and names friend 1:
./ermod-engine coop join 76561198000000001@192.168.1.10 76561198000000002@192.168.1.11

Friend 1 learns friend 2 when friend 2 joins. A session holds at most five players: the host and four joiners.

If a player uses a port other than 7777 (--port), the others add it to that player's address: 76561198000000002@192.168.1.11:7790.

Mods in co-op

Mods that change the game (a game rule, or a param such as a class's starting level) must match between players. Mods that only draw, monitor or log may differ.

The host's mods are the session's. A joiner whose game-changing mods differ from the host's is held at the door. Open the ermod menu with ` (backtick). It lists the host's mods, downloaded for you, each with an Enable button, and a Switch off button for each of yours the host does not run. Match the host and you join by yourself. Nothing is written to your mods directory until you press Enable.

The README's In the game section has the menu's keys.

By default the host admits everyone whose mods match. With coop_join_approval = "ask" in the host's engine.cfg, the host chooses Allow or Refuse in the ermod menu for each player instead. Once you are in, a mod that would change the game differently from the host's cannot be loaded until you leave.

Leaving

Quit the game. The coop command ends when the game does.
Or press Leave in the co-op section of the ermod menu. It ends co-op in the running game.
Or run ./ermod-engine coop leave from another terminal. It does the same.

On leaving, every other player's game removes you and your character at once, and you keep playing alone in your own world. A player whose game crashes cannot say goodbye: the others drop that player after 45 seconds of silence.

The game signs in to co-op once per launch, as it loads your world. To play co-op again, quit the game and run coop host or coop join again.

When something does not work

The terminal says what went wrong on a line starting error: coop:. The common cases:

The joiner started before the host

coop join needs a host that is already hosting. A joiner that reaches its world first gets no session, and cannot get one later. The terminal says the join is waiting, and it waits forever. Quit the game on the joiner, wait for the host's you are hosting, and run coop join again.

Wrong game build

Co-op needs build 2.7.0.0 or 2.7.1.0 on every machine. On another build the ermod menu's co-op section says not available for this game build, and the coop command stops with an error. Run ./ermod-engine check-build and update the game through Steam.

If a game patch is newer than your engine, you can try co-op anyway with --ignore-build-guard (engine releases after v0.2.0):

./ermod-engine coop host --ignore-build-guard
./ermod-engine coop join <host-id>@<host-ip> --ignore-build-guard

This runs co-op with addresses that were not checked against your game. Expect crashes, and wrong reads or writes to the characters in your modded profile; your own save is still never opened. Every player needs the same game build, the same engine release, and the flag. See When something does not work.

Mods do not match

The joiner's terminal says:

info: coop: the host knows you are here. The join waits until your game-changing mods match the host's: open the ermod menu (`), enable the host's mods it lists, and the join starts by itself

The host's menu says co-op: 1 peer(s) waiting to match your game-changing mods. The joiner enables what the menu lists; see Mods in co-op. A download that reads download failed (bytes did not match) did not arrive intact.

The friend never shows up

The host's menu still says 1 in the lobby, and no peer waits on mods. The host never heard from the friend. Check, in order:

The friend typed the host's address on the network they share (coop id lists them all), and the ID exactly.
Both machines are on the same LAN or the same VPN network.
No firewall blocks UDP port 7777 on either machine (network.md).
The host was hosting before the friend loaded its world.

Then quit the game on the joiner and run coop join again.

Same Steam ID on two machines

error: coop: two players have the same Steam ID. Two machines on one Steam account must be told apart: run one of them with --as <another SteamID64> (any one nobody here uses).

Add --as to one machine's command, and give the others that ID in place of its own:

./ermod-engine coop join 76561198000000001@192.168.1.10 --as 76561198000000009

The game sits on a loading screen after you join

The terminal says your game has sat on a loading screen for about 30 s since the join. This is a known hang: the game moves to another map, for example after you warp to the host's grace, and the load stalls. It sometimes clears on its own after a short wait. If it does not, quit the game, run coop join again, and send ermod-runtime.log with your bug report (./ermod-engine paths says where it is).

Other messages

Message	What to do
`the game is already running`	`coop` starts the game itself. Quit the game and run the command again.
`cannot tell this machine's Steam ID`	No save of yours exists yet. Play once through Steam, or give an ID with `--as`.
`a player is <SteamID64>@<a.b.c.d>…`	The ID or address is mistyped. Copy the line `coop id` printed.
`no world within 15 minutes`	The game sat at the title screen. Run the command again and press Continue.
`the game is still running, without co-op`	A step failed; the lines above say which. Quit the game and try again.

The logs

./ermod-engine paths

prints where the logs are, on the two log lines. ermod-runtime.log records what co-op did in the game; on the host, a line with learned peer means a friend's join arrived. Include both logs and ./ermod-engine --version in a bug report.

When the two screens disagree (an enemy alive on one and dead on the other, a player in the wrong place, an enemy standing frozen), run examples/coop_trace.lua on every machine. The host's overlay then shows each player's view side by side, with the enemies they disagree on, and its log records every machine's view. Attach the host's ermod-runtime.log from such a session. The install guide's When something does not work covers problems outside co-op.