Configurer un monde Valheim dédié pour jouer avec ses amis

Valheim server configuration is the single most important step between downloading the dedicated binary and actually playing with your crew on a stable, persistent world. Get the launch parameters, the world files or the open ports wrong, and your friends will bounce off a black loading screen instead of sailing toward the first islands. This guide breaks down exactly how a Valheim world runs behind the scenes, from naming conventions to crossplay quirks and backup habits.

Valheim Server Configuration: Launch Parameters, World Name and Password Rules

Every Valheim dedicated world is driven by a small set of command-line flags passed to start_server.sh on Linux or start_headless_server.bat on Windows. These flags define the world's identity, its network footprint and who can connect to it. Getting the Valheim server configuration right at this stage avoids most of the connection errors players report in the first ten minutes of testing.

The Core Launch Flags

./valheim_server.x86_64 -name "FlyServ Vikings" -port 2456 -world "Midgard01" -password "longjourney" -public 1 -crossplay

Each flag plays a specific role:

• -name: the display name shown in the in-game server browser. Keep it short, readable and free of special characters that some clients fail to render properly.
• -port: the base UDP port the process binds to. Valheim always reserves two additional ports above this value.
• -world: the save name used to generate (or load) the .db and .fwl files described further down.
• -password: must be at least 5 characters and cannot be identical to or contained within the world name, otherwise the process refuses to start.
• -public: set to 1 to list the world in the public browser, 0 to keep it visible only to invited players joining by IP or friends list.
• -crossplay: enables the PlayFab-based matchmaking layer required for Xbox and Steam players to meet in the same world.

World Naming and Password Rules

Avoid reusing a world name across different saves on the same machine; the game will simply load the oldest matching .fwl file it finds, which has caused more than one community to lose progress by accident. A clean naming scheme like ClanName_Season1 keeps multiple worlds and their backups easy to tell apart later.

If you would rather skip the manual binary management entirely, a preconfigured Valheim server hosting instance already applies these launch parameters through a panel, letting you focus on tuning Valknut difficulty mods and raid settings instead of babysitting startup flags.

Ports 2456-2458: Network and Firewall Setup

Valheim communicates over UDP only, and it reserves three consecutive ports starting from the value passed in -port. This is the part of Valheim server configuration that trips up the most people running the game from home, since routers and local firewalls both need to let traffic through.

Port	Protocol	Purpose
2456	UDP	Main game traffic
2457	UDP	Secondary game traffic
2458	UDP	Steam query / server browser listing

Opening the Ports on a Linux Machine

sudo ufw allow 2456:2458/udp
sudo ufw status verbose

On a home connection, you also need to forward the same UDP range on your router to the local IP address of the machine running the process, and ideally assign that machine a static local IP so the forwarding rule doesn't break after a reboot.

Crossplay and Port Behavior

When the -crossplay flag is active, Valheim relies on Microsoft's PlayFab relay service for matchmaking, which means Xbox and Steam players can often connect without manual port forwarding on either end. That said, keeping 2456-2458 open is still recommended: it improves connection stability for direct Steam joins, reduces reliance on the relay for latency-sensitive combat, and avoids fallback issues if PlayFab experiences downtime. Crossplay also requires every participant to link a Microsoft account inside Steam settings before the in-game friends list will show cross-platform invites.

World Save Files, Backups and Admin Access

Understanding where Valheim stores its data is the last piece of a solid Valheim server configuration, because it's what lets you move a world between machines, roll back after a griefing incident, or simply keep a safety copy before a big update.

File Locations

• Linux: ~/.config/unity3d/IronGate/Valheim/worlds_local/
• Windows: %USERPROFILE%\AppData\LocalLow\IronGate\Valheim\worlds_local\

Two files matter per world: WorldName.db, which holds terrain, structures and item placement, and WorldName.fwl, which stores metadata such as the seed and world key. Both files must be copied together; moving only one of them corrupts the save on load.

Backing Up Manually

tar -czf valheim_backup_$(date +%F).tar.gz \
  ~/.config/unity3d/IronGate/Valheim/worlds_local/Midgard01.db \
  ~/.config/unity3d/IronGate/Valheim/worlds_local/Midgard01.fwl

Schedule that command with cron if you manage the process yourself on a VPS, so a bad plugin update or a corrupted write never wipes out weeks of base building. If the group is running through a panel-managed instance instead, automated backups are typically handled on a schedule directly from the interface, which removes the need for manual scripting.

Admin List and Permissions

Create an adminlist.txt file next to your world data and add each trusted player's SteamID64, one per line, to grant console access for commands like ban, kick and save. Restart the process after editing the file for changes to take effect. Keeping this list short and reviewing it after every season reset is a simple habit that prevents accidental world resets or unwanted item spawning.

For a broader comparison of what's available across other survival titles, the All our game servers page lists the full catalog, and if you're managing the process yourself, the Linux VPS page covers running a dedicated process with full root access.

Keeping the Configuration Stable Over Time

A Valheim server configuration isn't a set-and-forget task. Updates to the game occasionally change default values, mod frameworks like BepInEx can conflict with launch flags, and a growing world file eventually increases load times and memory usage. Revisit your startup script after every major patch, confirm the ports are still open, and verify a recent backup exists before letting the group install new content mods.

Mod loaders in particular tend to add their own configuration files inside the BepInEx/config folder; back those up alongside the world files so a mod update doesn't silently reset balance tweaks your group agreed on. For official patch details and known launch parameter changes, check the Source maintained by the community wiki.

A correctly tuned Valheim server configuration comes down to four things: clear launch flags, a properly named and password-protected world, open UDP ports 2456-2458, and a reliable backup routine for the save files. Nail those and your group can focus on exploring Midgard instead of troubleshooting connections.

FAQ

Why does my Valheim world fail to start after changing the password?

The password must be at least 5 characters and cannot match or be contained in the world name. Check both values in your launch flags and restart the process.

Do I still need to forward ports if crossplay is enabled?

Not strictly, since PlayFab handles matchmaking, but keeping 2456-2458 UDP open improves connection stability for direct Steam joins and avoids relying solely on the relay service.

How do I move a Valheim world to a different machine?

Copy both the .db and .fwl files for that world into the matching worlds_local folder on the destination machine, then launch with the same -world name.