Valheim world modifiers on a dedicated server

Valheim's world modifiers, the difficulty sliders and checkboxes on the Join World screen, can be set on a dedicated server with launch arguments. We started Linux Valheim 1.0.20 servers on our own panel with every preset and every modifier value, then read the settings each one wrote into the world. The numbers below are those settings, straight from the game, except where a column says it comes from the community wiki.

1. The launch arguments#

Dedicated servers got world modifiers in Patch 0.217.22 on 5 October 2023: "World modifiers and presets can now be set to dedicated servers using parameters in the startup batfile (see manual) or using the console as an admin." Iron Gate's dedicated server guide, which also ships beside the server as a PDF and is still current for 1.0.20, documents three arguments:

The same patch "Added -resetmodifiers startup parameter to dedicated servers". Iron Gate's guide does not list it, but the 1.0.20 server accepts it; section 6 shows what it does. Names and values are not case sensitive: Iron Gate writes the presets with capitals and its examples in lower case, and our server applied -preset Easy -modifier Raids None exactly as it applied lower case.

2. What each preset sets#

A preset is a bundle of the modifiers and keys in sections 3 and 4. This is what each preset wrote into the world on our server:

Every preset replaced what the world had before. That is Iron Gate's "overwrite any other previous modifiers" in practice: a Hardcore world started with -preset easy kept none of Hardcore's settings.

3. The five modifiers, value by value#

Each modifier value writes one or more settings into the world. We measured every value on a reset world, where a setting the value does not write stays at the game's normal 100%. The tables show what our server wrote; where a setting needs explaining, the explanation comes from the community wiki and says so.

Combat (-modifier combat veryeasy|easy|hard|veryhard), in percent of normal:

The keys behind the columns are playerdamage, enemydamage, enemyspeedsize and enemyleveluprate. The wiki notes that hard and very hard make high-level, starred enemies more likely. Its own combat table gives easy an enemy speed and size of 90; the game wrote 95.

Death penalty (-modifier deathpenalty casual|veryeasy|easy|hard|hardcore). skillreductionrate is a percentage of the normal skill loss on death. The meaning of each item key is from the wiki's list of keys:

Resources (-modifier resources muchless|less|more|muchmore|most) writes resourcerate, in percent of normal: 50, 75, 150, 200 and 300. The wiki notes that the rate applies to drops from creatures and lootable objects, that fish, trophies and boss drops do not change, and that small drops round up, so 150% often behaves like double.

Raids (-modifier raids none|muchless|less|more|muchmore) writes eventrate. A higher rate means raids come less often. The interval and chance columns were measured by the wiki, which also notes that night attacks still happen with raids set to none:

Portals (-modifier portals casual|hard|veryhard) writes one key: casual writes teleportall, hard writes nobossportals and veryhard writes noportals. In the wiki's words, casual lets everything through a portal except tamed animals, hard makes portals unavailable while a boss is active, and veryhard allows no portals at all.

4. The four keys#

Each -setkey writes a key of the same name into the world:

• -setkey nobuildcost: build pieces cost no materials. Recipes still have to be discovered.
• -setkey playerevents: raids follow each player's own boss progress rather than the server's, which suits groups at different stages.
• -setkey passivemobs: enemies do not attack until you provoke them.
• -setkey nomap: no map and no minimap for anyone on the server.

Each key is its own argument, so a server with two of them carries -setkey twice. The descriptions are the wiki's; the key names are Iron Gate's.

5. A start line with modifiers#

On a server you run yourself, the arguments go on the line that starts the server in your copy of start_server.sh (Linux) or start_headless_server.bat (Windows), after the usual name, port, world and password. Put the preset first, then the modifiers it should not undo, then the keys:

./valheim_server.x86_64 -name "Hard mode" -port 2456 -world "HardWorld" -password "secret" -preset hard -modifier resources more -modifier raids less -setkey nomap

That line gives the Hard preset, raises resources, turns raids from Hard's more down to less, and hides the map. Put -preset after the modifiers instead and the preset wins: "overwrite any other previous modifiers" is literal. Our server wrote exactly what the line asks for: Hard's combat settings, resourcerate 150, eventrate 150 in place of Hard's 60, and nomap.

A modifier after a preset follows the same rule as any change (section 6): it writes its own settings and leaves the preset's others in place. -preset hard -modifier combat veryeasy kept Hard's enemy level-up rate of 120, because very easy does not write one. Lowering raids works cleanly because every raids value writes the same eventrate key.

6. An existing world, and changing it#

Modifiers live in the world, not on the command line. On our server a start with -preset hardcore wrote Hardcore's settings into the world's metadata file (_main.N.fwl2 in the 1.0 save layout). The next start, with no modifier argument at all, logged nothing about modifiers and left every one of those settings in place. Removing an argument changes nothing: the world keeps what it was last given, and because the settings are stored in the world's own files, they travel with the world when you copy it.

Changing a modifier is where servers go wrong. A new value only writes its own settings and never removes the old value's:

• Switching values leaves settings behind. A world on combat hard that was started with -modifier combat easy took easy's damage and speed figures but kept hard's enemy level-up rate of 120, because easy does not write one.
• default does not undo a modifier. -modifier combat default logged Setting world modifier: combat->default, yet all four of hard's combat settings stayed in the world. Only the summary changed.
• Keys have no off switch. No launch argument removes nomap or nobuildcost on its own; the admin console's removekey can.

So change modifiers by starting clean. Start once with -preset normal followed by everything you want, or with a preset followed by your changes, minding the catch in section 5. -preset normal cleared every Hardcore setting before applying the modifiers after it on the line. -resetmodifiers logged Resetting world modifiers and left only the world name and seed in the metadata. If the line keeps a -preset, the world resets at every start, so changes an admin makes in the game's console last only until the next restart.

A typo does not stop the server. -modifier combat bogus -preset bogus started as usual, changed nothing, and logged Could not parse 'combat' with a value of 'bogus' as a world modifier. and Could not parse 'bogus' as a world modifier preset., so read the log after any change.

Admins can also change modifiers while the server runs. Patch 0.217.22 gave the in-game console these commands for admins on a dedicated server: setworldpreset, setworldmodifier, setkey, removekey, resetkeys and listkeys, the last of which "displays list on dedicated server". Our guide to Valheim admin lists and console commands covers getting admin rights.

7. Check the server log#

The server prints one line per preset or modifier it applied, a little before the Valheim version line and before Game server connected. These are from our server:

Setting world modifier preset: hardcore
Setting world modifier: combat->hard
Setting world modifier: resources->more
Resetting world modifiers

A -setkey argument prints nothing; its key shows only in the world file. A start with no modifier arguments prints none of these lines even when the world has modifiers, so a silent start means nothing changed, not that nothing is set. A value the server cannot read prints a Could not parse line instead. On our Linux servers the lines appeared in the console output.

Where ForgeWorld Gaming fits#

A ForgeWorld Gaming Valheim server has a World modifiers field on the Startup tab. It starts at keep: the server passes nothing, and the world keeps the modifiers it already has, which is what you want for a world you uploaded. Pick a preset (normal, casual, easy, hard, hardcore, immersive or hammer) and the server applies it at every start. Pick custom and every start resets the world to normal, then applies the Combat, Death penalty, Resources, Raids and Portals fields and the No build cost, Player-based raids, Passive enemies and No map switches. Those fields do nothing in any other mode.

Because a preset or custom resets the world at every start, the Startup tab is the whole truth: change a field, restart, and no old setting is left behind. Changes an admin makes in the game console last only until the next restart; to keep them, or a world's own settings, leave the field on keep. To change one thing about a preset, use custom with the preset's pieces from section 2: Hard with no map is custom with Combat hard, Raids more and No map on. To clear a world's modifiers once, pick normal, start the server, then set the field back to keep. The Console tab shows the Setting world modifier lines about half a minute into a start; watch it then, because later output pushes them out of the history the console keeps.

We proved this on throwaway servers on our own panel on 22 October 2026. On keep, the server's command line carried no modifier argument. With the field on hard, only -preset hard reached the server, even with custom fields filled in. With custom, the server received -preset normal followed by the chosen modifiers and switches, and Hard's settings left the world. Setting one custom field back to normal removed its setting at the next start, and keep afterwards left the world as custom had made it. The panel refused any value outside a field's list, and a server created before the change still started on its original command line. Valheim servers created from 22 October 2026 have these fields.

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