Frequently Asked Questions
All iris questions that we can think of will be put here
There is a table of contents on the right

When to update Iris

Updating Iris is not like any other plugin. To draw a comparison between Iris and Mojang - When you update your server's Minecraft version, it will result in any new chunk that is generated to not be aligned with existing chunks, in every vanilla world.
Iris generates worlds for you as well, so it has the same problem. The difference is that Iris updates a lot, and Mojang barely, which makes users think it is safe to update, when in reality, it may do more harm.

So, when should you update Iris?

You should only update Iris when you are ready to delete all Iris worlds. If you are even thinking about updating Iris in any other case, contact support to discuss it first.
Always Make Backups FIRST
If you are sure you want to update Iris, see Updating the Overworld.

PaperMC warnings

In order to prevent PaperMC from spamming a lot of warnings during the creation of your world (which are harmless and useless), you can add the following settings to your paper.yml configuration, replacing the existing configuration:
early-warning-every: 5000000
early-warning-delay: 10000000

Timed Out during world creation

Servers kick players after a certain amount of time. You can increase this time replacing the timeout-time setting the following value in */spigot.yml.
timeout-time: 60000
You need to replace the existing setting, not add this as a new one.

Pterodactyl server crash (RAM)

Pterodactyl is known for shutting down servers that are using full RAM, like what happens when creating an Iris world, or pregenerating one. To resolve this issue there are two steps you can take, both involve setting the startup flags.
-XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1HeapWastePercent=7 -XX:G1NewSizePercent=15 -XX:G1MaxNewSizePercent=40 -jar server.jar
Make sure to set server.jar to your actual jar file (see the end of the flags)
If that does not work, try these:
-XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags= -Dterminal.jline=false -Dterminal.ansi=true -jar server.jar
Again, you need to set server.jar to your actual jar file (see the end of the flags)

Restart after downloading a pack

This is related to the requirement that Datapacks are already installed upon server startup, while Iris is not ready before startup. Iris uses Datapacks to make amazingly colored biomes such as the Sakura biome:
Iris' Sakura Forest
The intention is for your server to be able to provide all of the custom colors that Iris has to offer, in the generator. If you do not want this feature in your world, remove the Custom-Derivatives section from each of the biomes in the pack.

Why is it unsafe to update Iris?

Iris undergoes many changes to the generator. This means that in a lot of cases the terrain generation changes significantly. Even slight changes in the seed of the generation causes vast differences around the edges of existing chunks, when they are supposed to nicely flow into new chunks.
You might wonder why we do not simply blend the biomes:
To answer this, a quote from our lead developer: "Generally its not possible to do something like that without ending up with hard borders / having to edit millions of chunks possibly. By changing the biome map, everything changes. Things that were a desert are now a forest. I could blend it by using an interpolator, but... ignoring the intense CPU [required for] that, it would still look terrible, because it would still look like a wall, just smoother, and the biomes would still be hard-cut. Just update when your ready to make a new map, its not a big issue 😛
If you are or know a developer that would be willing to add this to Iris in a relatively effective (efficient) way that is also maintainable and scalable, feel free to make a PR to the Iris repository.

Red logo on startup

The broken console logo
Set in the settings.json Configuration -> General -> useConsoleCustomColors to false
The fixed console logo

"NoClassDefFoundError: io/papermc/lib/PaperLib"

Instead of using gradlew build or the task > build > build task, use gradlew shadowJar or the tasks > shadow > shadowJar task when building the plugin.

Unsupported plugins

There are a few plugins that mess too much with Iris' content and (soft) dependencies. We try to ensure smooth cooperation with most plugins, but these cross a line, unfortunately.

Unsupported plugins:

  • Ultra Regions
  • Region Manager
  • Plugman
  • Hotplug
  • Any other WorldGenerator that takes over chunk generation uninstructed (EWG, RWG, DWG do not work. Terra may work.)

Uninstalling Iris

There are many things Iris controls which will break when you uninstall the plugin. A lot of these features may cause issues in survival servers so we strongly recommend keeping Iris installed.
Features that are likely to break:
  • Strongholds cannot be found with eyes of ender: Iris allows you to directly control how many strongholds can spawn and how far apart they are. Because we don't follow the same method as vanilla, eyes of ender require Iris to be installed to lead to the correct locations. If you uninstall Iris, eyes of ender will lead to locations where there is nothing (where vanilla would place one)
  • No mob and animal spawns: Iris does not spawn mobs when it generates chunks, but instead has its own spawning system to evenly distribute mobs/animals over the entire server. These mobs will no longer spawn, and mobs that spawn in structures like silverfish and guardians will also no longer spawn.
  • New chunks will not be custom: New chunks will be normal vanilla chunks which do not align properly with existing chunks. Removing these manually can be difficult if you wish to amend it.
  • Custom particle & sound effects will disappear: There are custom particles & sound effects which will no longer be (dis)played and replaced by (boring) vanilla equivalents. Iris uses these to add biome immersion, and all of this would be removed.
  • Custom leaf decay systems: Iris spawns custom trees which have leaves which are too far away from logs without them decaying. Iris controls leaf decay systems and uninstalling the plugin may result in leaves being removed where they shouldn't.
If you decide to uninstall Iris because of issues with server performance (Iris seems to be causing lag), please contact support first, so we can search for a solution. We would then love to see a timings report, /timings report.

RandomTP / Wild Plugin with Iris

There are many wild and RandomTP plugins out there, but most actively generate chunks. The plugin we recommend since it works best in combination with Iris is the one linked below:
Other plugins may work as well, but this one has been tested by our staff and seems to work well with Iris.

Broken JSON file configuration

  • Delete the */plugins/Iris/packs/overworld folder
  • Restart. If there is still an error, please contact support.

Biomes larger / smaller

Diagram of Dimension settings' effects
In this diagram, you see what settings affect biome sizes. To make biomes larger, you can increase the zoom on the region's specific biomes here, which will make the collection of biomes that are in a category larger. You can also change all biome & region sizes to be larger, this setting is found here.

Reduce object spawn chance

To reduce the number of times an object spawns in a single area, follow the following steps:
1. Find the name of the object by getting an Object Dust with /iris object dust and clicking the object. Remember this name, we need it in step 4.
2. Find the name of the biome by running /iris find
3. Open the configuration file for the biome by locating it in the */plugins/iris/packs/overworld/biomes folder. Each of the folders in there is for one region. The name of the region is included in the name of the biome. Open the biome file. (If you are in a studio world, you can use /iris studio editbiome to directly open the file)
4. Find the "objects" section, which looks similar to the following (more or fewer settings may be present)
"objects": [
"place": [
"chance": 0.1,
"density": 2,
"mode": "MIN_HEIGHT"
In here, there are 2 options to take into account, chance and density.
Chance dictates the fractional chance of an object spawning per chunk, if it is 0.1, it has a 1 in 10 or 10% chance of spawning. You can decrease this number to decrease the number of times it spawns.
Density dictates the number of times the object spawns if the chance roll was successful. So, for example, if the 10% chance of the example is successful, there are going to be 2 objects of the objects included in the place list, in that chunk. You can decrease this number to see less clusters of objects spawning.
Another option is to remove one or more of the objects from the list under place, this will remove that object from the biome entirely. Note: Do not remove all objects from the list. Instead, set the chance to 0.

"Unable to find spawn biome"

We honestly do not know. It happens often when creating vanilla worlds with a world manager as well. We have never heard of a case where it is harmful in any way, so we presume it is safe to ignore.


We offer support on our Discord. Ask questions you cannot answer using the Wiki there. We ask you to look on the wiki for a solution for your issue before going there. Thank you for using Iris!
  • The Volmit Software Team
Last modified 11d ago