I am hosting a server with Kovacic's Mod installed onto it. When I enter the server, I walk far away from spawn and OP myself, yet nothing happens. I still cannot place blocks that are from the mod. The strange part is that I can break blocks and place non-mod blocks. Can someone tell me how to fix this?

I have the following mods installed:

  • Railcraft
  • treecapitator
  • armor status
  • bspkrs core
  • damage indicators
  • instant massive structures
  • animal bikes
  • flans (WW2 and modern weapons)
  • archimedes ships
  • assasiancraft
  • better title screen
  • coroutil
  • craft guide
  • mo creatures
  • elemental creepers
  • custom mod spawners
  • food plus
  • ichunutil
  • moarores
  • morph beta
  • furniture mod
  • optifine
  • reiminimap
  • weapons mod
  • weather
  • witchery
  • Why can you not place them? What happens when you try?
    – SirBenet
    Commented Mar 1, 2015 at 15:27
  • When I place blocks form the mod they appear for a split second before going away from my inventory and the world Commented Mar 1, 2015 at 15:28
  • If I'm understanding correctly, Kovacic's Minecraft is just an installer that lets you install mods onto your client. What individual mods are you using? What version of Minecraft are you using? And how have you installed these mods onto your server? (I may be wrong, but I don't think KM does this)
    – SirBenet
    Commented Mar 1, 2015 at 15:36
  • im using 1.7.10 and i put the mods in a folder in my server called mods along with in the %appdata% .minecraft mods folder. im using the following mods: Railcraft-treecapitator-armor status-bspkrs core-damage indicators-instant massive structures-animal bikes-flans (WW2 and modern weapons)-archimedes ships-assasiancraft-better title screen-coroutil-craft guide-mo creatures-elemental creepers-custom mod spawners-food plus-ichunutil-moarores-morph beta-furniture mod-optifine-reiminimap-weapons mod-weather-witchery Commented Mar 1, 2015 at 15:45
  • 1
    From your description of what's happening it sounds like you haven't installed the mods correctly server side, or have them disabled. Launch the server, does it allow you to connect with a vanilla unmodded client? Also, have you installed forge on the server? I don't think the default server recognizes or use a "Mods" folder.
    – SirBenet
    Commented Mar 1, 2015 at 16:04

1 Answer 1


The reason you can't place modded blocks is because your server isn't modded. You've placed the mods where a modded server could find them, but that's Server Modding Step #2 and you never did Server Modding Step #1: install Forge. Forge is the most important mod, since it is what allows a server to use other mods at all.

What you're seeing, is your client and your server having this conversation:

Client: I'm going to place a block now!
Server: OK! Hit me with it!
Client: There's my block! By the way, I am showing it to my player ahead of time to make the graphics run smoothly without block lag, so let me know when you've got the block placed too.
Server: OK! Oh wait, I have no idea what that is! I will make it air, OK?
Client: Oh, OK! I will make it air too. I'm taking away the block and showing my player air now. Are we cool?
Server: We are cool! Now what do you want to do next?

Your client and server are cooperating to make sure that what you see and what exists on the server are always in sync. Since the server is responsible for storing the world, it gets final say over what exists. Your modded client can try all it wants to place mod blocks, but the unmodded server will always "correct" your client and tell it that, sorry, that thing doesn't exist.

Fix this by modding your server

To fix this, you need to

  1. mod your server
  2. copy the mods to your server (this is Step #2 that you've already done)
  3. copy your mods' configuration files to the server (missing this can also make it impossible to place blocks!)

1. Mod your server

Figure out what version of Forge you have installed and go get the same-version installer from the Forge file download page. You want the link called "Installer" that matches your version.

Now run this, and from the window that pops up choose "server". This will result in a modded server .jar file that you now need to put wherever your server's normal, unmodded .jar file is living right now. (Depending on your host, you might need to rename the new .jar to match the old one, or tell a dashboard the name of the new one.) Restart your server now and make sure it comes up clean.

Congrats, you've modded the server! It now has the built-in ability to load and understand mods.

2. Copy your mods to the server

Your server needs to have an exact copy of the mods your client has, except for any mods that are client-only. For example, Optifine, MAtmos, minimap mods, and the like should never be installed on a server. (Note: Modern versions of Forge no longer need this careful separation, and now will just ignore client-side mods.)

Copy all the rest to the server's mods/ folder; you already know how that part works.

3. Copy the config files to the server

Mods use configuration files to know which options are enabled and how their blocks are stored in the world save. Any mismatch here between client and server can result in mods simply not working, mods crashing the server, or placed blocks turning into completely different blocks.

Find your config files, and place them into the server's config/ folder exactly the same way they are in your client’s files. This process mirrors how you copy your mods into the server's files.

You're done! (Re)launch your server, make sure it comes up without errors or crashes and with a lot of messages about loading your mods, and then connect with your modded client.

  • Configurations should not cause issues. Both Forge and Fabric will have the server-side config supersede the client-side ones, in this case thit will be the default options. This can be a problem with heavily config-driven mods such as Loot++, but should be fine normally.
    – Egor Hans
    Commented Mar 12, 2021 at 15:05
  • @EgorHans Is that the case now? It wasn't always, and even if Forge now takes control of config file content on the clients I'm not sure I'd trust a list of 100+ mods to not have one or two doing something weird or wrong to break that. Commented Mar 16, 2021 at 19:55
  • I very rarely play Multiplayer myself, but pretty much all Reddit and MinecraftForum seems to agree it's fine to have different config on client and server. Also, the observations from questions around here seem to indicate as well that when it comes to config, the server has the final say and differences on the client are just ignored.
    – Egor Hans
    Commented Mar 17, 2021 at 9:12
  • @EgorHans Cool, that's a definite improvement over the state of the art five years ago. Commented Mar 22, 2021 at 5:03

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