Minecraft – Best method to create rare items on a minecraft server

In my opinion, your best bet here is to use Essentials' GroupManager. It's simple to set up, gives OPs all available commands and lets normal users play with basic permissions. All you have to do is download the Essentials Suite from here, paste the Jar files into your plugins directory and start the server to let it generate the default files.

Then, open plugins/GroupManager/Worlds/World/Groups.yml with your favourite text editor and tweak it a little. By default, new players will be added to the default group, which has no building permissions. If you change build: false to build: true under the info section, they'll be able to place and destroy blocks, and use a very basic set of commands.

groups:
  Default:
    default: true
    permissions:
    - essentials.help
    - essentials.helpop
    - essentials.list
    - essentials.motd
    - essentials.rules
    - essentials.spawn
    inheritance: []
    info:
      prefix: '&e'
      build: false
      suffix: ''

  ...

If you want to give your users some more freedom, change default: false to default: true for the Builder group. You can also remove some commands you don't want them to have while still conserving the other ones, such as essentials.kit and essentials.kit.tools. You can also change the group of the already existing users editing plugins/GroupManager/Worlds/World/Users.yml.

For more advanced Permission management, I'd recommend Permissions 3.x before DefaultCommands.

Edit: Here's a really useful command reference for GroupManager: forums.fragnet.net/minecraft/588-essentials-command-reference.html

This entirely depends on what the mod changes.

• If you have a mod that changes things that only the client cares about (e.g., adds realistic shadow shaders) then the client mod will work fine in multiplayer. (These will not have any effect installed on the server.)

  • A UI mod will only change clients. Installing it on the server will have no effect.

• If it changes something that only the server is responsible for managing (e.g., changing the world generator algorithm) then the client doesn't have to know about the mod at all and it can be server-only. (These will not have any effect installed on the client when playing multiplayer.)

• If it changes the world in a way that client and server must both understand (i.e., new items/blocks), then it has to be on the server and the client. (What happens if there is a mod mismatch depends on the mod.)

  • In your specific example, no, adding new blocks to your client will not let you use them on a multiplayer server. You might be able to join, or you might not. You might be able to join, but get kicked as soon as you try to use a custom block. It entirely depends on what code you change. The possible interactions are as many as there are lines of code in Minecraft that can be changed.
  • Adding a new-block mod to a server will make it incompatible with clients. This might manifest as disconnects, crashes, or client-side "ghosts". The client must have a client-side mod that matches the server-side mod.
  • A permissions mod is server-side only, but a UI mod is client-side only. To make a UI mod able to change server-side permissions, you have to have a client mod and a server mod that know how to interact with each other.

These things entirely depend on how the mod is coded. Without knowing what your mod changes, we can't even guess. More technically, where server mods start and client mods begin are a matter of what specific Java functions they change and how those functions operate as part of Minecraft's server-client architecture.