rcon-cli: Always getting Error executing: <command> (null)

[Alestrix]

I assume this is a misconfiguration on my side as nobody else seems to have this issue.

I run the minecraft image with TYPE=FOLIA (I have 24 vcores available at low clock speed, so I need the multithreading) via a docker compose file. Due to client requirements (according to my son "optipac" or similar is not compatible with 1.20.2) I need to run version 1.20.1.

RCON is properly started according to the logs:

$ docker logs mc | grep RCON | grep -v "RCON Client"
*** Warning, you've not updated in a while! ***
*** Please download a new build as per instructions from https://papermc.io/downloads/paper ***
[20:12:52] [Server thread/INFO]: Thread RCON Listener started
[20:12:52] [Server thread/INFO]: RCON running on 0.0.0.0:25575

I am ignoring the warning as I have pulled and deployed this image just two days ago, so I assume it has to do with the VERSION=1.20.1.

When I try to issue an rcli command via docker exec, I get this:

$ docker exec -ti  mc rcon-cli list
Error executing: list (null)

rcon-cli is properly authenticating to the server as I get an authentication error if I run rcon-cli with --password and use an incorrect password.

The only thing I see on the console (docker logs -f mc) when I run the rcon-cli command is this:

[20:27:35] [RCON Listener #1/INFO]: Thread RCON Client /127.0.0.1 started
[20:27:35] [RCON Client /127.0.0.1 #10/INFO]: Thread RCON Client /127.0.0.1 shutting down

The same thing happens when I connect in interactive mode:

$ docker exec -ti mc rcon-cli
> /help
Error executing: /help (null)
> help
Error executing: help (null)
> list
Error executing: list (null)
> quit
Error executing: quit (null)
> :q
Error executing: :q (null)
> :quit
Error executing: :quit (null)
> ^C

Then the console shows this:

[20:34:16] [RCON Listener #1/INFO]: Thread RCON Client /127.0.0.1 started
[20:34:35] [RCON Client /127.0.0.1 #12/INFO]: Thread RCON Client /127.0.0.1 shutting down

For completeness sake here's my docker-compose:

version: "3.3"

services:
  mc:
    image: itzg/minecraft-server:stable
    ports:
    - "25567:25565"
    user: 1000:1000
    container_name: mc
    environment:
      UID: 1000
      GID: 1000
      MEMORY: 2560M
      TZ: "Europe/Berlin"
      ENABLE_ROLLING_LOGS: "true"
      USE_AIKAR_FLAGS: "true"
      MOTD: ~~redacted~~
      DIFFICULTY: "hard"
      SNOOPER_ENABLED: "false"
      PREVENT_PROXY_CONNECTIONS: "false"
      STOP_SERVER_ANNOUNCE_DELAY: 30
      GUI: "false"
      ENABLE_WHITELIST: "true"
      WHITELIST: ~~redacted~~
      RCON_PASSWORD: ~~redacted~~
      EULA: "TRUE"
      TYPE: FOLIA
      VERSION: 1.20.1
    volumes:
    - /opt/docker-mc/data:/data
    - /opt/docker-mc/mods:/mods:ro

[Alestrix]

PS: Removed all containers and images, recreated the setup with the :latest tag but still see the same issue.

[itzg]

Since the prompt is showing up, I agree with your assessment that the rcon authentication is fine. I am seeing the same problem, so I am wondering if it is a bug in Folia. What kinds of things are wanting to do via rcon? Similar to the whitelist, maybe there's non-rcon ways to achieve the equivalent.

[Alestrix]

One thing I wanted to do is just /list the currently online players to see whether I can temporarily shut down the server. Alternatively, /say a notification about the upcoming "maintenance".

I'm new to Minecraft servers, started this just two days ago so my son has one to play on with his friends. So if there are non-rcon ways of doing that (while still deploying the server through a docker compose file) I'd love to hear about this.

[itzg]

OK, those are necessary uses for rcon. A player count can at least be retrieved by exec'ing the bundled mc-monitor status.

If you haven't already, seems to be reasonable to report an issue with Folia.

I'd also recommend trying Paper server type since it's by the same people and has good optimizations already that might still be enough to squeeze out performance on your system.

[Alestrix]

Ok, according to this issue this is expected behavior as rcon is not supported in Folia. I am wondering whether this might justify a note in the docs?

[Alestrix]

Closing as resolved since this is a Folia issue as rcon is not supported by Folia.