Note: Still trying to navigate communities here on Lemmy to replace those from Reddit. If there is a better place such a question, I would welcome the suggestion.

I’m running a Synology NAS, which uses some flavor of Linux distribution. From there, among everything else running, I have a docker container hosting a Minecraft Bedrock Server. The MCBE server is great for fun, but not so great for resource usage. To handle this, most folks setup something to schedule the server to restart.

Within Synology, there is a task scheduler where I can run a user-defined script to restart the whole container: docker restart mcbe-world

This works, but it’s a dirty reboot though. I worried about corrupting the world (which I do regularly backup). From within the Minecraft server terminal, the /stop command will gracefully shut it down.

I can’t update the container with another application, like screen, because each MCBE update means replacing the entire container (and so destroying the changes). I am looking to somehow redirect a command to the server if possible.

Using docker exec -it mcbe-world , I can execute what I want within the container.

The person here said, one can “inject commands by running the command as the appropriate account and redirecting it into the server” and they gave the example sudo su -s /bin/bash -c "echo say foobar > /run/service@name" Unfortunately, this isn’t so clear and straight forward to me.

Would anyone here be able to articulate this more clearly for me or have an idea as to how I might issue that /stop command from the Synology scheduled script BEFORE restarting the container?

Thanks!

UPDATE: Solution here: https://beehaw.org/comment/1088961

    • YEEEESSS!!! THIS!!! Thank you! I’ve been able to hobble together a script now that I have a Synology automated task calling early each morning after world backups are complete. I’m so very grateful to you all. I’ve learned a lot. A proper “stop” is being issues now which reduces the chance of world corruption which would make my family very very grumpy.

      Here’s the script just in case someone finds themselves in a similar situation as me. This is not my wheelhouse and it’s not pretty. I know it can be better, but I’ve spent too much time on this as it is and need to go fix a washing machine now. Ugh…


      #!/bin/bash
      
      # Define the countdown duration in seconds
      countdown_duration=20
      
      # Function to send a message to the Docker container
      send_cmd() {
        cmd="$1"
        sudo sh -c "echo '$cmd' | socat EXEC:'docker attach mcbe-world',pty STDIN"
      }
      
      # Announce
      announce_text="Daily server restart commencing in $countdown_duration seconds..."
      send_cmd "say $announce_text"
      
      # Perform the countdown
      for ((i = $countdown_duration; i >= 1; i--)); do
        #echo "Restaring in $i seconds"
        countdown_text="Restarting in $i seconds"
        send_cmd "say $countdown_text"
        sleep 1
      done
      
      # Gracefully shutdown server
      #  Note: stopping forces the mcbe container to restart on it's own. 
      #  Not sure why that's the case, but it's the end result I want...
      send_cmd "stop"
      

      P.S. I really need to figure out how to get the RCON solution working because that would be a more elegant way to handle things.

      P.P.S Example run (yes, the timing and spelling were updated after this screenshot 😁)

    • docker exec mcbe-world just gives access to the container so commands can be executed. /stop is a specific command for the MC server running in that container. The process is already running and I am trying to figure out how to issue a command to it… and the other comment in this post referencing “rcon” might be a solution…

      • yes, and that command I pasted will run that /stop command inside the docker container. The same way you can list files or do any other commands on a running container:

        # docker exec heimdall ls -la /
        total 148
        drwxr-xr-x   1 root root  4096 Jul 14 07:09 .
        drwxr-xr-x   1 root root  4096 Jul 14 07:09 ..
        -rwxr-xr-x   1 root root     0 Jul 14 07:09 .dockerenv
        drwxr-xr-x   1 abc  abc   4096 Jul 14 07:09 app
        drwxr-xr-x   1 root root  4096 Jun 17 15:30 bin
        drwxr-xr-x   2 root root 12288 Jun 17 15:30 command
        drwxr-xr-x   7 abc  abc   4096 Dec  3  2022 config
        drwxr-xr-x   1 abc  abc   4096 Jun 23 20:35 defaults
        drwxr-xr-x   5 root root   340 Aug 19 04:52 dev
        -rwxr--r--   1 root root 18257 Jan  1  1970 docker-mods
        drwxr-xr-x   1 root root  4096 Aug 19 04:52 etc
        drwxr-xr-x   2 root root  4096 Jun 23 20:35 heimdall
        
    • This looked so promising.

      Via SSH, I can indeed use docker attach and from within I can issue a stop for MC server. Works fine.

      However, the Synology task scheduler via DSM doesn’t seem to be able to similarly attach and then issue the stop command. I get this back via email (for when a scheduled task fails):

      Task Scheduler has completed a scheduled task.

      Task: MC Graceful Restart Start time: Tue, 29 Aug 2023 17:19:41 -0500 Stop time: Tue, 29 Aug 2023 17:19:42 -0500 Current status: 127 (Interrupted) Standard output/error:

      the input device is not a TTY /bin/bash: line 1: stop: command not found