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
Check this out: https://stackoverflow.com/a/62142025
So adapted for your requirements:
echo '/stop' | socat EXEC:"docker attach mcbe-world",pty STDINYEEEESSS!!! 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 😁)
Nice, glad to help!
As for the automatic restarting, the whole Docker container exits, if the main process (specified as CMD in the Dockerfile) exits (in this case the minecraft server) and Synology probably auto-restarts the containers on exit by default.
Good to know about the main proc. I wasn’t aware. And it is indeed set to auto restart. I just hadn’t realized the stop alone would trigger that. I had figured I would need to take the additional step.
what about the minecraft rcon console? Or op’ing yourself and issuing /stop from ingame?
Ooh. I was not aware of the RCON protocol. Looking into now. This may be the exact thing I need. Thanks for the lead.
Well,RCON has not fared well. Afaik, I’ve set things up correctly but the client I’m using (mcrcon) keep returning
Error 111: Connection refused.- This post got me to direct things to the right IP which I could get with
docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' mcbe-world. - docker port mcbe-world shows that the rcon port is open
- the server.properties files for the mc server has the relevant rcon lines
- This post got me to direct things to the right IP which I could get with
just run
docker exec mcbe-world /stopthen just wait a bit till it shuts down cleanly and then start it again…AFAIK /stop is not just a shell command, it needs to be given to stdin of the minecraft process. The broader question here is how to pass something to stdin of a running process.
docker exec mcbe-worldjust gives access to the container so commands can be executed./stopis 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
Are you able to
docker attachto the container?This looked so promising.
Via SSH, I can indeed use
docker attachand from within I can issue astopfor 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
If you aren’t starting your container with the
-itoptions (fordocker run), try setting them so that it allocates a tty. The fact that it works with SSH however makes me think that perhaps the Synology task runner can’t run interactive commands likedocker attachbecause it has no stdin. In that case you’ll need to do something like this: https://serverfault.com/questions/885765/how-to-send-text-to-stdin-of-docker-container/947763#947763 to pipe the stop command into the stdin of the bedrock server.If you aren’t starting your container with the
-itoptions, try setting it so that it allocates a tty. The fact that it works with SSH however makes me think that perhaps the Synology task runner can’t run interactive commands likedocker attachbecause it has no stdin. In that case you’ll need to do something like this: https://serverfault.com/questions/885765/how-to-send-text-to-stdin-of-docker-container/947763#947763 to pipe the stop command into the stdin of the bedrock server.
