Minecraft Rock-on fails to start, update

BLUF (Bottom Line Up Front): Minecraft Server Rock-on broken due to Java version mismatch, is not updating itself. Send Help Please.

Having a bit of trouble with the Minecraft Rock-on (itgz/minecraft-server docker image). Following error message in the logs:

[init] server.properties already created, skipping
[init] log4j2.xml already created, skipping
[init] Checking for JSON files.
[init] Setting initial memory to 1G and max to 1G
[init] Starting the Minecraft server…
Error: A JNI error has occurred, please check your installation and try again
Exception in thread “main” java.lang.UnsupportedClassVersionError: net/minecraft/server/Main has been compiled by a more recent version of the Java Runtime (class file version 60.0), this version of the Java Runtime only recognizes class file versions up to 52.0

2021-06-20T14:19:34.594-0400 WARN mc-server-runner sub-process failed {“exitCode”: 1}
2021-06-20T14:19:34.594-0400 INFO mc-server-runner Done

According to the project’s page at Dockerhub, this issue was fixed a while back and all is well. Except, for me it isn’t. :frowning: The Rockstor WebUI says mc server running, but the log shows it’s restarting every so often because the container dies due to Java version mismatch, lather/rinse/repeat.

And the project page says that this was a known issue, fixed recently, and the container will automatically pull and update itself at startup. Restarting container/rock-on service/entire NAS doesn’t have any effect.

I considered uninstalling and then reinstalling to see if the newer version of the container would show up. If there’s a way to do this in the WebUI I’ve not spotted it. I know that the CLI (delete-rockon) is an option, and I’ve backed up the configuration already. Just don’t want to uninstall and then re-install a non-working container.

Sorry for the short novel, but any advice you can offer is greatly appreciated.


@KeithF Welcome to the Rockstor community.

If you first stop the Rock-on then an option to uninstall is presented. We don’t show the uninstall option unless the container is stopped. That may help. And as long as you re-install it with the exact same subvol/subvols as it’s config/data setup then you should pick-up from where you left off. At least that is the hope.

Hope that helps and let us know how you get on.

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Well, I feel smart… I didn’t notice the Uninstall button appeared until after the Rock-on is shut down. :roll_eyes:

So yes, after I shut down the Rock-on, uninstalled it, and then re-installed it…


We’re back up, running a 1.17 server and my kids are not sending me threatening messages about the sad state of non-Minecraftness on our local network… Not saying that it was almost a “24” level hostage situation here. :rofl:

Thanks for the assist, Philip - it’s greatly appreciated!