We have now moved from a MineOS issue (MineOS version to old) to a linux os (Turnkey issue).
first off:
usually I use “java -version” and not “javac -version”. Hexparrot wrote a bit about that (and expected versions) here: Servers won’t start after Java 7 to 8 Upgrade
User tNt alsowrote about java updating in Hexparrot megathread : Megathread for MineOS webui issues