When the server will not start
The four failures the panel recognises, what causes them and how to fix each one.
Most failed starts come down to a handful of causes. The panel watches the console and opens a window when it recognises one — but it is worth knowing what each means.
EULA not accepted
The most common one on a brand new server, and not really an error at all. Minecraft requires you to accept Mojang's licence before it runs.
One click in the window that appears. Full details in Accepting the Minecraft EULA.
Out of memory
The server tried to use more RAM than the plan allows and was stopped. The console shows an out-of-memory error, or the server simply dies mid-sentence with exit code 137.
Common causes, in order:
- a modpack heavier than the plan can carry
- a world that has grown over months of play
- more players than the plan was sized for
- a plugin or mod with a memory leak
The fix is either a larger plan or a lighter setup. Restarting only postpones it — if a server runs out of memory every few hours, a nightly restart hides the symptom rather than solving anything.
The event is recorded in your Activity log, so you can see how often it happens.
Java version mismatch
Minecraft versions require specific Java versions, and mismatches stop the server before it starts. The console says something about an unsupported class file version, or that the server requires a newer Java.
Rough guide:
| Minecraft | Java |
|---|---|
| 1.21 and newer | 21 |
| 1.18 – 1.20 | 17 |
| 1.17 | 16 |
| 1.16 and older | 8 |
The Java tab switches versions. Modpacks are the usual exception — an older pack may need older Java even on a newer Minecraft, so check the pack's own requirements.
Engine file missing
The server jar is not where the game expects it. Almost always follows a manual upload into the wrong folder, or a half-finished install.
Reinstalling the engine from Version and engine puts it back. Take a backup first — reinstalling replaces server files.
Nothing matched, and it still will not start
Read the console from the beginning of the boot. The useful line is the first mention of an error, not the last line before it stopped. Java stack traces are long, but their first line names the cause.
Minecraft servers also have a Log analysis tab: point it at a log file and it flags known problems — missing dependencies, port conflicts, mods that failed to load. Quicker than reading a few thousand lines by hand.
If you are still stuck, open a ticket from Help centre with:
- your server ID from the header
- the first twenty lines after the error appears
- what changed just before it stopped working
That last point solves more tickets than anything else. A server that ran fine yesterday and not today usually changed in a way somebody remembers.