Minecraft server keeps crashing and restarting in a loop

What is actually happening

Every hosting panel, and every start.sh wrapped in while true, restarts a dead server. None of them notice that it is dying the same way every time.

The usual shape: a mod crashes on a block or entity that is still in the world. The server restarts, loads that chunk, and crashes identically. Every 40 seconds, all night, until the disk fills with identical crash reports or your host suspends you for the restart churn.

Diagnose it in ten seconds

ls -t crash-reports/ | head -5

Open those five and compare their Caused by: lines. If they match, the server is looping and restarting it again will not help. Stop the server, fix the cause, then start it.

Compare crashes, don't count them

The naive guard — "stop after 5 restarts" — gets this wrong in both directions. It stops a server that crashed five times for five unrelated reasons, and it cheerfully allows four identical crashes first.

What actually works is a signature built from two things:

• the root cause line (the last Caused by:, or the top exception), with every run of digits replaced;
• the first non-vanilla jar in the trace.

The digit-stripping is not optional and it is the step everyone skips. The same bug reports a different index, coordinate or entity id every single time it fires — Index 42 then Index 7. Without normalising those, every crash looks unique, and a loop detector built on exact matching never fires at all.

Finding what to actually fix

Crash reports name the thing being ticked when the server died:

-- Entity being ticked --
-- Block entity being ticked --

Those sections give coordinates. Load the world in single-player, go there, and remove it — or disable that mod's spawning in its config. See ticking entity crashes.

Doing this automatically

Forge Server Doctor performs the whole procedure above — reads the report, finds the real cause under the wrappers, skips the vanilla frames, and names the mod jar. 24 failure modes, each with its fix. The free edition covers the six most common startup failures.