Read the end of the log first
The last lines before the process died usually name the cause: an exception with a module, an OutOfMemoryError, or a fatal error during startup. That single excerpt is worth more than the whole file.
Distinguish a crash from a failed start. A start failure exits within seconds with a configuration or jar error; a crash happens after running, often mid-session and often repeatedly.
Memory failures
java.lang.OutOfMemoryError means the Java heap ran out. Either the allocation is too small for the workload, or something is holding memory it should release — a leak, frequently traced to a specific plugin or mod.
If it happens at a consistent point, such as during a save or when a large modpack loads, the ceiling is simply too low. If it happens after hours of uptime, suspect a leak.
Configuration and dependency failures
Malformed YAML, a bad JVM flag, or an invalid server.properties value can prevent startup outright. Paper validates its configuration and names the file and line, which makes these fast to fix.
On plugin servers, a missing library such as Vault or PlaceholderAPI produces a stack trace naming the dependency. Install it the same way you install any plugin, then restart.
Corrupt world data
Region files can be damaged by a hard kill mid-save, a full disk, or hardware faults. The symptom is a crash or exception naming a specific chunk or region file, often when a player logs in near it.
This is the failure mode backups exist for. Restore the world, then investigate the disk and the shutdown procedure so it does not repeat.
FAQ
Common questions
My server restarts on its own. Is that a crash?
Usually yes, especially if the process is managed and configured to restart. Look for a stack trace or an exit reason in the log before the restart, and check whether uptime resets at the same time.
Does a crash corrupt the world?
It can, if the process dies while writing. Most crashes leave the world intact, but a hard kill during a save is the risky case — which is why a clean stop and regular backups matter so much.
