Troubleshooting
Common Minecraft server errors and what they mean
Server errors look terrifying and turn out to be boring. A handful of causes explain almost all of them. These are the ones that come up again and again, with what each means and what to try first.
“Failed to bind to port”
Something already owns port 25565. Nine times out of ten that something is a second copy of your own server, still running in the background after you thought you closed it. Look for a server that’s already open, or for one in the Mineshire tray icon.
Want two servers at once on purpose? Give the second a different server-port in server.properties.
“Connection timed out” and “Connection refused”
Both mean the player’s game never got through, but for different reasons. Timed out points at a router or firewall dropping the traffic. Refused is different: the machine answered, but no server was listening. Maybe it’s off. Maybe it’s on another port.
Test it in rings. Localhost on the same PC comes first, then your local address from another device, and the outside world comes last. The posts on letting friends join and on port forwarding cover each step.
“Can’t keep up! Is the server overloaded?”
The server fell behind. One message after somebody flies into brand new terrain is harmless. A steady stream isn’t, and it usually comes from view distance, too many entities or a slow processor. The lag post has the fixes.
“Outdated client” and “Outdated server”
The two sides run different versions, and the message says which one is behind. Update the player’s game, or move the server to the version your players use. Plugin servers can sometimes accept a range of versions through a helper plugin.
UnsupportedClassVersionError
A mouthful, with a short meaning: your Java is too old for this server file. Install the Java version that release asks for. Mineshire downloads the Java build each version needs, so you shouldn’t see this one there.
OutOfMemoryError
The server ate every bit of memory you gave it. Nudge -Xmx up, from 2G to 3G for example, and keep watching the graph. If it still happens at any size, suspect a leak, which more often than not is a plugin or mod. The RAM post goes deeper on picking a number.
It shuts itself down right after starting
Two usual suspects here. One: it quits instantly and leaves eula.txt behind, so open that file, change eula=false to eula=true and go again. Two: it dumps a wall of red first. Scroll right up to the top, because that first error is the real one and the rest is fallout, often from a mod or plugin made for another version.
Reading a crash without panic
Resist reading from the bottom. The first line that says ERROR or Exception usually holds the answer, so look there for a name you recognise, such as a plugin. Earlier runs sit in the logs folder, the current one is latest.log, and bad crashes leave a file in crash-reports too.
Asking for help? Paste the log as text. A screenshot of the last three lines hides exactly what people need. The console in Mineshire has a Share button for this, and the log leaves your computer only if you press it.
Quick answers
“Unknown host” means their game can’t find that address at all. Look for a typo, and check you gave them your public address and not the local one that only works at home.
The logs live in a logs folder inside the server folder, and the newest run is latest.log.