Question 1

Why can my friends suddenly not join my Core Keeper server?

Accepted Answer

The usual cause is that no password was set. With an empty password the server creates a brand new random one every time it starts and writes it into GameID.txt. Players join using the string ;;;, so the details everyone saved stop working after the next restart or update. Setting a password yourself makes it stable.

Question 2

Why does my Core Keeper server crash right after starting?

Accepted Answer

If the log shows a failed dlopen of steamclient.so or “InitGameServer returned false”, the Steam game-server API could not initialise. Core Keeper looks for steamclient.so in $HOME/.steam/sdk64/ and the process dies shortly after Unity finishes loading. Linking that file from the server's own linux64 folder fixes it.

Question 3

Why can nobody connect by IP address?

Accepted Answer

If the server is started without a port argument it uses the Steam relay network and refuses direct IP connections altogether. Starting it with an explicit port enables direct connections and cross-play. The game port and the port immediately above it both need to be open on UDP, because the second one is the query port.

Question 4

Does a Core Keeper server save the world automatically?

Accepted Answer

No. Core Keeper writes the world inside its shutdown handler rather than on a timer, so a server that is force-killed loses everything since the last clean stop. A graceful stop shows a WorldSave line in the log and writes the world to /worlds/.world.gzip.