Context

$ carla_server/CarlaUE4.sh --world-port=2000 -opengl

Error

LowLevelFatalError [File:Unknown] [Line: 102] 
Exception thrown: bind: Address already in use
Signal 11 caught.
Malloc Size=65538 LargeMemoryPoolOffset=65554 
CommonUnixCrashHandler: Signal=11
Malloc Size=65535 LargeMemoryPoolOffset=131119 
Malloc Size=122688 LargeMemoryPoolOffset=253824 
Engine crash handling finished; re-raising signal 11 for the default handler. Good bye.
Segmentation fault (core dumped)

Solution

$ ps -df | grep Carla
$ kil [PID]