Docker + Cassandra ulimit error

I would expect you would get that warning but that Cassandra would continue to start up and run correctly. As pointed out in the other answer, Docker restricts certain operations for safety reasons. In this case, the Casssandra init script is trying to allow unlimited locked memory. Assuming you are running with swap disabled (as it is a Cassandra best practice) then you can safely ignore this error.

I run Cassandra in Docker for my development environment and also get this warning, but Cassandra starts and runs just fine. If it is not starting up, check the cassandra log files for another problem.