Failed to set ulimit inside docker container

I made a ubuntu image with a new custom call "user" and then I create a container with the following command

 sudo docker run -u=user -ti test1 /bin/bash

      

        
        
        
      

    

I check that there are only two processes

user@1bc12c468f29:/$ ps
  PID TTY          TIME CMD
   1 ?        00:00:00 bash
   12 ?        00:00:00 ps

      

        
        
        
      

    

But after I installed

ulimit -u 10

      

        
        
        
      

    

I cannot create any new process, not even ls

user@1bc12c468f29:/$ ulimit -u 10
user@1bc12c468f29:/$ ls
bash: fork: retry: No child processes
bash: fork: retry: No child processes
bash: fork: retry: No child processes
bash: fork: retry: No child processes
bash: fork: Resource temporarily unavailable

      

        
        
        
      

    

Should ulimit -u 10 allow 10 processes at the same time?