code: func (c *ContainerServer) ContainerKill(container string, killSignal syscall.Signal) (string, error) {
  	ctr, err := c.LookupContainer(container)
  	if err != nil {
  		return "", errors.Wrapf(err, "failed to find container %s", container)
  	}
  	c.runtime.UpdateContainerStatus(ctr)
  	cStatus := ctr.State()
  
  	// If the container is not running, error and move on.
  	if cStatus.Status != oci.ContainerStateRunning {
  		return "", errors.Errorf("cannot kill container %s: it is not running", container)
  	}
  
  	if err = c.runtime.SignalContainer(ctr, killSignal); err != nil {
  		return "", err
  	}
  
  	c.ContainerStateToDisk(ctr)
  	return ctr.ID(), nil
  }
docs: // ContainerKill sends the user provided signal to the containers primary process.