code: func joinExistingNamespaces(namespaces []configs.Namespace) error {
  	for _, ns := range namespaces {
  		if ns.Path != "" {
  			f, err := os.OpenFile(ns.Path, os.O_RDONLY, 0)
  			if err != nil {
  				return err
  			}
  			err = system.Setns(f.Fd(), uintptr(ns.Syscall()))
  			f.Close()
  			if err != nil {
  				return err
  			}
  		}
  	}
  	return nil
  }
docs: // joinExistingNamespaces gets all the namespace paths specified for the container and
  // does a setns on the namespace fd so that the current process joins the namespace.