code: public void setOwner(String src, String username, String groupname
                        ) throws IOException {
      checkOpen();
      clearFileStatusCache();
      
      try {
        namenode.setOwner(src, username, groupname);
      } catch(RemoteException re) {
        throw re.unwrapRemoteException(AccessControlException.class,
                                       FileNotFoundException.class);
      }
    }
docs: Set file or directory owner.
  @param src path name.
  @param username user id.
  @param groupname user group.
  @throws <code>FileNotFoundException</code> is file does not exist.