@Override
  public int run(String args[]) throws Exception {
    if (args.length != 1) {
      usage(null);
      return 1;
    }

    String cmd = args[0];

    if ("start".equals(cmd)) {
      return start();
    } else if ("stop".equals(cmd)) {
      System.err.println("To shutdown the regionserver run "
        + "hbase-daemon.sh stop regionserver or send a kill signal to " + "the regionserver pid");
      return 1;
    } else {
      usage("Unknown command: " + args[0]);
      return 1;
    }
  }
Class responsible for parsing the command line and starting the RegionServer.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServerCommandLine.java