code: public static void main(String argv[]) throws Exception {
      StringUtils.startupShutdownMessage(TaskTracker.class, argv, LOG);
      try {
        if (argv.length == 0) {
          JobConf conf = new JobConf();
          ReflectionUtils.setContentionTracing
          (conf.getBoolean("tasktracker.contention.tracking", false));
          new TaskTracker(conf).run();
          return;
        }
        if ("-instance".equals(argv[0]) && argv.length == 2) {
          int instance = Integer.parseInt(argv[1]);
          if (instance == 0 || instance == 1) {
            JobConf conf = new JobConf();
            JobConf.overrideConfiguration(conf, instance);
            // enable the server to track time spent waiting on locks
            ReflectionUtils.setContentionTracing
            (conf.getBoolean("tasktracker.contention.tracking", false));
            new TaskTracker(conf).run();
            return;
          }
        }
        System.out.println("usage: TaskTracker [-instance <0|1>]");
        System.exit(-1);
      } catch (Throwable e) {
        LOG.error("Can not start task tracker because "+
                  StringUtils.stringifyException(e));
        System.exit(-1);
      }
    }
docs: Start the TaskTracker, point toward the indicated JobTracker