code: public void start() {
      mMasterProcess = AlluxioMasterProcess.Factory.create();
      Runnable runMaster = new Runnable() {
        @Override
        public void run() {
          try {
            LOG.info("Starting Alluxio master {}.", mMasterProcess);
            mMasterProcess.start();
          } catch (InterruptedException e) {
            // this is expected
          } catch (Exception e) {
            // Log the exception as the RuntimeException will be caught and handled silently by JUnit
            LOG.error("Start master error", e);
            throw new RuntimeException(e + " \n Start Master Error \n" + e.getMessage(), e);
          }
        }
      };
      mMasterThread = new Thread(runMaster);
      mMasterThread.setName("MasterThread-" + System.identityHashCode(mMasterThread));
      mMasterThread.start();
      TestUtils.waitForReady(mMasterProcess);
      // Don't start a secondary master when using the Raft journal.
      if (ServerConfiguration.getEnum(PropertyKey.MASTER_JOURNAL_TYPE,
          JournalType.class) == JournalType.EMBEDDED) {
        return;
      }
      if (!mIncludeSecondary) {
        return;
      }
      mSecondaryMaster = new AlluxioSecondaryMaster();
      Runnable runSecondaryMaster = new Runnable() {
        @Override
        public void run() {
          try {
            LOG.info("Starting secondary master {}.", mSecondaryMaster);
            mSecondaryMaster.start();
          } catch (InterruptedException e) {
            // this is expected
          } catch (Exception e) {
            // Log the exception as the RuntimeException will be caught and handled silently by JUnit
            LOG.error("Start secondary master error", e);
            throw new RuntimeException(e + " \n Start Secondary Master Error \n" + e.getMessage(), e);
          }
        }
      };
      mSecondaryMasterThread = new Thread(runSecondaryMaster);
      mSecondaryMasterThread
          .setName("SecondaryMasterThread-" + System.identityHashCode(mSecondaryMasterThread));
      mSecondaryMasterThread.start();
      TestUtils.waitForReady(mSecondaryMaster);
    }
docs: Starts the master.