/**
   * Nachos main entry point.
   *
   * @param args the command line arguments.
   */
  public static void main(final String[] args) {
    System.out.print("nachos 5.0j initializing...");

    Lib.assertTrue(Machine.args == null);
    Machine.args = args;

    processArgs();

    Config.load(configFileName);

    // get the current directory (.)
    baseDirectory = new File(new File("").getAbsolutePath());
    // get the nachos directory (./nachos)
    nachosDirectory = new File(baseDirectory, "nachos");

    String testDirectoryName = Config.getString("FileSystem.testDirectory");

    // get the test directory
    if (testDirectoryName != null) {
      testDirectory = new File(testDirectoryName);
    } else {
      // use ../test
      testDirectory = new File(baseDirectory.getParentFile(), "test");
    }

    securityManager = new NachosSecurityManager(testDirectory);
    privilege = securityManager.getPrivilege();

    privilege.machine = new MachinePrivilege();

    TCB.givePrivilege(privilege);
    privilege.stats = stats;

    securityManager.enable();
    createDevices();
    checkUserClasses();

    autoGrader = (AutoGrader) Lib.constructObject(autoGraderClassName);

    new TCB()
        .start(
            new Runnable() {
              public void run() {
                autoGrader.start(privilege);
              }
            });
  }
  /**
   * Return the name of the process class that the kernel should use. In the multi-programming
   * project, returns <tt>nachos.userprog.UserProcess</tt>. In the VM project, returns
   * <tt>nachos.vm.VMProcess</tt>. In the networking project, returns
   * <tt>nachos.network.NetProcess</tt>.
   *
   * @return the name of the process class that the kernel should use.
   * @see nachos.userprog.UserKernel#run
   * @see nachos.userprog.UserProcess
   * @see nachos.vm.VMProcess
   * @see nachos.network.NetProcess
   */
  public static String getProcessClassName() {
    if (processClassName == null) processClassName = Config.getString("Kernel.processClassName");

    Lib.assertTrue(processClassName != null);
    return processClassName;
  }
  /**
   * Return the name of the shell program that a user-programming kernel must run. Make sure
   * <tt>UserKernel.run()</tt> <i>always</i> uses this method to decide which program to run.
   *
   * @return the name of the shell program to run.
   */
  public static String getShellProgramName() {
    if (shellProgramName == null) shellProgramName = Config.getString("Kernel.shellProgram");

    Lib.assertTrue(shellProgramName != null);
    return shellProgramName;
  }