code: protected void printUsage() {
      System.out.println("Usage: alluxio " + getShellName() + " [generic options]");
      SortedSet<String> sortedCmds = new TreeSet<>(mCommands.keySet());
      for (String cmd : sortedCmds) {
        System.out.format("%-60s%n", "\t [" + mCommands.get(cmd).getUsage() + "]");
      }
    }
docs: Prints usage for all commands.