apache/hadoop · error · HadoopIllegalArgumentException

Did not expect argument: {}

Error message

Did not expect argument: {}

What it means

'hdfs getconf' maps each mode (-namenodes, -secondaryNodes, -backupNodes, -includeFile, -excludeFile, -nnrpcaddresses) to a CommandHandler. The base checkArgs enforces that these modes take zero positional arguments; if any leftover argument remains after option parsing, it is rejected with this HadoopIllegalArgumentException naming the first unexpected token.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/GetConf.java:170

    
    CommandHandler(String key) {
      this.key = key;
    }

    final int doWork(GetConf tool, String[] args) {
      try {
        checkArgs(args);

        return doWorkInternal(tool, args);
      } catch (Exception e) {
        tool.printError(e.getMessage());
      }
      return -1;
    }

    protected void checkArgs(String args[]) {
      if (args.length > 0) {
        throw new HadoopIllegalArgumentException(
            "Did not expect argument: " + args[0]);
      }
    }

    
    /** Method to be overridden by sub classes for specific behavior */
    int doWorkInternal(GetConf tool, String[] args) throws Exception {

      String value = tool.getConf().getTrimmed(key);
      if (value != null) {
        tool.printOut(value);
        return 0;
      }
      tool.printError("Configuration " + key + " is missing.");
      return -1;
    }
  }
  

View on GitHub (pinned to 2add963021)

Solutions

1. Drop the positional argument: 'hdfs getconf -namenodes' with nothing after it.
2. Check 'hdfs getconf' with no arguments to list all modes and which ones take operands (only -confKey takes one).
3. In scripts, quote the whole command so stray empty arguments are not appended.

Example fix

# before
hdfs getconf -namenodes ns1
# Did not expect argument: ns1

# after
hdfs getconf -namenodes

// zero-operand getconf modes
String[] positional = argsAfterOptions;
if (positional.length > 0) {
  throw new IllegalArgumentException(
      "this getconf mode takes no positional argument: " + positional[0]);
}
ToolRunner.run(new GetConf(), fullArgs);

try {
  return ToolRunner.run(new GetConf(conf), argv);
} catch (Exception e) {
  // GetConf.doWork already prints e.getMessage(); a nonzero exit means bad usage
  System.err.println("getconf usage: run 'hdfs getconf' with no args to list modes");
  return -1;
}

When it happens

Trigger: Running 'hdfs getconf -namenodes someArg', or any getconf mode that expects no operand given a trailing token — often a value the user assumed the mode accepts.

Common situations: Users trying 'hdfs getconf -excludeFile host1' expecting a filtered answer; shell scripts passing an always-present argument variable that is empty-string handled differently; copy-paste from dfsadmin syntax.

Related errors

• usage: -confKey [key]
• Invalid or extra Arguments: {}
• invalid args: {}
• Unknown processor {} (valid processors: xml, binary, stats)
• Illegal option {}

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/5e5ebc9268a6d67c. Report an issue: GitHub.