apache/hadoop · error · IOException

Illegal command: {}

Error message

Illegal command: {}

What it means

Error "Illegal command: {}" thrown in apache/hadoop.

Source

Thrown at hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-nativetask/src/main/java/org/apache/hadoop/mapred/nativetask/handlers/NativeCollectorOnlyHandler.java:162

    }
        
    if (command.equals(GET_OUTPUT_PATH)) {
      p = output.getOutputFileForWrite(-1);
    } else if (command.equals(GET_OUTPUT_INDEX_PATH)) {
      p = output.getOutputIndexFileForWrite(-1);
    } else if (command.equals(GET_SPILL_PATH)) {
      p = output.getSpillFileForWrite(spillNumber++, -1);
      
    } else if (command.equals(GET_COMBINE_HANDLER)) {
      if (null == combinerHandler) {
        return null;
      }
      final ReadWriteBuffer result = new ReadWriteBuffer(8);
      
      result.writeLong(combinerHandler.getId());
      return result;
    } else {
      throw new IOException("Illegal command: " + command.toString());
    }
    if (p != null) {
      final ReadWriteBuffer result = new ReadWriteBuffer();
      result.writeString(p.toUri().getPath());
      return result;
    } else {
      throw new IOException("MapOutputFile can't allocate spill/output file");
    }
  }
}

View on GitHub (pinned to 2add963021)

Solutions

1. Verify the native task protocol: the Java side sent a command id the native handler does not recognize; ensure hadoop-client-nativetask Java and native library versions match.
2. Rebuild libnativetask.so from the same Hadoop source version as the Java client.

When it happens

Trigger: Thrown by NativeCollectorOnlyHandler when the native task side sends a command id the Java handler does not recognize. Indicates a version mismatch between libnativetask native library and the Java nativetask code; rebuild both from the same source tree.

Common situations: Version skew between Java nativetask code and the compiled native library; corrupted command stream.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/e9ed3809c699786d. Report an issue: GitHub.