apache/hadoop · error · HadoopIllegalArgumentException

-protocol needs one parameter

Error message

-protocol needs one parameter

What it means

-protocol consumes exactly one following parameter, the scheme name. parseProtocolArgs checks index+1 >= args.length and throws HadoopIllegalArgumentException('-protocol needs one parameter') when -protocol is the last token, i.e., the scheme value is missing. Parsing aborts before the scheme is ever inspected for validity.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/log/LogLevel.java:218

            "-setlevel needs three parameters");
      }
      operation = Operations.SETLEVEL;
      hostName = args[index+1];
      className = args[index+2];
      level = args[index+3];
      return index+4;
    }

    private int parseProtocolArgs(String[] args, int index) throws
        HadoopIllegalArgumentException {
      // make sure only -protocol is specified
      if (protocol != null) {
        throw new HadoopIllegalArgumentException(
            "Redundant -protocol command");
      }
      // check number of arguments is sufficient
      if (index+1 >= args.length) {
        throw new HadoopIllegalArgumentException(
            "-protocol needs one parameter");
      }
      // check protocol is valid
      protocol = args[index+1];
      if (!isValidProtocol(protocol)) {
        throw new HadoopIllegalArgumentException(
            "Invalid protocol: " + protocol);
      }
      return index+2;
    }

    /**
     * Send HTTP/HTTPS request to get log level.
     *
     * @throws HadoopIllegalArgumentException if arguments are invalid.
     * @throws Exception if unable to connect
     */
    private void doGetLevel() throws Exception {

View on GitHub (pinned to 2add963021)

Solutions

1. Follow -protocol with exactly one value: http or https.
2. Default the scheme variable in scripts ('${SCHEME:-http}') so the flag never dangles.
3. Omit -protocol entirely when plain http is acceptable — it is the default.

Example fix

# before
hadoop loglevel -getlevel nn:9871 cls -protocol

# after
hadoop loglevel -getlevel nn:9871 cls -protocol https

int i = Arrays.asList(args).indexOf("-protocol");
if (i >= 0 && i + 1 >= args.length) {
  throw new HadoopIllegalArgumentException("-protocol needs a value: http or https");
}

When it happens

Trigger: 'hadoop loglevel -getlevel h c -protocol' with nothing after the flag; shell variable holding the scheme expanding to empty so the flag ends the command; line breaks splitting the flag from its value in a pasted script.

Common situations: Truncated copy-paste; unquoted/empty scheme variables in automation; heredocs or line continuations losing the trailing token.

Related errors

• -getlevel needs two parameters
• -setlevel needs three parameters
• Redundant -protocol command
• "Invalid protocol: " + protocol
• Expect either -getlevel or -setlevel

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/ec7980b6d5ca6b3c. Report an issue: GitHub.