apache/hadoop · error · IllegalArgumentException

Invalid transport: %s

Error message

Invalid transport: %s

What it means

During MiniKdc startup (prepareKdcServer), the 'transport' property must equal TCP or UDP. The comparison transport.trim().equals("TCP") is case-sensitive: any value other than exactly TCP or UDP after whitespace trimming throws IllegalArgumentException. Lowercase 'tcp'/'udp' are rejected.

Source

Thrown at hadoop-common-project/hadoop-minikdc/src/main/java/org/apache/hadoop/minikdc/MiniKdc.java:316

    // transport
    simpleKdc.setWorkDir(workDir);
    simpleKdc.setKdcHost(getHost());
    simpleKdc.setKdcRealm(realm);
    if (transport == null) {
      transport = conf.getProperty(TRANSPORT);
    }
    if (port == 0) {
      port = NetworkUtil.getServerPort();
    }
    if (transport != null) {
      if (transport.trim().equals("TCP")) {
        simpleKdc.setKdcTcpPort(port);
        simpleKdc.setAllowUdp(false);
      } else if (transport.trim().equals("UDP")) {
        simpleKdc.setKdcUdpPort(port);
        simpleKdc.setAllowTcp(false);
      } else {
        throw new IllegalArgumentException("Invalid transport: " + transport);
      }
    } else {
      throw new IllegalArgumentException("Need to set transport!");
    }
    simpleKdc.getKdcConfig().setString(KdcConfigKey.KDC_SERVICE_NAME,
            conf.getProperty(INSTANCE));
    if (conf.getProperty(DEBUG) != null) {
      krb5Debug = getAndSet(SUN_SECURITY_KRB5_DEBUG, conf.getProperty(DEBUG));
    }
    if (conf.getProperty(MIN_TICKET_LIFETIME) != null) {
      simpleKdc.getKdcConfig().setLong(KdcConfigKey.MINIMUM_TICKET_LIFETIME,
          Long.parseLong(conf.getProperty(MIN_TICKET_LIFETIME)));
    }
    if (conf.getProperty(MAX_TICKET_LIFETIME) != null) {
      simpleKdc.getKdcConfig().setLong(KdcConfigKey.MAXIMUM_TICKET_LIFETIME,
          Long.parseLong(conf.getProperty(MiniKdc.MAX_TICKET_LIFETIME)));
    }
  }

View on GitHub (pinned to 2add963021)

Solutions

1. Set the 'transport' property to the exact uppercase string "TCP" or "UDP"
2. Build the configuration from MiniKdc.createConf() and override only what you need, so defaults remain valid
3. Assert the value in test setup: check conf.getProperty("transport").trim() is "TCP" or "UDP" before constructing MiniKdc

Example fix

// before
Properties conf = new Properties();
conf.setProperty("transport", "tcp"); // throws Invalid transport: tcp

// after
Properties conf = MiniKdc.createConf(); // defaults include transport=TCP
conf.setProperty("org.name", "EXAMPLE");
conf.setProperty("transport", "TCP"); // explicit and correctly cased

String t = conf.getProperty("transport");
Preconditions.checkArgument(
    "TCP".equals(t.trim()) || "UDP".equals(t.trim()),
    "minikdc transport must be TCP or UDP (case-sensitive), got: %s", t);

When it happens

Trigger: A Properties config with transport set to "tcp" or "udp" (lowercase), an empty string, a typo like "TPC", or any other value. Leading/trailing whitespace is tolerated by trim(), but case is not.

Common situations: Copy-pasting configs where other Hadoop properties are case-insensitive; hand-built Properties instead of MiniKdc.createConf() (which defaults transport to "TCP"); editing minikdc.properties files for test harnesses.

Related errors

• Missing configuration properties: %s
• Need to set transport!
• Invalid rule: ${remaining}
• Invalid rule mechanism: ${ruleMech}
• Server asks us to fall back to SIMPLE auth, but this client

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/586f1c2388b92e9f. Report an issue: GitHub.