apache/hadoop · warning

(unable to get root cause for %s)

Error message

(unable to get root cause for %s)

What it means

printExceptionAndFreeV calls org.apache.hadoop.util.ExceptionUtils.getRootCauseMessage over JNI to build the human-readable reason for a failed libhdfs operation; if getExceptionUtilString gets NULL back (the invokeMethod threw, or the string copy hit OOM), this placeholder with the exception class name is printed instead. Diagnostics are degraded but the errno mapping still happens and the TLS strings are saved (as NULL), so hdfsGetLastExceptionRootCause() will also return NULL for this failure.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/exception.c:190

        excErrno = gExceptionInfo[i].excErrno;
    } else {
        noPrint = 0;
        excErrno = EINTERNAL;
    }

    // We don't want to use ExceptionDescribe here, because that requires a
    // pending exception. Instead, use ExceptionUtils.
    rootCause = getExceptionUtilString(env, exc, "getRootCauseMessage");
    stackTrace = getExceptionUtilString(env, exc, "getStackTrace");
    // Save the exception details in the thread-local state.
    setTLSExceptionStrings(rootCause, stackTrace);

    if (!noPrint) {
        vfprintf(stderr, fmt, ap);
        fprintf(stderr, " error:\n");

        if (!rootCause) {
            fprintf(stderr, "(unable to get root cause for %s)\n", className);
        } else {
            fprintf(stderr, "%s", rootCause);
        }
        if (!stackTrace) {
            fprintf(stderr, "(unable to get stack trace for %s)\n", className);
        } else {
            fprintf(stderr, "%s", stackTrace);
        }
    }

    destroyLocalReference(env, exc);
    free(className);
    return excErrno;
}

int printExceptionAndFree(JNIEnv *env, jthrowable exc, int noPrintFlags,
        const char *fmt, ...)
{

View on GitHub (pinned to 2add963021)

Solutions

1. Align the hadoop-common jar on the process CLASSPATH with the libhdfs release - build CLASSPATH with `hdfs classpath --glob` from the matching installation.
2. Print the failing process's CLASSPATH to find stale or duplicate hadoop-common jars.
3. Fall back to the errno mapping and hdfsGetLastExceptionStackTrace() (fetched separately) to diagnose the original failure.
4. If OOM is suspected (both root cause and stack trace unavailable), raise LIBHDFS_OPTS -Xmx.

// verify the diagnostic surface exists before relying on root-cause strings
CLASSPATH="$(hdfs classpath --glob)" java org.apache.hadoop.util.ExceptionUtils 2>/dev/null \
  || echo "hadoop-common too old/mixed: root-cause diagnostics will be NULL"

const char *rc = hdfsGetLastExceptionRootCause();
if (!rc) {
    /* root cause unavailable: fall back to stack trace + mapped errno */
    const char *st = hdfsGetLastExceptionStackTrace();
    handle_failure(errno, st ? st : "no diagnostics available");
} else {
    handle_failure(errno, rc);
}

When it happens

Trigger: A libhdfs operation threw a Java exception AND the diagnostic call failed: hadoop-common on CLASSPATH is too old to contain ExceptionUtils.getRootCauseMessage (added in Hadoop 3.x), the JVM threw while formatting (OOM), or newCStr could not allocate the C copy of the message.

Common situations: Mixed-version deployments: newer libhdfs (3.x) with a 2.x hadoop-common jar on CLASSPATH; partially upgraded clusters; custom bundles that strip 'unused' classes from hadoop-common.

Related errors

• (unable to get stack trace for %s)
• could not find method %s from class %s with signature %s
• PrintExceptionAndFree: error determining class name of excep
• error:
• error: (no exception)

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/f8e905251aca410b. Report an issue: GitHub.