apache/druid · error

Failed to read log for task: %s

Error message

Failed to read log for task: %s

What it means

The middle manager worker's log endpoint (GET /druid/worker/v1/task/{id}/log) failed with an IOException while reading or streaming the task's log file. The resource logs a warning and returns HTTP 500.

Source

Thrown at indexing-service/src/main/java/org/apache/druid/indexing/worker/http/WorkerResource.java:194

      return Response.status(501)
                     .type(MediaType.TEXT_PLAIN)
                     .entity(StringUtils.format(
                         "Log streaming not supported by [%s]",
                         taskRunner.getClass().getName()
                     ))
                     .build();
    }
    try {
      final Optional<InputStream> stream = ((TaskLogStreamer) taskRunner).streamTaskLog(taskId, offset);

      if (stream.isPresent()) {
        return Response.ok(stream.get()).build();
      } else {
        return Response.status(Response.Status.NOT_FOUND).build();
      }
    }
    catch (IOException e) {
      log.warn(e, "Failed to read log for task: %s", taskId);
      return Response.serverError().build();
    }
  }
}

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Check worker logs for the full IOException stack trace
2. Verify druid.indexer.logs.directory points at the location holding task logs and is readable
3. Ensure the task's log file exists on this worker and was not purged by log retention
4. Fix filesystem permissions or disk issues on the worker host

// Check the task exists on this worker first
// GET /druid/worker/v1/task/{taskId}/status -> 200

try { workerLog(taskId); } catch (WebApplicationException e) { if (e.getResponse().getStatus() == 500) { /* read the log file directly from druid.indexer.logs.directory */ } }

When it happens

Trigger: GET /druid/worker/v1/task/{taskId}/log when opening/reading the task log file (TaskLogStreamer/log task dir) throws IOException.

Common situations: Log file deleted or rotated while streaming; wrong druid.indexer.logs.directory; filesystem permissions or disk errors on the worker.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• Failed to stream logs from: %s
• Failed to stream logs for task[%s] starting at offset[%d]
• Failed to stream log for task %s
• User [%s] does not exist.
• User [%s] already exists.

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/5cd6b98c57ca0757. Report an issue: GitHub.