hashicorp/nomad · error

Failed to signal task: %s, err: %v

Error message

Failed to signal task: %s, err: %v

What it means

When signaling all tasks in an allocation (empty taskName), allocRunner.Signal iterates every task runner and aggregates individual failures into a multierror, wrapping each as "Failed to signal task: <name>, err: <cause>". The error name of the failing task and underlying cause (e.g. task not running, driver error) are embedded in the message.

Source

Thrown at client/allocrunner/alloc_runner.go:1493

// taskName is empty, then it is sent to all tasks.
func (ar *allocRunner) Signal(taskName, signal string) error {
	event := structs.NewTaskEvent(structs.TaskSignaling).SetSignalText(signal)

	if taskName != "" {
		tr, ok := ar.tasks[taskName]
		if !ok {
			return fmt.Errorf("Task not found")
		}

		return tr.Signal(event, signal)
	}

	var err *multierror.Error

	for tn, tr := range ar.tasks {
		rerr := tr.Signal(event.Copy(), signal)
		if rerr != nil {
			err = multierror.Append(err, fmt.Errorf("Failed to signal task: %s, err: %v", tn, rerr))
		}
	}

	return err.ErrorOrNil()
}

// Reconnect logs a reconnect event for each task in the allocation and syncs the current alloc state with the server.
func (ar *allocRunner) Reconnect(update *structs.Allocation) (err error) {
	event := structs.NewTaskEvent(structs.TaskClientReconnected)
	event.Time = time.Now().UnixNano()
	for _, tr := range ar.tasks {
		tr.AppendEvent(event)
	}

	// Update the client alloc with the server side indexes.
	ar.setIndexes(update)

	// Calculate alloc state to get the final state with the new events.

View on GitHub (pinned to 482b49bf1a)

Solutions

  1. Parse the task name from the multierror message and inspect the underlying cause for that task
  2. Check task state with `nomad alloc status <alloc-id>` — wait for tasks to be running before signaling
  3. Signal individual tasks by name to isolate which one fails and why
  4. Retry the signal after the task restarts or becomes healthy
Defensive patterns

Strategy: try-catch

Validate before calling

alloc, _, err := client.Allocations().Info(ctx, allocID, nil)
if err == nil {
  for tn, ts := range alloc.TaskStates {
    if ts.State != structs.TaskStateRunning { log.Printf("task %s not running; signal may fail", tn) }
  }
}

Try / catch

if err := client.Allocations().Signal(ctx, allocID, "", sig); err != nil {
  var merr *multierror.Error
  if errors.As(err, &merr) {
    for _, e := range merr.Errors { log.Printf("signal sub-failure: %v", e) }
  }
}

Prevention

When it happens

Trigger: Calling Signal with an empty taskName while one or more task runners fail tr.Signal — e.g. task is not running, driver cannot deliver the signal, or the driver does not support the signal.

Common situations: Group-wide signal during a deployment where one task crashed before the signal; signaling a group whose task driver (e.g. some exec drivers) cannot forward signals; signal sent while a task is mid-restart.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/f805e9a3ffb01823. Report an issue: GitHub.