What causes "Task not found" in hashicorp/nomad?

Verify the task name with `nomad alloc status ` and use the exact name from the Task list

Task not found

Error message

Task not found

What it means

allocRunner.Signal returns this when asked to send a signal to a task whose name does not exist in the allocation's task map. It is a client-side lookup failure: the task name passed to the Signal API does not match any task defined in the allocation's task group. Nomad throws it to prevent signaling a non-existent task.

Source

Thrown at client/allocrunner/alloc_runner.go:1482

	}()

	select {
	case <-waitCh:
	case <-ctx.Done():
	}

	return err.ErrorOrNil()
}

// Signal sends a signal request to task runners inside an allocation. If the
// 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.

View on GitHub (pinned to 482b49bf1a)

Solutions

Verify the task name with `nomad alloc status <alloc-id>` and use the exact name from the Task list
Confirm the allocation ID belongs to the task group containing the target task
If signaling all tasks, omit the taskName (pass empty string) so Signal iterates every task
Update any hardcoded task names in job files/scripts after job spec changes

Example fix

// before
client.Allocations().Signal(ctx, allocID, "sidecar", "SIGUSR1")
// after
alloc, _, _ := client.Allocations().Info(ctx, allocID, nil)
taskName := alloc.TaskGroup // check `nomad alloc status` for exact task names
count, _, _ := alloc.TaskGroup
_ = count
client.Allocations().Signal(ctx, allocID, "envoy-sidecar", "SIGUSR1")

Defensive patterns

Strategy: validation

Validate before calling

alloc, _, err := client.Allocations().Info(ctx, allocID, nil)
if err != nil { return err }
found := false
for _, t := range alloc.TaskStates { if t.Name == taskName { found = true } }
if !found { return fmt.Errorf("task %q not present in alloc %s", taskName, allocID) }

Prevention

Always resolve task names from `nomad alloc status` or the alloc's TaskStates, never hardcode
Re-fetch the allocation after job updates before signaling
Pass empty taskName to signal all tasks when you don't need per-task targeting

When it happens

Trigger: Calling Client.Allocations().Signal(allocID, taskName, signal) with a taskName that is empty-check passed but does not match any task in ar.tasks (e.g. typo, task restarted under a different name, or signaling an alloc from a different group).

Common situations: Typoed task name in a script or CI job; hardcoding a task name that changed after a job spec edit; signaling a task in the wrong allocation (alloc belongs to a different group); race where the alloc was updated and the task name no longer exists.

Related errors

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/67dbfd751d27824b. Report an issue: GitHub.