hashicorp/nomad · error

No nomad log file defined

Error message

No nomad log file defined

What it means

The agent 'monitor' endpoint with on_disk=true tails the Nomad agent's own log file. The file path comes from the agent configuration (log_file). If on_disk is requested but no log file is configured on the agent, there is nothing to tail, so the endpoint returns this 400 error instead of streaming.

Source

Thrown at client/agent_endpoint.go:220

	encoder := codec.NewEncoder(conn, structs.MsgpackHandle)

	if err := decoder.Decode(&args); err != nil {
		handleStreamResultError(err, new(int64(500)), encoder)
		return
	}

	// Check acl
	if aclObj, err := a.c.ResolveToken(args.AuthToken); err != nil {
		handleStreamResultError(err, new(int64(403)), encoder)
		return
	} else if !aclObj.AllowAgentRead() {
		handleStreamResultError(structs.ErrPermissionDenied, new(int64(403)), encoder)
		return
	}

	nomadLogPath := a.c.GetConfig().LogFile
	if args.OnDisk && nomadLogPath == "" {
		handleStreamResultError(errors.New("No nomad log file defined"), new(int64(400)), encoder)
	}

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	opts := monitor.MonitorExportOpts{
		Logger:       a.c.logger,
		LogsSince:    args.LogsSince,
		ServiceName:  args.ServiceName,
		NomadLogPath: nomadLogPath,
		OnDisk:       args.OnDisk,
		Follow:       args.Follow,
		Context:      ctx,
	}

	frames := make(chan *sframer.StreamFrame, streamFramesBuffer)
	errCh := make(chan error)
	var buf bytes.Buffer
	frameSize := 1024

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Set log_file in the agent's config (e.g. log_file = "/var/log/nomad/") and restart the agent before using on_disk=true
2. Use on_disk=false to stream in-memory logs instead of the file
3. Make the client check/fall back when on-disk logging is unavailable
4. Standardize log_file across all agent configs

Example fix

// before (agent config)
# no log_file set
// after
log_file = "/var/log/nomad/"

if req.OnDisk {
  // confirm the agent has log_file configured (e.g. via agent self)
  self, err := client.Agent().Self()
  if err != nil { return err }
  cfg := self.Config["Client"]
  if lf, ok := cfg["LogFile"].(string); !ok || lf == "" {
    return errors.New("on_disk requested but agent has no log_file configured")
  }
}

resp, err := client.Agent().Monitor(ctx, ch, &api.MonitorQuery{OnDisk: true})
if err != nil {
  if strings.Contains(err.Error(), "No nomad log file defined") {
    // fall back to in-memory log streaming
    return client.Agent().Monitor(ctx, ch, &api.MonitorQuery{OnDisk: false})
  }
  return err
}

When it happens

Trigger: Calling the Agent Monitor API with on_disk=true against an agent whose config does not set log_file (the default config may leave it empty or only set log_json/log_level).

Common situations: Agents running with default configuration that never set log_file; clients assuming on-disk logging is always enabled; mixed fleets where some agents configure log_file and others do not; upgrades where log_file was removed from config.

Understand the failure class

Background: "missing required config value" errors: why libraries refuse to start when a configuration key is empty, unset, or blank — this error's family across 48 libraries.

Related errors

• Unknown log level
• No nomad log file defined
• failed to create stdout logfile for %q: %v
• failed to create stderr logfile for %q: %v
• nil logger passed

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/a378da6f2c4db867. Report an issue: GitHub.