diff --git a/outputs/file/file_output.go b/outputs/file/file_output.go
index 14ebb724..6aad7590 100644
--- a/outputs/file/file_output.go
+++ b/outputs/file/file_output.go
@@ -19,13 +19,14 @@ import (
 	"text/template"
 	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
+	"golang.org/x/sync/semaphore"
+	"google.golang.org/protobuf/proto"
+
 	"github.com/openconfig/gnmic/formatters"
 	"github.com/openconfig/gnmic/outputs"
 	"github.com/openconfig/gnmic/types"
 	"github.com/openconfig/gnmic/utils"
-	"github.com/prometheus/client_golang/prometheus"
-	"golang.org/x/sync/semaphore"
-	"google.golang.org/protobuf/proto"
 )
 
 const (
@@ -38,7 +39,7 @@ const (
 func init() {
 	outputs.Register("file", func() outputs.Output {
 		return &File{
-			Cfg:    &Config{},
+			cfg:    &Config{},
 			logger: log.New(io.Discard, loggingPrefix, utils.DefaultLoggingFlags),
 		}
 	})
@@ -46,7 +47,7 @@ func init() {
 
 // File //
 type File struct {
-	Cfg    *Config
+	cfg    *Config
 	file   *os.File
 	logger *log.Logger
 	mo     *formatters.MarshalOptions
@@ -78,7 +79,7 @@ type Config struct {
 }
 
 func (f *File) String() string {
-	b, err := json.Marshal(f)
+	b, err := json.Marshal(f.cfg)
 	if err != nil {
 		return ""
 	}
@@ -89,7 +90,7 @@ func (f *File) SetEventProcessors(ps map[string]map[string]interface{},
 	logger *log.Logger,
 	tcs map[string]*types.TargetConfig,
 	acts map[string]map[string]interface{}) {
-	for _, epName := range f.Cfg.EventProcessors {
+	for _, epName := range f.cfg.EventProcessors {
 		if epCfg, ok := ps[epName]; ok {
 			epType := ""
 			for k := range epCfg {
@@ -127,7 +128,7 @@ func (f *File) SetLogger(logger *log.Logger) {
 
 // Init //
 func (f *File) Init(ctx context.Context, name string, cfg map[string]interface{}, opts ...outputs.Option) error {
-	err := outputs.DecodeConfig(cfg, f.Cfg)
+	err := outputs.DecodeConfig(cfg, f.cfg)
 	if err != nil {
 		return err
 	}
@@ -137,24 +138,24 @@ func (f *File) Init(ctx context.Context, name string, cfg map[string]interface{}
 	for _, opt := range opts {
 		opt(f)
 	}
-	if f.Cfg.Format == "proto" {
+	if f.cfg.Format == "proto" {
 		return fmt.Errorf("proto format not supported in output type 'file'")
 	}
-	if f.Cfg.Separator == "" {
-		f.Cfg.Separator = defaultSeparator
+	if f.cfg.Separator == "" {
+		f.cfg.Separator = defaultSeparator
 	}
-	if f.Cfg.FileName == "" && f.Cfg.FileType == "" {
-		f.Cfg.FileType = "stdout"
+	if f.cfg.FileName == "" && f.cfg.FileType == "" {
+		f.cfg.FileType = "stdout"
 	}
 
-	switch f.Cfg.FileType {
+	switch f.cfg.FileType {
 	case "stdout":
 		f.file = os.Stdout
 	case "stderr":
 		f.file = os.Stderr
 	default:
 	CRFILE:
-		f.file, err = os.OpenFile(f.Cfg.FileName, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
+		f.file, err = os.OpenFile(f.cfg.FileName, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
 		if err != nil {
 			f.logger.Printf("failed to create file: %v", err)
 			time.Sleep(10 * time.Second)
@@ -162,41 +163,46 @@ func (f *File) Init(ctx context.Context, name string, cfg map[string]interface{}
 		}
 	}
 
-	if f.Cfg.Format == "" {
-		f.Cfg.Format = defaultFormat
+	if f.cfg.Format == "" {
+		f.cfg.Format = defaultFormat
 	}
-	if f.Cfg.FileType == "stdout" || f.Cfg.FileType == "stderr" {
-		f.Cfg.Indent = "  "
-		f.Cfg.Multiline = true
+	if f.cfg.FileType == "stdout" || f.cfg.FileType == "stderr" {
+		f.cfg.Indent = "  "
+		f.cfg.Multiline = true
 	}
-	if f.Cfg.Multiline && f.Cfg.Indent == "" {
-		f.Cfg.Indent = "  "
+	if f.cfg.Multiline && f.cfg.Indent == "" {
+		f.cfg.Indent = "  "
 	}
-	if f.Cfg.ConcurrencyLimit < 1 {
-		f.Cfg.ConcurrencyLimit = defaultWriteConcurrency
+	if f.cfg.ConcurrencyLimit < 1 {
+		switch f.cfg.FileType {
+		case "stdout", "stderr":
+			f.cfg.ConcurrencyLimit = 1
+		default:
+			f.cfg.ConcurrencyLimit = defaultWriteConcurrency
+		}
 	}
 
-	f.sem = semaphore.NewWeighted(int64(f.Cfg.ConcurrencyLimit))
+	f.sem = semaphore.NewWeighted(int64(f.cfg.ConcurrencyLimit))
 
 	f.mo = &formatters.MarshalOptions{
-		Multiline:        f.Cfg.Multiline,
-		Indent:           f.Cfg.Indent,
-		Format:           f.Cfg.Format,
-		OverrideTS:       f.Cfg.OverrideTimestamps,
-		CalculateLatency: f.Cfg.CalculateLatency,
+		Multiline:        f.cfg.Multiline,
+		Indent:           f.cfg.Indent,
+		Format:           f.cfg.Format,
+		OverrideTS:       f.cfg.OverrideTimestamps,
+		CalculateLatency: f.cfg.CalculateLatency,
 	}
-	if f.Cfg.TargetTemplate == "" {
+	if f.cfg.TargetTemplate == "" {
 		f.targetTpl = outputs.DefaultTargetTemplate
-	} else if f.Cfg.AddTarget != "" {
-		f.targetTpl, err = utils.CreateTemplate("target-template", f.Cfg.TargetTemplate)
+	} else if f.cfg.AddTarget != "" {
+		f.targetTpl, err = utils.CreateTemplate("target-template", f.cfg.TargetTemplate)
 		if err != nil {
 			return err
 		}
 		f.targetTpl = f.targetTpl.Funcs(outputs.TemplateFuncs)
 	}
 
-	if f.Cfg.MsgTemplate != "" {
-		f.msgTpl, err = utils.CreateTemplate(fmt.Sprintf("%s-msg-template", name), f.Cfg.MsgTemplate)
+	if f.cfg.MsgTemplate != "" {
+		f.msgTpl, err = utils.CreateTemplate(fmt.Sprintf("%s-msg-template", name), f.cfg.MsgTemplate)
 		if err != nil {
 			return err
 		}
@@ -227,13 +233,13 @@ func (f *File) Write(ctx context.Context, rsp proto.Message, meta outputs.Meta)
 	defer f.sem.Release(1)
 
 	numberOfReceivedMsgs.WithLabelValues(f.file.Name()).Inc()
-	rsp, err = outputs.AddSubscriptionTarget(rsp, meta, f.Cfg.AddTarget, f.targetTpl)
+	rsp, err = outputs.AddSubscriptionTarget(rsp, meta, f.cfg.AddTarget, f.targetTpl)
 	if err != nil {
 		f.logger.Printf("failed to add target to the response: %v", err)
 	}
-	bb, err := outputs.Marshal(rsp, meta, f.mo, f.Cfg.SplitEvents, f.evps...)
+	bb, err := outputs.Marshal(rsp, meta, f.mo, f.cfg.SplitEvents, f.evps...)
 	if err != nil {
-		if f.Cfg.Debug {
+		if f.cfg.Debug {
 			f.logger.Printf("failed marshaling proto msg: %v", err)
 		}
 		numberOfFailWriteMsgs.WithLabelValues(f.file.Name(), "marshal_error").Inc()
@@ -246,7 +252,7 @@ func (f *File) Write(ctx context.Context, rsp proto.Message, meta outputs.Meta)
 		if f.msgTpl != nil {
 			b, err = outputs.ExecTemplate(b, f.msgTpl)
 			if err != nil {
-				if f.Cfg.Debug {
+				if f.cfg.Debug {
 					log.Printf("failed to execute template: %v", err)
 				}
 				numberOfFailWriteMsgs.WithLabelValues(f.file.Name(), "template_error").Inc()
@@ -254,9 +260,9 @@ func (f *File) Write(ctx context.Context, rsp proto.Message, meta outputs.Meta)
 			}
 		}
 
-		n, err := f.file.Write(append(b, []byte(f.Cfg.Separator)...))
+		n, err := f.file.Write(append(b, []byte(f.cfg.Separator)...))
 		if err != nil {
-			if f.Cfg.Debug {
+			if f.cfg.Debug {
 				f.logger.Printf("failed to write to file '%s': %v", f.file.Name(), err)
 			}
 			numberOfFailWriteMsgs.WithLabelValues(f.file.Name(), "write_error").Inc()
@@ -278,12 +284,12 @@ func (f *File) WriteEvent(ctx context.Context, ev *formatters.EventMsg) {
 		evs = proc.Apply(evs...)
 	}
 	toWrite := []byte{}
-	if f.Cfg.SplitEvents {
+	if f.cfg.SplitEvents {
 		for _, pev := range evs {
 			var err error
 			var b []byte
-			if f.Cfg.Multiline {
-				b, err = json.MarshalIndent(pev, "", f.Cfg.Indent)
+			if f.cfg.Multiline {
+				b, err = json.MarshalIndent(pev, "", f.cfg.Indent)
 			} else {
 				b, err = json.Marshal(pev)
 			}
@@ -293,13 +299,13 @@ func (f *File) WriteEvent(ctx context.Context, ev *formatters.EventMsg) {
 				return
 			}
 			toWrite = append(toWrite, b...)
-			toWrite = append(toWrite, []byte(f.Cfg.Separator)...)
+			toWrite = append(toWrite, []byte(f.cfg.Separator)...)
 		}
 	} else {
 		var err error
 		var b []byte
-		if f.Cfg.Multiline {
-			b, err = json.MarshalIndent(evs, "", f.Cfg.Indent)
+		if f.cfg.Multiline {
+			b, err = json.MarshalIndent(evs, "", f.cfg.Indent)
 		} else {
 			b, err = json.Marshal(evs)
 		}
@@ -309,7 +315,7 @@ func (f *File) WriteEvent(ctx context.Context, ev *formatters.EventMsg) {
 			return
 		}
 		toWrite = append(toWrite, b...)
-		toWrite = append(toWrite, []byte(f.Cfg.Separator)...)
+		toWrite = append(toWrite, []byte(f.cfg.Separator)...)
 	}
 
 	n, err := f.file.Write(toWrite)
@@ -330,7 +336,7 @@ func (f *File) Close() error {
 
 // Metrics //
 func (f *File) RegisterMetrics(reg *prometheus.Registry) {
-	if !f.Cfg.EnableMetrics {
+	if !f.cfg.EnableMetrics {
 		return
 	}
 	if err := registerMetrics(reg); err != nil {