diff --git a/config.go b/config.go
index 841cd93..92894e1 100644
--- a/config.go
+++ b/config.go
@@ -55,22 +55,22 @@ func EditConfig(path string) error {
 	return cmd.Run()
 }
 
-func GetConfig(path string, settings map[string]string) (Config, error) {
+func GetConfig(path string, settings map[string]string) (*Config, error) {
 	f, err := ioutil.ReadFile(path)
 	if err != nil {
-		return Config{}, err
+		return nil, err
 	}
 
 	config := string(f)
 
 	c, err := ParseConfig(config, settings)
 	if err != nil {
-		return Config{}, err
+		return nil, err
 	}
 
 	addDefaultEnvs(&c, path)
 
-	return c, err
+	return &c, err
 
 }
 
diff --git a/main.go b/main.go
index e004004..d5c9a4f 100644
--- a/main.go
+++ b/main.go
@@ -59,7 +59,7 @@ func newLogger(path string) *log.Logger {
 func main() {
 	options, err := ParseOptions(os.Args[1:])
 	if err == ErrHelp {
-		fmt.Fprintf(os.Stdout, usage)
+		fmt.Fprint(os.Stdout, usage)
 		os.Exit(0)
 	}
 
@@ -100,7 +100,7 @@ func main() {
 		}
 		config, err := GetConfig(configPath, options.Settings)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 
@@ -118,25 +118,25 @@ func main() {
 		}
 		config, err := GetConfig(configPath, options.Settings)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 
 		err = smug.Stop(config, options, context)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 	case CommandNew, CommandEdit:
 		err := EditConfig(configPath)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 	case CommandList:
 		configs, err := ListConfigs(userConfigDir)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 
@@ -144,13 +144,13 @@ func main() {
 	case CommandPrint:
 		config, err := smug.GetConfigFromSession(options, context)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 
 		d, err := yaml.Marshal(&config)
 		if err != nil {
-			fmt.Fprintf(os.Stderr, err.Error())
+			fmt.Fprint(os.Stderr, err.Error())
 			os.Exit(1)
 		}
 
diff --git a/smug.go b/smug.go
index 0f87743..90aa96b 100644
--- a/smug.go
+++ b/smug.go
@@ -77,7 +77,7 @@ func (smug Smug) switchOrAttach(target string, attach bool, insideTmuxSession bo
 	return nil
 }
 
-func (smug Smug) Stop(config Config, options *Options, context Context) error {
+func (smug Smug) Stop(config *Config, options *Options, context Context) error {
 	windows := options.Windows
 	if len(windows) == 0 {
 		sessionRoot := ExpandPath(config.Root)
@@ -100,7 +100,7 @@ func (smug Smug) Stop(config Config, options *Options, context Context) error {
 	return nil
 }
 
-func (smug Smug) Start(config Config, options *Options, context Context) error {
+func (smug Smug) Start(config *Config, options *Options, context Context) error {
 	var sessionName string
 	var err error
 
@@ -210,11 +210,17 @@ func (smug Smug) Start(config Config, options *Options, context Context) error {
 	}
 
 	if !options.InsideCurrentSession {
-		smug.tmux.KillWindow(sessionName + defaultWindowName)
-		smug.tmux.RenumberWindows(sessionName)
+		err := smug.tmux.KillWindow(sessionName + defaultWindowName)
+		if err != nil {
+			return err
+		}
+		err = smug.tmux.RenumberWindows(sessionName)
+		if err != nil {
+			return err
+		}
 	}
 
-	if len(windows) == 0 && len(config.Windows) > 0 && options.Detach == false {
+	if len(windows) == 0 && len(config.Windows) > 0 && !options.Detach {
 		return smug.switchOrAttach(sessionName+config.Windows[0].Name, attach, context.InsideTmuxSession)
 	}
 
@@ -236,7 +242,7 @@ func (smug Smug) GetConfigFromSession(options *Options, context Context) (Config
 	}
 
 	for _, w := range tmuxWindows {
-		tmuxPanes, err := smug.tmux.ListPanes(options.Project + ":" + w.Id)
+		tmuxPanes, err := smug.tmux.ListPanes(options.Project + ":" + w.ID)
 		if err != nil {
 			return Config{}, err
 		}
diff --git a/smug_test.go b/smug_test.go
index 4eab1cf..3684a70 100644
--- a/smug_test.go
+++ b/smug_test.go
@@ -9,7 +9,7 @@ import (
 )
 
 var testTable = map[string]struct {
-	config           Config
+	config           *Config
 	options          *Options
 	context          Context
 	startCommands    []string
@@ -17,7 +17,7 @@ var testTable = map[string]struct {
 	commanderOutputs []string
 }{
 	"test with 1 window": {
-		Config{
+		&Config{
 			Session:     "ses",
 			Root:        "~/root",
 			BeforeStart: []string{"command1", "command2"},
@@ -48,7 +48,7 @@ var testTable = map[string]struct {
 		[]string{"ses", "win1"},
 	},
 	"test with 1 window and Detach: true": {
-		Config{
+		&Config{
 			Session:     "ses",
 			Root:        "root",
 			BeforeStart: []string{"command1", "command2"},
@@ -78,7 +78,7 @@ var testTable = map[string]struct {
 		[]string{"xyz"},
 	},
 	"test with multiple windows and panes": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 			Windows: []Window{
@@ -125,7 +125,7 @@ var testTable = map[string]struct {
 		[]string{"ses", "ses", "win1", "1"},
 	},
 	"test start windows from option's Windows parameter": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 			Windows: []Window{
@@ -157,7 +157,7 @@ var testTable = map[string]struct {
 		[]string{"xyz"},
 	},
 	"test attach to the existing session": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 			Windows: []Window{
@@ -176,7 +176,7 @@ var testTable = map[string]struct {
 		[]string{""},
 	},
 	"test start a new session from another tmux session": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 		},
@@ -194,7 +194,7 @@ var testTable = map[string]struct {
 		[]string{"xyz"},
 	},
 	"test switch a client from another tmux session": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 			Windows: []Window{
@@ -213,7 +213,7 @@ var testTable = map[string]struct {
 		[]string{""},
 	},
 	"test create new windows in current session with same name": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 			Windows: []Window{
@@ -236,7 +236,7 @@ var testTable = map[string]struct {
 		[]string{"ses", ""},
 	},
 	"test create new windows in current session with different name": {
-		Config{
+		&Config{
 			Session: "ses",
 			Root:    "root",
 			Windows: []Window{
diff --git a/tmux.go b/tmux.go
index e00750f..82b48e3 100644
--- a/tmux.go
+++ b/tmux.go
@@ -13,9 +13,6 @@ const (
 
 const (
 	EvenHorizontal = "even-horizontal"
-	EvenVertical   = "even-vertical"
-	MainHorizontal = "main-horizontal"
-	MainVertical   = "main-vertical"
 	Tiled          = "tiled"
 )
 
@@ -24,7 +21,7 @@ type Tmux struct {
 }
 
 type TmuxWindow struct {
-	Id     string
+	ID     string
 	Name   string
 	Layout string
 	Root   string
@@ -146,7 +143,7 @@ func (tmux Tmux) ListWindows(target string) ([]TmuxWindow, error) {
 	for _, w := range windowsList {
 		windowInfo := strings.Split(w, ";")
 		window := TmuxWindow{
-			Id:     windowInfo[0],
+			ID:     windowInfo[0],
 			Name:   windowInfo[1],
 			Layout: windowInfo[2],
 			Root:   windowInfo[3],